Csitari, B. | bioRxiv Science

bioRxiv2024

A matter of salt: global assessment of the effect of salt ionic composition as a driver of aquatic bacterial diversity

While the strong general effects of salinity on microbial diversity are well-known and described for marine and freshwater habitats, the impact of the specific composition of major inorganic ions remains largely unexplored. In this study, we assess how microbial community structure in inland saline aquatic habitats is influenced by ionic composition as compared to salinity, spatial factors, and other environmental parameters. We collected and analysed 16S rRNA gene V4 and V3-V4 amplicon datasets from freshwater to hypersaline aquatic environments worldwide (in total 375 samples from 130 lakes). With an emphasis on saline inland waters characterised by highly variable ionic composition, we demonstrated that the ionic composition of the major ions explained more variability in community composition than bulk salinity and that the geographic location of the sampling sites had only an ambiguous effect. We also identified the taxa contributing the most to the observed dissimilarity between communities from sites with different ionic composition and found mostly lineages known to be characteristic for a given habitat type, such as Actinobacteria acI in freshwater, Halomonadaceae in saline, or Nitriliruptorales in soda and soda-saline habitats. Many of these habitat type-specific indicator lineages were monophyletic, underpinning ionic composition as a crucial eco-evolutionary driver of aquatic microbial diversity.

microbiology↗

bioRxiv2023

Contrasting Response of Microeukaryotic and Bacterial Communities to the Interplay of Seasonality and Stochastic Events in Shallow Soda Lakes

Seasonal environmental variation is a leading driver of microbial planktonic community assembly and interactions. Yet, unexpected departures from general seasonal successional trends are often reported. To understand the role of local stochastic events in modifying seasonal succession, we sampled fortnightly throughout three seasons (spring, summer, and autumn) five nearby shallow soda lakes exposed to the same seasonal meteorological changes. We characterised their microeukaryotic and bacterial communities by 18S and 16S rRNA gene sequencing, respectively. Biological interactions were inferred by the analyses of synchronous and time-shifted interaction networks, and the keystone taxa were topologically identified. The pans showed similar succession patterns during the study period with spring being characterised by high relevance of trophic interactions and certain level of community stability followed by a more dynamic and variable summer-autumn period both in respect of community composition and microbial interactions. Adaptation to general seasonal changes happened through the abundant shared core microbiome of the pans. However, stochastic events such as desiccation and cyanobacterial blooms disrupted common network attributes and introduced shifts from the prevalent seasonal trajectory. These were more pronounced for microeukaryotes than for bacteria which was reflected in increased turnover and contribution of non-core microeukaryotes. Our results demonstrated that despite being extreme and highly variable habitats, shallow soda lakes exhibit certain similarities in the seasonality of their planktonic communities, yet random stochastic events such as droughts can instigate substantial deviations from prevalent trends for the microeukaryotic but not bacterial communities.

microbiology↗