Diversity, distribution and population dynamics of fecal bacteroidales communities in the marine environment of Hong Kong: Implications to water quality monitoring

Fecal pollution of water environment poses serious threats to public health. Because each species of animal host carries a different variety of fecal pathogens, the identification of pollution sources (i.e. animal species) is the key to accurate health risk assessment and effective implementation of mitigation measures. Since a decade ago, Bacteroidales have emerged as a promising bacterial indicator for fecal pollution source tracking. However, existing knowledge on Bacteroidales has been mainly acquired from temperate zones; due to possible variations in the diversity and environmental fate of Bacteroidales in different climate zones, the applicability of the bacteria to source-tracking in the warmer regions of the world is not known. This study investigated for the first time the diversity, distribution and population dynamics of Bacteroidales community in the feces of warm-blooded animals and in the coastal seawaters of a tropical / subtropical region (Hong Kong). The analysis of the 16S rRNA genes retrieved from the feces of different species of warm-blooded animals in Hong Kong revealed a large number of novel sequences, indicating that the diversity of Bacteroidales in warmer regions of the world is different from that in the temperate zone. A highly host-specific distribution of Bacteroidales lineages was observed among the eight species of warm-blooded animals investigated in the study. These lineages were found in and only in seawater samples collected from coastal regions that are known to be polluted by the feces of the corresponding host types (e.g. effluent of pig farms, household sewage, and terrestrial runoff from grazed pastures). Novel genetic markers were identified for the host-specific lineages; those markers demonstrated highly specific and sensitive source identification for field samples. Bacteroidales cells showed rapid decay in subtropical Hong Kong seawaters. Although Bacteroidales are obligate anaerobes, a high level of dissolved oxygen alone in seawater did not affect the decay of Bacteroidales communities, but it effectively accelerated the decay rate when interacting with light. The results indicate a significant effect of photo-oxidation on the decay of Bacteroidales in natural environment. Close correlations were observed between the decay of Bacteroidales and other fecal microorganisms (i.e. E. coli), demonstrating the potential of using the bacteria in indicating the health risks. The findings in this study greatly enrich the knowledge of biology and ecology of fecal Bacteroidales and support the application of Bacteroidales in fecal pollution source tracking in the warm regions of the world.