Microalgae are the richest source of natural carotenoids—accessory photosynthetic pigments used as natural antioxidants, safe colorants, and nutraceuticals. Microalga Bracteacoccus aggregatus IPPAS C-2045 responds to stresses, including high light, with carotenogenesis—gross accumulation of secondary carotenoids (the carotenoids structurally and energetically uncoupled from photosynthesis). Precise mechanisms of cytoplasmic transport and subcellular distribution of the secondary carotenoids under stress are still unknown. Using multimodal imaging combining micro-Raman imaging (MRI), fluorescent lifetime (τ) imaging (FLIM), and transmission electron microscopy (TEM), we monitored ultrastructural and biochemical rearrangements of B. aggregatus cells during the stress-induced carotenogenesis. MRI revealed a decline in the diversity of molecular surrounding of the carotenoids in the cells compatible with the relocation of the bulk of the carotenoids in the cell from functionally and structurally heterogeneous photosynthetic apparatus to the more homogenous lipid matrix of the oleosomes. Two-photon FLIM highlighted the pigment transformation in the cell during the stress-induced carotenogenesis. The structures co-localized with the carotenoids with shorter τ (mainly chloroplast) shrunk, whereas the structures harboring secondary carotenoids with longer τ (mainly oleosomes) expanded. These changes were in line with the ultrastructural data (TEM). Fluorescence of B. aggregatus carotenoids, either in situ or in acetone extracts, possessed a surprisingly long lifetime. We hypothesize that the extension of τ of the carotenoids is due to their aggregation and/or association with lipids and proteins. The propagation of the carotenoids with prolonged τ is considered to be a manifestation of the secondary carotenogenesis suitable for its non-invasive monitoring with multimodal imaging.

The productivity of microalgal cultures and their resilience to unfavorable conditions is largely determined by the availability of mineral nutrients, particularly nitrogen. Nitrogen starvation is a strong stressor that induces a broad range of responses in microalgae at the cell and cell population (culture) levels. These responses such as lipogenesis and secondary carotenogenesis are widely used in biotechnology to obtain valuable secondary metabolites of microalgae. It was believed that microalgal cells lack specific structures that function as long-term nitrogen depot, but recent studies assigned this role to microcrystalline inclusions constituted by nitrogenous bases (most often guanine). It is also known that purine microcrystals are biophotonic structures widespread in nature. These structures modify the intensity and spectral composition of radiation in illuminated cells and tissues of living organisms. In this regard, we studied (i) the dynamics of the formation of guanine crystals in the cells of green carotenogenic microalgae from the genus Coelastrella (C. thermophila NAMSU CM1/23 and C. rubescens IPPAS C-2066) depending on the availability of nitrogen in the medium and (ii) the effect of the presence of these crystals on cell resilience to high light intensity. Nitrogen-rich crystal inclusions were accumulated in cells when the cultures reached the stationary growth phase in a medium with ample nitrate nitrogen. During rapid growth, these inclusions were hardly detectable in the cells and disappeared during cultivation in the absence of nitrogen. Optical polarization microscopy and Raman microspectroscopy demonstrated that these nitrogen-rich inclusions are birefringent microcrystals composed of guanine. C. thermophila cells harboring abundant guanine crystals showed resistance to short-term (10–15 min) exposure to high-intensity light (600 µmol PAR quanta/m2/s). The results obtained are discussed in the context of the multifaceted role of guanine crystals in the stress tolerance of microalgae.

