| Reactive oxygen species?ROS?can be produced by photooxidation and intracellular processes of some organic compounds.In the past,it was generally believed that light related processes?including photosynthesis?are the main sources of ROS in the environment,which is of great significance to the biogeochemical cycle of organic matter and metal elements in the environment.In recent years,it has been found that bacteria could produce extracellular ROS under lightless condition,but related studies are rare,and there is no report on the influencing factors,reaction conditions and other characteristics of bacterial formation of extracellular ROS under lightless condition.Based on this,we studied the characteristics of extracellular ROS produced by marine bacteria Pseudoalteromonas sp.GCY under the lightless and aerobic condition,and discussed the formation mechanism of extracellular ROS preliminarily.Firstly,the formation characteristics of extracellular H2O2 were studied.The growth substrates?peptone,beef extract,yeast,glucose,sodium acetate,sodium lactate?,humic acid substitute?anthraquinone-2-sulfonate,AQS?,and organic pollutans?OPs?including ibuprofen?IBP?,phenol,bisphenol A?BPA?,sulfamethoxazole?SMX?et al were investigated.The results showed that the strain could produce extracellular H2O2 in peptone,beef extract and yeast extract system.Under the same concentration,the extracellular H2O2 concentration of beef extract system were higher.The concentration of extracellular H2O2 was related to the growth phases of the strain,the exponential phase concentration is zero,then gradually increases in stationary phase.Glucose,sodium acetate and sodium lactate had no effect on the concentration of extracellular H2O2.AQS of 300 mg·L-1 and IBP of 200 mg·L-1 could increase the concentration of extracellular H2O2 significantly.Secondly,the formation characteristics of extracellular O2-were studied.The effects of the above substrates,OPs,and Na+concentration,temperature and pH on the ability of producing extracellular O2-were investigated.The results showed that the production of extracellular O2-was also related to the growth phases of the strain,with the strongest logarithmic period and the weakest stable period.At the same concentration,the capacity of producing extracellular O2-in beef extract system is stronger than that in peptone system,and the molecular weight range of the main promoting substances in beef extract is 10-50 kDa.BPA of 100 mg·L-1 and SMX of 250 mg·L-1 can inhibit the growth of bacteria,and significantly promote the O2-production capacity of the system,but no degradation of SMX was detected in the experiment.Other concentrations of BPA and SMX,and other OPs had no significant effect.The capacity to produce O2-is related to the concentration of NaCl.When the concentration of NaCl is 12mg·L-1,the capacity is the highest.The activity of NAD?P?H oxidoreductase of GCY was at a high level at low temperature?4??and alkaline condition?pH 8.0-10.0?,which may be the result of long-term adaptation to marine environment.In addition,the formation of siderophore and·OH in the system of 6 g·L-1 peptone and beef extract was detected.Finally,the formation mechanism of extracellular ROS was discussed.Firstly,the formation mechanism of extracellular H2O2 was discussed.The diffusion of intracellular H2O2 and O2-disproportionation had limited contribution to the concentration of extracellular H2O2.Extracellular H2O2 was mainly produced by L-amino acid oxidase?lAAO?.The relative strength of LAAO and catalase activity led to the change of H2O2 concentration.It was speculated that the production of extracellular H2O2 was growth uncoupled type.Secondly,the formation mechanism of extracellular O2-was discussed.The formation of extracellular O2-was related to NAD?P?H oxidoreductase.The strongest ability of GCY to produce extracellular O2-during the logarithmic period was probably due to the vigorous growth and reproduction,and the active activity of NAD?P?H enzyme,and the enhanced ability to produce O2-in the decay period might be related to cell death.Therefore,it is speculated that the production of extracellular O2-is partially growth coupled type.The effect of BPA and SMX on O2-production ability can not be simply attributed to the stress of high concentration OPs,but may be related to their own characteristics.In addition,the formation mechanism of·OH is also discussed,its formation is related to Fenton reaction and Haber-Weiss reaction. |
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