Effects of Land Uses on Fecal Indicator Bacteria in the Water and Soil of a Tropical Watershed

Abstract

Effects of different land uses on densities of Escherichia coli, enterococci, and Clostridium perfringens in the water and soil of a tropical watershed were investigated. Densities of fecal indicator bacteria (FIBs) in the watershed exhibited a clear land-use dependency in the stream water. Significantly higher concentrations were detected in the urban portion of the stream (417, 420, and 44 CFU 100 mL −1 for E. coli, enterococci, and C. perfringens, respectively) than in the forest portion (54, 32, and 5 CFU 100 mL −1 for E. coli, enterococci, and C. perfringens, respectively). High concentrations of FIBs were also detected in the soil of the watershed with concentration ranges of 603-1,820,000, 69-17,000, and 0-525 CFU 100 g soil −1 for E. coli, enterococci, and C. perfringens, respectively, which however were not affected by the different land uses. Prior cumulative rainfall significantly correlated with concentrations of E. coli and enterococci in the urban stream water (r=0.73-0.87, P<0.05), but not with the alternative FIB C. perfringens. Poor correlations were observed in the forest reach of the stream for all FIBs. Furthermore, the concentration of C. perfringens only correlated strongly and significantly with E. coli and enterococci in stream water (r=0.70-0.82, P<0.05), but not in tropical soil, indicating different survival and transport behaviors.

Correlation of Intracellular Trehalose Concentration with Desiccation Resistance of Soil Escherichia coli Populations

“…2). It is worth noting that the desiccation die-off experiments were conducted in the absence of other environmental stresses (such as sunlight irradiation, temperature fluctuations, and competition/antagonism from indigenous soil microbial communities) that also affect E. coli survival (13,18). In natural soil environments, the soil desiccation stress, together with other environmental stresses, determines the fate of soil E. coli populations.…”

“…The selected soil strains were considered naturalized soil E. coli populations, based on their repeated detection in soil samples from the Manoa watershed (Table 1). Given the enormous genotypic diversity of E. coli (18), considerable variations in E. coli strain responses to any environmental condition are expected. Therefore, when the majority of soil E. coli strains exhibit the same trait (i.e., high desiccation resistance), it is reasonable to attribute such a trait to specific habitat adaptation and to consider those strains to be naturalized to the soil environments.…”

“…Tropical soils in Hawaii have been reported to contain high levels of E. coli (5,16,20), and recent sampling efforts in the Manoa watershed on the Island of Oahu, HI, also detected high levels of E. coli (603 to 1,820,000 CFU/100 g of soil) during a 9-month sampling period (18). By constructing a soil E. coli library for the Manoa watershed, numerous E. coli strains were frequently found at different sampling locations and on different sampling dates (19).…”

“…De novo trehalose synthesis was further determined for 15 E. coli strains from both soil and nonsoil sources to determine its prevalence as a specific desiccation response. Most E. coli strains (14/ 15) synthesized significantly more trehalose under the desiccation condition, and the soil E. coli strains produced more trehalose (106.5 ؎ 44.9 mol/mg of protein [mean ؎ standard deviation]) than the nonsoil reference strains (32.5 ؎ 10.5 mol/mg of protein).T raditionally, Escherichia coli in the environment has been often considered residual cells from recent fecal inputs (46), but this has been contradicted by recent reports of the ubiquitous presence of high levels of E. coli cells in soil samples (5,18,23). Studies using molecular tools have detected unique genotypic compositions of E. coli populations in soil (6,19,23), and the persistence of certain E. coli strains over extended periods of time in soils further supports the notion that certain soil E. coli populations are naturalized members of indigenous soil microbial communities (23).…”

“…T raditionally, Escherichia coli in the environment has been often considered residual cells from recent fecal inputs (46), but this has been contradicted by recent reports of the ubiquitous presence of high levels of E. coli cells in soil samples (5,18,23). Studies using molecular tools have detected unique genotypic compositions of E. coli populations in soil (6,19,23), and the persistence of certain E. coli strains over extended periods of time in soils further supports the notion that certain soil E. coli populations are naturalized members of indigenous soil microbial communities (23).…”