| Doctor Dong put forward firstly a set of theories in recently that H2 released from Hup" legume root nodule can improve the reproduction of hydrogen-oxidizing bacteria and the developed bacteria colony increased plant growth. But due to the special characteristic of hydrogen-oxidizing bacteria, the isolation of soil hydrogen-oxidizing bacteria is extremely difficult and less progress was made in research of the characteristic of the group of hydrogen-oxidizing bacteria and the mechanism of promoting the plant growth. In this study the soils from Hup" nodules were cultured in H2 mixture gas for isolating hydrogen-oxidizing bacteria. The characteristic of hydrogen-oxidizing bacteria was also studied primaryly. The main content as follows:A set of equipment of gas-cycle incubation system(H2 treatment system) was developed that provided stable H2 exposure rate (4.16×10-5 -1.25×10-4mol·L-1) by electrolysis, gas flow rate is 280ml/min. The equipment was used in soil enrichment and hydrogen-oxidizing bacteria culture.Soil samples collected from Hup" legume rhizosphere were exposed 4.16×10-5 mol·L-1 H2 concentration, gas flow rate 280ml/min. Soil were incubated about one month in room temperature. Gas chromatography was used to assay the H2 oxidizing ability in soil. The concentration of soil H2 decreased from 4.08×10-5 mol·L-1 to 5.40×10-6mol·L-1, and then keep stable, this result showed that the quantity of the group of hydrogen-oxidizing bacteria was increased mostly. The enriched soils were treated with fungicides, antibiotics or sterilization and exposed to 4.16×10-5 mol·L-1H2 mixture gas to research the nature of the H2 uptake agent in soil. The results showed the H2 uptake ability of H2 treated soil disappeared when the soil was autoclaved. The soil with streptomycin treatment after 24h culture exhibited decreased H2 uptake capabilities of 58.21±9.4%, and after 2 weeks the soil decreased H2 uptake capabilities were 96.06±2.3%. The soil with benomyl treatment after 24h culture exhibited decreased H2 uptake capabilities of 86.85±5.9%, and after 2 weeks the soil decreased H2 uptake capabilities were 22.16±6.7%, the capabilities of soil recovered significantly. All results suggested that H2 uptake agent of soil is due to the biotic nature and the H2 uptake agent is bacteria but not fungi. Mineral salt agar medium(MSA) was used to separate hydrogen-oxidizing bacteria which were able to utilize hydrogen as sole energy. 40 bacterium strains were isolated by incubation system with 1.25×10-4mol·L-1 H2 mixture gas, and the capabilities of uptake hydrogen of these strains were measured. The results showed that the volume of uptake hydrogen of 22 strains more than 1.25×10-4mol·L-1, account for 55% in total, and 9 strains in the 22 strains was consumed completely, account for 22.5% in total. The results of autotrophic growth tests showed that 22 bacterium strains had the ability to grow chemolithoautotrophically.20 strains were preliminarily identified as hydrogen-oxidizing bacteria.The ability of heterotrophy and the capability of utilizing different carbon resources were studied through cultivating bacteria in liquid MSA medium with different carbon resources without H2 mixture gas. Bacteria colony form and physiological- biochemical characteristics were also studied. The results showed that the group of hydrogen -oxidizing bacteria were small bacillus, the results of catalase test and ammonia production test were all positive, the results of acid and gas production from glucose test, V.P test, M.R test, 3-keto-Lactose production test and L-Phenylalaninase test were all negative.The growth-promoting capability of 20 strains was tested. A03, A06, A10, A11, A14, A26, A31, A35 and A39, the total 10 bacteria strains were tested that they could markedly promote root growth of wheat and corn in different extent. Increasing amplitude of rootage was from 117% to 397%. The wheat root increasing amplitude treated by A06 strain and A11 strain was 361% and 393.6%, The corn root increasing amplitude treated by A06 strain and A11 strain was 226.3% and 219.7%.In order to judge whether the strains have 1-aminocyclopropane-1- carboxylate deaminase, the ability of 9 bacteria strains on using ACC as nitrogen resource were examined through thin layer chromatography analysis. The results showed that the A06 strain could utilize ACC as nitrogen resource, suggesting that this strain has ACC deaminase. Judging from the results of plant growth promoting test and thin layer chromatography, the A06 strain are sure to be plant growth-promoting rhizobacteria (PGPR).The ability of promoting wheat root growth in threatening condition (temperature and pH)were also studied, but the results showed the A06 strain could not alleviate the damage come from threatening condition. The sequence of 16s rDNA fragements were analyzed. The homology between strain A06 and other strains of Variovorax paradoxus is 100%.It suggested that strain A06 was belong to Variovorax paradoxus.
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