Characteristics of cultivable microbial community number and structure at the southeast edge of Tengger Desert

Desertification is a common environmental challenge for humans,which restricts social and economic development.Biotechnologies have been used for the management of soils in areas of desertification and the use of microorganisms has shown potential benefits,but such research is still in the initial stages.Here,we have studied the microbial distribution and diversity in soil crust and in the soil under the crust along sand dunes of different fixed ages at the southeast edge of the Tengger Desert,China.The Shapotou and Yiwanquan regions were selected as sampling sites,which represented an artificial restoration region and a natural restoration region,respectively.The results showed that the number of culturable bacteria varied between 3.7×103 to 2.8×106 CFU/g,which was similar with other deserts worldwide.The number of culturable bacteria increased with the degree of sand dune fixation,and decreased with depth,which was similar to the trend of soil improvement in areas of desertification.Such characteristics did not show any significant differences between the artificial restoration region and the natural restoration region(P0.05).The genera Arthrobacter and Bacillus were the dominant bacteria at the southeast edge of the Tengger Desert.The genus Arthrobacter comprised 12.8%—69.5% and the genus Bacillus comprised 4.7%—60.7% of the total culturable bacteria,and these percentages increased and decreased with the degree of sand dune fixation,respectively.This result implied that Arthrobacter may play a significant role during preliminary soil crust formation.The results also showed that the quantity of culturable bacteria was positively correlated with the concentration of total soil carbon and total soil nitrogen(P0.05),but negatively correlated with pH values(P0.05).These results showed that microorganism number was closely related with the improvement status of desertification.Such results are likely to be caused by the interaction between soil microorganisms and soil carbon,nitrogen and organic acid.Based on 16S rDNA gene sequences and the phylogenetic tree,the culturable bacteria in the study area belonged to 18 genera: Acinetobacter,Afipia,Arthrobacter,Bacillus,Balneimonas,Brevundimonas,Chitinophaga,Chryseobacterium,Flavobacterium,Herbaspirillum,Janthinobacterium,Lysobacter,Microbacterium,Paenibacillus,Paracoccus,Phyllobacterium,Sphingomonas and Variovorax,and fell into six phylogenetic groups: high G+C Gram positive bacteria,low G+C Gram positive bacteria,α-Proteobacteria,β-Proteobacteria,γ-Proteobacteria and Cytophaga-Flavobacterium-Bacteroides(CFB) group bacteria.Such a culturable bacterial community structure was similar with previous studies of desert ecosystems.Similar results also showed that the high proportion of G+C Gram positive,low G+C Gram positive and Proteobacteria,and a low proportion of CFB group bacteria could be the main bacterial community structure in the desert ecosystem.Blast results also showed that these bacterial strains had a variety of functions.Some strains showed accelerated function for the restoration of desertified areas.For example,Afipia,Balneimonas,and Herbaspirillum had close relationships with nodule formation in plants.In contrast,some isolates in our study could also inhibit the restoration of desertified areas;some bacteria were plant pathogens,and some were identified as aerobic denitrifying bacteria.Besides these,pathogenic microorganisms and bacterial strains with potential applications were also found in desertification soil.The results of this study add to our knowledge of microorganism usage during the management of desertification.