Microcystin-LR does not induce alterations to transcriptomic or metabolomic profiles of a model heterotrophic bacterium

Abstract

Microcystins are secondary metabolites produced by several freshwater, bloom-forming cyanobacterial species. Microcystin-producing cyanobacteria co-occur with a complex community of heterotrophic bacteria. Though conflicting, studies suggest that microcystins affect the physiology of heterotrophic bacteria by inducing oxidative stress and increasing cell envelope permeability. Based on these observations, we hypothesized that exposure to microcystin should induce differential expression in genes responding to oxidative and envelope stress and trigger shifts in metabolite pools. We tested this hypothesis by exposing Escherichia coli MG1655 to 1 and 10 mg/L microcystin-LR and monitored global changes to gene expression, cellular metabolite pools, and lipid composition using RNA-sequencing and UPLC-MS. Contrary to reported studies, we observed no evidence that microcystin-LR induced oxidative or cell envelope stress in E. coli under the tested conditions. Our results suggest a potential difference in mechanism by which microcystin-LR interacts with heterotrophic bacteria vs. cyanobacteria.

Lrg1 Regulates β (1,3)-Glucan Masking in Candida albicans through the Cek1 MAP Kinase Pathway

“…Expression values for each gene were calculated from unique gene reads (the maximum number of hits for a read was set to 1) and normalized by gene length and sequencing depth, yielding the expression value of transcripts per million (TPM). To determine if gene expression values were correct, the TPM reads of five housekeeping genes ( TEF1 , ACT1 , TUB1 , ENO1 , and PMA1 ) were evaluated to calculate the average for each condition, which was further plotted as described previously (70). To identify genes that were differentially expressed under treatment and control conditions, the P values calculated for the individual genes were adjusted for false-discovery rate (FDR), and genes with an FDR-adjusted P value of < 0.05 in the treatment group were considered differentially expressed.…”

Growth Substrate and Prophage Induction Collectively Influence Metabolite and Lipid Profiles in a Marine Bacterium

“…Water-soluble metabolites were extracted from filtered samples using 4:4:2 acetonitrile:methanol:water with 0.1 M formic acid as previously described ( 54 ). Analysis of the extracted metabolites was carried out using UHPLC-HRMS (Thermo Scientific, San Jose, CA, USA) with a previously validated untargeted metabolomics method ( 55 ).…”