Toxicity of Select Organic Acids to the Slightly Thermophilic Acidophile Acidithiobacillus Caldus

• Published in: Environmental toxicology and chemistry 2009-02, Vol.28 (2), p.279-286
• Main Authors: Aston, John E, Apel, William A, Lee, Brady D, Peyton, Brent M
• Format: Article
• Language: English
• Subjects: Acetates; Acid mine drainage; Acidithiobacillus; Acidithiobacillus - drug effects; Acidithiobacillus - growth & development; Acidithiobacillus caldus; Acids - toxicity; Aerobic conditions; Autotrophs; Bacteria; Biomining; Cells; Cellular; Chemiosmosis; Confidence intervals; Cytoplasm; Diffusion; Drainage systems; Engineering research; Envelopes; Fatty acids; Field emission; Growth rate; Instability; Ion chromatography; Malate; microbial growth; Microbiology; Micrographs; Natural environment; Organic acids; organic acids and salts; Organic Chemicals - toxicity; Phospholipids; Presses; Sulfur; thermophilic bacteria; Toxic; Toxicity; Toxicology
• ISSN: 0730-7268; 1552-8618
• DOI: 10.1897/08-277.1

Acidithiobacillus caldus is a thermophilic acidophile found in commercial biomining, acid mine drainage systems, and natural environments. Previous work has characterized A. caldus as a chemolithotrophic autotroph capable of utilizing reduced sulfur compounds under aerobic conditions. Organic acids are especially toxic to chemolithotrophs in low-pH environments, where they diffuse more readily into the cell and deprotonate within the cytoplasm. In the present study, the toxic effects of oxaloacetate, pyruvate, 2-ketoglutarate, acetate, malate, succinate, and fumarate on A. caldus strain BC13 were examined under batch conditions. All tested organic acids exhibited some inhibitory effect. Oxaloacetate was observed to inhibit growth completely at a concentration of 250 μM, whereas other organic acids were completely inhibitory at concentrations of between 1,000 and 5,000 μM. In these experiments, the measured concentrations of organic acids decreased with time, indicating uptake or assimilation by the cells. Phospholipid fatty acid analyses indicated an effect of organic acids on the cellular envelope. Notable differences included an increase in cyclic fatty acids in the presence of organic acids, indicating possible instability of the cellular envelope. This was supported by field emission scanning-electron micrographs showing blebbing and sluffing in cells grown in the presence of organic acids.