Source and Fate of Fecal Indicator Bacteria in Tropical Soil, Sand, and Seawater Environments

Abstract

Fecal contamination of coastal recreational water can adversely impact public health and economic well-being of many coastal communities. Enterococci and E. coli are common fecal indicator bacteria (FIBs) used in water quality monitoring and regulation. This dissertation investigates the source and fate of FIBs in Hawaii’s tropical soil, sand and seawater environments. Since Hawaii’s soils are known to contain high levels of E. coli that can serves as alternative sources to waterways, the second chapter of this dissertation investigated the survival of soil E. coli strains under desiccation stress. The soil E. coli strains showed significantly higher desiccation resistance than a laboratory reference strain and several strains isolated from wastewater, and the de novo synthesis and accumulation of trehalose was identified as an important mechanism for soil E. coli desiccation resistance. Since beach sand is often reported to contain high levels of FIBs while beach erosion or replenishment activities can abruptly affect beach sand abundance, the third chapter investigated the contribution of beach sand to the decay of FIBs in beach systems. The presence of subtidal sand significantly enhanced the decay of E. faecalis in beach microcosms, and the indigenous microbiota of the subtidal sand was largely responsible for the decay enhancement. To further understand the fate of FIBs in beach systems, the fourth chapter determined the decay patterns of FIBs in beach sand and seawater separately and compared them to the overall microbial community dynamics. Biphasic decay patterns of FIBs and other fecal bacteria were observed in both beach sand and seawater, while the decay rates in beach sand were significantly smaller than that in seawater, providing a kinetic explanation to the observed high abundance of FIBs in beach sand. In the fifth chapter, microbial communities in beach sand and seawater microcosms contaminated by municipal wastewater were tracked using next-generation sequencing of the 16S rRNA gene amplicons, and the exogenous nutrients in the wastewater appeared to determine the microbial community dynamics to a significant extent. Based on results presented, conclusions and recommendations were also made in the sixth chapter of the dissertation.