College of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou, Zhejiang Province, 310018, China.
College of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou, Zhejiang Province, 310018, China.
Food Microbiol. 2021 Aug;97:103755. doi: 10.1016/j.fm.2021.103755. Epub 2021 Feb 10.
Shewanella baltica is a typical specific spoilage organism causing the deterioration of seafood, but the exact regulation of its adaptive and competitive dominance in diverse environments remains undefined. In this study, the regulatory function of two sigma factors, RpoS and RpoN, in environmental adaptation and spoilage potential were evaluated in S. baltica SB02. Two in-frame deletion mutants, ΔrpoS and ΔrpoN, were constructed to explore the roles in their motility, biofilm formation, stress response and spoilage potential, as well as antibiotics by comparing the phenotypes and transcription with those of wild type (WT) strain. Compared with WT strain, the ΔrpoN showed the slower growth and weaker motility due to loss of flagella, while swimming of the ΔrpoS was increased. Deletion of rpoN significantly decreased biofilm biomass, and production of exopolysaccharide and pellicle, resulting in a thinner biofilm structure, while ΔrpoS formed the looser aggregation in biofilm. Resistance of S. baltica to NaCl, heat, ethanol and three oxidizing disinfectants apparently declined in the two mutants compared to WT strain. The ΔrpoN mutant decreased sensory score, accumulation of trimethylamine, putrescine and TVB-N and protease activity, while a weaker effect was observed in ΔrpoS. The two mutants had significantly higher susceptibility to antibiotics than WT strain, especially ΔrpoN. Deficiency of rpoN and rpoS significantly repressed the activities of two diketopiperazines related to quorum sensing (QS). Furthermore, transcriptome analyses revealed that RpoN was involved in the regulation of the expression of 143 genes, mostly including flagellar assembly, nitrogen and amino acid metabolism, ABC transporters. Transcript changes of seven differentially expressed coding sequences were in agreement with the phenotypes observed in the two mutants. Our findings reveal that RpoN, as a central regulator, controls the fitness and bacterial spoilage in S. baltica, while RpoS is a key regulatory factor of stress response. Characterization of these two sigma regulons in Shewanella has expanded current understanding of a possible co-regulatory mechanism with QS for adaptation and spoilage potential.
波罗的海希瓦氏菌是一种典型的特定腐败菌，可导致海产品变质，但它在不同环境中的适应性和竞争优势的具体调节机制仍未确定。在本研究中，评估了两种 sigma 因子 RpoS 和 RpoN 在波罗的海希瓦氏菌 SB02 环境适应和腐败潜能中的调控功能。构建了两个无义突变体 ΔrpoS 和 ΔrpoN，通过比较表型和转录组，来研究它们在运动性、生物膜形成、应激反应和腐败潜能以及抗生素方面的作用。与野生型（WT）菌株相比，ΔrpoN 由于鞭毛缺失而表现出生长缓慢和运动能力减弱，而 ΔrpoS 的游动性增加。rpoN 缺失显著降低了生物膜生物量和胞外多糖和菌膜的产生，导致生物膜结构变薄，而 ΔrpoS 在生物膜中形成更松散的聚集。与 WT 菌株相比，两种突变体对 NaCl、热、乙醇和三种氧化消毒剂的抗性明显下降。ΔrpoN 突变体降低了感官评分、三甲胺、腐胺和 TVB-N 的积累和蛋白酶活性，而 ΔrpoS 的影响较弱。与 WT 菌株相比，两种突变体对抗生素的敏感性显著增加，尤其是 ΔrpoN。rpoN 和 rpoS 的缺失显著抑制了与群体感应（QS）相关的两种二酮哌嗪的活性。此外，转录组分析表明，RpoN 参与了 143 个基因表达的调控，这些基因主要包括鞭毛组装、氮和氨基酸代谢、ABC 转运体。两个突变体观察到的表型一致的七个差异表达编码序列的转录变化。我们的研究结果表明，RpoN 作为一个中央调控因子，控制着波罗的海希瓦氏菌的适应性和细菌腐败，而 RpoS 是应激反应的关键调控因子。对希瓦氏菌中这两个 sigma 调控子的表征扩展了对适应和腐败潜能的可能协同调控机制与 QS 的认识。
