| Poly-?-glutamic acid(y-PGA)is an extracellular polymer produced by microorganisms.It can be applied in different fields.Sodium nitrate is used as nitrogen source and terminal electron acceptor in cell growth,for providing specific material and energy.It has been proved that sodium nitrate can improve ?-PGA biosynthesis by Bacillus licheniformis WX-02.However,the moleculer mechanism of sodium nitrate effect is still unknown.In this paper,iTRAQ,a comparative proteomics technology,was carried out to investigate the intracellular changes of B.licheniformis WX-02 with 5 g/L sodium nitrate addition at the beginning of fermentation.In order to choose a proper time for sampling,we did research on the fermentation curves under sodium nitrate addition and no addition.It turned out that at 12 h,the cellular processes were quite active.Then samples at 12 h were prepared for proteomic analysis.1533 proteins were detected at last and 495 proteins with differential expression were identified,in which 193 proteins were up-regulated and 301 were down-regulated.These proteins took part in most physiological activity.Proteins up-regulated were mainly involved in citrate cycle,amino acid transport and metabolism,energy metabolism,secondary metabolism,replication,transcription and translation.Proteins down-regulated were mainly involved in glycolysis,pentose phosphate pathway,coenzyme transport and metabolism,posttranslation modification and chaperones,signal transduction mechanisms,cell wall and cell membrane biogenesis.Throught analysis we found that sodium nitrate affected y-PGA biosynthesis maily due to several aspects as follows:maintaining activities of strains;enhancing citrate cycle and providing sufficient glutamate;gluatamte maily used for polymerizing instead of other pathways and increasing ?-PGA secretion. |
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