Poly-hydroxybutyrate-co-hydroxyhexanoate (PHBH) is a biodegradable, water-insoluble polymer produced by specific bacteria. The monomers of PHBH are the hydroxyalkanoic acids 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HH). Previously, we reported that 3HB and 3HH showed marked antibacterial activities against the shrimp pathogenic bacterium Vibrio penaeicida, and that addition of 5% (w/w) PHBH to the standard aquaculture diet significantly increased survival rate in kuruma shrimp (Marsupenaeus japonicus) after challenge by V. penaeicida, which we attributed to the degradation of PHBH to its monomers in the shrimp gut. In the present study, we isolated four strains of bacteria with high PHBH-degrading activity and evaluated their inhibitory effects on V. penaeicida with PHBH: one strain from shrimp gut contents (E1; Pseudoalteromonas shioyasakiensis/P. mariniglutinosa), two strains from coastal surface seawater (F1; P. shioyasakiensis/P. mariniglutinosa, and F5; Alcanivorax dieselolei/A. xenomutans), and one strain that was a contaminant in commercial PHBH powder (Y1; Bacillus pseudofirmus). Strains E1, F1, and Y1 showed strong PHBH-degrading activity within 24 h of inoculation to PHBH-containing agar plates. Although none of the isolates alone had any effect on the growth of V. penaeicida, when cultured with E1 or F1 and PHBH, the growth of V. penaeicida was markedly suppressed. Incubation with E1 and PHBH resulted in a gradual reduction in the concentration of V. penaeicida from 2 days after the start of incubation until the concentration was 1.2% of that in the control (V. penaeicida alone). Incubation with F1 and PHBH resulted in a rapid reduction in the concentration of V. penaeicida from 2 days after the start of incubation until the concentration was only 0.32% of that of the control. Compared with strains E1 and F1, Y1 showed similar PHBH-degrading activity but did not show any suppressive effect on the growth of V. penaeicida until 5 days after the start of incubation. In addition, this suppressive effect was relatively weak compared with that of the other two strains, suggesting that Y1 can quickly degrade PHBH but that it takes several days to produce monomers. Together, these results suggest that addition to the aquaculture diet of PHBH and PHBH-degrading bacteria that rapidly degrade PHBH to its monomers may speed up degradation of PHBH to its monomers in the shrimp gut, and that it would increase resistance to infection mortality by V. penaeicida in kuruma shrimp.

聚羟基丁酸酯-共羟基己酸酯 (PHBH) 是一种由特定细菌产生的可生物降解、不溶于水的聚合物。PHBH 的单体是羟基链烷酸 3-羟基丁酸酯 (3HB) 和 3-羟基己酸酯 (3HH)。之前，我们报道了3HB和3HH对虾病原菌Vibrio penaeicida显示出显着的抗菌活性，并且在标准水产养殖日粮中添加5% (w/w) PHBH可显着提高库鲁马虾（Marsupenaeus japonicus）攻击后的存活率。由五penaeicida，这是我们在虾肠归因于PHBH的降解，其单体。在本研究中，我们分离了四株具有高 PHBH 降解活性的细菌，并评估了它们对 PHBH 的抑制作用。V. penaeicida with PHBH：来自虾肠道内容物的一种菌株（E1；Pseudoalteromonas shioyasakiensis/P. mariniglutinosa），来自沿海表面海水的两种菌株（F1；P. shioyasakiensis/P. mariniglutinosa和 F5；Alcanivorax diodeei/A. xenomutans） , 以及一种菌株是商业 PHBH 粉末中的污染物（Y1; Bacillus pseudofirmus）。菌株 E1、F1 和 Y1 在接种到含 PHBH 的琼脂平板后 24 小时内表现出强烈的 PHBH 降解活性。尽管单独的分离株都没有对V. penaeicida的生长产生任何影响，但当与 E1 或 F1 和 PHBH 一起培养时，V. penaeicida被明显压制。与 E1 和 PHBH 一起孵育导致从孵育开始 2 天后对虾的浓度逐渐降低，直到浓度为对照（单独对虾）的1.2% 。与 F1 和 PHBH 一起培养导致从培养开始 2 天后对虾的浓度迅速降低，直到浓度仅为对照浓度的 0.32%。与菌株 E1 和 F1 相比，Y1 具有相似的 PHBH 降解活性，但对对虾对虾生长没有任何抑制作用直到孵化开始后 5 天。此外，与其他两种菌株相比，这种抑制作用相对较弱，表明 Y1 可以快速降解 PHBH，但产生单体需要几天时间。总之，这些结果表明，除了PHBH和PHBH降解菌的养殖饮食，迅速降解PHBH其单体可PHBH的降解加快其在虾肠单体，而且会增加感染的死亡率阻力V . 车马虾中的对虾。