Project description:The rate, timing, and mode of species dispersal is recognized as a key driver of the structure and function of communities of macroorganisms, and may be one ecological process that determines the diversity of microbiomes. Many previous studies have quantified the modes and mechanisms of bacterial motility using monocultures of a few model bacterial species. But most microbes live in multispecies microbial communities, where direct interactions between microbes may inhibit or facilitate dispersal through a number of physical (e.g., hydrodynamic) and biological (e.g., chemotaxis) mechanisms, which remain largely unexplored. Using cheese rinds as a model microbiome, we demonstrate that physical networks created by filamentous fungi can impact the extent of small-scale bacterial dispersal and can shape the composition of microbiomes. From the cheese rind of Saint Nectaire, we serendipitously observed the bacterium Serratia proteamaculans actively spreads on networks formed by the fungus Mucor. By experimentally recreating these pairwise interactions in the lab, we show that Serratia spreads on actively growing and previously established fungal networks. The extent of symbiotic dispersal is dependent on the fungal network: diffuse and fast-growing Mucor networks provide the greatest dispersal facilitation of the Serratia species, while dense and slow-growing Penicillium networks provide limited dispersal facilitation. Fungal-mediated dispersal occurs in closely related Serratia species isolated from other environments, suggesting that this bacterial-fungal interaction is widespread in nature. Both RNA-seq and transposon mutagenesis point to specific molecular mechanisms that play key roles in this bacterial-fungal interaction, including chitin utilization and flagellin biosynthesis. By manipulating the presence and type of fungal networks in multispecies communities, we provide the first evidence that fungal networks shape the composition of bacterial communities, with Mucor networks shifting experimental bacterial communities to complete dominance by motile Proteobacteria. Collectively, our work demonstrates that these strong biophysical interactions between bacterial and fungi can have community-level consequences and may be operating in many other microbiomes.

Project description:Abstract Hypersaline lakes are of immense ecological value as they niche some of the most exclusive extremophilic communities dominated by bacterial and archaeal domains, with few eukaryotic algal representatives. A handful reports describe Picocystis as a key primary producer with great production rates in extremely saline habitats. An extremely haloalkaliphilic picoalgal strain, Picocystis salinarum SLJS6 isolated from hypersaline lake Sambhar, Rajasthan, India, grew robustly in an enriched soda lake medium containing mainly Na2CO3, 50 g/L; NaHCO3, 50g/L, NaCl, 50 g/L (salinity ≈150 ‰) at pH 10. To elucidate the molecular basis of such tolerance to high inorganic carbon and NaCl concentrations, a high-throughput LFQ (label-free quantitation) based quantitative proteomics approach was applied. Out of the total 383 proteins identified in treated samples, 225 were Differentially abundant proteins (DAPs), of which 150 were statistically significant (p value <0.05) including 70 upregulated and 64 downregulated proteins after 3 days of salt and alkalinity stress. Gene ontology analysis was done to annotate and classify the DAPs into functional groups. The analysis linked most DAPs to photosynthesis, oxidative phosphorylation, glucose metabolism and ribosomal structural components envisaging that photosynthesis and ATP synthesis were central to the alkalinity-salinity response. Key components of photosynthetic machinery like photosystem reaction centres, ATP synthase, Rubisco, Fructose-bisphosphate aldolase were significantly upregulated. Enzymes Peptidylprolyl isomerases (PPIase), important for correct protein folding showed remarkable marked-up regulation along with other chaperon proteins indicating their role in alleviating stress. Enhanced photosynthetic activity exhibited by Picocystis salinarum in highly saline-alkaline condition is noteworthy as photosynthesis is suppressed by salt stress in most photosynthetic organisms. This study provided the first evidence of a tailored regulatory mechanism of alkalinity and salt tolerance in extremophilic alga P. salinarum, potentially unraveling the basis of resilience in this not so known organism and paves the way for a promising future production host and model or¬ganism for deciphering the molecular mechanisms of os¬motic stress responses.

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