Free-living amoebae represent a significant eukaryotic group that thrives in drinking water systems, posing considerable risks to water quality due to their inherent pathogenicity and associations with various microorganisms. However, the symbiotic microbial profiles of different amoeba species and the impact of amoeba-bacteria interactions on the antibiotic resistome within drinking water systems remain poorly understood. In this study, we obtained 24 amoeba isolates from tap water, encompassing diverse phyla within the amoeba lineage. Through metagenome sequencing, we uncovered variations in symbiotic microbiome composition across different amoeba species and strains. Notably, amoebae acted as vectors for human pathogens, including bacteria and viruses. The majority of symbionts carried multiple antibiotic-resistance genes and virulence factors. Furthermore, dominant symbiotic species could be cultured independently, underscoring the critical role of amoebae in preserving and transmitting antibiotic-resistant opportunistic pathogens in drinking water systems. Disinfection experiments demonstrated highly diverse viability of amoebae and their protective capabilities for symbionts against chlorine disinfection. Our findings expand the germplasm bank for amoebae and symbiotic bacteria derived from tap water and emphasize the necessity for further research on amoeba-bacteria symbiosis to ensure drinking water quality and public health safety.

As emerging pollutants, microplastics have become pervasive on a global scale, inflicting significant harm upon ecosystems. However, the impact of these microplastics on the symbiotic relationship between protists and bacteria remains poorly understood. In this study, we investigated the mechanisms through which nano- and microplastics of varying sizes and concentrations influence the amoeba-bacterial symbiotic system. The findings reveal that nano- and microplastics exert deleterious effects on the adaptability of the amoeba host, with the magnitude of these effects contingent upon particle size and concentration. Furthermore, nano- and microplastics disrupt the initial equilibrium in the symbiotic relationship between amoeba and bacteria, with nano-plastics demonstrating a reduced ability to colonize symbiotic bacteria within the amoeba host when compared to their microplastic counterparts. Moreover, nano- and microplastics enhance the relative abundance of antibiotic resistance genes and heavy metal resistance genes in the bacteria residing within the amoeba host, which undoubtedly increases the potential transmission risk of both human pathogens and resistance genes within the environment. In sum, the results presented herein provide a novel perspective and theoretical foundation for the study of interactions between microplastics and microbial symbiotic systems, along with the establishment of risk assessment systems for ecological environments and human health.

Amoeba-bacteria interactions are prevalent in both natural ecosystems and engineered environments. Amoebae, as essential consumers, hold significant ecological importance within ecosystems. Besides, they can establish stable symbiotic associations with bacteria. Copper plays a critical role in amoeba predation by either killing or restricting the growth of ingested bacteria in phagosomes. However, certain symbiotic bacteria have evolved mechanisms to persist within the phagosomal vacuole, evading antimicrobial defenses. Despite these insights, the impact of copper on the symbiotic relationships between amoebae and bacteria remains poorly understood. In this study, we investigated the effects of copper stress on amoebae and their symbiotic relationships with bacteria. Our findings revealed that elevated copper concentration adversely affected amoeba growth and altered cellular fate. Symbiont type significantly influenced the responses of the symbiotic relationships to copper stress. Beneficial symbionts maintained stability under copper stress, but parasitic symbionts exhibited enhanced colonization of amoebae. Furthermore, copper stress favored the transition of symbiotic relationships between amoebae and beneficial symbionts toward the host's benefit. Conversely, the pathogenic effects of parasitic symbionts on hosts were exacerbated under copper stress. This study sheds light on the intricate response mechanisms of soil amoebae and amoeba-bacteria symbiotic systems to copper stress, providing new insights into symbiotic dynamics under abiotic factors. Additionally, the results underscore the potential risks of copper accumulation in the environment for pathogen transmission and biosafety.

Heavy metals and micro-/nanoplastic pollution seriously threaten the environment and ecosystems. While many studies investigated their effects on diverse microbes, few studies have focused on soil protists, and it is unclear how soil protists respond to the combined effect of micro-/nanoplastics and heavy metals. This study investigated how soil protistan and bacterial communities respond to single or combined copper and micro-/nanoplastics. The bacterial community exhibited an instantaneous response to single copper pollution, whereas the combined pollution resulted in a hysteresis effect on the protistan community. Single and combined pollution inhibited the predation of protists and changed the construction of ecological networks. Though single and combined pollution did not significantly affect the overall community structure, the exposure experiment indicated that combined pollution harmed soil amoeba's fitness. These findings offer valuable new insights into the toxic effects of single and combined pollution of copper and plastics on soil protistan and bacterial communities. Additionally, this study shows that sequencing-based analyses cannot fully reflect pollutants' adverse effects, and both cultureindependent and dependent methods are needed to reveal the impact of pollutants on soil microbes.

Drinking water systems host a wide range of microorganisms essential for biosafety. However, one major group of waterborne pathogens, protozoa, is relatively neglected compared to bacteria and other microorganisms. Until now, little is known about the growth and fate of protozoa and their associated bacteria in drinking water systems. In this study, we aim to investigate how drinking water treatment affects the growth and fate of protozoa and their associated bacteria in a subtropical megacity. The results showed that viable protozoa were prevalent in the city's tap water, and amoebae were the major component of tap water protozoa. In addition, protozoan-associated bacteria contained many potential pathogens and were primarily enriched in amoeba hosts. Furthermore, this study showed that current drinking water disinfection methods have little effect on protozoa and their associated bacteria. Besides, ultrafiltration membranes unexpectedly served as an ideal growth surface for amoebae in drinking water systems, and they could significantly promote the growth of amoeba-associated bacteria. In conclusion, this study shows that viable protozoa and their associated bacteria are prevalent in tap water, which may present an emerging health risk in drinking water biosafety.