Coal mining endangers the environment by contaminating of soil, surface, and ground water with coal mine drainage water (CMW) polluted by heavy metals. Microalgal cultures, hyper-accumulators of heavy metals, represent a promising solution for CMW biotreatment. A bottleneck of this approach is the availability of microalgal strains that combine a large capacity for heavy metal biocapture with a high resilience to their toxic effects. Biotopes contaminated with heavy metals are frequently inhabited by microalgae evolved to be resilient to heavy metal toxicity. Therefore, the autochthonous (locally isolated) microalgal strains are a priori considered to be superior for biotreatment of heavy metal-polluted waste streams. Still, strains from biocollections combine a high pollutant resilience with other biotechnologically important traits such as high productivity, high CO2 sequestration rate etc. Moreover, the strains available “off-the-shelf” would enable rapid development of bioprocesses. Here, we compared the efficiency of CMW biotreatment with autochthonous (isolated from the coal mine drainage sump) and allochthonous microalgae (from a geographically distant phosphate-polluted site). Both autochthonous strains and allochthonous strains turned to be interchangeable under our experimental conditions. Still, the autochthonous strains showed a higher capacity for sequestration of iron, zinc, and manganese, the specific pollutants of the studied CMW. It can be important when the duration of unattended exploitation of the CMW treatment facility is a priority or spikes of the heavy metal concentration in CMW are expected. Therefore, the “off-the-shelf” strains can be a plausible solution for rapid development of CMW treatment technologies from scratch (although screening for acute toxicity of CMW is imperative). On the other hand, locally isolated strains can offer distinct advantages and should be always considered if sufficient time and other resources are available for the development of microalgae-based process for CMW treatment.

Pharmaceuticals including antibiotics are among the hazardous micropollutants (HMP) of the environment. Incomplete degradation of the HMP leads to their persistence in water bodies causing a plethora of deleterious effects. Conventional wastewater treatment cannot remove HMP completely and a promising alternative comprises biotechnologies based on microalgae. The use of immobilized microalgae in environmental biotechnology is advantageous since immobilized cultures allow the recycling of the microalgal cells, support higher cell densities, and boost tolerance of microalgae to stresses including HMP. Here, we report on a comparative study of HMP (exemplified by the antibiotic ceftriaxone, CTA) removal by suspended and chitosan-immobilized cells of Lobosphaera sp. IPPAS C-2047 in flasks and in a column bioreactor. The removal of CTA added in the concentration of 20 mg/L was as high as 65% (in the flasks) or 85% (in the bioreactor). The adsorption on the carrier and abiotic oxidation were the main processes contributing 65-70% to the total CTA removal, while both suspended and immobilized cells took up 25-30% of CTA. Neither the immobilization nor CTA affected the accumulation of arachidonic acid (ARA) by Lobosphaera sp. during bioreactor tests but the subsequent nitrogen deprivation increased ARA accumulation 2.5 and 1.7 times in the suspended and chitosan-immobilized microalgae, respectively. The study of the Lobosphaera sp. microbiome revealed that the immobilization of chitosan rather than the CTA exposure was the main factor displacing the taxonomic composition of the microbiome. The possibility and limitations of the use of chitosan-immobilized Lobosphaera sp. IPPAS C-2047 for HMP removal coupled with the production of valuable long-chain polyunsaturated fatty acids is discussed.

A novel chlorophyte algae strain with outstanding resilience to high inorganic phosphate (Pi) concentrations in the medium was isolated from a phosphorus-polluted site near a rock phosphate mine. According to the morphological, ultrastructural and genetic criteria the strain was assigned to the species Micractinium simplicissimum H.Chae, H.-G. Choi & J.H.Kim. This strain retained cell viability and growth capacity in the presence of Pi concentrations up to 14 g L–1. The uptake of Pi by the cells was moderate (equal to ca. 0.7% increase in cell dry weight P percentage) regardless of the amount of the exogenic Pi added to the culture. At the same time, approximately a half of the Pi removed by the M. simplicissimum from the culture was reversely adsorbed by the cell surface and/or the intercellular matrix and cell debris. The ultrastructural studies indicated the metabolically active status of the cells together with the presence of phosphorus-rich (likely, polyphosphate) inclusions outside and inside the cells (mainly in vacuoles). We hypothesized that the Pi resilience of the studied strain stems from its high Pi adsorption capacity together with its ability to throttle the Pi influx into the cell preventing the rapid buildup of intracellular Pi and potentially toxic short-chain polyphosphate.

