Response Of Bacillus Sp. F26 To Reactive Oxygen Species Stress Characterized By Catalase Synthesis

Reactive oxygen species (ROS) , including superoxide radicals(O₂^-), hydrogen peroxide(H₂O₂)and hydroxyl radicals(OH·)are a group of activated molecules that continuously formed during normal aerobic metabolism in micro-organism. The condition known as oxidative stress results when the production of ROS exceeds the capacity of the cells to remove them safely. In the condition of oxidative stress, ROS can oxidize protein, nucleic acids and lipid peroxidation, lead further to disruption of normal metabolism, mutations, and ultimately cell death. To protect cells against ROS, all aerobic micro-organism instinctively respond to the stress using enzymatic and non-enzymatic defence systems, and thus show different biological phenomenon. It has been proven that the changes of activities of antioxidative enzyme,including superoxide dismutase(SOD) and catalase (CAT), can directly reflect the level of cells response to oxidative stress. Study the mechanism of cells response to oxidative stress is helpful to understand the causation of human disease caused by ROS and find effective means of protection and clearance.In this paper, a slight halophilic alkaliphile strain, Bacillus sp. F26 produced high level of intracellular CAT was selected, the oxidative response of micro-organisms to different forms of ROS stress including separated stress(H₂O₂ and O₂^-), different mode of stress (instantaneous and continual) and incorporate stress(H₂O₂,O₂^- and OH·), were investigated by using diverse generating source of ROS, which were characterized by synthesis of CAT, the most important antioxidative enzyme in Bacillus sp. F26. Moreover, the crucial functions of antioxidative enzymes(SOD and CAT)in microbial in protection against oxidative stress and environmental stress were discussed. The main contents of this dissertation included as follows:(1) The optimal nutrient and environmental conditions for CAT synthesis by Bacillus sp. F26 were first investigated. The results shown that glucose and mixed source of beef extract and corn steep liquid were suitable carbon source and nitrogen source for cell growth and CAT synthesis, respectively. Phosphorus and magnesium are necessary for cells to produce CAT. The importance order of factors influenced CAT synthesis was glucose > MgCl₂ > beef extract > KH₂PO₄. The optimal medium compositions for CAT synthesis contained:10 g·L^-1 of glucose, 15 g·L^-1 beef extract, 5g·L^-1 of yeast extract, 1 g·L^-1 of KH2PO4, 0.2 g·L^-1 of MgCl2, 50 g·L^-1 of NaCl, 10 g·L^-1 of Na2CO3. The effects of environmental conditions on cell growth and CAT production were associated with the isolated environmental characteristics of Bacillus sp. F26. Alkaliphilic environmental and high oxygen level were benefit for cell growth and CAT...