THE IMPACT OF MICROBIAL CHELATES ON MINERAL WEATHERING AND MICROBIAL METABOLIC ACTIVITY

Abstract

Geological materials are composed of elements, which can be released into the environment by dissolution or desorption processes and directly impact the metabolic activity of microorganisms. If subjected to environmental stress, microorganisms can adapt by applying unique strategies to safeguard their survival or perpetuate their ecological role in a given habitat. Microbial chelate production improves the chances of obtaining key metals that regulate enzymatic activity. In this dissertation, geochemical controls such as mineral solubility and desorption of nutrients from clays are examined with respect to their influence upon metabolic activity. In turn, the impact of microorganisms upon mineral weathering is investigated with respect to mineral composition and cellular design. A relationship between geologic host materials and biological activity is purported. The role of microorganisms upon mineral weathering was investigated by collecting soil samples from the tropical rainforest of Barro Colorado Island, Panama. Microorganisms can utilize specific chelating agents to mobilize metals of nutritive benefit, i.e., siderophores for Fe3+ (Pseudomonas putida), and methanobactin for Cu (Methylosinus trichosporium OB3b). Enhanced Fe3+ solubility from minerals of a Panamanian soil was demonstrated in abiotic and biotic microcosms supplemented with the siderophore, desferrioxamine. Similarly, Cu and SiO2 solubility was enhanced by methanobactin in increasing concentrations, provided that Cu was present in the mineral phase. To evaluate the vital effect upon Cu leaching from mineral sources, rates of mineral weathering were compared with rates of CH4 oxidation in the presence of Methylosinus trichosporium OB3b. The results indicate that methanotroph activity is sensitive to variations in solid phase Cu concentration provided that Cu is being made bioavailable. A final study investigating how NH4+ and Cu desorption from montmorillonite impacts methanotrophy showed that rates of CH4 oxidation were inhibited by the release of these nutrients in excess amounts. Microorganisms are sensitive to a diverse assortment of geological materials provided that key nutrients such as Fe, Cu or inorganic-N are present and made bioavailable by mineral dissolution or desorption processes. The efficiency of enzyme activity is controlled by both mineral composition and surrounding geochemical processes. In addition, microorganisms actively participate in the promotion of metal solubility from mineral sources. The findings of this dissertation illustrate that biological and geochemical processes are tied together and are responsible for driving metal cycling in soil environments. Furthermore, a novel linkage between mineral weathering and carbon cycling is revealed, and hinges upon the activity of methanotrophs and their requirement for Cu.