College of Food Science and Biotechnology, Food Safety Key Laboratory of Zhejiang Province, Zhejiang Gongshang University, Hangzhou, Zhejiang, 310018, China.
College of Food Science and Biotechnology, Food Safety Key Laboratory of Zhejiang Province, Zhejiang Gongshang University, Hangzhou, Zhejiang, 310018, China.
Food Microbiol. 2023 Jun;112:104214. doi: 10.1016/j.fm.2023.104214. Epub 2023 Jan 6.
Psychrotrophic Pseudomonas as the dominant spoilage bacteria, have biofilm forming ability, increasing persistence and contamination in the chilled food. Biofilm formation of spoilage Pseudomonas at cold temperature was documented, however, role of extracellular matrix in mature biofilm and stress resistance of psychrotrophic Pseudomonas are much less abundant. The aim of this study was to investigate the biofilm forming characteristics of three spoilers P. fluorescens PF07, P. lundensis PL28, and P. psychrophile PP26 at 25 °C, 15 °C and 4 °C, and to explore their stress resistance to chemical and thermal treatments of mature biofilms. The results showed that biofilm biomass of three Pseudomonas at 4 °C was significantly higher than that at 15 °C and 25 °C. The secretion of extracellular polymeric substances (EPS) greatly increased in those Pseudomonas under low temperature, of which extracellular protein constituted about 71.03%-77.44%. Compared to 25 °C, the mature biofilms were observed to more aggregation and thicker spatial structure at 4 °C ranging from 42.7 to 54.6 μm, in contrast to 25.0-29.8 μm at 25 °C, especially strain PF07. These Pseudomonas biofilms switched into moderate hydrophobicity, and their swarming and swimming were significantly inhibited at low temperature. Furthermore, the resistance to NaClO and heating at 65 °C apparently enhanced for mature biofilm formed at 4 °C, indicating the difference in EPS matrix production influenced the stress resistance of biofilm. In addition, three strains contained alg and psl operons for exopolysaccharide biosynthesis, and biofilm related genes of algK, pslA, rpoS, and luxR were significantly up-regulated, while flgA gene was down-regulated at 4 °C compared to 25 °C, consistent with the above phenotype changes. Thus, the dramatic increase of mature biofilm and their stress resistance in psychrotrophic Pseudomonas were associated with large secretion and protection of extracellular matrix under low temperature, which provide a theoretical basis for subsequent biofilm control during cold chain.
低温腐败假单胞菌作为优势腐败菌，具有形成生物膜的能力，增加了冷藏食品中的持久性和污染。已记录了低温下腐败假单胞菌的生物膜形成，但细胞外基质在成熟生物膜中的作用以及低温假单胞菌的抗应激能力还知之甚少。本研究旨在研究三种腐败菌荧光假单胞菌 PF07、隆德假单胞菌 PL28 和嗜冷假单胞菌 PP26 在 25°C、15°C 和 4°C 下的生物膜形成特性，并探讨其对成熟生物膜的化学和热处理的抗应激能力。结果表明，三种假单胞菌在 4°C 下的生物膜生物量明显高于 15°C 和 25°C。低温下，三种假单胞菌大量分泌胞外聚合物（EPS），其中胞外蛋白约占 71.03%-77.44%。与 25°C 相比，在 4°C 下观察到成熟生物膜更聚集，空间结构更厚，范围从 42.7 到 54.6μm，而在 25°C 下为 25.0-29.8μm，尤其是 PF07 菌株。这些假单胞菌生物膜转变为中等疏水性，在低温下其 swarm 和 swimming 明显受到抑制。此外，在 4°C 下形成的成熟生物膜对 NaClO 和 65°C 加热的抵抗力明显增强，表明 EPS 基质产生的差异影响了生物膜的抗应激能力。此外，三株菌都含有 alg 和 psl 操纵子用于合成胞外多糖，algK、pslA、rpoS 和 luxR 等生物膜相关基因在 4°C 时明显上调，而 flgA 基因在 4°C 时下调，与上述表型变化一致。因此，低温下假单胞菌成熟生物膜的大量增加及其抗应激能力与低温下细胞外基质的大量分泌和保护有关，为后续冷链中生物膜控制提供了理论依据。
