Relationship between differential retention of Escherichia coli and Enterococcus faecalis and variations in enzyme activity in the scallop Patinopecten yessoensis

Comparative Analyses of the Exopalaemon carinicauda Gut Bacterial Community and Digestive and Immune Enzyme Activity during a 24-Hour Cycle

The change in life activities throughout a cycle of approximately 24 h is called the circadian rhythm. Circadian rhythm has an important impact on biological metabolism, digestion, immunity, and other physiological activities, but the circadian rhythm of crustaceans has rarely been studied. In this study, the activity of digestive enzymes (α-amylase, trypsin, and lipase) and immune enzymes (superoxide dismutase, lysozyme, and catalase), as well as the circadian rhythm of the intestinal bacterial community of Exopalaemon carinicauda, were studied. The results showed that the digestive and immune enzyme activities of E. carinicauda changed significantly (p < 0.05) at four time points throughout the day by one-way ANOVA analysis, with the highest value at 24:00 and the lowest value at 12:00. The highest values of alpha diversity and richness were observed in the 24:00 samples, which were significantly higher than those in the other groups (p < 0.05). The principal coordinate analysis (PCoA) results obviously showed that the samples from the same sampling time had higher similarity in the bacterial community structure. Candidatus hepatoplasma had the highest abundance among the intestinal microorganisms at 24:00, and Marinomonas had the highest abundance at 12:00. This study contributed to the understanding of digestive enzyme activity, immune enzyme activity, and the circadian rhythm of the intestinal bacterial community structure in E. carinicauda. It will play an important role in optimizing feeding times and improving digestion and nutrient utilization for E. carinicauda. The results of this study provide a basis for further study on the physiological mechanism of diurnal variation of intestinal flora in crustaceans.

Assessing microbial contamination and antibiotic resistant bacteria using zebra mussels (Dreissena polymorpha)

Aquatic pollution with faecal bacteria and subsequent consumption of contaminated water or food is a worldwide issue that causes severe health effects (e.g. meningitis, salmonellosis, dysentery). In addition, the excessive use of antibiotics in animal husbandry and human medicine has enhanced the selective pressure on pathogenic bacteria, further increasing human health risks and detrimental effects on natural microbial communities. This urges the need to monitor faecal contamination using a time-integrated approach, as grab water samples can miss pathogen peaks. We tested the ability of zebra mussels (Dreissena polymorpha) to take up and depurate faecal indicator bacteria such as Escherichia coli and intestinal enterococci. Furthermore, we quantified the frequency of antibiotic resistant bacteria in water and mussels both in controlled laboratory tests and under in situ conditions downstream of a sewage treatment plant (STP). Laboratory results show that bacterial indicators in mussels were 132 times higher than their concentration in water, and that mussels retained bacteria up to 2 days after pulse exposure. Field results show decreasing bacterial concentrations in both water and mussels downstream the STP, with maximum E. coli concentrations ranging 173-9 cfu mL^-1 in water and 2970-330 cfu g^-1 in mussels. Similarly, enterococci ranged 59-4 cfu mL^-1 and 1450-240 cfu g^-1 in water and mussels, respectively. High proportions of antibiotic resistant E. coli were found in mussels (72%) and water (65%), and slightly lower proportion of resistant enterococci was found in mussels (47%) and in water (34%). Moreover, 33% of the bacteria isolated from mussels were resistant to multiple antibiotics, which emphasizes that resistance is a common feature in surface waters and highlights the need for safe water management. Our results show that zebra mussels provide an efficient, time-integrating tool for quantifying faecal indicators, including resistant and multidrug resistant bacteria.

Quality assessment of pollution indicators in marine water at critical locations of the Gulf of Mannar Biosphere Reserve, Tuticorin

The present study focused on the shoreline environment of urban and industrial areas, and the aim of this study was to assess the coastal water quality in the Gulf of Mannar Biosphere Reserve. Water samples were collected from five different coastal sites during the premonsoon and monsoon seasons. The samples were analyzed following the standard methods. The results showed that the levels of microbiological indicators in the samples highly exceeded the regional and national standard seawater permissible limits, and environmental parameters such as the total suspended solid and dissolved oxygen were affected significantly (p<0.05). To identify frequent pollution indicators, their levels should be estimated to determine possible pollution in coastal ecosystems due to human interventions.