Effects of organic acids and heavy metals on the biomining bacterium : Acidithiobacillus caldus strain BC13

Abstract

Acidithiobacillus caldus is an important microorganism to biomining and acid-mine formation. However, its degree of characterization is not commensurate to its significance in such systems. Specifically, studies enumerating effects of organic acids and metals on this microorganism are limited. The work presented in this dissertation improves understanding of At. caldus with respect to interactions with these compounds. All experiments discussed in this dissertation used At. caldus strain BC13. The organic acids; pyruvate, acetate, 2-ketoglutarate, succinate, fumarate, malate, and oxaloacetate were each toxic to At. caldus strain BC13. Depending on the organic acid tested, concentrations between 250 and 5,000 uM completely inhibited the growth of At. caldus strain BC13 (chapter two). Subsequent experiments, reported in chapter three, showed that At. caldus strain BC13 used pyruvate as a sole carbon source. Chapter four discusses the toxicities of the heavy metals; lead, zinc, and copper to At. caldus strain BC13. Lead was by far the most toxic metal tested, with an observed minimum inhibitory concentration of 7.5 mM. Conversely, zinc and copper had minimum inhibitory concentrations of 75 and 250 mM, respectively. The sorption of lead, zinc, and copper was also studied, and is discussed in chapter 5. Between pH 5.5 and 7.0, zinc and copper sorbed to At. caldus strain BC13 with similar capacity and affinity as that observed to other acidithiobacilli, however at pH 2.0, significant sorption of zinc and copper to viable cells was observed, whereas previous work did not report sorption of zinc or copper to viable acidithiobacilli cells below pH 3.0. Chapter six reports efforts to qualify changes in protein expression of At. caldus strain BC13 when exposed to organic acids or heavy metals. Matrix assisted laser desorption ionization mass spectrometry and one-dimensional gel electrophoresis qualified the up-regulation of an integral membrane protein with a molecular weight of approximately 25 kDa. Efforts to identify up-regulated proteins were not successful, but any proteins that are regulated in response to organic acids or heavy metals in biomining microorganisms would likely be of commercial application.