Abstract
Bacterial diseases cause production failures in shrimp aquacultures. To understand environmental conditions and bacterial community dynamics contributing to white faeces disease (WFD) events, we analysed water quality and compared bacterial communities in water as well as in intestines and faeces of healthy and diseased shrimps, respectively, via 16S rRNA gene sequencing and qPCR of transmembrane regulatory protein (toxR), thermolabile haemolysin (tlh), and thermostable direct haemolysin genes of pathogenic Vibrio parahaemolyticus as a proxy for virulence. WFD occurred when pH decreased to 7.71–7.84, and Alteromonas, Pseudoalteromonas and Vibrio dominated the aquatic bacterial communities. The disease severity further correlated with increased proportions of Alteromonas, Photobacterium, Pseudoalteromonas and Vibrio in shrimp faeces. These opportunistic pathogenic bacteria constituted up to 60% and 80% of the sequences in samples from the early and advances stages of the disease outbreak, respectively, and exhibited a high degree of co-occurrence. Furthermore, toxR and tlh were detected in water at the disease event only. Notably, bacterial community resilience in water occurred when pH was adjusted to 8. Then WFD ceased without a mortality event. In conclusion, pH was a reliable indicator of the WFD outbreak risk. Dissolved oxygen and compositions of water and intestinal bacteria may also serve as indicators for better prevention of WFD events.
Highlights
Bacterial diseases cause production failures in shrimp aquacultures
To address the research needs and hypotheses outlined above, we provide a comprehensive overview of the bacterial dynamics and the water quality in shrimp ponds over the course of a white faeces disease (WFD) event, by (i) investigating water quality parameters, (ii) elucidating the Bacterial community composition (BCC) in rearing water (WB), separated into FL and PA bacteria, in the intestines of healthy L. vannamei (IB), and in white faecal strings (FSB), (iii) quantifying pathogenic Vibrio by their virulence gene copy numbers, and (iv) analysing bacterial co-occurrence patterns in healthy and diseased shrimps
Because bacterial communities of fresh shrimp faeces and that of the full intestines of healthy P. vannamei have been shown to be comparable[17,34], we only dissected the intestines of healthy shrimps and analysed them together with the fresh faecal strings collected from diseased shrimp
Summary
Bacterial diseases cause production failures in shrimp aquacultures. To understand environmental conditions and bacterial community dynamics contributing to white faeces disease (WFD) events, we analysed water quality and compared bacterial communities in water as well as in intestines and faeces of healthy and diseased shrimps, respectively, via 16S rRNA gene sequencing and qPCR of transmembrane regulatory protein (toxR), thermolabile haemolysin (tlh), and thermostable direct haemolysin genes of pathogenic Vibrio parahaemolyticus as a proxy for virulence. Bacterial diseases are a major problem for Penaeus vannamei pond aquaculture in Asia and Latin America They have been causing severe annual economic losses reaching approximately USD 1 billion over last decade[1,2]. Acute hepatopancreatic necrosis disease (AHPND) and white faeces disease (WFD) are the most infectious and lethal ones[3,4] The latter has frequently been occurring in Asian shrimp aquaculture since 2 0093,5,6, which reduced shrimp survival to 20–30%6. The viable plate count method, which selects certain pathogenic b acteria[18], was shown to be inadequate to identify the bacterial population[19], which may be associated with the disease These practices have been unsuccessful to predict WFD in P. vannamei aquaculture
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