OBJECTIVES:The study objective was to assess occupational exposure to bacteria and antimicrobial resistance genes (ARGs) present on air filters of utility vehicles used in the working environment of mechanical-biological treatment (MBT) facilities, in the context of workers health risks. MATERIAL AND METHODS:The study was conducted in summer 2024 in 9 air filters from utility vehicles used in MBT plants in Poland. External filters were removed from the vehicle's ventilation system, packed and shipped according to instructions. From the duplicate filters samples DNA was isolated and high-throughput next-generation sequencing (NGS) was carried out. Bioinformatic data analysis was conducted to detect bacteria and ARGs in air filters' surfaces. RESULTS:Totally, 34 bacterial taxa were detected in relative abundance ≥0.5%. The genera most frequently present at the highest relative abundances: Saccharomonospora, Thermobifida, Nocardiopsis, Pectobacterium, Aerococcus, Thermoactinomyces, Novibacillus and Streptomyces. Across all bacteria isolated from the analyzed filters, regardless of their relative abundance, a total of 91 taxa were classified into risk groups 2 or 3 (86 and 5 taxa, respectively). The most frequently detected ARGs were those encoding resistance to a single class of antibiotics (AAC(3)-VIIa, aadA2, ANT(6)-Ia, APH(3'')-Ia, APH(3'')-Ib, APH(6)-Id, cml, cmx, lnuA, lnuD, novA, parY, sul2, vanHF, vanJ, vanRA, vanRI, vanRO - each at least on 4 air filters). Antimicrobial resistance genes encoding multi antibiotic resistance were also detected: CRP, emtA, erm(34), erm(36), ermA, ermC, ermF, ermG, ermT, ermX, ernB, H-NS, mel, msrA, msrE, mtrA, optrA, ramA, ykkD - each at least on 1 air filter. CONCLUSIONS:Despite the limited number of analyzed filters, the study demonstrated a high bacterial species diversity in the MBT plant environment. The MBT workers are exposed to bacteria with high pathogenic potential and to ARGs encoding resistance to antibiotics used exclusively in human medicine, used in human and veterinary medicine, and not intended for human use. Int J Occup Med Environ Health. 2026;39(2):179-201.

Streptococcus anginosus, part of the Streptococcus anginosus group (SAG), is a human commensal increasingly recognized as an opportunistic pathogen responsible for abscesses formation and infections, also invasive ones. Despite its growing clinical importance, the genetic determinants of its pathogenicity remain poorly understood. This study aimed to identify essential genes in S. anginosus 980/01, a bloodstream isolate, under nutrient-rich laboratory conditions using a transposon mutagenesis combined with Transposon-Directed Insertion Site Sequencing (TraDIS). A mutant library was generated using the ISS1 transposon delivered via the thermosensitive plasmid pGh9:ISS1. Following transposition, insertions were mapped using Illumina sequencing and subsequently analyzed. Essential genes were identified based on the absence of insertions and statistical filtering. The library exhibited 98% genome saturation with over 130,000 unique insertion sites. Among 1825 genes, 348 (19.1%) were essential, 1446 non-essential, and 30 non-conclusive. Comparative analyses were performed with S. pyogenes MGAS5005 and S. agalactiae A909. Similarly to the latter, essential genes were enriched in functions related to translation, transcription, and cell wall biosynthesis. However, 40 genes uniquely essential to S. anginosus 980/01 were identified, suggesting unique survival strategies in S. anginosus. This study presents the first genome-wide identification of essential genes for S. anginosus 980/01, highlighting conserved and unique essential genes. These findings provide a basis for understanding its physiology and key genetic determinants of bacterial viability, and may help to uncover the pathogenic potential of S. anginosus in future studies.

