Bacterial community in intestine of black tiger shrimp Penaeus monodon

Abstract

The black tiger shrimp Penaeus monodon is an important aquaculture species for Thailand. In recent years, the industry faced with several problems such as a lack of suitable broodstocks, environmental impact, and diseases. Intestinal bacteria of aquatic animals play a crucial role in the host-animals well-being such as improving digestive system and disease resistance, but the understanding of shrimp-bacteria interaction is limited. The objective of this thesis was to examine several aspects of the intestinal bacterial community associated with black tiger shrimp (Penaeus monodon) including (1) the differences in the intestinal bacterial community of farmed juvenile shrimp of different sizes in the same cohort, (2) the diversity of the intestinal bacteria community in different segments of the gastrointestinal tract, and (3) the variation in the intestinal bacterial community upon a challenge with shrimp pathogen Vibrio harveyi. In addition, pure culture isolates collected from the intestines of P. monodon were also screened for inhibitory effects against V. harveyi and V. parahaemolyticus. Bacterial communities from the intestinal tracts of 60 farmed-raised juveniles and 5 different segments of the GI tracts of 8 wild-caught adult shrimps were analyzed using PCR-DGGE, cluster analysis, and 16S rDNA sequencing. The intestinal bacterial communities of P. monodon are a diverse group of bacteria that generally included 3 to 4 main phyla including Proteobacteria (β-, δ-, γ- and α-), Fusobacteria, Firmicutes and Bacteroidetes. Regardless of the source or life-history of the shrimp, γ- Proteobacteria is the most abundant in the intestinal community and can be found in all segments. Other phyla were less abundant and limited to certain segments in their distribution. Vibrio spp. or Photobacterium sp. are dominant genera that can be found in farm-raised juvenile and wild-caught adults. Bacterial communities from farm-raised juvenile shrimp of different sizes showed no distinct clustering pattern by size at either 2 or 5 month. However, the differences in bacterial communities between 2 and 5 month old juveniles were pronounced. Bacterial communities in different segments of the GI tract of wild-caught adults were different in both the diversity and composition. The change in the intestinal bacterial community upon challenge with V. harveyi can usually be observed after 48 hrs. Seventeen pure culture isolates were shown to inhibit the growth of both V. harveyi and V. parahaemolyticus using co-culture methods. Twelve isolates that were selected for further characterization were closely related to Vibrio spp. (8 isolates), Shewanella spp. (2 isolate), Pseudomonas sp. (1 isolate), and Pseudoalteromonas sp. (1 isolate).