Exogenous Protein as an Environmental Stimulus of Biofilm Formation in Select Bacterial Strains

A screening of environmental conditions that would elicit robust biofilm in a collection of Serratia marcescens isolated from soil revealed that exogenous milk protein increased biofilm productivity up to ten-fold. A select screening of fish pathogens, freshwater and human isolates identified several other species that responded similarly to exogenous protein. The optimal protein concentration was species specific;S. marcescens at 5% milk protein, Aeromonas sp. at 2% - 3%, Flavobacterium columnare at 1% and Pseudomonas aeruginosa at 0.1% - 0.4%. Media supplemented with milk protein also increased the cell counts in biofilm as well as the protein incorporated into the biofilm matrix. These data suggest that relatively high concentrations of exogenous protein may serve as an environmental trigger for biofilm formation, particularly for pathogenic bacteria exposed to relatively high concentrations of protein in bodily fluids and mucosal surfaces.

The Effects of Antibiotics, Metals, and Biotic Interactions on the Assembly of Taxonomically Diverse Single and Mixed Species Biofilms

To better understand the assembly of the sturgeon egg microbiome, we purified six bacterial isolates from eggs and characterized their ability to form biofilms under the stress of tobramycin, with and without exogenous protein. In experiments with single species biofilms, tobramycin reduced the metabolic activity of all isolates and increased biofilm biomass of three. The addition of exogenous protein to the assay countered the inhibition of biofilm and metabolic activity by tobramycin of Pseudomonas sp., Brevundimonas sp., Flavobacterium columnare and mixed biofilms of Pseudomonas-F. columnare and Brevundimonas-Hydrogenophaga. Two of the isolates (Pseudomonas spp.) that produced antimicrobial activity, were effective at reducing biofilm formation by Brevundimonas, but enhanced biofilm formation in other isolates. Increasing concentrations of Mg2+ had no effect on biofilm formation but Ca2+ enhanced biofilm formation of Pseudomonas aeruginosa PA01 (positive control) and Brevundimonas. Biofilm assembly by these two bacteria was inhibited by low concentrations of Ni2+. Mixed biofilms of Brevundimonas and Hydrogenophage consistently produced more robust biofilm than the strains in isolation, suggesting synergism. Established Brevundimonas biofilm appeared adept at recruiting pelagic Acidovorax and Hydrogenophaga into biofilm, suggesting that it plays an important role in the selection of species into the microbiome.

Phylogenetic Analysis of Anaerobic Co-Digestion of Animal Manure and Corn Stover Reveals Linkages between Bacterial Communities and Digestion Performance

Over 3 million tons of manures are produced annually in the United States and pose environmental and health risks if not remediated. Anaerobic digestion is an effective method in treating organic wastes to reduce environmental impacts and produce methane as an alternative energy. Previous studies suggested that optimization of feed composition, hydraulic retention time, and other operational conditions can greatly improve total solids removal and increase methane productivity. These environmental factors improve functionality by altering the microbial community structure but explicit details of how the bacterial community shifts are poorly understood. Our investigations were conducted to investigate the relationship between environmental factors, microbial community structure and bioreactor efficiency by using metagenomic analysis of the microbial communities. Our results indicated that the bioreactor with the greatest methane production, digestion efficiency and reduced levels of E. coli/Shigella had a distinctive community structure at the genus level with unique and abundant uncultivated strains of Bacteroidetes. Moreover the same bioreactor was enriched in Aminomonas paucivorans and Clostridia populations that can utilize secondary metabolites produced during cellulose/hemicellulose degradation to generate hydrogen and acetate. Hence specific digestion conditions that enrich for these populations may provide a route to the optimization of co-digestion systems and control the variability in reactor performance.

Microbial communities biostimulated by ethanol during uranium （VI） bioremediation in contaminated sediment as shown by stable isotope probing

Stable isotope probing （SIP） was used to identify microbes stimulated by ethanol addition in microcosms containing two sediments collected from the bioremediation test zone at the US Department of Energy Oak Ridge site, TN, USA. One sample was highly bioreduced with ethanol while another was less reduced. Microcosms with the respective sediments were amended with ^13C labeled ethanol and incubated for 7 days for SIP. Ethanol was rapidly converted to acetate within 24h accompanied with the reduction of nitrate and sulfate. The accumulation of acetate persisted beyond the 7 d period. Aqueous U did not decline in the microcosm with the reduced sediment due to desorption of U but continuously declined in the less reduced sample. Microbial growth and concomitant 13C-DNA production was detected when ethanol was exhausted and abundant acetate had accumulated in both microcosms. This coincided with U（VI） reduction in the less reduced sample. I3C originating from ethanol was ultimately utilized for growth, either directly or indirectly, by the dominant microbial community members within 7 days of incubation. The microbial community was comprised predominantly of known denitrifiers, sulfate-reducing bacteria and iron （Ⅲ） reducing bacteria including Desulfovibrio, Sphingomonas, Ferribacterium, Rhodanobacter, Geothrix, Thiobacillus and others, including the known U（VI）-redueing bacteria Acidovorax, Anaeromyxobacter, Desulfovibrio, Geobac- ter and Desulfosporosinus. The findings suggest that ethanol biostimulates the U（VI）-reducing microbial com- munity by first serving as an electron donor for nitrate, sulfate, iron （IH） and U（VI） reduction, and acetate which then functions as electron donor for U（VI） reduction and carbon source for microbial growth.