Bacterial diversity of the sediments transiting through the gut of Holothuria scabra (Holothuroidea; Echinodermata)

This work analyzes bacterial diversity of sediments transiting through the gut of Holothuria scabra which is an important bioturbator in tropical shallow waters. This edible holothurian species has a social and economic importance for coastal populations in many developing countries. Bacterial biodiversity was analyzed by sequencing the 16S rRNA of bacterial cultures and clones. DAPI and FISH methods were used to determine and compare the number of bacteria found in the various gut compartments. A total of 116 phylotypes belonging to the gamma-Proteobacteria (60.5 %), alpha-Proteobacteria (24.5 %), Bacteroidetes (6 %), Actinobacteria (2.75 %), Fusobacteria (1.75 %), Firmicutes (1.75 %), Cyanobacteria (1.75 %) and delta-Proteobacteria (1 %) were identified. The number of bacteria is significantly greater (1.5x) in the foregut than in the ambient sediments. The number of bacteria significantly decreases in the midgut and remains stable until defecation. Some gamma-Proteobacteria, especially Vibrio, are less affected by digestion than other bacterial taxa. The season has an impact on the bacterial diversity found in the sediments transiting through the gut: in the dry season, gamma-Proteobacteria are the most abundant taxon, while alpha-Proteobacteria dominate in the rainy season. Vibrio is the most frequent genus with some well-known opportunistic pathogens like V. harveyi, V. alginolyticus and V. proteolyticus. Findings show that sediment-associated microbial communities are significantly modified by H. scabra during their transit through the gut which supports the view that holothurians play a substantial role in the structuring of bacterial communities at the sediment-seawater interface.