We characterized the microbiologically mediated oxidative precipitation of Fe(II) from coalminederived acidic mine drainage (AMD) along flow-paths at two sites in northern Pennsylvania. At the Gum Boot site, dissolved Fe(II) was efficiently removed from AMD whereas minimal Fe(II) removal occurred at the Fridays-2 site. Neither site received human intervention to treat the AMD. Culturable Fe(II) oxidizing bacteria were most abundant at sampling locations along the AMD flow path corresponding to greatest Fe(II) removal and where overlying water contained abundant dissolved O 2 . Rates of Fe(II) oxidation determined in laboratory-based sediment incubations were also greatest at these sampling locations. Ribosomal RNA intergenic spacer analysis and sequencing of partial 16S rRNA genes recovered from sediment bacterial communities revealed similarities among populations at points receiving regular inputs of Fe(II)-rich AMD and provided evidence for the presence of bacterial lineages capable of Fe(II) oxidation. A notable difference between bacterial communities at the two sites was the abundance of Chloroflexi-affiliated 16S rRNA gene sequences in clone libraries derived from the Gum Boot sediments. Our results suggest that inexpensive and reliable AMD treatment strategies can be implemented by mimicking the conditions present at the Gum Boot field site.

The role of fecal indicator bacteria (FIB) in water quality assessment is to provide a warning of the increased risk of pathogen presence. An effective surrogate for waterborne pathogens would have similar survival characteristics in aquatic environments. Although the effect of abiotic factors such as sunlight and salinity on the survival of FIB and pathogens are becoming better understood, the effect of the indigenous microbiota is not well characterized. The influence of biotic factors on the survival of non-pathogenic Escherichia coli, Enterococcus faecalis, and E. coli O157:H7 were compared in fresh (river) water and sediments over 5 days. Treatments were (i) disinfection (filtration of water and baking of sediments) to remove indigenous protozoa (predators) and bacteria (competitors), and (ii) kanamycin treatment to reduce competition from indigenous bacteria. The disinfection treatment significantly increased survival of E. coli, E. coli O157:H7 and Ent. faecalis in the water column. In sediments, survival of FIB but not that of E. coli O157:H7 increased in disinfected treatments, indicating that the pathogen's survival was unaffected by the natural microbiota. Location (water or sediment) influenced bacterial survival more than species/type in the disinfection experiment. In the competition experiments where only the natural bacterial flora was manipulated, the addition of kanamycin did not affect the survival of Ent. faecalis, but resulted in greater survival of E. coli in water and sediment. Species/type influenced survival more than the level of competition in this experiment. This study demonstrates the complexity of interactions of FIB and pathogens with indigenous microbiota and location in aquatic habitats, and argues against over-generalizing conclusions derived from experiments restricted to a particular organism or habitat.

SUMMARY Fecal microorganisms can enter water bodies in diverse ways, including runoff, sewage discharge, and direct fecal deposition. Once in water, the microorganisms experience conditions that are very different from intestinal habitats. The transition from host to aquatic environment may lead to rapid inactivation, some degree of persistence, or growth. Microorganisms may remain planktonic, be deposited in sediment, wash up on beaches, or attach to aquatic vegetation. Each of these habitats offers a panoply of different stressors or advantages, including UV light exposure, temperature fluctuations, salinity, nutrient availability, and biotic interactions with the indigenous microbiota (e.g., predation and/or competition). The host sources of fecal microorganisms are likewise numerous, including wildlife, pets, livestock, and humans. Most of these microorganisms are unlikely to affect human health, but certain taxa can cause waterborne disease. Others signal increased probability of pathogen presence, e.g., the fecal indicator bacteria Escherichia coli and enterococci and bacteriophages, or act as fecal source identifiers (microbial source tracking markers). The effects of environmental factors on decay are frequently inconsistent across microbial species, fecal sources, and measurement strategies (e.g., culture versus molecular). Therefore, broad generalizations about the fate of fecal microorganisms in aquatic environments are problematic, compromising efforts to predict microbial decay and health risk from contamination events. This review summarizes the recent literature on decay of fecal microorganisms in aquatic environments, recognizes defensible generalizations, and identifies knowledge gaps that may provide particularly fruitful avenues for obtaining a better understanding of the fates of these organisms in aquatic environments.

The reported fate of Escherichia coli in the environment ranges from extended persistence to rapid decline. Incomplete understanding of factors that influence survival hinders risk assessment and modeling of the fate of fecal indicator bacteria (FIB) and pathogens. FIB persistence in subtropical aquatic environments was explored in outdoor mesocosms inoculated with five E. coli strains. The manipulated environmental factors were (i) presence or absence of indigenous microbiota (attained by natural, disinfected, and cycloheximide treatments), (ii) freshwater versus seawater, and (iii) water column versus sediment matrices. When indigenous microbes were removed (disinfected), E. coli concentrations decreased little despite exposure to sunlight. Conversely, under conditions that included the indigenous microbiota (natural), significantly greater declines in E. coli occurred regardless of the habitat. The presence of indigenous microbiota and matrix significantly influenced E. coli decline, but their relative importance differed in freshwater versus seawater. Cycloheximide, which inhibits protein synthesis in eukaryotes, significantly diminished the magnitude of E. coli decline in water but not in sediments. The inactivation of protozoa and bacterial competitors (disinfected) caused a greater decline in E. coli than cycloheximide alone in water and sediments. These results indicate that the autochthonous microbiota are an important contributor to the decline of E. coli in fresh and seawater subtropical systems, but their relative contribution is habitat dependent. This work advances our understanding of how interactions with autochthonous microbiota influence the fate of E. coli in aquatic environments and provides the framework for studies of the ecology of enteric pathogens and other allochthonous bacteria in similar environments.T he sanitary quality of recreational waters in Florida and across the United States is currently assessed by enumeration of fecal indicator bacteria (FIB) (i.e., fecal coliforms, Escherichia coli, and enterococci), which are also intended to act as pathogen surrogates (1, 2). The validity of this paradigm is the subject of ongoing debate, and it is argued that the current regulatory standards do not adequately protect human health, due mainly to the differences in survival and transport characteristics between the FIB and pathogens (3-9). When the assumed predictive relationship is absent (e.g., FIB not detected but pathogens present), public health may be threatened by exposure of humans to pathogens. On the other hand, FIB that are detected in the absence of pathogens can lead to unnecessary beach and shellfishing area closures, which can pose economic hardships in coastal communities.While the roles of sediments and aquatic vegetation as a refuge and a potential reservoir of FIB are the subjects of many studies (10-16), the relative influence of indigenous microbiota on the persistence and rate of decline of FIB in aquatic environments is less well characterized. Germicidal sunlight r...