BACKGROUND:Prototheca (Chlorophyta: Trebouxiophyceae) is a genus of non-photosynthetic microalgae that causes increasingly frequent infections in both humans and animals, collectively referred to as protothecosis The genetic landscape of the Prototheca algae has remained largely uncharted until recent advances in sequencing and genomics. In this study, a combination of Illumina and Oxford Nanopore technologies was employed for sequencing of 18 mitochondrial genomes, representing all currently recognized Prototheca species. RESULTS:The genomes differed in terms of size and GC content, ranging from 38 kbp to 68 kbp and from 25 to 30%, respectively. The gene content and gene order within the mitochondrial DNA exhibited specific characteristics. The gene content was conserved but showed variable number of hypothetical proteins and a clustering tendency for nad genes. Noteworthy, most genes were located on the clockwise strand, with type I introns, containing long open reading frames encoding homing endonucleases, suggesting a mechanism for intron mobility and genome plasticity. Comparative genomic analyses and phylogenetic classification across the 21 core genes showed a close relationship between the mitochondrial genomes, as evidenced by average nucleotide identity (ANI) and average amino acid identity (AAI), supportive for the current cytb gene-based taxonomy. The phylogenetic tree constructed from concatenated alignments of the core genes confirmed the presence of three distinct Prototheca clades, indicating the polyphyletic nature of the genus. CONCLUSIONS:In conclusion, this work provides another important step toward elucidating the genetics of Prototheca algae, serving as a framework for future studies on the phylogeny and evolution of these peculiar microorganisms.

Although intragenic CpG dinucleotides are conserved during evolution, they are also sensitive to methylation-dependent mechanisms. Methylation status of the TP53 introns 1, 3 and 4 have been analysed in stage III ovarian carcinoma (OC). In the present study, the methylation of exon 4 (10 CpG pairs) was analysed in advanced-stage OC to investigate TP53 methylation and compare exon and intron 4 methylation patterns. A total of 80 samples from patients with advanced-stage OC and metastatic lesions were examined, along with 80 samples derived from healthy patients who had never been diagnosed with cancer. Methylation analysis of the human A2780 ovarian cancer cell line was also performed. Exon and intron 4 were methylated in OC, corresponding metastases and paired healthy tissue. The DNA from the human A2780 ovarian cancer cell line and the normal samples from healthy subjects was also methylated. The data indicate the existence of an intragenic mechanism of regulation of TP53 activity that involves demethylation/methylation processes. This mechanism provides the ability to alter the response from cell cycle arrest to apoptosis by manipulating only the expression of long or short p53 isoforms.

Staphylococcus aureus is a significant human pathogen responsible for various nosocomial and community-acquired infections, leading to considerable morbidity and mortality worldwide. Temperate bacteriophages contribute to its virulence and facilitate the dissemination of pathogenicity traits. We isolated a novel siphovirus of the Phietavirus genus, ASZ22RN, derived from a prophage of an S. aureus clonal complex 7 strain and capable of propagating in the prophage-free laboratory strain RN4220. ASZ22RN either productively infected or lysed from without all 47 tested S. aureus clinical strains across 12 clonal complexes (CCs), demonstrating its ability to puncture their cell envelopes. When ASZ22RN was propagated in RN4220 cells harboring an S. aureus-Escherichia coli plasmid replicating via theta mode, it transduced the plasmid to plasmid-free RN4220 with low frequency. The transduction frequency increased by nearly five orders of magnitude when the plasmid contained a fragment of ASZ22RN DNA (terS). Most terS+ plasmid-transducing particles carried plasmid concatamers, while some carried plasmid-phage DNA hybrids, as demonstrated by DNA sequencing. Strains from all tested CCs served as recipients for transduction, regardless of the presence of type I restriction-modification enzymes targeting plasmid/phage DNA, or prophages with lysis-lysogeny switch regions conferring superinfection immunity to ASZ22RN. Our results indicate that intracellular phage defense systems do not prevent phage-mediated plasmid transfer and demonstrate a simple method for introducing plasmids constructed in E. coli into clinical S. aureus isolates. Moreover, the presence of the ASZ22RN lysis-lysogeny switch region in 21% of tested ASZ22RN-resistant strains highlights superinfection exclusion as a dominant mechanism of resistance to siphoviruses in staphylococci. IMPORTANCE:This study highlights the capacity of a newly isolated staphylococcal Phietavirus, ASZ22RN, to transfer a low-copy-number shuttle Staphylococcus aureus-Escherichia coli plasmid to various S. aureus strains representing major clonal complexes from among clinical isolates. By increasing the plasmid transduction efficiency in an ASZ22RN-specific manner, we show that the primary factor determining a given strain's ability to be a recipient in transduction is the capacity of transducing phage to puncture the cell envelopes of this strain. This can be determined not only based on productive phage infection but also lysis from without. Major intracellular mechanisms protecting S. aureus from productive phage infection do not impede the transduction-mediated acquisition of plasmids. Moreover, the lack of phage DNA in most of the plasmid-transducing virions indicates the lack of phage contamination in most transductants. Our results offer a promising approach for developing efficient pipelines to introduce plasmids constructed in E. coli to clinical S. aureus isolates.

