Pantoea vagans之表面移行及生物膜生成能力對截切香瓜品質之影響

Abstract

Pantoea spp.在環境中普遍存在，過去的研究已經證實Pantoea spp.的存在會導致香瓜腐敗。而表面移行為許多細菌在環境中快速定殖的運動模式，且與生物膜的形成有關，這兩種表型能夠提升細菌在環境中的存活率。然而文獻多著重於表面移行及生物膜形成與植株的關係，尚未探討對截切後水果的影響，因此本研究試圖透過具有表面移行及生物膜形成能力的Pantoea vagans M17來瞭解這兩種表型對截切香瓜品質的影響。穿透式電子顯微鏡及膠體電泳的結果證實本研究中的半固態培養條件能夠促使Pantoea spp.分化成具表面移行能力的菌株。當培養基pH值接近中性時 (pH 6.5) 菌株運動性提升，而較高pH值 (pH 8.0) 觀察到較厚的生物膜生成。此外，Pantoea spp.在最適生長溫度 (30℃) 會表現較強的表面移行及生物膜形成。以超高壓滅菌香瓜汁作為培養基質時，P. vagans M17不但生長良好，可以形成生物膜，表面移行能力也顯著提升。為進一步了解香瓜成分對菌株的影響，以佔比較高的糖類對P. vagans M17的表面移行作用進行測試，發現棉子糖對菌株之表面移行現象具有濃度效應，而添加蔗糖的效果優於其他糖類。另外發現蔗糖及L-蘋果酸共同存在下能夠顯著增加P. vagans M17的表面移行能力。最後，接菌試驗顯示P. vagans M17會對截切香瓜品質造成不良影響，包含外觀出現黏液以及顯著改變有機酸含量。未來的研究可以配合P. vagans M17全基因定序的資料，逐步了解這兩種表型與截切香瓜品質的關聯性，期望將來能透過更精準的方式延長產品貨架期。

The genus Pantoea is a group of ubiquitous bacteria which has been proven to lead to rot of melon. Swarming of the bacteria is a powerful way to rapidly colonize cells which may be related to biofilm development and increase bacterial survival in the environment. However, previous research mainly focused on the bacterial swarming motility and biofilm formation in plants rather than their impact on fresh-cut fruits. As a result, this study employed Pantoea vagans M17 exhibiting swarming motility and biofilm formation to investigate the impact of these two phenotypes on the quality of fresh-cut melons. The results of transmission electron microscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed that Pantoea spp. was able to differentiate into swarmer cells on the semisolid medium used in this study. Bacterial motility was promoted at neutral pH (pH 6.5) while biofilm formation was enhanced at higher pH (pH 8.0). Furthermore, Pantoea spp. exhibited stronger swarming effect and biofilm formation at its optimal growth temperature (30℃). When we cultured P. vagans M17 with HPP melon juice as the substrate, not only enabled bacterial cell growth and biofilm formation but also significantly promoted swarming effect. In order to learn more about the impact of melon composition on Pantoea spp., sugars accounting for the most proportion of melon nutrient content were taken to test the swarming motility of P. vagans M17. We discovered that raffinose impacted swarming with concentration-effect relation and sucrose supported swarming effect better than the other sugars. In addition, compared with supplemented sucrose and L-malic acid individually, swarming motility of P. vagans M17 was significantly increased on the medium supplemented both. Lastly, inoculation of P. vagans M17 on fresh-cut melons showed slimy surface and significant changes on the content of organic acids. Future research could better understand the correlation between the phenotypes and quality of fresh-cut melons with the whole genome sequence information of P. vagans M17. Hoping we could take more precise ways to extend the shelf life in the near future.