The results of the complex multimodal optical study utilizing Raman and fluorescence lifetime imaging of the cells of micro alga Bracteacoccus aggregatus BM5/15 are presented.

Carotenoids astaxanthin and β-carotene are widely used natural antioxidants. They are key components of functional food, cosmetics, drugs and animal feeding. They hold leader positions on the world carotenoid market. In current work, we characterize the new strain of the green microalga Bracteacoccus aggregatus BM5/15 and propose the method of its culturing in a bubble-column photobioreactor for simultaneous production of astaxanthin and β-carotene. Culture was monitored by light microscopy and pigment kinetics. Fatty acid profile was evaluated by tandem gas-chromatography–mass spectrometry. Pigments were obtained by the classical two-stage scheme of autotrophic cultivation. At the first, vegetative, stage biomass accumulation occurred. Maximum specific growth rate and culture productivity at this stage were 100–200 mg∙L−1∙day−1, and 0.33 day−1, respectively. At the second, inductive, stage carotenoid synthesis was promoted. Maximal carotenoid fraction in the biomass was 2.2–2.4%. Based on chromatography data, astaxanthin and β-carotene constituted 48 and 13% of total carotenoid mass, respectively. Possible pathways of astaxanthin synthesis are proposed based on carotenoid composition. Collectively, a new strain B. aggregatus BM5/15 is a potential biotechnological source of two natural antioxidants, astaxanthin and β-carotene. The results give the rise for further works on optimization of B. aggregatus cultivation on an industrial scale.

To date, it has been increasingly clear, that microbiota plays essential role in the host microorganism. Due to high phylogenetic diversity and wide distribution understanding of gut microbiota of fish is ambiguous. We elucidate previously undescribed diversity of bacteria in the White Sea fish posterior intestine based on 16S rRNA metabarcoding: shorthorn sculpin (Myoxocephalus scorpius), lumpfish (Cyclopterus lumpus) arctic flounder (Liopsetta glacialis), cod (Gadus morhua), and herring (Clupea pallasii). Proteobacteria were most abundant in all the samples. All datasets contained high number of reads corresponded to Psychrobacter, Halomonas, Pseudoalteromonas and Vibrio abundant in the White Sea water.Vast majority of bacterial reads corresponded to the Vibrionaceae (Aliivibrio, Vibrio, and Photobacterium). It is in accordance with our previous study focused on bioluminescent bacteria, where we isolated strains of these genera from the same fish intestine samples. The datasets of G. morhua and Cl. pallasii were enriched by reads of Shewanella (also isolated previously microbiologically due to luminescence of some its strains); the datasets of G. morhua and M. scorpius contained high number of Mycoplasma, which is in line with previous reports on the microbiome of marine fish gut from other geographical regions. Collectively, on the one hand, the study is a confirmation of known data on marine fish gut microbiome, on the other hand, it reveals some specific patterns of White Sea fish gut microbiota, e.g. presence of bacteria common for water from this region.

The internal surface of the animal gastrointestinal tract is covered by microbial biofilms. They play an important role in the development and functioning of the host organism and protect it against pathogens. Microbial communities of gastrointestinal biofilms are less elucidated than luminal microbiota. Therefore, the studies of biofilm formation by gastrointestinal microorganisms are a topical issue. For the first time, we report the formation of a biofilm in vitro by the strains of bioluminescent bacteria isolated from the intestines of marine fish. These bacteria exhibit co-aggregation and tend to attach to solid surfaces. The attachment of cells is accompanied by appearance of the pili. Then, we observed the formation of microcolonies and the production of extracellular polymer substances (EPSs) connecting bacterial cells into an integrated system. The presence of acidic polysaccharides is shown in the EPS when using the ruthenium red staining. Acidic polysaccharides in this matrix is a biochemical evidence of microbial biofilms. On the fibers of the polymer matrix, these bacteria form the "mushroom body"-type structures. Matured biofilms exhibit a specific three-dimensional architecture with pores and channels formed by cells and EPS. We also demonstrated the formation of a biofilm by binary culture of the luminous enterobacterium Kosakonia cowanii and a Gram-positive Macrococcus sp. The data obtained help to understand the role of these bacteria in the intestines of fish. They lead to a new study in the field of investigation of the intestinal microbiome of fish.

