Fig 1.

Optical densities of A. flavithermus E16 (A), A. flavithermus DSM 2641 (B), Geobacillus sp. F75 (C), and G. thermoleovorans DSM 5336 (D) planktonic cultures grown in casein digest medium (1 g/liter) supplemented with a total cation concentration of 2 mM with varied proportions of Na⁺, K⁺, Ca²⁺, and Mg²⁺, relative to the optical density of the respective bacterial isolate grown in casein digest medium (1 g/liter) unsupplemented with cations (baseline control). N, K, C, and M designate free Na⁺, K⁺, Ca²⁺, and Mg²⁺, respectively. CM1:5 refers to a Ca²⁺-Mg²⁺ ratio of 1:5, NKC refers to a Na⁺-K⁺-Ca²⁺ ratio of 1:1:2, and all other treatments have equal proportions of each supplemented cation. The cultures were incubated at 55°C for 10 h. Two replicates were done, and each replicate consisted of an average of triplicate cultures. The error bars represent 95% confidence intervals (P ≤ 0.05), which were determined using SAS statistical analysis software.