Isolation of bacteria able to degrade poly-hydroxybutyrate-co-hydroxyhexanoate, and the inhibitory effects of the degradation products on shrimp pathogen Vibrio penaeicida.

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.

Effects of the Monomeric Components of Poly-hydroxybutyrate-co-hydroxyhexanoate on the Growth of Vibrio penaeicida In Vitro and on the Survival of Infected Kuruma Shrimp (Marsupenaeus japonicus).

Here, we investigated the inhibitory effects of the biodegradable, water-insoluble polymer poly-hydroxybutyrate-co-hydroxyhexanoate (PHBH) and its two constituent monomers, the hydroxyalkanoic acids 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HH), on the growth of the shrimp-pathogenic bacterium Vibrio penaeicida. In vitro experiments revealed that 3HH showed greater growth inhibitory activity than 3HB against V. penaeicida. In addition, the activities of hydroxyalkanoic acids were pH dependent, being greater at pH 6.0 than at pH 7.0. Investigation of the pH of the shrimp gut revealed a pH range of 5.9-6.7 (mean 6.29 ± SD 0.20), indicating that the physiological environment was suitable for 3HB and 3HH to exert their inhibitory activities against V. penaeicida. In vivo bacterial challenge experiments revealed that survival rates in kuruma shrimp (Marsupenaeus japonicus) infected by V. penaeicida were significantly increased in shrimp reared on feed containing PHBH (0.1%-5% w/w PHBH) compared with that in shrimp reared on standard diet alone. Supplementation with PHBH had no significant effects on three shrimp growth parameters: increase in body weight, daily feeding rate, and feed conversion ratio. These results suggest that supplementation of standard diet with PHBH will increase shrimp resistance to infection by V. penaeicida, thereby increasing shrimp aquaculture productivity.

Structures and properties of a diastereoisomeric molecular compound of (2S,3S)- and (2R,3S)-N-acetyl-2-amino-3-methylpentanoic acids.

An X-ray crystal structural analysis revealed that (2S,3S)-N-acetyl-2-amino-3-methylpentanoic acid (N-acetyl-L-isoleucine; Ac-L-Ile) and (2R,3S)-N-acetyl-2-amino-3-methylpentanoic acid (N-acetyl-D-alloisoleucine; Ac-D-aIle) formed a molecular compound containing one Ac-L-Ile molecule and one Ac-D-aIle molecule as an unsymmetrical unit. This molecular compound is packed with strong hydrogen bonds forming homogeneous chains consisting of Ac-L-Ile molecules or Ac-D-aIle molecules and weak hydrogen bonds connecting these homogeneous chains in a fashion similar to that observed for Ac-L-Ile and Ac-D-aIle. Recrystallization of an approximately 1:1 mixture of Ac-L-Ile and Ac-D-aIle from water gave an equimolar molecular compound due to its lower solubility than that of Ac-D-aIle or especially Ac-L-Ile. The results suggest that the equimolar mixture of Ac-L-Ile and Ac-D-aIle could be obtained from an Ac-L-Ile-excess mixture by recystallization from water.

DBFOX-Ph/metal complexes: evaluation as catalysts for enantioselective fluorination of 3-(2-arylacetyl)-2-thiazolidinones.

We examined the catalytic enantioselective fluorination of 3-(2-arylacetyl)-2-thiazolidinones 1 with N-fluorobenzenesulfonimide (NFSI) by DBFOX-Ph/metal complexes under a variety of conditions. After optimization of the metal salts, solvents and additives, we found that the fluoro-2-thiazolidinones 2 were obtained in good to high yields with moderate to good enantioselectivities (up to 78% ee) when the reaction was carried out in the presence of DBFOX-Ph (11 mol%), Ni(ClO(4))(2).6H(2)O (10 mol%) and 2,6-lutidine (0 or 1.0 equiv) in CH(2)Cl(2).