Debnath Anusuya, Mizuno Tamaki, Miyoshi Shin-Ichi
Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 1-1-1, Tsushima-naka, Kita-ku, Okayama 700-8530, Japan.
Microorganisms. 2020 Aug 26;8(9):1303. doi: 10.3390/microorganisms8091303.
Vibrios can degrade chitin surfaces to soluble N-acetyl glucosamine oligosaccharides (GlcNAc) that can be utilized as a carbon source and also induce a state of natural genetic competence. In this study, we characterized chitin-dependent growth and natural competence in and its regulation. We found that growth on chitin was regulated through chitin sensors ChiS (sensor histidine kinase) and TfoS (transmembrane transcriptional regulator) by predominantly controlling the expression of chitinase VPA0055 (ChiA2) in a TfoX-dependent manner. The reduced growth of Δ, Δ and Δ mutants highlighted the critical role played by ChiA2 in chitin breakdown. This growth defect of Δ mutant could be recovered when chitin oligosaccharides GlcNAc or GlcNAc were supplied instead of chitin. The Δ mutant was also able to grow on GlcNAc but the Δ mutant could not, which indicates that GlcNAc catabolic operon is dependent on ChiS and independent of TfoS. However, the Δ mutant was unable to utilize GlcNAc because the periplasmic enzymes required for the breakdown of GlcNAc were found to be downregulated at the mRNA level. We also showed that natural competence can be induced only by GlcNAc, not GlcNAc, because the expression of competence genes was significantly higher in the presence of GlcNAc compared to GlcNAc. Moreover, this might be an indication that GlcNAc and GlcNAc were detected by different receptors. Therefore, we speculate that GlcNAc-dependent activation of ChiS and GlcNAc-dependent activation of TfoS might be crucial for the induction of natural competence in through the upregulation of the master competence regulator TfoX.
弧菌可将几丁质表面降解为可溶性的N - 乙酰葡糖胺寡糖（GlcNAc），这些寡糖可作为碳源利用，还能诱导自然遗传转化状态。在本研究中，我们对[具体弧菌名称未给出]中几丁质依赖性生长、自然转化及其调控进行了表征。我们发现，几丁质上的生长通过几丁质传感器ChiS（传感组氨酸激酶）和TfoS（跨膜转录调节因子）进行调控，主要以TfoX依赖性方式控制几丁质酶VPA0055（ChiA2）的表达。Δ[具体基因敲除突变体名称未给出]、Δ[具体基因敲除突变体名称未给出]和Δ[具体基因敲除突变体名称未给出]突变体生长减缓，突出了ChiA2在几丁质分解中的关键作用。当提供几丁质寡糖GlcNAc或GlcNAc而非几丁质时，Δ[具体基因敲除突变体名称未给出]突变体的这种生长缺陷能够得到恢复。Δ[具体基因敲除突变体名称未给出]突变体也能够在GlcNAc上生长，但Δ[具体基因敲除突变体名称未给出]突变体不能，这表明GlcNAc分解代谢操纵子依赖于ChiS且独立于TfoS。然而，Δ[具体基因敲除突变体名称未给出]突变体无法利用GlcNAc，因为发现GlcNAc分解所需的周质酶在mRNA水平上被下调。我们还表明，自然转化只能由GlcNAc诱导，而非GlcNAc，因为与GlcNAc相比，在GlcNAc存在时感受态基因的表达显著更高。此外，这可能表明GlcNAc和GlcNAc是由不同受体检测到的。因此，我们推测，通过上调主要感受态调节因子TfoX，GlcNAc依赖性激活ChiS和GlcNAc依赖性激活TfoS可能对[具体弧菌名称未给出]中自然转化的诱导至关重要。
