Abstract
ABSTRACTPorous media filters are used widely to remove bacteria from contaminated water, such as stormwater runoff. Biofilms that colonize filter media during normal function can significantly alter performance, but it is not clear how characteristics of individual populations colonizing porous media combine to affect bacterial retention. We assess how four bacterial strains isolated from stormwater and a laboratory strain, Pseudomonas aeruginosa PAO1, alter Escherichia coli retention in experimental sand columns under conditions of stormwater filtration relative to a clean-bed control. Our results demonstrate that these strains differentially affect E. coli retention, as was previously shown for a model colloid. To determine whether E. coli retention could be influenced by changes in relative abundance of strains within a microbial community, we selected two pairs of biofilm strains with the largest observed differences in E. coli retention and tested how changes in relative abundance of strain pairs in the biofilm affected E. coli retention. The results demonstrate that E. coli retention efficiency is influenced by the retention characteristics of the strains within biofilm microbial community, but individual strain characteristics influence retention in a manner that cannot be determined from changes in their relative abundance alone. This study demonstrates that changes in the relative abundance of specific members of a biofilm community can significantly alter filter performance, but these changes are not a simple function of strain-specific retention and the relative abundance. Our results suggest that the microbial community composition of biofilms should be considered when evaluating factors that influence filter performance.IMPORTANCE The retention efficiency of bacterial contaminants in biofilm-colonized biofilters is highly variable. Despite the increasing number of studies on the impact of biofilms in filters on bacterial retention, how individual bacterial strains within a biofilm community combine to influence bacterial retention is unknown. Here, we studied the retention of an E. coli K-12 strain, as a model bacterium, in columns colonized by four bacterial strains isolated from stormwater and P. aeruginosa, a model biofilm-forming strain. Simplified two-strain biofilm communities composed of combinations of the strains were used to determine how relative abundance of biofilm strains affects filter performance. Our results provide insight into how biofilm microbial composition influences bacterial retention in filters and whether it is possible to predict bacterial retention efficiency in biofilm-colonized filters from the relative abundance of individual members and the retention characteristics of cultured isolates.
Highlights
IMPORTANCE The retention efficiency of bacterial contaminants in biofilm-colonized biofilters is highly variable
To investigate the extent to which stormwater isolates influence bacterial retention in porous media, we tested the retention of an E. coli K-12 strain in laboratory-scale sand columns colonized by four strains isolated from sand columns inoculated with stormwater runoff (SW1 to 4) and a model laboratory strain, P. aeruginosa PAO1, individually (Fig. 1a)
E. coli retention in columns colonized by the five individual strains shows high reproducibility within replicate columns modified by the same strain and significant differences across columns modified by different strains
Summary
IMPORTANCE The retention efficiency of bacterial contaminants in biofilm-colonized biofilters is highly variable. The removal efficiency of bacterial contaminants in deployed filters can be variable and unpredictable [10, 15] Such variability is often attributed to a series of factors, including specifications of filter design (e.g., the dimensions of filter, the component of porous media) [6, 16, 17], influent water chemistry (e.g., pH, salinity, the presence of natural organic matters) [18,19,20], environmental conditions (e.g., interval between dry and wet event, temperature) [21, 22], colonization of the media surface by microbial communities that disperse into filters with influent water during operation [23,24,25,26,27,28,29], and the degradation or predation of captured bacterial contaminants within biofilm (e.g., protozoa grazing and viral infection of pathogens) [30]. The variability induced by biofilm formation will make prediction and control of retention of microbial contaminants in deployed filters difficult without a fundamental understanding of factors that create this variability
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