Project description: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.
Project description:Activating the cryptic secondary metabolic gene clusters is a vital research field in Streptomyces. The marine Streptomyces sp. FJNU027 strain which could produce tirandamycins was cultured in the oligotrophic medium. Compared with normal medium, a differential product in oligotrophic culture was found by HPLC assay. After mass fermentation, 2 mg of the differential product was obtained from 30 L fermentation broth by solvent extraction, column chromatography over sephadex LH-20 and reverse phase C18, and other methods. It was identified as 4,4',5,5'-tetramethyl-[1,1'- diphenyl]-2,2'-diol by NMR and MS data. The production of this compound was enhanced with the increment of cultural time. Transcriptome sequencing analysis showed that the highest upregulated genes under oligotrophic condition were glycosidase, TraR/DksA C4-type zinc finger protein and ribonuclease encoding genes, while the expression of a MarR family transcriptional regulator was most significantly decreased under oligotrophic condition. The results indicate that oligotrophic culture is an effective method for altering the secondary metabolism of Streptomyces.
