Influence of clay minerals on the Bacillus halophilus Y38 activity under anaerobic condition

Studies of interaction between clay minerals and Bacillus halophilus Y38 have provided basic information on extremophile growth and physiological characteristics in hypersaline environments, which are of growing concern in microbiology, geobiology, environmental and pharmaceutical researches. In this study, we investigated B. halophilus Y38 strain growing in HGM hypersaline medium (sodium ion concentration > 55 mg mL-1, chloride ion concentration > 80 mg mL-1), with smectite, rectorite and kaolinite of different aggregate sizes (100 μm, 100–50 μm, and < 50 μm, respectively). Metabolic heat flow significantly increased in smaller particles, indicating that the stimulation of the B. halophilus Y38 growth by the clay minerals increased with decreasing aggregate sizes, and, thus, the close relationship between the bacterial growth and the mineral surface area. The CO2 flux (FCO2), total thermal effect (Qtotal), cell growth rate (Kcell) and protein synthesis rate (kprotein) were the key physiological parameters in metabolic and energy conservation reactions. These metabolic results showed that the stimulation by clay minerals on the B. halophilus activity was in the order smectite > rectorite > kaolinite. Our data may provide a strategy to evaluate the influence of clay minerals on the microbial growth and cell activity, and supplied a new experimental procedure to study interactions between minerals and microorganisms.

Research Highlights
► The first report to assess the growth of B. halophilus in hypersaline medium.
► B. halophilus Y38 growth increased with the decrease of clay minerals aggregate size.
► The stimulation abilities of clay minerals were smectite > rectorite > kaolinite.
► A new experimental model to study interactions between minerals and microorganisms.