title: High yield expression of an AHL-lactonase from Bacillus sp. B546 in Pichia pastoris and its application to reduce Aeromonas hydrophila mortality in aquaculture.
abstract: BACKGROUND
  Aeromonas hydrophila is a serious pathogen and can cause hemorrhagic septicemia in fish. To control this disease, antibiotics and chemicals are widely used which can consequently result in "superbugs" and chemical accumulation in the food chain. Though vaccine against A. hydrophila is available, its use is limited due to multiple serotypes of this pathogen and problems of safety and efficacy. Another problem with vaccination is the ability to apply it to small fish especially in high numbers. In this study, we tried a new way to attenuate the A. hydrophila infection by using a quorum quenching strategy with a recombinant AHL-lactonase expressed in Pichia pastoris.
  
  
  RESULTS
  The AHL-lactonase (AiiAB546) from Bacillus sp. B546 was produced extracellularly in P. pastoris with a yield of 3,558.4 +/- 81.3 U/mL in a 3.7-L fermenter when using 3-oxo-C8-HSL as the substrate. After purification with a HiTrap Q Sepharose column, the recombinant homogenous protein showed a band of 33.6 kDa on SDS-PAGE, higher than the calculated molecular mass (28.14 kDa). Deglycosylation of AiiAB546 with Endo H confirmed the occurrence of N-glycosylation. The purified recombinant AiiAB546 showed optimal activity at pH 8.0 and 20 degrees C, exhibited excellent stability at pH 8.0-12.0 and thermal stability at 70 degrees C, was firstly confirmed to be significantly protease-resistant, and had wide substrate specificity. In application test, when co-injected with A. hydrophila in common carp, recombinant AiiAB546 decreased the mortality rate and delayed the mortality time of fish.
  
  
  CONCLUSIONS
  Our results not only indicate the possibility of mass-production of AHL-lactonase at low cost, but also open up a promising foreground of application of AHL-lactonase in fish to control A. hydrophila disease by regulating its virulence. To our knowledge, this is the first report on heterologous expression of AHL-lactonase in P. pastoris and attenuating A. hydrophila virulence by co-injection with AHL-lactonase.
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, PR China.
authors.forename: Ruidong
authors.initials: R
authors.lastname: Chen
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Zhou
authors.forename: Yanan
authors.initials: Y
authors.lastname: Cao
authors.forename: Yingguo
authors.initials: Y
authors.lastname: Bai
authors.forename: Bin
authors.initials: B
authors.lastname: Yao
mesh_terms: D016980:Aeromonas hydrophila / Q000166:cytology* / Q000472:pathogenicity; D000818:Animals; D001407:Bacillus / Q000201:enzymology*; D002265:Carboxylic Ester Hydrolases / Q000096:biosynthesis*; D003001:Cloning, Molecular / Q000379:methods; D005399:Fishes / Q000382:microbiology; D016905:Gram-Negative Bacterial Infections / Q000188:drug therapy / Q000517:prevention & control; D050296:Microbial Viability; D010843:Pichia / Q000235:genetics*
chemical_list: D002265:Carboxylic Ester Hydrolases; C432003:N-acyl homoserine lactonase