有機酸對Enterobacter mori FS08運動性及生物膜形成的影響

Abstract

細菌的運動性包括泳動和表面移行能力，對宿主定殖和環境適應至關重要。與泳動能力相關的趨化性推動細菌向營養源移動或遠離有害物質。表面移行的細胞則透過細菌群的聚集，逐漸轉變為生物膜狀態。若食物成分是引誘劑，將導致細菌趨化性增加，從而使細菌積累，這可能會導致食物腐敗。我們先前的研究自截切小黃瓜中分離的Enterobacter mori FS08具顯著的泳動能力，並且小黃瓜汁對這株菌是很強的引誘劑。然而，此菌株與小黃瓜之間的關聯性尚未建立。本研究旨在 (1) 確認E. mori FS08是否促進小黃瓜腐敗；(2) 探討小黃瓜中的有機酸成分對E. mori FS08運動性相關表型的影響。實驗結果發現直接將E. mori FS08接種至新鮮截切小黃瓜上會導致外觀變質，並且消耗小黃瓜中的醣類成分。菌株特性分析中，觀察到有機酸在相同pH值下，並不會影響E. mori FS08的活菌數。值得注意的是，L-蘋果酸增強了泳動能力和正向趨化反應，但減少生物膜形成。反之，檸檬酸與DL-乳酸抑制了泳動和表面移行能力，且檸檬酸的抑制更為顯著，但這兩種有機酸皆促進了生物膜的形成。進一步的實驗證實添加L-蘋果酸使運動性相關基因 (fliC、flgM與motA) 表現量提升，添加檸檬酸則無顯著變化。而經過L-蘋果酸處理的轉錄組分析結果，鑑定出與運動性和生物膜形成相關的差異表達基因，其中fis (促進運動性的轉錄調節因子)、ahpC (氧化壓力防禦基因，其解毒作用可減少生物膜形成)、narK (硝酸鹽轉運蛋白，硝酸鹽會抑制生物膜形成) 表現量上升。另外，調控生物膜形成的群體感應相關基因亦受到抑制。這些實驗結果證明小黃瓜中的有機酸成分會調控訊息途徑影響細菌行為，可作為新鮮截切小黃瓜的預防措施和控制方法的重要參考。

Bacterial motility, encompassing swimming and swarming motility, is pivotal for host colonization and environmental adaptation. Chemotaxis, associated with swimming motility, propels bacteria toward nutrient sources or away from harmful substances. Swarming cells often aggregate and progressively transit to biofilm forming status. If the food factors are attractants, it will cause the increase of chemotaxis in bacteria, which results in bacteria accumulation. This may potentially lead to food spoilage. Our previous study isolated Enterobacter mori FS08 from fresh-cut cucumbers, exhibits pronounced swimming motility; however, the association between this strain and cucumber has not yet been established. The current study aimed to 1) investigate if E. mori FS08 leads to the spoilage of cucumber; 2) explore the impact of organic acids in cucumber on motility-related phenomena. The results demonstrate that E. mori FS08 caused cucumber spoilage by directly inoculating the strain onto fresh-cut cucumbers. The strain characterization indicated that organic acids did not affect the viable bacterial count of E. mori FS08 by the pH levels. Notably, L-malic acid enhanced swimming motility and positive chemotaxis response, but reduced biofilm formation. In contrast, citric acid and DL-lactic acid inhibited swimming and swarming motility, with citric acid having a more significant effect. However, both organic acids promoted biofilm formation. The subsequent analysis by qPCR found that the addition of L-malic acid led to the higher expression of motility-related genes (fliC, flgM, and motA), while the addition of citric acid showed no significant changes. Further transcriptomic analysis revealed that, in response to L-malic acid treatment, differentially expressed genes related to motility and biofilm formation were identified. The expression of fis (a transcriptional regulator promoting motility), ahpC (an oxidative stress defense gene whose detoxification activity can reduce biofilm formation), and narK (a nitrate transporter protein, with nitrate inhibiting biofilm formation) were upregulated. Additionally, quorum sensing-related genes that regulate biofilm formation were also downregulated. This study elucidated how organic acid components in cucumbers affect bacterial behavior and regulatory pathways, providing valuable insights into future preventative measures and control methods for fresh-cut cucumber handling.