Human milk (HM) is a complex biological fluid that plays a significant role in infant health, influenced by maternal dietary habits and body composition. This study aimed to explore how maternal diet and nutritional status affect the microbial composition of HM. In this pilot study, 15 mothers were recruited from a maternity ward and assessed for dietary habits through a semi-structured food frequency questionnaire and a 3-day dietary record. Maternal body composition was evaluated using bioelectrical impedance analysis. HM samples were collected for microbiota analysis, focusing on the diversity and composition of bacterial communities via 16S rRNA sequencing. The study identified that maternal nutrient intake significantly correlated with the composition of HM microbiota. Specifically, Firmicutes abundance showed positive correlations with animal protein (τ = 0.39; p = 0.043), total carbohydrates (τ = 0.39; p = 0.043), and vitamin A (τ = 0.429; p = 0.026). Bacteroidota was positively correlated with retinol (τ = 0.39; p = 0.043). Higher consumption of dietary fiber (>24 g/day) did not yield significant differences in bacterial composition compared to lower intake (<24 g/day) (p = 0.8977). Additionally, no significant differences were found in overall bacterial abundance across different maternal characteristics such as age, mode of delivery, or breastfeeding type. This study underscores the importance of maternal diet in shaping the HM microbiota, which may have implications for infant health. Dietary modifications during lactation could be a strategic approach to promote beneficial microbial colonization in HM. Further research is warranted to confirm these findings and explore the underlying mechanisms.

Atopic dermatitis (AD) is a common inflammatory skin disease, for which dysbiosis of the skin mycobiome is considered a triggering factor. The aim of this study was to explore the skin mycobiome of AD patients and healthy volunteers (HV). The study included 50 AD patients and as many HV. Culture-based species identification involved a battery of conventional phenotypic tests and PCR sequencing of the internal transcribed spacer (ITS) 1 and 2 regions within the rDNA cluster. Culture-independent, metataxonomic sequencing was performed with ITS1 as the target region. The overall culture-positive rate was higher in AD patients than in HV (74% vs 28%). Among the former, Rhodotorula spp. dominated, followed by Candida spp., Malassezia spp. and Naganishia albida. The congruence between PCR sequencing and phenotyping was 68.6%. Upon metataxonomy of AD samples, 33 (66%) demonstrated close clustering with HV samples ('control-like' AD), while 17 (34%) displayed a remarkably different mycobiome composition ('AD-specific'), with Cladosporium, Malassezia, Candida, Diplodia, Saccharomyces, Penicillium and Aspergillus genera showing increased abundance. Patients with 'AD-specific' mycobiomes were more commonly exposed to air-conditioning compared to 'control-like' AD patients (p = 0.030). A subset of patients with AD has a different cutaneous mycobiome make-up dominated by environmental moulds, and Malassezia and Candida yeasts. Anthropogenic factors may affect the cutaneous mycobiome composition in AD and should be taken into account in microbiome studies.

Objective: Advanced-stage ovarian cancer (OC) is among the most fatal female genital tract neoplasms worldwide. Although different genetic mechanisms have been shown to be involved in ovarian carcinogenesis, the role of TP53 introns methylation is still unresolved. We performed methylation analysis of introns 1, 3, and 4 of the TP53 to identify patterns in primary stage III OCs, corresponding metastases, and healthy tissues. Methods: The study involved samples of paraffin-embedded tissues obtained from 80 patients with stage III OCs, who underwent surgery at the Department of Gynecology and Gynecologic Oncology of the Military Institute of Medicine in Warsaw, Poland. Altogether, 40 serous-type G2/3 OCs and 40 endometrioid-type G2/3 OCs were included. From the same patient, metastatic and normal tissues were simultaneously analyzed. As a control group, 80 tissue samples were collected from patients after bariatric operations. Human ovarian cancer A2780 cell line was also investigated. Total genomic DNA was isolated from paraffin-embedded tissue blocks and the methylation analysis was performed by bisulfite DNA conversion, DNA amplification with specific primers, cloning, and DNA sequencing. Results: All of the samples of intron 1 of TP53 were un-methylated in OCs, metastatic tissues, and in healthy tissues from the same patient. Also, no methylation of TP53 intron 1 was detected in cells from the human A2780 ovarian cancer cell line and in all samples from control group. In all samples, introns 3 and 4 of the TP53 were methylated in primary tumors, metastatic tissue, and in healthy tissue from the same patient, in human A2780 ovarian cell line, and in DNA samples from healthy patients. None of the clinicopatholocal features was related to the TP53 introns methylation status. Conclusions: Our data on TP53 introns methylation sheds new light on the mechanism of p53 activity for a better understanding of cancer biology. The study suggests the existence of an additional regulation rule of TP53 activity that involves demethylation-methylation mechanisms. Methylation at introns 3 and 4 may also overall help in protecting TP53 against damage by viral restrictases or viral DNA integration.

