Relation between the relative abundance and collapse of Aphanizomenon flos-aquae and microbial antagonism in Upper Klamath Lake, Oregon.

Aphanizomenon flos-aquae (AFA) is the dominant filamentous cyanobacterium that develops into blooms in Upper Klamath Lake, Oregon, each year. During AFA bloom and collapse, ecosystem conditions for endangered Lost River and shortnose suckers deteriorate, thus motivating the need to identify processes that limit AFA abundance and decline. Here, we investigate the relations between AFA and other members of the microbial community (photosynthetic and nonphotosynthetic bacteria and archaea), how those relations impact abundance and collapse of AFA, and the types of microbial conditions that suppress AFA. We found significant spatial variation in AFA relative abundance during the 2016 bloom period using 16S rRNA sequencing. The Pelican Marina site had the lowest AFA relative abundance, and this was coincident with increased relative abundance of Candidatus Sericytochromatia, Flavobacterium, and Rheinheimera, some of which are known AFA antagonists. The AFA collapse coincided with phosphorus limitation relative to nitrogen and the increased relative abundance of Cyanobium and Candidatus Sericytochromatia, which outcompete AFA when dissolved inorganic nitrogen is available. The data collected in this study indicate the importance of dissolved inorganic nitrogen combined with microbial community structure in suppressing AFA abundance.

Microbial community response to a bioaugmentation test to degrade trichloroethylene in a fractured rock aquifer, Trenton, N.J.

Bioaugmentation is a promising strategy for enhancing trichloroethylene (TCE) degradation in fractured rock. However, slow or incomplete biodegradation can lead to stalling at degradation byproducts such as 1,2-dichloroethene (cis-DCE) and vinyl chloride (VC). Over the course of 7 years, we examined the response of groundwater microbial populations in a bioaugmentation test where an emulsified vegetable oil solution (EOS®) and a dechlorinating consortium (KB-1®), containing the established dechlorinator Dehalococcoides (DHC), were injected into a TCE-contaminated fractured rock aquifer. Indigenous microbial communities responded within 2 days to added substrate and outcompeted KB-1®, and over the years of monitoring, several other notable turnover events were observed. Concentrations of ethene, the end product in reductive dechlorination, had the strongest correlations (P< .05) with members of Candidatus Colwellbacteria but their involvement in reductive dechlorination is unknown and warrants further investigation.DHC never exceeded 0.6% relative abundance of groundwater microbial communities, despite its previously presumed importance at the site. Increased concentrations of carbon dioxide, acetic acid, and methane were positively correlated with increasing ethene concentrations; however, concentrations of cis-DCE and VC remained high by the end of the monitoring period suggesting preferential enrichment of indigenous partial dechlorinators over bioaugmented complete dechlorinators. This study highlights the importance of characterizing in situ microbial populations to understand how they can potentially enhance or inhibit augmented TCE degradation.

Mineralogical variables that control the antibacterial effectiveness of a natural clay deposit.

As antibiotic-resistant bacterial strains emerge and pose increased global health risks, new antibacterial agents are needed as alternatives to conventional antimicrobials. Naturally occurring antibacterial clays have been identified which are effective in killing antibiotic-resistant bacteria. This study examines a hydrothermally formed antibacterial clay deposit near Crater Lake, OR (USA). Our hypothesis is that antibacterial clays buffer pH and Eh conditions to dissolve unstable mineral phases containing transition metals (primarily Fe(2+)), while smectite interlayers serve as reservoirs for time release of bactericidal components. Model pathogens (Escherichia coli ATCC 25922 and Staphylococcus epidermidis ATCC 14990) were incubated with clays from different alteration zones of the hydrothermal deposit. In vitro antibacterial susceptibility testing showed that reduced mineral zones were bactericidal, while more oxidized zones had variable antibacterial effect. TEM images showed no indication of cell lysis. Cytoplasmic condensation and cell wall accumulations of <100 nm particles were seen within both bacterial populations. Electron energy loss analysis indicates precipitation of intracellular Fe(3+)-oxide nanoparticles (<10 nm) in E. coli after 24 h. Clay minerals and pyrite buffer aqueous solutions to pH 2.5-3.1, Eh > 630 mV and contain elevated level (mM) of soluble Fe (Fe(2+) and Fe(3+)) and Al(3+). Our interpretation is that rapid uptake of Fe(2+) impairs bacterial metabolism by flooding the cell with excess Fe(2+) and overwhelming iron storage proteins. As the intracellular Fe(2+) oxidizes, it produces reactive oxygen species that damage biomolecules and precipitates Fe-oxides. The ability of antibacterial clays to buffer pH and Eh in chronic non-healing wounds to conditions of healthy skin appears key to their healing potential and viability as an alternative to conventional antibiotics.

Effects of the antimicrobial sulfamethoxazole on groundwater bacterial enrichment.

The effects of "trace" (environmentally relevant) concentrations of the antimicrobial agent sulfamethoxazole (SMX) on the growth, nitrate reduction activity, and bacterial composition of an enrichment culture prepared with groundwater from a pristine zone of a sandy drinking-water aquifer on Cape Cod, MA, were assessed by laboratory incubations. When the enrichments were grown under heterotrophic denitrifying conditions and exposed to SMX, noticeable differences from the control (no SMX) were observed. Exposure to SMX in concentrations as low as 0.005 µM delayed the initiation of cell growth by up to 1 day and decreased nitrate reduction potential (total amount of nitrate reduced after 19 days) by 47% (p=0.02). Exposure to 1 µM SMX, a concentration below those prescribed for clinical applications but higher than concentrations typically detected in aqueous environments, resulted in additional inhibitions: reduced growth rates (p=5×10(-6)), lower nitrate reduction rate potentials (p=0.01), and decreased overall representation of 16S rRNA gene sequences belonging to the genus Pseudomonas. The reduced abundance of Pseudomonas sequences in the libraries was replaced by sequences representing the genus Variovorax. Results of these growth and nitrate reduction experiments collectively suggest that subtherapeutic concentrations of SMX altered the composition of the enriched nitrate-reducing microcosms and inhibited nitrate reduction capabilities.