The Interplay Between Predation, Competition, and Nutrient Levels Influences the Survival of Escherichia coli in Aquatic Environments

Abstract

Nutrient levels, competition from autochthonous microorganisms, and protozoan predation may all influence survival of fecal microorganisms as they transition from the gastrointestinal tract to aquatic habitats. Although Escherichia coli is an important indicator of waterborne pathogens, the effects of environmental stressors on its survival in aquatic environments remain poorly understood. We manipulated organic nutrient, predation, and competition levels in outdoor microcosms containing natural river water, sediments, and microbial populations to determine their relative contribution to E. coli survival. The activities of predator (protozoa) and competitor (indigenous bacteria) populations were inhibited by adding cycloheximide or kanamycin. We developed a statistical model of E. coli density over time that fits with the data under all experimental conditions. Predation and competition had significant negative effects on E. coli survival, while higher nutrient levels increased survival. Among the main effects, predation accounted for the greatest variation (40 %) compared with nutrients (25 %) or competition (15 %). The highest nutrient level mitigated the effect of predation on E. coli survival. Thus, elevated organic nutrients may disproportionately enhance the survival of E. coli, and potentially that of other enteric bacteria, in aquatic habitats.

Persistence and Decay of Fecal Microbiota in Aquatic Habitats

“…At lower nutrient concentrations, studies have shown that the presence of biota can confound the effect of nutrient addition in the water column (89, 92), diminishing the effect of nutrients on FIB persistence. This finding is consistent with those of another laboratory-based study in which the effect of organic carbon addition on FIB persistence was concentration dependent (90).…”

“…In particular, elevated indicator concentrations were observed when organic carbon levels were at or above 7 mg/liter (83). Other studies conducted using incremental levels of organic carbon also reported enhanced survival of E. coli in the water column (90,91). In both studies, the positive effect of nutrient addition on E. coli varied depending on nutrient levels and/or the presence of biota (predators and competitors) (90,91).…”

“…The symbol size corresponds to the number of studies with results that fall within each category (greater decay in marine water or freshwater or no effect). (84)(85)(86), fecal material (87)(88)(89), and synthetic/artificial nutrients (89)(90)(91). The majority of these studies have been conducted in the laboratory and can be divided into several categories based on experimental design; some studies utilized both sediments and the overlying water column (81,(87)(88)(89), while others focused on the water column only (83,92).…”

Landscape-Scale Factors Affecting the Prevalence of Escherichia coli in Surface Soil Include Land Cover Type, Edge Interactions, and Soil pH

“…Thus, much of the biodiversity in the E. coli species may be generated and maintained via transient-to-semipermanent residence in extrahost habitats (7). This process can confound the use of E. coli as an indicator organism for fecal contamination in water quality testing (8,9). Therefore, understanding the ecology of E. coli in extrahost habitats can inform not only our environmental and public health policy but also our concept of microbial species.…”

Effect of freshwater sediment characteristics on the persistence of fecal indicator bacteria and genetic markers within a Southern California watershed

“…Decay of bacteria and fecal markers in sediments is particularly understudied even though sediments, soils, and beach sands have been implicated as potential reservoirs in a variety of climates and environments (Alm et al, 2014;Craig et al, 2004;Garzio-Hadzick et al, 2010;Haller et al, 2009;Lee et al, 2006). Sediments can promote persistence of fecal organisms both by providing protection from ultraviolet radiation, temperature fluctuations, and predation by microorganisms in the overlying water column (Davies et al, 1995;Korajkic et al, 2013;Wanjugi and Harwood, 2013;Wheeler Alm et al, 2003) and by supplying critical nutrients (Craig et al, 2004;Labelle et al, 1980;Mika et al, 2009;Wanjugi et al 2016). Under favorable sediment conditions, fecal indicator bacteria (FIB) exhibit extended survival and even regrowth, which can lead to false positive indications of recent fecal pollution in water quality monitoring when organisms colonize sediment and levels no longer correspond with the presence of fecal pollution and pathogens (Byappanhalli and Fujioka, 1998;Byappanahalli et al, 2012;Davies and Bavor, 2000;Garzio-Hadzick et al, 2010;Lee et al, 2006).…”