Metagenomic Analysis of the Gastrointestinal Microbiota of Gadus morhua callarias L. Originating from a Chemical Munition Dump Site

Abstract

Several hundred thousand tonnes of munitions containing chemical warfare agents (CWAs) are lying on the seafloor worldwide. CWAs have started leaking from corroded munitions, and their presence in the environment and in organisms inhabiting dump sites has been detected. The presence of CWAs in the water negatively affects fish, macrobenthos and free-living bacteria. It can be expected that the presence of CWAs would also affect the gut-associated bacteria in fish, which are vital for their condition. The main aim of this study was to test if the microbiota of cod collected in the Baltic Bornholm Deep (highly polluted with CWAs) is dysregulated. To investigate this, we conducted metagenomic studies based on 16S rRNA gene sequencing. We found that the microbiota of cod inhabiting the dump site were significantly less taxonomically diverse compared to those from a non-polluted reference site. Moreover, taxa associated with fish diseases (e.g., Vibrionaceae, Aeromonadaceae) were more prevalent, and probiotic taxa (e.g., Actinobacteriota, Rhodobacteraceae) were less frequent in the guts of individuals from the dump site, than those from the reference site. The differences in vulnerability of various bacterial taxa inhabiting cod gastrointestinal tracts to CWAs were hypothesised to be responsible for the observed microbiota dysregulation.

Seaweed and Seaweed-Based Functional Metabolites as Potential Modulators of Growth, Immune and Antioxidant Responses, and Gut Microbiota in Fish

“…The dietary inclusion of Gracilaria gracilis enhanced the abundance of the microbes Sulfitobacter and Methylobacterium in the gut of European seabass [197]. These microbes are capable of producing short-and medium-chain fatty acids and can lower the pH of the intestine, thus playing a crucial role in suppressing pathogenic bacteria and potentially representing a promising method of enhancing disease resistance in fish [213,214]. Similarly, dietary supplementation of fucoidan, a polysaccharide derived from brown seaweed (Undaria pinnatifida), is reported to elevate the intestinal digestive enzyme activities and, thereby, modulate the intestinal microbial communities in gibel carp (Carassius auratus gibelio) when added at a level of 30 g/kg WW [190].…”