Responses of Different Iron and Nitrogen Transformation Functional Microorganisms to Fe(Ⅱ) Chemical Oxidation

In redox fluctuation areas such as groundwater level fluctuation zone,surface water-groundwater interaction zone,O₂ reacts with Fe(Ⅱ) to produce reactive oxygen species (ROSs),such as ·OH,·O₂^-,H₂O₂,etc. These ROSs are of biological toxicity and may have impact on the survival of microorganisms,and different functional microorganisms may respond differently to ROSs produced by Fe(Ⅱ) chemical oxidation. To validate this scientific hypothesis,a Fe (Ⅱ) oxidizing bacteria Pseudogulbenkiania sp. strain 2002 (strain 2002),two ammonia oxidation bacteria Rhodococcus sp. (A1) and Arthrobacter oxydans (A2) were selected as model strains,and contrasted with the iron reducing bacteria Shewanella oneidensis strain MR-1 (MR-1).The numbers of microorganisms,changes of cell structures,and the contribution of ROS were studied. The results show that different functional microorganisms respond differently to Fe(Ⅱ) chemical oxidation. After oxidation of 0.2 mmol/L Fe(Ⅱ) for 60 min,the MR-1 numbers decreased by 1.61 orders of magnitude,A1 and A2 decreased by 0.74 and 1.37 orders of magnitude,respectively,while the survival of strain 2002 was virtually unaffected by Fe (Ⅱ) oxidation. It was observed through transmission electron microscope that the outer membranes of MR-1,A1 and A2 bacteria cells were damaged to varying degrees,while strain 2002 was intact. The results of quenching test show that ROS produced in solution and in the cell caused death of functional microorganisms,but different microorganisms had different response mechanisms to ROS due to their adsorption ability to Fe(Ⅱ) and their resistance to ROS. The results of this study are of great significance for interpreting the microbial community evolution in the redox fluctuation region and the biogeochemical processes in the Great Oxygen Explosion in the history of the earth.