Abstract
The halophilic aquatic bacterium, Vibrio parahaemolyticus, is an important aquatic pathogen, also capable of causing acute hepatopancreatic necrosis disease (AHPND) in shrimp resulting in significant economic losses. Therefore, there is an urgent need to develop anti-infective strategies to control AHPND. The gnotobiotic Artemia model is used to establish whether a phenolic compound phloroglucinol is effective against the AHPND strain V. parahaemolyticus MO904. We found that pretreatment with phloroglucinol, at an optimum concentration (30 µM), protects axenic brine shrimp larvae against V. parahaemolyticus infection and induced heat shock protein 70 (Hsp70) production (twofolds or more) as compared with the control. We further demonstrated that the Vibrio-protective effect of phloroglucinol was caused by its prooxidant effect and is linked to the induction of Hsp70. In addition, RNA interference confirms that phloroglucinol-induced Hsp70 mediates the survival of brine shrimp larvae against V. parahaemolyticus infection. The study was validated in xenic Artemia model and in a Macrobrachium rosenbergii system. Pretreatment of xenic brine shrimp larvae (30 µM) and Macrobrachium larvae (5 µM) with phloroglucinol increases the survival of xenic brine shrimp and Macrobrachium larvae against subsequent V. parahaemolyticus challenge. Taken together, our study provides substantial evidence that the prooxidant activity of phloroglucinol induces Hsp70 production protecting brine shrimp, A. franciscana, and freshwater shrimp, M. rosenbergii, against the AHPND V. parahaemolyticus strain MO904. Probably, phloroglucinol treatment might become part of a holistic strategy to control AHPND in shrimp.
Highlights
The acute hepatopancreatic necrosis disease (AHPND), originally known as early mortality syndrome, is a newly emerging shrimp disease causing havoc in the shrimp industry [1]
In this study, using a highly controlled gnotobiotic brine shrimp model system, we aimed to investigate whether phloroglucinol potentiates the generation of prooxidant activity and heat shock protein 70 (Hsp70) production in vivo and whether this putative effect could contribute to the induction of protective responses in Artemia against pathogenic V. parahaemolyticus MO904 strain
The results obtained in the gnotobiotic brine shrimp model system were validated in a xenic brine shrimp and Macrobrachium larvae, and we present novel finding which demonstrates that phloroglucinol is a potent in vivo enhancer of Hsp70 and this effect mediates the induction of resistance in xenic brine shrimp and Macrobrachium larvae against V. parahaemolyticus
Summary
The acute hepatopancreatic necrosis disease (AHPND), originally known as early mortality syndrome, is a newly emerging shrimp disease causing havoc in the shrimp industry [1]. The disease is caused by a specific virulent strain of Gram-negative marine bacterium, Vibrio parahaemolyticus, ubiquitous in estuarine and coastal waters [2]. The shrimp production in AHPND-affected regions has dropped to ~60%, and the disease has caused global loss of $1 billion per year to the shrimp farming industry [5, 6]. The V. parahaemolyticus becomes virulent VPAHPND by acquiring a 63- to 70-kb plasmid (pVA1) encoding the binary toxin PirAVp/ PirBVp, which consist of two subunits PirA and PirB, and is homologous to the Photorhabdus luminescens insect-related (Pir) toxins PirA/PirB [7,8,9]. To enable the prevention of V. parahaemolyticus, an approach that focuses on understanding the host immune system and develops effective anti-infective strategies, in general, will have the highest chance of decreasing the risk of pathogenic V. parahaemolyticus infection in shrimps
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