Study On The Correlation Between LAAO Differential Expression And Adaptation To Hydrogen Peroxide

L-Amino acid oxidase?LAAO;EC 1.4.3.2?is dimeric flavoprotein with function in catalyzing the transformation of L-amino acids to the corresponding a-keto acids with the generation of ammonia and hydrogen peroxide.LAAOs exhibit broad biological activities including antimicrobial,anti-HIV,antitumor cell and induction of cell apoptosis,all of which are believed to be associated with the H₂O₂ production.Recently,a yellow-pigmented LAAO-producing marine bacterium designated as Pseudoalteromonas sp.B3 was successfully isolated from the intertidal sea area.Later on,a red-pigmented spontaneous mutant strain designated as R3 was isolated from the culture plate of B3.Compared to B3,R3 displays a stronger ability to produce LAAO.In the present study,we aim to identify the mechanism underlying the differential expression of LAAO through analyzing the correlation between LAAO expression and adaptation to hydrogen peroxide.Firstly,the oxidative damage to stains B3 and R3 was investigated.The results indicated that intracellular H₂O₂ accumulation could cause cell damage,including lipid peroxidation and DNA strand breakage resulting in bacterial growth inhibition.In addition,Compared to R3,stain B3 showed a more obvious cell damage,which may be related to the weaker H₂O₂ scavenging ability in B3.Subsequently,the response of ROS scavenging system under oxidative stress was investigated by qRT-PCR.The results indicated that the ROS scavenging system in both strains could be activated by oxidative stress and the transcriptional level of three detoxification genes including rpoS?ahp and cat were also significantly promoted.Compared to stain B3,the transcriptional level of rpoS?ahp and cat genes were more higher in strain R3,suggesting that the response of oxidative stress was more sensitive,and the capacity of ROS scavenging was more powerful in strain R3.Taken together,these results indicated that the difference of ROS scavenging ability was the major reason for the mechanism of the differential expression of LAAO.The mechanism for the differential expression of LAAO was revealed in this paper.It also paves the road for further investigationg on the regulation and transcription of LAAO synthetic genes,the biosynthesis of LAAO and heterologous expression of LAAO in vitro.