Compounds derived from natural sources pave the way for novel drug development. Cyanobacteria is an ubiquitous phylum found in various habitats. The fitness of those microorganisms, within different biotopes, is partially dependent on secondary metabolite production. Their enhanced production under biotic/abiotic stress factors accounts for better survival rates of cells, and thereby cyanobacteria are as an enticing source of bioactive compounds. Previous studies have shown the potent activity of extracts and fractions from Pseudanabaena galeata (Böcher 1949) strain CCNP1313 against cancer cells and viruses. However, active agents remain unknown, as the selected peptides had no effect on the tested cell lines. Here, we present a bottom-up approach, pinpointing key structures involved in secondary metabolite production. Consisting of six replicons, a complete genome sequence of P. galeata strain CCNP1313 was found to carry genes for non-ribosomal peptide/polyketide synthetases embedded within chromosome spans (4.9 Mbp) and for a ribosomally synthesized peptide located on one of the plasmids (0.2 Mbp). Elucidation of metabolite synthesis pathways led to prediction of their structure. While none of the synthesis-predicted products were found in mass spectrometry analysis, unexplored synthetases are characterized by structural similarities to those producing potent bioactive compounds.

BACKGROUND:Plastids are usually involved in photosynthesis, but the secondary loss of this function is a widespread phenomenon in various lineages of algae and plants. In addition to the loss of genes associated with photosynthesis, the plastid genomes of colorless algae are frequently reduced further. To understand the pathways of reductive evolution associated with the loss of photosynthesis, it is necessary to study a number of closely related strains. Prototheca, a chlorophyte genus of facultative pathogens, provides an excellent opportunity to study this process with its well-sampled array of diverse colorless strains. RESULTS:We have sequenced the plastid genomes of 13 Prototheca strains and reconstructed a comprehensive phylogeny that reveals evolutionary patterns within the genus and among its closest relatives. Our phylogenomic analysis revealed three independent losses of photosynthesis among the Prototheca strains and varied protein-coding gene content in their ptDNA. Despite this diversity, all Prototheca strains retain the same key plastid functions. These include processes related to gene expression, as well as crucial roles in fatty acid and cysteine biosynthesis, and membrane transport. CONCLUSIONS:The retention of vestigial genomes in colorless plastids is typically associated with the biosynthesis of secondary metabolites. In contrast, the remarkable conservation of plastid membrane transport system components in the nonphotosynthetic genera Prototheca and Helicosporidium provides an additional constraint against the loss of ptDNA in this lineage. Furthermore, these genes can potentially serve as targets for therapeutic intervention, indicating their importance beyond the evolutionary context.

