貝萊斯芽孢桿菌FZB42之dfn基因簇拮抗馬鈴薯瘡痂病菌之角色探討

馬鈴薯為世界上四大重要作物之一，而瘡痂病為馬鈴薯常見病害，主要病原為馬鈴薯瘡痂病菌 （Streptomyces scabies），造成薯塊表面木栓化病斑，使馬鈴薯薯塊品質降低。本實驗室研究發現液化澱粉芽孢桿菌 （Bacillus amyloliquefaciens） Ba01能有效抑制瘡痂病菌生長及降低罹病度。為找出可能影響芽孢桿菌抑制瘡痂病菌的作用機制，本實驗利用模式菌株貝萊斯芽孢桿菌 （Bacillus velezensis） FZB42搭配隨機突變系統進行試驗，再以突變株比較野生株拮抗瘡痂病菌之能力差異，推測二次代謝物difficidin （dfn） 基因影響其抑制瘡痂病菌的能力。為證實此一推測，本實驗以dfn基因簇 （gene cluster） 及基因簇中J區域 （dfnJ domain） 進行目標基因突變。發現dfn基因簇與dfnJ domain突變株與野生株B. velezensis FZB42比較，其抑制瘡痂病菌能力皆顯著降低，而dfnJ domain互補株則回復似野生株抑菌能力。以上結果顯示B. velezensis FZB42 dfn基因簇與dfnJ domain於抑制馬鈴薯瘡痂病菌機制扮演重要角色。

Potato is one of four major food crops in the world. Potato common scab mainly caused by Streptomyces scabies widely occurs in planting fields. It causes cork symptoms on the surface of potato tubers and decreases the quality of potato tuber. Previous study in our laboratory found that Bacillus amyloliquefaciens Ba01 can inhibit the growth ability of S. scabies and decrease the disease severity of potato common scab. To further investigate antibacterial mechanism of Bacillus spp., we conduct random insertion mutation by TnYLB-1 transposon system in Bacillus velezensis FZB42. Mutants were obtained and tested whether these mutants affect the inhibition ability against S. scabies. According to the experiments above, we speculated that difficidin gene (dfn) encoding a secondary metabolite of B. velezensis FZB42, affects the inhibition ability against S. scabies. To test whether dfn plays important role in anti-S. scabies activity, we knock out dfn gene cluster and dfnJ domain in B. velezensis FZB42. We found that dfn gene cluster and dfnJ domain mutants have significantly reduced inhibition zones compared to the wild type, while complementary strain of dfnJ domain behaved wild type inhibition level against S. scabies. Based on above results, we suggest that dfn gene cluster and dfnJ domain play important roles in combating S. scabies.