Lu Zhongjing, Pérez-Díaz Ilenys M, Hayes Janet S, Breidt Fred
Department of Molecular & Cellular Biology, Kennesaw State University, Kennesaw, GA, United States.
United States Department of Agriculture, Agricultural Research Service, Washington, DC, United States.
Front Microbiol. 2020 Jun 26;11:1306. doi: 10.3389/fmicb.2020.01306. eCollection 2020.
Cucumber fermentations are one of the most important vegetable fermentations in the United States. The fermentation is usually driven by lactic acid bacteria (LAB) indigenous to fresh cucumbers. But LAB are greatly outnumbered by many Gram-negative bacteria on fresh cucumbers, which may influence the growth of LAB and the incidence of bloater defect (hollow cavities formed inside fermented cucumbers) leading to serious economic loss to the pickle industry. Rapid elimination of Gram-negative bacteria is crucial to the dominance of LAB and the reduction of bloater defect in the fermentation. Various factors can affect the viability of Gram-negative bacteria in cucumber fermentation. Bacteriophages (phages) may be one of such factors. This study explored the abundance, diversity, and functional role of phages infecting Gram-negative bacteria in a commercial cucumber fermentation. Cover brine samples were taken from a commercial fermentation tank over a 30-day period. On day 1 and day 3 of the fermentation, 39 Gram-negative bacteria and 26 independent phages were isolated. Nearly 67% of Gram-negative bacterial isolates were susceptible to phage infection. Phage hosts include , , , , , , , and species. About 88% of the isolated phages infected the members in the family and 58% of phages infected species. Eight phages with unique host ranges were characterized. These phages belong to the , , or family and showed distinct protein profiles and DNA fingerprints. The infectivity of a phage against e was evaluated in cucumber juice as a model system. The phage infection at the multiplicity of infection 1 or 100 resulted in a 5-log reduction in cell concentration within 3 h and rapidly eliminated its host. This study revealed the abundance and variety of phages infecting Gram-negative bacteria, particularly , in the commercial cucumber fermentation, suggesting that phages may play an important role in the elimination of Gram-negative bacteria, thereby facilitating the dominance of LAB and minimizing bloater defect. To our knowledge, this is the first report on the ecology of phages infecting Gram-negative bacteria in commercial cucumber fermentations.
黄瓜发酵是美国最重要的蔬菜发酵之一。这种发酵通常由新鲜黄瓜中天然存在的乳酸菌（LAB）驱动。但是新鲜黄瓜上革兰氏阴性菌的数量远远超过乳酸菌，这可能会影响乳酸菌的生长以及胀气缺陷（发酵黄瓜内部形成空洞）的发生率，给泡菜产业带来严重的经济损失。快速清除革兰氏阴性菌对于乳酸菌在发酵过程中的主导地位以及减少胀气缺陷至关重要。各种因素会影响黄瓜发酵中革兰氏阴性菌的生存能力。噬菌体可能是其中一个因素。本研究探讨了商业黄瓜发酵中感染革兰氏阴性菌的噬菌体的丰度、多样性及其功能作用。在30天的时间里从一个商业发酵罐中采集覆盖盐水样本。在发酵的第1天和第3天，分离出39株革兰氏阴性菌和26种独立的噬菌体。近67%的革兰氏阴性菌分离株易受噬菌体感染。噬菌体宿主包括[具体菌属]、[具体菌属]、[具体菌属]、[具体菌属]、[具体菌属]、[具体菌属]、[具体菌属]和[具体菌属]等菌种。约88%的分离噬菌体感染了[某科]中的成员，58%的噬菌体感染了[某菌属]菌种。对8种具有独特宿主范围的噬菌体进行了表征。这些噬菌体属于[具体噬菌体家族]、[具体噬菌体家族]或[具体噬菌体家族]，并显示出不同的蛋白质谱和DNA指纹图谱。在黄瓜汁作为模型系统中评估了一种噬菌体对[某菌]的感染性。感染复数为1或100时的噬菌体感染导致细胞浓度在3小时内降低5个对数，并迅速清除其宿主。本研究揭示了商业黄瓜发酵中感染革兰氏阴性菌，特别是[某菌属]的噬菌体的丰度和种类，表明噬菌体可能在清除革兰氏阴性菌方面发挥重要作用，从而促进乳酸菌的主导地位并使胀气缺陷最小化。据我们所知，这是关于商业黄瓜发酵中感染革兰氏阴性菌的噬菌体生态学的首次报告。
