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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 (AiiA B546 ) 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 AiiA B546  with Endo H confirmed the occurrence of  N -glycosylation. The purified recombinant AiiA B546  showed optimal activity at pH 8.0 and 20°C, exhibited excellent stability at pH 8.0-12.0 and thermal stability at 70°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 AiiA B546  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.

microbial cell factories

High yield expression of an AHL-lactonase from Bacillus sp. B546 in Pichia pastoris and its application to reduce Aeromonas hydrophila mortality in aquaculture