Dynamics of bacterial community in Tonle Sap Lake, a large tropical flood-pulse system in Southeast Asia.

Tonle Sap Lake, the largest freshwater body in Southeast Asia, plays an important role in lives and environment. The lake is reportedly under anthropogenic pressure and suffers from eutrophication. The floating villagers suffer from waterborne diseases. However, the shift in bacterial community due to human activities in this great lake has not yet been reported. We aimed to determine the dynamics of the bacterial community and their concentration in the lake using 67 surface waters, 53 sub-layer waters and 59 sediment samples by Next Generation Sequencing (NGS). The bacterial communities in the surface water and sub-layer water were similar but they differed from the sediment; however, their abundance showed spatiotemporal variations. The bacterial diversity reached the highest value in the dry season but lowest value in the rainy season in the surface water and sediment. Their diversity in the sub-layer water was highest in the transition from dry to rainy season. The total 16S rRNA gene copy number in the sediment were >100 times higher than that measured in the water. The Cyanobacteria, Actinobacteria, and Proteobacteria concentrations in the lake water increased in the dry season and reached a peak in the transition from dry to rainy season. The concentrations of Proteobacteria and Firmicutes elevated in the lake water and sediment, respectively, in the floating villages which were >10 times higher than the places with non-point sources. The bacterial concentration and its diversity in the Tonle Sap Lake changed based on the lake water volume between rainy and dry season. The bacterial concentration in the Tonle Sap Lake diluted with the water inflow from Mekong River and its tributaries in the rainy season. As influenced by the fecal waste, the bacterial community in the floating villages differed from the places with non-point source.

Fate of Escherichia coli in dialysis device exposed into sewage influent and activated sludge.

Tracing the fate of pathogens in environmental water, particularly in wastewater, with a suitable methodology is a demanding task. We investigated the fate of Escherichia coli K12 in sewage influent and activated sludge using a novel approach that involves the application of a biologically stable dialysis device. The ion concentrations inside the device could reach that of surrounding solution when it was incubated in phosphate buffered saline for 2 h. E. coli K12 above 107 CFU mL-1 (inoculated in distilled water, influent, activated sludge) were introduced into the device and incubated in influent and activated sludge for 10 days. Without indigenous microorganisms, E. coli K12 could survive even with the limited ions and nutrients concentrations in influent and activated sludge. E. coli K12 abundance in influent and activated sludge were reduced by 60 and 85%, respectively, after just 1 day. The establishment of microbial community in wastewater played an important role in reducing E. coli K12. Bacteriophage propagated in filtered influent or activated sludge when E. coli K12 was introduced, but not in raw influent or activated sludge. The methodology developed in this study can be applied in the actual environmental water to trace the fate of pathogens.