Background The antibiotic resistance determinants and associated mobile genetic elements (MGEs) were detected among Streptococcus pyogenes (group A streptococci [GAS]) clinical isolates of an M77 serotype collected in Poland between 2003 and 2017.Methods The genomes of 136 M77 GAS isolates were sequenced using short- and selected with long-read approach; whole genome sequences were analyzed to determine the genetic context of macrolide resistance determinants.Results The analysed strains were collected from in- and outpatients. Sequencing data analysis revealed that all strains carried the tet(O) gene. They were classified as a single sequence type, ST63. The unique erythromycin-resistance determinant, the erm(TR), was detected in 76.5% (n = 104) of isolates. It was found predominantly (n = 74) within a novel hybrid integrative conjugative element composed of the ICESp1108-like sequence and ICESp2906 variant, which was then named ICESp1109. However, in strains isolated before 2008, erm(TR) was located within ICESp2905 (n = 27) and in 3 strains - within stand-alone ICESp1108-like sequences.Conclusions Based on phylogenetic analysis results, the clonal dissemination of the macrolide-resistant S. pyogenes M77/ST63 strain with hybrid ICESp1109 was observed between 2008 and 2017. ICESp1109 is the novel hybrid ICE in gram-positive bacteria. A novel hybrid 103-kb integrative and conjugative element, ICESp1109, was identified in macrolide- and tetracycline-resistant Streptococcus pyogenes M77/ST63 strains collected in Poland between 2003 and 2017. Whole genome-based phylogenetic analysis revealed its clonal dissemination since 2008.

Plastids are usually involved in photosynthesis, but the secondary loss of this function is a widespread phenomenon in various lineages of algae and plants. In addition to the loss of genes associated with photosynthesis, the plastid genomes of colorless algae are frequently reduced further. To understand the pathways of reductive evolution associated with the loss of photosynthesis, it is necessary to study a number of closely related strains. Prototheca , a chlorophytean genus of facultative pathogens, provides an excellent opportunity to study this process with its well-sampled array of diverse colorless strains.We have sequenced the plastid genomes of 13 Prototheca strains and reconstructed a comprehensive phylogeny that reveals evolutionary patterns within the genus and among its closest relatives. Our robust phylogenomic analysis revealed three independent losses of photosynthesis among the Prototheca strains and considerable coding content variability in their ptDNA. Despite this diversity, all Prototheca strains retain the same key plastid functions. These include processes related to gene expression, as well as crucial roles in fatty acid and cysteine biosynthesis, membrane transport, and organelle division. While the retention of vestigial genomes in colorless plastids is typically associated with the biosynthesis of secondary metabolites, the remarkable conservation of plastid membrane transport and organellar division systems in the nonphotosynthetic genera Prototheca and Helicosporidium provides an additional constraint against the loss of ptDNA in this lineage. Furthermore, these genes can potentially serve as targets for therapeutic intervention, indicating their importance beyond the evolutionary context.### Competing Interest StatementThe authors have declared no competing interest.

Salmonella diarizonae (IIIb) is frequently isolated from reptiles and less frequently from birds and mammals. However, its isolation from invasive human infections has not been widely reported. Migratory mallard ducks are excellent bioindicators of pathogen presence and pathogen antibiotic resistance (AMR). We present the first isolation from a mallard duck in central Europe of the antibiotic-resistant Salmonella enterica subsp. diarizonae with the unique antigenic pattern 58:r:z53 and report its whole-genome sequencing, serosequencing, and genotyping, which enabled the prediction of its pathogenicity and comparison with phenotypic AMR. The isolated strain was highly similar to S. diarizonae isolated from humans and food. Twenty-four AMR genes were detected, including those encoding aminoglycoside, fluoroquinolone, macrolide, carbapenem, tetracycline, cephalosporin, nitroimidazole, peptide antibiotic, and disinfecting agent/antiseptic resistance. Six Salmonella pathogenicity islands were found (SPI-1, SPI-2, SPI-3, SPI-5, SPI-9, and SPI-13). An iron transport system was detected in SPI-1 centisome C63PI. Plasmid profile analyses showed three to be present. Sequence mutations in the invA and invF genes were noted, which truncated and elongated the proteins, respectively. The strain also harbored genes encoding type-III secretion-system effector proteins and many virulence factors found in S. diarizonae associated with human infections. This study aims to elucidate the AMR and virulence genes in S. enterica subsp. diarizonae that may most seriously threaten human health.

