Population structure, persistence, and seasonality of autochthonous Escherichia coli in temperate, coastal forest soil from a Great Lakes watershed

Abstract

The common occurrence of Escherichia coli in temperate soils has previously been reported, however, there are few studies to date to characterize its source, distribution, persistent capability and genetic diversity. In this study, undisturbed, forest soils within six randomly selected 0.5 m2 exclosure plots (covered by netting of 2.3 mm2 mesh size) were monitored from March to October 2003 for E. coli in order to describe its numerical and population characteristics. Culturable E. coli occurred in 88% of the samples collected, with overall mean counts of 16 MPN g(-1), ranging from < 1 to 1657 (n = 66). Escherichia coli counts did not correlate with substrate moisture content, air, or soil temperatures, suggesting that seasonality were not a strong factor in population density control. Mean E. coli counts in soil samples (n = 60) were significantly higher inside than immediately outside the exclosures; E. coli distribution within the exclosures was patchy. Repetitive extragenic palindromic polymerase chain reaction (Rep-PCR) demonstrated genetic heterogeneity of E. coli within and among exclosure sites, and the soil strains were genetically distinct from animal (E. coli) strains tested (i.e. gulls, terns, deer and most geese). These results suggest that E. coli can occur and persist for extended periods in undisturbed temperate forest soils independent of recent allochthonous input and season, and that the soil E. coli populations formed a cohesive phylogenetic group in comparison to the set of fecal strains with which they were compared. Thus, in assessing E. coli sources within a stream, it is important to differentiate background soil loadings from inputs derived from animal and human fecal contamination.

Beach Sand and Sediments are Temporal Sinks and Sources of Escherichia coli in Lake Superior

“…The horizontal, fluorophore-enhanced repetitive extragenic palindromic PCR (HFERP) technique, done using the BOXA1R primer, was used to determine DNA fingerprints of all 3633 confirmed E. coli isolates, as described previously (14). Genetic relatedness among the E. coli isolates from the DBC beach was assessed by using Pearson's product-moment correlation coefficient and the unweighted pair group method with an arithmetic mean (UPGMA) clustering method as previously described (6,12,28,29). E. coli strains having HFERP DNA fingerprint similarity values of 92% were considered to be identical (6).…”

The bacterial species definition in the genomic era

“…The recent description of Escherichia albertii (Huys et al 2003), a new species that probably spans the genetic gap between E. coli and Salmonella (Hyma et al 2005), as well as analysis of environmental E. coli isolates (Byappanahalli et al 2006;Ishii et al 2006) indicate, however, that the genomic clusters recovered in this group may be the effect of sampling biases rather than naturally occurring clusters. The latter is also more consistent with our prediction that E. coli, owing to its opportunistic lifestyle-namely the possibility to thrive in humid soils and freshwater systems and in a variety of animals-as well as its average-to-large genome size, is more likely to show a continuum of diversity as opposed to genomic clusters.…”

Escherichia coli in the Environment: Implications for Water Quality and Human Health

“…Byappanahalli et al 20) reported that E. coli strains were repeatedly isolated from exclosure-protected temperate forest soils in Indiana, and their genetic structure was different from these bacteria isolated from animals ( Fig. 2A).…”

“…E. coli faces many stresses in the environment, including low and high temperatures 7,48,74,76,93,115) , limited moisture 8,13,19,20,30,76,93,115) , variation in soil texture 30,39,76) , low organic matter content 97,115) , high salinity 97) , solar radiation 110) , and predation 12,14,19,25,93) . Recent studies, however, have shown that E. coli can survive for long periods of time in the environment, and potentially replicate, in water, on algae, and in soils in tropical 16,19,20,22,37,38) , subtropical 30,93) , and temperate environments 9,17,20,48,49,61,99,109) . Relatively high concentrations of nutrients and warm temperatures in tropical and subtropical environments are likely factors enabling E. coli to survive and grow outside of the host 22,116) .…”