Table_5_Sigma factor RpoS positively affects the spoilage activity of Shewanella baltica and negatively regulates its adhesion effect.XLS

Shewanella baltica is the dominant bacterium that causes spoilage of seafood. RpoS is an alternative sigma factor regulating stress adaptation in many bacteria. However, the detailed regulatory mechanism of RpoS in S. baltica remains unclear. This study aims to investigate the regulatory function of RpoS on spoilage activity and adhesion ability in S. baltica. Results revealed that RpoS had no effect on the growth of S. baltica, but positively regulated the spoilage potential of S. baltica accompanied by a slower decline of total volatile basic nitrogen, lightness, and the sensory score of fish fillets inoculated with rpoS mutant. RpoS negatively regulated the adhesion ability, which was manifested in that the bacterial number of rpoS mutant adhered to stainless steel coupon was higher than that of the S. baltica in the early stage, and the biofilm formed on glass slide by rpoS mutant was thicker and tighter compared with S. baltica. Transcriptomic analysis showed that a total of 397 differentially expressed genes were regulated by RpoS. These genes were mainly enrichment in flagellar assembly, fatty acid metabolism/degradation, and RNA degradation pathways, which were associated with motility, biofilm formation and cold adaptation. This study demonstrated that RpoS is a primary regulator involved in flagellar assembly mediated biofilm formation and cold adaptation-related spoilage activity of S. baltica. Our research will provide significant insights into the control of microbiological spoilage in seafood.

波罗的海希瓦氏菌（Shewanella baltica）是导致海鲜腐败的优势菌种。RpoS是一类在多种细菌中调控应激适应的替代σ因子（alternative sigma factor），但其在波罗的海希瓦氏菌中的具体调控机制仍未明确。本研究旨在探究RpoS对波罗的海希瓦氏菌腐败活性与黏附能力的调控功能。结果显示，RpoS对波罗的海希瓦氏菌的生长无显著影响，但可正向调控其腐败潜力：接种rpoS突变株的鱼片，其总挥发性盐基氮的下降速率更为迟缓，鱼肉亮度与感官评分的衰减也更缓慢。RpoS可负向调控菌株的黏附能力，具体表现为：早期黏附于不锈钢试片的rpoS突变株菌落数高于野生型波罗的海希瓦氏菌，且rpoS突变株在载玻片上形成的生物被膜更厚、结构更致密。转录组分析表明，RpoS共调控397个差异表达基因，这些基因主要富集于鞭毛组装、脂肪酸代谢/降解以及RNA降解通路，这些通路与菌株运动性、生物被膜形成及冷适应密切相关。本研究证实，RpoS是参与鞭毛组装介导的生物被膜形成以及波罗的海希瓦氏菌冷适应相关腐败活性的核心调控因子。本研究可为海鲜微生物腐败的防控提供重要理论参考。