Program     Ocean Circulation, Ecosystem and Hypoxia around Hong Kong Waters       Poster Microbiological evaluation of anthropogenic pollution in Pearl River Estuary and the adjacent South China Sea P-SPS4-07-S Fangzhou Chen* , Division of Environment and Sustainability The Hong Kong University of Science and Technology Mandy Ly Tang, Department of Ocean Science The Hong Kong University of Science and Technology Xiu Pei Kou, Division of Environment and Sustainability The Hong Kong University of Science and Technology Stanley Ck Lau, Department of Ocean Science and Division of Environment and Sustainability The Hong Kong University of Science and Technology Presenter Email: fchenac@ust.hk The Pearl River Delta is polluted by industrial, agricultural, and municipal wastes. Different types of pollution can cause different impacts to the diversity and ecosystem function of the bacterial communities in the receiving waters through the introduction of exogenous bacteria and/or alteration of the indigenous bacterial communities. The exogenous bacteria include the pathogens of humans and different species of farm animals, antibiotic resistant bacteria, metal resistant bacteria, etc. Therefore, the investigation of bacterial community composition and function in polluted waters provide an opportunity to trace the source of pollution and evaluate the ecosystem impacts of pollution. In this study, we collected water samples from various locations in Pearl River estuary and the adjacent South China Sea and analysed the bacterial communities therein for (1) community composition using 16S rRNA genes amplicon sequencing, (2) community function using metagenomic and metatranscriptomic sequencing, and (3) the abundance of class 1 integron as a proxy of the anthropogenic pollution level. Our results thus far indicate that bacterial community composition in the waters changed gradually from the head of estuary to open ocean with freshwater groups such as Actinobacteria and Verrucomicrobia being replaced by marine groups such as the SAR406 clade. Hypoxia appeared to have stronger impacts on particle-attached bacteria than the free-living counterpart. In regard to anthropogenic impacts, the PRE was fecally polluted, with E. coli concentrations exceeding 1000 CFU/100ml being detected at the head of the estuary. The prevalence of class 1 integron genes in E. coli and total bacterial community was higher in PRE than in the coastal water of Hong Kong and South China Sea, suggesting that the bacterial communities in the former are heavily impacted by multi-stressors of anthropogenic sources. The sequence analysis of the class 1 integron gene cassettes as well as the metagenome and metatranscriptome revealed the nature of the stressors and their effects on community functions with respect to pollutant degradation and sequestration, stress response, and the expression of pathogenic genes.