A strain of aeroterrestrial green microalgae Coelastrella rubescens IBSS-156, isolated from an epilithic lichen, has been previously shown to efficiently produce green biomass and accumulate significant amounts of secondary carotenoids. In this study, using a two-stage batch culture, we analyzed time-course changes in variable chlorophyll a (Chl a) fluorescence parameters. Additionally, regression models were developed to correlate autofluorescence signals with spectrophotometric measurements of Chl a and total carotenoid content. Maximum quantum efficiency of photosystemII (F_v/F_m) remained high throughout the vegetative stage. At the end of this stage, under nutrient-limited conditions, the relative electron transport rate (rETR) declined to half its peak value during exponential growth. Stress induced a strong response in the algal photosynthetic apparatus during the early red stage. Within the first three days, F_v/F_m and rETR remained extremely low, but both increased sharply by day 5. During secondary carotenoid accumulation, fluorescence parameters remained at 70–80% of the vegetative-stage maximum, followed by a sharp decline toward the end of the red stage. Therefore, changes in variable fluorescence parameters can serve as markers of C. rubescens cellular physiology during biotechnological cultivation, denoting the completion of specific stages. Flow cytometry and pigment assay regression enabled real-time monitoring of C. rubescens biomass and carotenoids.

The structure of fungal assemblages has been studied in silty sediments of the southwestern Kara Sea at 11 stations in November 2023. Using cultivation method, 23 fungal species from six genera, five families, five orders, four classes, and two phyla (Ascomycota and Mucoromycota), as well as unidentified yeasts and sterile mycelium from three morphotypes, were isolated. In terms of species richness, representatives of the class Eurotiomycetes (12 species of Penicillium and 5 species of Aspergillus) were dominant. For the first time, the structure of fungal assemblages was analyzed depending on a combination of abiotic factors: sampling depth, average particle diameter, the percentage of sand, silt, and clay fractions, organic matter (OM), and organic carbon (C_org). Based on these abiotic parameters, two groups of stations were identified: group I (shallow water areas, depths of 21 and 26 m, silty-sand sediments) and group II (deep water areas, depth ≥122 m, silty-pelitic ooze). The abundance and morphotype diversity of filamentous fungi at shallow-water stations were 2.4–4-fold higher than at deep-water stations. The following factors were shown to influence the structure, clay fraction, OM, C_org, and mean particle diameter.