Culturable Bacterial Diversity Of Biological Soil Crusts In Mu Us Desert And Screening And Identification Of Antagonistic Bacterial Strain 5A5-3

In order to understand the soil bacterial diversity of biological soil crusts of Mu Us Desert in Inner Mongolia Erdos Wushenqi areas, 54 of biological soil crusts and soil samples were studied. The quantity of bacterium were mesured by plate culture; Isolated strains with different morphological characteristic of colonies; Also, the phylogenetic diversity of generalized bacteria in biological soil crusts and soil was analyzed by 16S rDNA sequences of isolates. A strain named 5A5-3 with a rather higher antagonistic activity against pathogens had inhibition zone diameter than 15 mm was screened via preliminary sereening from bacterias isolated from 54 samples The strain 5A5-3 was further characterized by morphological and culture observation, physiological and biochemical experiments and 16S rDNA sequence analysis. The test results were as follows:The quantity of culturable bacteria biomass was in the order of 105.Each biomass of bacteria in BSCs sample was higher than in the soil layer. Changes of biomass in different distances of four directions did not have a consistent trend. The diversity of the morphological characteristic of colonies was more relatively rich in BSCs samples than soil samples. 190 of bacterias with different morphological characteristic of colonies were isolated from BSCs samples, and 84 from soil samples.When 16S rDNA sequences of 274 isolates were aligned the closest relatives in the GenBank database with BLAST, the similarity of 269 isolates were higher than 97%, and 5 isolates were lower than 97%. The strains were clustered into operational taxonomic units (OTUs) at a level of sequence similarity of≥97%, OTUs formed by strains from BSCs samples and soil samples respectively were: 60 and 29. While Species richness (S), Shannon–Wiener index(H) and Evenness index(E) of bacteria in BSCs samples respectively were: 22.25±2.06,2.7016±0.0567和0.9081±0.0189; and which of soil samples respectively were: 13.00±2.45,2.3093±0.2037 and 0.8329±0.0735. Bacteria diversity index of Species richness (S), Diversity index (H) and Evenness index (E) in BSCs samples were significantly higher than the soil samples, while the Dominance index(D) of the soil samples was higher than BSCs samples.Phylogenetic analysis based on the partial 16S rDNA sequences indicated that isolates were mostly clustered into Fimicutes, Proteobacteria, Actinobacteria and Bacteroidetes. Bacillus was the dominant kind of bacteria, the separation frequency of which in BSCs samples and soil samples were 86.84% and 56.41%. Analysised by genus level, bacterial diversity in different samples showed high distinctive.The similarity of 4 strains from BSCs samples were lower than 97%,while only 1 isolates from soil samples. BSCs was more potentially to discover new bacterial species. A strain named 5A5-3 with a rather higher antagonistic activity against Fusarium oxysporium and Fusarium moniliforme respectively. Based on the results of physiological and biochemical experiments and 16S rDNA sequence analysis, the strain was initially identified as Bacillus velezensis.