Abstract
The mangrove oysters (Crassostrea gasar) are molluscs native to the Amazonia region and their exploration and farming has increased considerably in recent years. These animals are farmed on beds built in the rivers of the Amazonia estuaries and, therefore, the composition of their microbiome should be directly influenced by environmental conditions. Our work aimed to evaluate the changes in bacterial composition of oyster's microbiota at two different seasons (rainy and dry). For this purpose, we amplified and sequenced the V3-V4 regions of the 16S rRNA gene. Sequencing was performed on the Illumina MiSeq platform. According to the rarefaction curve, the sampling effort was sufficient to describe the bacterial diversity in the samples. Alpha-diversity indexes showed that the bacterial microbiota of oysters is richer during the rainy season. This richness is possibly associated with the diversity at lower taxonomic levels, since the relative abundance of bacterial phyla in the two seasons remained relatively constant. The main phyla found include Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria. Similar results were found for the species Crassostrea gigas, Crassostrea sikamea, and Crassostrea corteziensis. Beta-diversity analysis showed that the bacterial composition of oyster's gut microbiota was quite different in the two seasons. Our data demonstrate the close relationship between the environment and the microbiome of these molluscs, reinforcing the need for conservation and sustainable management of estuaries in the Amazonia.
Highlights
The phylum Mollusca is one of the largest and most important in the animal kingdom
It was possible to notice a considerable variation in total suspended solids, turbidity, apparent color, conductivity, ammonium, total phosphorous, salinity, and precipitation. Such abiotic variations possibly had influenced in the gastrointestinal microbiota composition of oysters from T1 to T2
Rarefaction curve shows that the oyster microbiota is richer during the rainy season (Figure 1A), with values close to those of the respective diversity estimators, showing that the depth of the sequencing was sufficient for the description of the bacterial community (Figure 2)
Summary
From the six classes that make up the phylum, we can highlight the Bivalvia class, composed of about 7,500 species of soft-bodied animals protected by a shell, which acts as a skeleton for the connection of muscles and protects against predators (Gosling, 2003; Dame, 2011). These animals breathe and feed using their gills, having a food base of microalgae, phytoplankton, microzooplankton, dissolved organic matter, and bacteria (Gosling, 2003). Oysters tend to accumulate a large number of microorganisms present in the water, which can compose their gut microbiota (Harris, 1993; Li et al, 2017). The proliferation in the intestine can contribute to digestion, preconditioning the food, complementing the enzymes present in the digestive tract (Harris, 1993)
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