Mechanisms underlying growth inhibition of a denitrifier by reduced sulfur compounds

Competition among nitrate reducing bacteria (NRB) and sulfate reducing bacteria (SRB) for resources in anoxic environments is generally thought to be governed largely by thermodynamics. It is now recognized that intermediates of nitrogen and sulfur cycling (e.g., hydrogen sulfide, nitrite, etc.) can also directly impact NRB and SRB activities in freshwater, wastewater and sediment, and therefore may play important roles in competitive interactions. Here, using Intrasporangium calvum C5 as a model NRB, we performed comparative transcriptomic and metabolomic analyses to demonstrate that the reduced sulfur compounds cysteine and sulfide differentially inhibit respiratory growth on nitrate, and that inhibition by each can be selectively relieved by a specific carbon source. These findings provide mechanistic insights into the interplay and stratification of NRBs and SRBs in diverse environments. Time series mRNA profiling of a bacterial strain subjected to reduced sulfur stress. Three conditions were tested, a reference (Regular) and four treatments. Each consists of measurements at four growth phases and were made in triplicate. Multiple sequencing runs were performed to obtain enough reads (e.g., L001, L002, L003, L004).