A novel bacterium, designated E313T, was isolated from brown algae Saccharina japonica in Weihai, China. The strain is a Gram-stain-negative, non-flagellated, non-gliding, aerobic, rod-shaped bacterium that grows optimally at 28 °C with pH levels between 7.0 and 7.5 and in the presence of 2–3

Spiribacter is the most abundant bacterial genus in the intermediate-salinity zones of hypersaline environments. However, Spiribacter strains are extremely difficult to isolate in pure culture. Therefore, the characteristics, genome features, and adaption mechanisms that allow Spiribacter strains to thrive in highly saline conditions are largely unknown. Here, we show that Spiribacter is predominant in brines from marine solar salterns and sulfate-type salt lakes with intermediate to saturated salinities. Using a high-salt medium, we isolated a novel strain, Spiribacter halobius E85T, which possesses a relatively large and distinct genome. The genome of strain E85T has a length of 4.17 Mbp, twice that of other Spiribacter species genomes and the largest described genome within the family Ectothiorhodospiraceae. Comparative genomic analyses indicate that approximately 50% of E85T genes are strain-specific, endowing functional differences in its metabolic capabilities, biosynthesis of compatible solutes, and transport and pumping of solutes into the cell from the environment. Hundreds of insertion sequences result in many pseudogenes and frequent gene fragment rearrangements in the E85T genome. Dozens of genomic islands, which show a significant preference for replication, recombination and repair, and cell motility and may have been gained from other bacterial species, are scattered in the genome. This study provides important insights into the general genetic basis for the abundance of Spiribacter in hypersaline environments and the strain-specific genome evolutionary strategies of strain E85T.

Two novel rod-shaped and Gram-negative bacterial strains, designated A6E486 T and 5E331 T , were isolated from a coastal sediment sample taken from Xiaoshi Island, Weihai, China, and a fresh kelp sample collected from a kelp culture area, Rongcheng, China, respectively. Growth of strain A6E486 T occurred at 20°C–43°C (optimum, 33°C–35°C) at pH 5.5–7.5 (optimum, 6.5) and in the presence of 1.0%–5.5% (w/v) NaCl (optimum, 2.5%–3.0%). Strain 5E331 T grew with 1.5%–5.0% (w/v) NaCl (optimum, 3.0%) at 15°C–40°C (optimum, 33°) and pH 6.0–8.5 (optimum, 7.0). The similarity of 16S rRNA gene sequence between the two strains was 95.2%. The phylogenetic analysis based on 16S rRNA gene sequence showed that strains A6E486 T and 5E331 T belong to the genus Kordiimonas , sharing the highest similarity to the genus Kordiimonas (94.6%–96.8%, 94.9%–96.1%, respectively). Strains A6E486 T and 5E331 T had percentage of conserved protein (POCP) values of 56.0%–67.3% and average nucleotide identity (ANI) values of 68.8%–73.1% to members of the genus Kordiimonas . The major polar lipids detected in the two strains were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), and unidentified glycolipids, aminolipids, and lipids. The predominant respiratory quinone of the two strains was Q-10. Based upon the results presented in this study, strains A6E486 T and 5E331 T represent two novel species of the genus Kordiimonas , for which the names Kordiimonas marina and Kordiimonas laminariae are proposed with the type strains A6E486 T (= KCTC 82758 T = MCCC 1H00470 T ) and 5E331 T (= KCTC 92199 T = MCCC 1H00515 T ), respectively. Comparative genomic analysis showed that seven species of the genus Kordiimonas shared 1,258 core genes and had differences in carbohydrate metabolism, energy metabolism, and cofactor and vitamin metabolism. The pan-genome of the genus Kordiimonas was open. The prediction of secondary metabolites showed that most strains of the genus Kordiimonas had the ability to produce homoserine lactones, one of the most important signal molecules in the quorum-sensing system of Gram-negative bacteria. Additionally, numerous genes involved in bacterial defense, motility and chemotaxis, cold adaptation, and environment stress response were found in the genus Kordiimonas , indicating the marine-adapted lifestyle of members of the genus Kordiimonas .

An orange-pigmented, Gram-negative, strictly aerobic, non-flagellated, and rod-shaped bacterium, designated strain 1368T, was isolated from coastal sediment collected from Xiaoshi Island, Weihai, China. The optimal growth conditions were determined to be at 37 °C, pH 7.0 and in 2%–3% (w/v) NaCl. According to the phylogenetic analysis of the 16S rRNA gene sequence, strain 1368T showed the highest sequence similarity of 97.8% to Robertkochia marina JCM 18552T, followed by R. solimangrovi KCTC 72252T (96.5%). The DNA G + C content was 45.7% and the major fatty acids were iso-C15:0, iso-C15:1 G and iso-C17:0 3-OH. The major polar lipids were one phosphatidylethanolamine, two unidentified aminolipids and two unidentified lipids. The predominant respiratory quinone was menaquinone-6 (MK-6). The DNA–DNA relatedness between the genomes of strain 1368T and R. marina JCM 18552T and R. solimangrovi KCTC 72252T was 18.2% and 18.4%, and the average nucleotide identity were 70.6% and 73.8%, respectively. On the basis of the phenotypic, genetic and physiological characteristics, strain 1368T was suggested to represent a novel species of the genus Robertkochia, for which the name Robertkochia sediminum sp. nov. is proposed. The type strain is 1368T (MCCC 1H00444T = KCTC 82418T).