A new ROS response factor YvmB protects Bacillus licheniformis against oxidative stress under adverse environment.

Bacillus spp., a class of aerobic bacteria, is widely used as a biocontrol microbe in the world. However, the reactive oxygen species (ROS) will accumulate once the aerobic bacteria are exposed to environmental stresses, which can decrease cell activity or lead to cell death. Hydroxyl radical (·OH), the strongest oxide in the ROS, can damage DNA directly, which is generated through Fenton Reaction by H2O2 and free iron. Here, we proved that the synthesis of pulcherriminic acid (PA), an iron chelator produced by Bacillus spp., could reduce DNA damage to protect cells from oxidative stress by sequestrating excess free iron, which enhanced the cell survival rates in stressful conditions (salt, antibiotic, and high temperature). It was worth noting that the synthesis of PA was found to be increased under oxidative stress. Thus, we demonstrated that the YvmB, a direct negative regulator of PA synthesis cluster yvmC-cypX, could be oxidized at cysteine residue (C57) to form a dimer losing the DNA-binding activity, which led to an improvement in PA production. Collectively, our findings highlight that YvmB senses ROS to regulate PA synthesis is one of the evolved proactive defense systems in bacteria against adverse environments.IMPORTANCEUnder environment stress, the electron transfer chain will be perturbed resulting in the accumulation of H2O2 and rapidly transform to ·OH through Fenton Reaction. How do bacteria deal with oxidative stress? At present, several iron chelators have been reported to decrease the ·OH generation by sequestrating iron, while how bacteria control the synthesis of iron chelators to resist oxidative stress is still unclear. Our study found that the synthesis of iron chelator PA is induced by reactive oxygen species (ROS), which means that the synthesis of iron chelator is a proactive defense mechanism against environment stress. Importantly, YvmB is the first response factor found to protect cells by reducing the ROS generation, which present a new perspective in antioxidation studies.

The MarR-like protein PchR (YvmB) regulates expression of genes involved in pulcherriminic acid biosynthesis and in the initiation of sporulation in Bacillus subtilis.

BACKGROUND: Cyclodipeptides and their derivatives constitute a large class of peptide natural products with noteworthy biological activities. In some yeasts and bacterial species, pulcherriminic acid derived from cyclo-L-leucyl-L-leucyl is excreted and chelates free ferric ions to form the pulcherrimin. In Bacillus subtilis, the enzymes YvmC and CypX are known to be involved in pulcherriminic acid biosynthesis. However, the mechanisms controlling the transcription of the yvmC-cypX operon are still unknown. RESULTS: In this work, we demonstrated that the B. subtilis YvmB MarR-like regulator is the major transcription factor controlling yvmC-cypX expression. A comprehensive quantitative proteomic analysis revealed a wide and prominent effect of yvmB deletion on proteins involved in cellular processes depending on iron availability. In addition, expression of yvmB depends on iron availability. Further analysis with real-time in vivo transcriptional profiling allowed us to define the YvmB regulon. We identified yvmBA, yvmC-cypX and yvnB for negative regulation and yisI for positive regulation. In combination with genetic approaches, gel mobility shift assays indicated that a 14-bp palindromic motif constitutes the YvmB binding site. It was unexpected that YvmB controls expression of yisI, whose encoding protein plays a negative role in the regulation of the sporulation initiation pathway. YvmB appears as an additional regulatory element into the cell's decision to grow or sporulate. CONCLUSION: Our findings reveal a possible role of the B. subtilis YvmB regulator in the regulatory networks connected to iron metabolism and to the control of proper timing of sporulation. YvmB was renamed as PchR controlling the pulcherriminic acid biosynthetic pathway of B. subtilis.