The biodiversity of microbial communities from phosphorus-polluted sites from Northern and Southern regions was investigated, groups of microorganisms with biotechnological potential were detected. According to the results, samples from Southern regions were characterized by lower biodiversity than the northern ones.

Bioluminescence is a spectacular feature of some prokaryotes. In the present work, we address the distribution of bioluminescence among bacteria isolated from the White Sea finfishes. Luminous bacteria are widely distributed throughout the World Ocean. Many strains have been isolated and described for tropical latitudes, while Nordic seas still remain quite a white spot in studying bioluminescence of bacteria. We describe the strains related to the two main genera of luminous bacteria, Photobacterium and Aliivibrio, as well as Shewanella and Vibrio. They are related to families Vibrionaceae and Shewanellaceae of the Gammaproteobacteria class. Here, we at the first time, report the bioluminescence of the Enterobacteriaceae Kosakonia cowanii. Moreover, we applied the polyphasic approach to identify and describe the isolated microorganisms. The data on sequencing, diversity of cell fine structure, and light emission spectra at room temperature on the solid medium are discussed. The bacteria are characterized by features in their light emission spectra. It may reflect possible molecular mechanisms of bioluminescence as well as features of bacterial composition. The obtained data expands the existing body of knowledge about the bioluminescence spread among the bacteria of Nordic latitudes and provides complex information that is crucial for their precise identification.

Carotenogenic microalgae are unicellular photosynthetic organisms with the ability to accumulate carotenoids. Carotenoid accumulation is a protective reaction against environmental stress factors, such as bright light and extreme temperatures. It makes the survival of these microorganisms under harsh environmental conditions possible. The diversity of carotenogenic microalgae has been described in detail for Central Europe and North America, as well as for tropical and subtropical latitudes with relatively favorable environments. However, data about these microorganisms in polar and subpolar latitudes are scarce and restricted to few reports. We isolated several strains of carotenogenic microalgae from the coastal zone of the White Sea, where they were abundant. The obtained microalgae related to four species of Chlorophytes: Haematococcus lacustris, H. rubicundus, Coelastrella aeroterrestrica and Bracteacoccus aggregatus. The last three species have been reported for polar latitudes for the first time. Most likely, carotenogenic algae in the White Sea coast are abundant due to their high physiological and metabolic plasticity, which is essential for surviving under adverse conditions of the northern regions. Pigment composition of the strains is provided. Their predominant carotenoids were astaxanthin and beta-carotene. Further, the obtained strains may be considered as potential producers of natural pigments for biotechnology.

Haematococcus lacustris is a biotechnologically important green unicellular alga producing widely used keta-karotenoid astaxanthin. In natural habitats, it exists in the form of algal-bacterial community, and under laboratory conditions, it is also accompanied by bacteria. The issue of the bacterial composition of industrial algal cultures is widely recognized as important. However, there is a dearth of information about bacterial composition of H. lacustris communities. In current work, we analyze the composition of natural H. lacustris communities from the White Sea coastal temporal rock ponds. For the first time, a 16S rRNA gene-based metagenome of natural H. lacustris bacterial communities has been generated. Main results of its analysis are as follow. Bacterial families Comamonadaceae, Cytophagaceae, Xanthomonadaceae, Acetobacteraceae, Rhodobacteraceae, and Rhodocyclaceae were observed in all studied H. lacustris natural communities. They also contained genera Hydrogenophaga and Cytophaga. Bacteria from the Hydrogenophaga genus were present in H. lacustris cultures after their isolation under the conditions of laboratory cultivation. Similar to other planktonic microalgae, H. lacustris forms a phycosphere around the cells. In this zone, bacteria attached to the algal surface. The contact between H. lacustris and bacteria is maintained even after sample drying. The study provides information about possible members of H. lacustris core microbiome, which can be presented in the industrial and laboratory cultures of the microalga.