P1 is a model, temperate bacteriophage of the 94 kb genome. It can lysogenize representatives of the Enterobacterales order. In lysogens, it is maintained as a plasmid. We tested P1 interactions with the biocontrol P. agglomerans L15 strain to explore the utility of P1 in P. agglomerans genome engineering. A P1 derivative carrying the Tn9 (cmR) transposon could transfer a plasmid from Escherichia coli to the L15 cells. The L15 cells infected with this derivative formed chloramphenicol-resistant colonies. They could grow in a liquid medium with chloramphenicol after adaptation and did not contain prophage P1 but the chromosomally inserted cmR marker of P1 Tn9 (cat). The insertions were accompanied by various rearrangements upstream of the Tn9 cat gene promoter and the loss of IS1 (IS1L) from the corresponding region. Sequence analysis of the L15 strain genome revealed a chromosome and three plasmids of 0.58, 0.18, and 0.07 Mb. The largest and the smallest plasmid appeared to encode partition and replication incompatibility determinants similar to those of prophage P1, respectively. In the L15 derivatives cured of the largest plasmid, P1 with Tn9 could not replace the smallest plasmid even if selected. However, it could replace the smallest and the largest plasmid of L15 if its Tn9 IS1L sequence driving the Tn9 mobility was inactivated or if it was enriched with an immobile kanamycin resistance marker. Moreover, it could develop lytically in the L15 derivatives cured of both these plasmids. Clearly, under conditions of selection for P1, the mobility of the P1 selective marker determines whether or not the incoming P1 can outcompete the incompatible L15 resident plasmids. Our results demonstrate that P. agglomerans can serve as a host for bacteriophage P1 and can be engineered with the help of this phage. They also provide an example of how antibiotics can modify the outcome of horizontal gene transfer in natural environments. Numerous plasmids of Pantoea strains appear to contain determinants of replication or partition incompatibility with P1. Therefore, P1 with an immobile selective marker may be a tool of choice in curing these strains from the respective plasmids to facilitate their functional analysis.

IntroductionThe introduction of pneumococcal conjugate vaccines (PCV) into the national immunization programs (NIPs) has significantly reduced the number of pneumococcal infections. However, infections caused by isolates of non-vaccine serotypes (NVT) started spreading shortly thereafter and strains of NVT 19A have become the main cause of invasive pneumococcal disease burden worldwide. The aim of the study was to characterize serotype 19A invasive pneumococci of GPSC1/CC320 circulating in Poland before the introduction of PCV into the Polish NIP in 2017 and to compare them to isolates from other countries where PCVs were implemented much earlier than in Poland.MethodsAll the GPSC1/CC320 isolates were analyzed by serotyping, susceptibility testing, and whole genome sequencing followed by analyses of resistome, virulome, and core genome multilocus sequence typing (cgMLST), including comparative analysis with isolates with publicly accessible genomic sequences (PubMLST).ResultsDuring continuous surveillance the NRCBM collected 4237 invasive Streptococcus pneumoniae isolates between 1997 and 2016, including 200 isolates (4.7%) of serotype 19A. The most prevalent among 19A pneumococci were highly resistant representatives of Global Pneumococcal Sequence Cluster 1/Clonal Complex 320, GPSC1/CC320 (n = 97, 48.5%). Isolates of GPSC1/CC320 belonged to three sequence types (STs): ST320 (75.2%) ST4768 (23.7%), and ST15047 (1.0%), which all represented the 19A-III cps subtype and had complete loci for both PI-1 and PI-2 pili types. On the basis of the cgMLST analysis the majority of Polish GPSC1/CC320 isolates formed a group clearly distinct from pneumococci of this clone observed in other countries.ConclusionBefore introduction of PCV in the Polish NIP we noticed an unexpected increase of serotype 19A in invasive pneumococcal infections, with the most common being representatives of highly drug-resistant GPSC1/CC320 clone, rarely identified in Europe both before and even after PCV introduction.

Background Streptococcus pneumoniae (pneumococcus) represents an important human pathogen, responsible for respiratory and invasive infections in the community. The efficacy of polysaccharide conjugate vaccines formulated against pneumococci is reduced by the phenomenon of serotype replacement in population of this pathogen. The aim of the current study was to obtain and compare complete genomic sequences of two pneumococcal isolates, both belonging to ST320 but differing by the serotype. Results Here, we report genomic sequences of two isolates of important human pathogen, S. pneumoniae. Genomic sequencing resulted in complete sequences of chromosomes of both isolates, 2,069,241 bp and 2,103,144 bp in size, and confirmed the presence of cps loci specific for serotypes 19A and 19F. The comparative analysis of these genomes revealed several instances of recombination, which involved not only S. pneumoniae but also presumably other streptococci as donors. Conclusions We report the complete genomic sequences of two S. pneumoniae isolates of ST320 and serotypes 19A and 19F. The detailed comparative analysis of these genomes revealed the history of several recombination events, clustered in the region including the cps locus.

