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The transition between the planktonic state and the biofilm-associated state is a key developmental decision for pathogenic bacteria. Biofilm formation by Yersinia pestis is regulated by hmsHFRS genes (β-1, 6-N-acetyl-D-glucosamine synthesis operon) in its flea vector and in vitro. However, the mechanism of biofilm formation in Yersinia pseudotuberculosis remains elusive. In this study, we demonstrate that the LysR-type regulator RovM inversely regulates biofilm formation and motility in Y. pseudotuberculosis by acting as a transcriptional regulator of these two functions. RovM is strongly induced during growth in minimal media but strongly repressed in complex media. On one hand, RovM enhances bacterial motility by activating the expression of FlhDC, the master regulator of flagellar genes, via the recognition of an operator upstream of the flhDC promoter. On the other hand, RovM represses β-GlcNAc production under nutrition-limited conditions, negatively regulating hmsHFRS expression by directly binding to the −35 element of its promoter. Compared to wild-type bacteria, the rovM mutant established denser biofilms and caused more extensive mortality in mice and silkworm larvae. These results indicate that RovM acts as a molecular switch to coordinate the expression of genes involved in biofilm formation and motility in response to the availability of nutrients.

The type VI secretion system (T6SS) is a widespread and versatile protein secretion system found in most Gram-negative bacteria. Studies of T6SS have mainly focused on its role in virulence toward host cells and inter-bacterial interactions, but studies have also shown that T6SS4 in Yersinia pseudotuberculosis participates in the acquisition of zinc ions to alleviate the accumulation of hydroxyl radicals induced by multiple stressors. Here, by comparing the gene expression patterns of wild-type and zntR mutant Y. pseudotuberculosis cells using RNA-seq analysis, T6SS4 and 17 other biological processes were found to be regulated by ZntR. T6SS4 was positively regulated by ZntR in Y. pseudotuberculosis, and further investigation demonstrated that ZntR regulates T6SS4 by directly binding to its promoter region. T6SS4 expression is regulated by zinc via ZntR, which maintains intracellular zinc homeostasis and controls the concentration of reactive oxygen species to prevent bacterial death under oxidative stress. This study provides new insights into the regulation of T6SS4 by a zinc-dependent transcriptional regulator, and it provides a foundation for further investigation of the mechanism of zinc transport by T6SS.

Yersinia pseudotuberculosis (Yptb) is a primarily rodent pathogen that also causes gastrointestinal diseases in humans and various animal species worldwide. Zinc uptake is essential for bacterial growth and pathogenicity. In this experiment, we confirmed that the znuABC transcription level in Yptb is regulated by Zn2+ concentration, and then constructed a ΔznuCB mutant. This mutation drastically decreased the survival rate of the ΔznuCB strain under primary oxidative stress (caused by hydrogen peroxide and cumene hydroperoxide) compared to the wild-type strain, and all Yptb strains showed lower resistance to oxidative stress under zinc deprivation caused by znuCB deletion or addition of a chelator. Furthermore, reactive oxygen species (ROS) accumulation was increased in the ΔznuCB strain, which suggested that the wild-type strain acquired Zn2+ by means of the ZnuABC transporter to reduce intracellular ROS levels and, so, prevent oxidative damage to cells. Oral infection showed that znuCB deletion did not have a significant effect on bacterial pathogenicity in mice, indicating the existence of other zinc uptake systems in Yptb. Our results not only suggest the importance of zinc uptake for bacterial growth but also provide insight into the antioxidant function of zinc in Yptb.

To investigate mycothiol peroxidase (MPx) of Corynebacterium glutamicum that is a novel CysGPx family peroxidase using both the mycoredoxin and thioredoxin reducing systems as proton donors for peroxide detoxification and may be involved in the relief of acid stress. A Δmpx mutant exhibited significantly decreased resistance to acid stress and markedly increased accumulation of reactive oxygen species (ROS) and protein carbonylation levels in vivo. Over-expression of mpx increased the resistance of C. glutamicum to acid stress by reducing ROS accumulation. The stress-responsive extracytoplasmic function-sigma (ECF-σ) factor, SigH, mediated acid-induced expression of mpx in the wild-type under acid conditions, which in turn directly contributed to tolerance to acid stress. MPx is essential for combating acid stress by reducing intracellular ROS levels induced by acid stress in C. glutamicum, which adds a new dimension to the general physiological functions of CysGPx.