Probiotic Characterization of Arsenic-resistant Lactic Acid Bacteria for Possible Application as Arsenic Bioremediation Tool in Fish for Safe Fish Food Production.

Arsenic (As) contamination of water and food is a global problem posing a severe threat to environmental and human health; therefore, fish as an aquatic animal is immensely affected by the hazardous impacts of As. The present study aimed to explore the As-resistant probiotic bacteria and characterize their potential for applying as an As bioremediation tool in fish. As-resistant lactic acid bacteria (LAB) were isolated from sludge samples of an old stabilization pond/lagoon of wastewater treatment plant using spared plate techniques. The potential probiotic was selected by assessing the sequential probiotic characterization, As resistance and removal properties. The selected probiotic was identified by PCR-based molecular method using 16S rDNA. A total of 51 As-resistant LAB were isolated from sludge samples. Potential six As-resistant LAB strains (As4, 11, 20, 21, 41 and 48) were selected from 51 isolates through sequential probiotic characterizations using mimic fish gastrointestinal conditions. The selected probiotics displayed relatively elevated As (> 1000 mg L-1), cadmium (20-100 mg L-1) and lead (> 2000 mg L-1)-resistant patterns and excellent As-removal efficiencies (0.0012-0.0044 mg As mg cell-1 h-1) from water along with favourable various associative probiotic properties. The 16S rDNA sequence-based molecular identification and phylogenetic analysis revealed that the strains As4, 11, 20, 21, 41 and 48 belong to Limosilactobacillus fermentum (Lactobacillus fermentum according to old taxonomy). The As removal and survival in mimic gastrointestinal conditions of fish indicated that new Limosilactobacillus fermentum strains could be employed as the novel and potential probiotic tools for possible bioremediation of As and other pollutants in the fish to prevent the bioaccumulation and toxicity impacts of As in fish for cleaner and safe fish food production.

Biochemical, physiological (haematological, oxygen-consumption rate) and behavioural effects of mercury exposures on the freshwater snail, Bellamya bengalensis.

The widespread occurrence of Mercury (Hg) and its derivatives in the aquatic environment and risks to the health of local populations has necessitated investigations into its toxic effects on sessile species. The toxicity of Mercury was observed sequentially from 96 h acute exposure regime (behavioural endpoints) to chronic durations (haematological and biochemical toxicity endpoints) in Bellamya bengalensis. Time-dependent lethal endpoints for acute toxicity (LC50) of mercury i.e., 24,48,72 and 96 h were estimated as 0.94, 0.88, 0.69 and 0.40 mg/l respectively. Threshold effect values i.e., LOEC (Lowest Observed Effect Concentration), NOEC (No Observed Effect Concentration) and MATC (Maximum Acceptable Toxicant Concentration) at 96 h were found to be 0.10, 0.05, 0.039 mg/l respectively. The study of oxygen consumption rate and behavioural changes during acute toxicity and haematological and biochemical responses during chronic toxicity to sublethal concentrations (10% and 20% of 96 h LC50) of mercury to the snail were also conducted. The organisms showed initial elevation at 24 h but later gradual decrease in oxygen consumption rate with the increase of concentration of mercury and time of exposure. For behavioural studies, variable test concentrations from 0.00 to 1.00 mg/l were used for 24, 48, 72 and 96 h. The crawling activity and clumping tendency decreased with the progress of time at all treatment periods and stopped ultimately at 96 h of exposure from 0.7 mg/l onwards whereas touch reflex was not observed at 96 h exposure at all treatments except at 0.09 mg/l. In haemocyte count, no significant variation was observed among control values between various exposure periods (p > 0.05) though variations were observed in sub-lethal concentrations versus control at all treatment duration (7, 14, 21, 28d, p < 0.05). In biochemical response study, the protein content in hepatopancreas of the snails treated at sublethal concentrations of mercury (10% and 20% of 96 h LC50) reduced significantly versus control after 21d of exposure (p < 0.05). In gonads, the protein content of the treated snails significantly reduced at all treatment concentrations versus control at all exposure times (p < 0.05). Based on the safe levels indicated above, the concentration of 0.01 to 0.04 ppm of mercury can be considered safe for Bellamya bengalensis and any less-hardy aquatic species. These responses elicited by our molluscan model will not only help in biomonitoring of environmental mercury contamination in water bodies but will also provide support to ecological health and risk assessment.