Abstract
Eutrophication can lead to an uncontrollable increase in algal biomass, which has repercussions for the entire microbial and pelagic community. Studies have shown how nutrient enrichment affects microbial species succession, however details regarding the impact on community functionality are rare. Here, we applied a metaproteomic approach to investigate the functional changes to algal and bacterial communities, over time, in oligotrophic and eutrophic conditions, in freshwater microcosms. Samples were taken early during algal and cyanobacterial dominance and later under bacterial dominance. 1048 proteins, from the two treatments and two timepoints, were identified and quantified by their exponentially modified protein abundance index. In oligotrophic conditions, Bacteroidetes express extracellular hydrolases and Ton-B dependent receptors to degrade and transport high molecular weight compounds captured while attached to the phycosphere. Alpha- and Beta-proteobacteria were found to capture different substrates from algal exudate (carbohydrates and amino acids, respectively) suggesting resource partitioning to avoid direct competition. In eutrophic conditions, environmental adaptation proteins from cyanobacteria suggested better resilience compared to algae in a low carbon nutrient enriched environment. This study provides insight into differences in functional microbial processes between oligo- and eutrophic conditions at different timepoints and highlights how primary producers control bacterial resources in freshwater environments. The data have been deposited to the ProteomeXchange with identifier PXD004592.
Highlights
Freshwater ecosystems are subjected to nutrient enrichment on a local, regional, and global scale in a process known as eutrophication
Based on these patterns the samples selected for metaproteomic analyses were harvested at day 3, the peak of algal and cyanobacterial concentrations and day 12, the peak of bacterial concentrations
A label-free comparative metaproteomics approach was applied on an experimental microcosm community under differing trophic states
Summary
Freshwater ecosystems are subjected to nutrient enrichment on a local, regional, and global scale in a process known as eutrophication. Global aquatic fluxes of nitrogen and phosphorus have been amplified by 108 and 400%, respectively (Falkowski et al, 2000) These nutrient imbalances have led to a drastic increase in the occurrence of algal blooms, an event where photoautotrophic biomass may increase by several orders of magnitude (Elser et al, 2007). The microbial loop plays a crucial role in the biogeochemical cycling of Metaproteomics of Freshwater Microbial Microcosms elements, such as carbon, phosphorus and nitrogen, as well as organic matter. It is responsible for a substantial fraction of aquatic nutrient and energy fluxes (Azam and Malfatti, 2007). A better understanding of how the microbial loop and associated algae respond to nutrient enrichment, can reveal important features of how ecosystem processes are affected by eutrophication
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