Project description:We cultivated two halo-alkaliphilic cyanobacteria consortia in chemostats at pH 10.2-11.4. One consortium was dominated by Ca. Sodalinema alkaliphilum, the other by a species of Nodosilinea. These two cyanobacteria dominate natural communities in Canadian and Asian alkaline soda lakes. We show that increasing the pH decreased biomass yield. This decrease was caused, in part, by a dramatic increase in carbon transfer to heterotrophs. At pH 11.4, cyanobacterial growth became limited by bicarbonate uptake, which was mainly ATP-dependent. In parallel, the higher the pH, the more sensitive cyanobacteria became to light, resulting in photoinhibition and upregulation of DNA repair systems.
Project description:<p>Favoured by global changes, freshwater cyanobacterial harmful blooms generate major ecological, economical and public health challenges. <em>Microcystis</em>, one of the most widespread cyanobacterial genera, grows within a phycosphere where specialised interactions with its microbiome occur, and are suspected to influence bloom appearance and its potential toxicity. Using a combination of metagenomic, metabolomic and metabolic modelling, we characterised the culture-associated phycospheres of twelve <em>Microcystis</em> strains isolated from a French pond. The distribution of metabolic reactions within <em>Microcystis</em> was consistent with their genospecies, whereas the metabolic landscape at the community level diverged from cyanobacterial phylogeny indicating partial functional decoupling between cyanobacteria and their associated microbiomes. Bacteria associated with the simplified phycospheres substantially expand the metabolic repertoire of the system, while maintaining functional redundancy within and across communities. On the other hand, endometabolomic profiles were largely driven by cyanobacterial metabolic outputs whereas exometabolomic analysis did not reveal metabolites involved in exchange processes. Metabolic modelling, together with the identification of toxic specialised metabolites produced by specific biosynthetic gene clusters, further highlighted differences in metabolic potential among phycospheres. Together, these findings deepen the understanding of <em>Microcystis’</em> phycosphere functioning and demonstrate the value of multi-omics systems biology approaches, while suggesting that metabolic complementarity between species and across phycospheres could play a role in bloom-associated microbiome structure.</p>
