Selected Bacterial Strains Protect Artemia spp. from the Pathogenic Effects of Vibrio proteolyticus CW8T2

In this study Vibrio proteolyticus CW8T2 has been identified as a virulent pathogen for Artemia spp. Its infection route has been visualized with transmission electron microscopy. The pathogen affected microvilli and gut epithelial cells, disrupted epithelial cell junctions, and reached the body cavity, where it devastated cells and tissues. In vivo antagonism tests showed that preemptive colonization of the culture water with nine selected bacterial strains protected Artemia juveniles against the pathogenic effects. Two categories of the selected strains could be distinguished: (i) strains providing total protection, as no mortality occurred 2 days after the experimental infection with V. proteolyticus CW8T2, with strain LVS8 as a representative, and (ii) strains providing partial protection, as significant but not total mortality was observed, with strain LVS2 as a representative. The growth of V. proteolyticus CW8T2 in the culture medium was slowed down in the presence of strains LVS2 and LVS8, but growth suppression was distinctly higher with LVS8 than with LVS2. It was striking that the strains that gave only partial protection against the pathogen in the in vivo antagonism test showed also a restricted capability to colonize the Artemia compared to the strains providing total protection. The in vivo antagonism tests and the filtrate experiments showed that probably no extracellular bacterial compounds were involved in the protective action but that the living cells were required to protect Artemia against V. proteolyticus CW8T2.

本研究中，溶藻弧菌（Vibrio proteolyticus）CW8T2被鉴定为卤虫属（Artemia spp.）的强毒致病菌。其侵染途径已通过透射电子显微镜（transmission electron microscopy）完成可视化观察。该致病菌可侵染微绒毛与肠道上皮细胞，破坏上皮细胞连接结构，并侵入体腔，对体腔内的细胞与组织造成毁灭性破坏。体内拮抗试验结果显示，预先在养殖水体中定植9株筛选得到的细菌菌株，可使卤虫幼体免受该致病菌的致病危害。筛选得到的菌株可分为两类：（i）完全保护菌株：以菌株LVS8为代表，实验感染溶藻弧菌CW8T2后2天内无任何死亡案例发生；（ii）部分保护菌株：以菌株LVS2为代表，仅出现显著但未达全部的死亡率。当培养基中存在LVS2或LVS8菌株时，溶藻弧菌CW8T2的生长会受到抑制，且LVS8对其生长的抑制效果显著强于LVS2。值得注意的是，与提供完全保护的菌株相比，仅能提供部分保护的菌株在卤虫体内的定殖能力同样受限。体内拮抗试验与滤液试验结果表明，保护性作用可能并非由细菌胞外分泌物介导，而是需要活菌才能使卤虫免受溶藻弧菌CW8T2的侵染危害。