The state of cobalt fluoride in the vicinity of the critical value H c of a longitudinal magnetic field H, in which the magnetic subsystem of a CoF2 crystal with a strong Dzyaloshinskii interaction is transformed from the antiferromagnetic phase into the canted phase, has been investigated taking into account the increasing number of experimental studies related to the use of cobalt fluoride. It has been found that, despite the unusually high magnetic anisotropy of the crystal, the state of the magnetic subsystem at H = H c is extremely sensitive to a small deviation of the vector H from the C 4 axis. Another feature is that the high sensitivity disappears with an increase or decrease in the magnetic field by only a few thousandths of H c . The results of the investigations performed in this work are applicable to magnetically ordered crystals FeF3 and Cu2OSeO3, which, as well as the CoF2 crystals, are characterized by a strong Dzyaloshinskii interaction and a significant magnetic anisotropy. The revealed anomaly in the reduction of the effective magnetic anisotropy is of interest in connection with numerous attempts to decrease the magnetic anisotropy in crystals with giant magnetostriction, which are necessary for the use as sensors and vibrators.

С учетом роста экспериментальных исследований, связанных с использованием фторида кобальта, изучено состояние фторида кобальта в окрестности критического значения Hc продольного магнитного поля H, при котором магнитная подсистема кристалла CoF2 с большим взаимодействием Дзялошинского переходит из антиферромагнитной фазы в угловую. Обнаружено, что, несмотря на необычайно большую величину магнитной анизотропии кристалла, состояние магнитной подсистемы при H=Hc оказалось крайне чувствительным к незначительному отклонению вектора H от оси C4. Другая особенность состоит в том, что эта высокая чувствительность исчезает при увеличении или уменьшении магнитного поля всего лишь на тысячные доли Hc. Выполненные исследования применимы к магнитоупорядоченным кристаллам FeF3, Cu2OSeO3, которые, так же как и CoF2, обладают сильным взаимодействием Дзялошинского и значительной магнитной анизотропией. Обнаруженная аномалия в уменьшении эффективной магнитной анизотропии представляет интерес в связи с многочисленными попытками уменьшить магнитную анизотропию в кристаллах с гигантской магнитострикцией, которые необходимы для использования в качестве сенсоров и вибраторов.

Similarity and diversity of the phenotype and nucleotide sequences of certain genome loci among the single-celled microalgae isolated from White Sea benthic invertebrates were studied to extend the knowledge of oxygenic photoautotrophs forming microbial communities associated with animals. We compared four Desmodesmus isolates (1Hp86E-2, 1Pm66B, 3Dp86E-1, 2Cl66E) from the sponge Halichondria panicea, trochophore larvae of the polychaete Phyllodoce maculata, and the hydroids Dynamena pumila and Coryne lovenii, respectively. The microalgae appeared to be very similar featuring the phenotypic and genetic traits characteristics of unicellular representatives of the genus Desmodesmus. At the same time, isolates from different animal species displayed certain differences in (i) the epistructure morphology; (ii) type and number of the inclusions such as interthylakoid starch grains and cytoplasmic oil bodies and (iii) fatty acid composition; in Desmodesmus sp. 1Hp86E-2, these differences were most pronounced. Phylogenetic analysis based on ITS1-5.8S rRNA-ITS2 and rbcL sequences showed that all isolates studied differ from known classified representatives of Desmodesmus combining a deletion in the conservative 5.8S rRNA gene and long AC-microsatellite repeats in the ITS1 whereas 1Hp86E-2 represented a distinct branch within this group.

For the case when the line of the first order phase transitions does not transform into the line of the second order phase transitions, i.e. not as ends with the tricritical point but not with a critical one: critical lines, limiting the region of metastable states, by using the Landau theory of phase transitions were determined.