Antarctic hairgrass, Deschampsia antarctica Desv. (Poaceae), is one of the two flowering plants that have an established presence in Maritime Antarctica. It has adapted to varying edaphic and climatic conditions. D. antarctica’s associations with soil-dwelling bacteria have long been suspected to add to its remarkable resilience. In this study, three compartments within D. antarctica root system and soil have been investigated as microbial habitats: the rhizosphere (root-adjacent soil particles), rhizoplane (root surface) and endosphere (root interior). For this purpose, a modification of existing methods of bacterial extraction from cryophilic plant rhizocompartments was devised with the temperature sensitivity of the source material in mind. Next-generation targeted 16S rRNA gene amplicon sequencing and a culture-based approach were employed to explore the bacterial community residing within those three rhizocompartments. Results showed that each of the compartments housed a distinct bacterial community not only in terms of phylogenetic diversity but also concerning plant-beneficial and -adaptive traits. Although most cultivable bacteria displayed plant-growth promoting abilities such as rock-phosphate solubilisation and phytohormone production (Arthrobacter spp.), some could be potential pathogens (Clavibacter sp.). This study highlights the need for amending the still scarce information on the microbiome of Antarctic flora but also gives tools and insight to explore it further.

Pseudomonas aeruginosa, a human opportunistic pathogen, is a common cause of nosocomial infections. Its ability to survive under different conditions relies on a complex regulatory network engaging transcriptional regulators controlling metabolic pathways and capabilities to efficiently use the available resources. P. aeruginosa PA3973 encodes an uncharacterized TetR family transcriptional regulator. In this study, we applied a transcriptome profiling (RNA-seq), genome-wide identification of binding sites using ChIP-seq, as well as the phenotype analyses to unravel the biological role of PA3973. Transcriptional profiling of P. aeruginosa PAO1161 overexpressing PA3973 showed changes in the mRNA level of 648 genes. Concomitantly, ChIP-seq analysis identified more than 300 PA3973 binding sites in the P. aeruginosa genome. A 13 bp sequence motif was indicated as the binding site of PA3973. The PA3973 regulon encompasses the PA3972-PA3971 genes encoding a probable acyl-CoA dehydrogenase and a thioesterase. In vitro analysis showed PA3973 binding to PA3973p. Accordingly, the lack of PA3973 triggered increased expression of PA3972 and PA3971. The ∆PA3972-71 PAO1161 strain demonstrated impaired growth in the presence of stress-inducing agents hydroxylamine or hydroxyurea, thus suggesting the role of PA3972-71 in pathogen survival upon stress. Overall our results showed that TetR-type transcriptional regulator PA3973 has multiple binding sites in the P. aeruginosa genome and influences the expression of diverse genes, including PA3972-PA3971, encoding proteins with a proposed role in stress response.

Colobanthus quitensis (Kunth) Bartl. and Deschampsia antarctica Desv. are the only Magnoliophyta to naturally colonize the Antarctic region. The reason for their sole presence in Antarctica is still debated as there is no definitive consensus on how only two unrelated flowering plants managed to establish breeding populations in this part of the world. In this study, we have explored and compared the rhizosphere and root-endosphere dwelling microbial community of C . quitensis and D . antarctica specimens sampled in maritime Antarctica from sites displaying contrasting edaphic characteristics. Bacterial phylogenetic diversity (high-throughput 16S rRNA gene fragment targeted sequencing) and microbial metabolic activity (Biolog EcoPlates) with a geochemical soil background were assessed. Gathered data showed that the microbiome of C . quitensis root system was mostly site-dependent, displaying different characteristics in each of the examined locations. This plant tolerated an active bacterial community only in severe conditions (salt stress and nutrient deprivation), while in other more favorable circumstances, it restricted microbial activity, with a possibility of microbivory-based nutrient acquisition. The microbial communities of D . antarctica showed a high degree of similarity between samples within a particular rhizocompartment. The grass’ endosphere was significantly enriched in plant beneficial taxa of the family Rhizobiaceae , which displayed obligatory endophyte characteristics, suggesting that at least part of this community is transmitted vertically. Ultimately, the ecological success of C . quitensis and D . antarctica in Antarctica might be largely attributed to their associations and management of root-associated microbiota.