Identification and characterization of a new agar-degrading strain with the novel properties of saccharides inhibition and nitrogen fixation.

In this study, a new agar-degrading strain was isolated from soil with agar as a sole carbon source and energy. Based on its morphological, physiological, biochemical characterization and 16S rDNA sequence, the strain was identified as Streptomyces lavendulae UN-8. The extracellular agarase activity reached 0.03 U/ml after fermentation in shake flask (250 ml), which was close to other reported non-marine microorganisms. Furthermore, it is interesting that the growth of UN-8 would be inhibited by glucose (40 g/L) and maltose (40 g/L) with the inhibitory rate of 100% and 70%, respectively. Besides, UN-8 could be grown on the solid medium without any nitrogen sources, then the possible nitrogen fixation gene nifU was cloned from its genomic DNA. The deduced amino acid sequence of nifU has high similarity (98%) with nitrogen fixation protein NifU from Streptomyces sp. NRRL S-104 (KJY22454.1) and Streptomyces sp. NRRL F-4428 (KJK52526.1) based on NCBI blast. It is suggested that the nifU gene of UN-8 also encoded nitrogen fixation protein NifU. These results provided some new information for the further understanding of agar-degrading strain.