Searching for bacteria in sticky situations: Methods for investigating bacterial survival at solid-air interfaces involving Wyoming MX-80 bentonite

Effective removal of prokaryotic cells from clay interfaces such as bentonite is essential for quantitative assessment of microbial communities, considering that strong bentonite clay-DNA and –RNA complexes challenge the use of molecular-based techniques. In this study, aerobic bacteria were isolated from Wyoming MX-80 bentonite and sequenced for identification (16S rRNA). A glass-bentonite substrate and sterile bentonite powder were inoculated with Arthrobacter sp. (isolated from bentonite) to test cell removal efficiency using sonication and vortexing. Manipulation of pH (pH 7 versus pH 9) did not affect cell removal efficiency, while changes in temperature within limits (15–37 °C) did affect cell removal efficiency. To evaluate microbial survival during desiccation, bacterial isolates were inoculated onto glass and bentonite-covered glass coverslip substrates, and particulate bentonite. Substrates were desiccated, and cells were removed by vortexing at different time points over 31 days. Abundance of viable cells followed a first-order rate of decrease. Vegetative desiccation-tolerant Arthrobacter sp. isolates from bentonite clay had lower loss of viable, culturable cells (0.07 d⁻¹ to 0.89 d⁻¹) than did a Bacillus sp. isolate (>1 d⁻¹) or a Pseudomonas stutzeri isolate (0.79 to >1 d⁻¹), suggesting Arthrobacter sp. may be more tolerant of these prolonged periods of desiccation on the bentonite-air interface. Tolerance to matric stress by microorganisms varies depending on the cellular adaptation of the target species, the physical and chemical properties of the given solid-air environment, as well as the employed population and community-based survival mechanisms.