| Hydrogen oxidizing bacteria belonging to the plant growth promoting rhizobacteria, has immeasurable role on plant growth and development, so the mechanism for the growth of exploration has become a focus attention at home and abroad, in which few research on plant growth promoting of hydrogen oxidizing bacteria under heavy metals stress. Through this experiment search the strain that can protect plants against poison and promote the growth of plants, in order to facilitate the development of biological agents and bio-fertilizers for agricultural production. In this paper, using Vicia faba roots soil as research material, gas-cycle incubation system and mineral salt agar mediμM was used to separate hydrogen oxidizing bacteria in Vicia faba rhizosphere which were able to utilize hydrogen as sole energy. Screened the hydrogen oxidating bacteria by ability of hydrogen uptake hydrogen and grow chemolithoautotrophically test. Determination of colony morphology, physiological and biochemical tests and 16S rDNA of these hydrogen oxidizing bacteria,so as to indentiy hydrogen oxidizing bacteria genera and species, the strain of some growth promoting characteristics were measured, such as:ACC deaminase, IAA, phosphorus solubilizing ability, HCN, Cr tolerance test. Adopting the method of Belimov:the Pak choi seedlings inoculated hydrogen oxidizing bacteria was transfered into the Hoagland semi solid culture containing Cr6+(10μM), dark grown under a week, measurement of physiological indexes of Pak choi seedlings, screening the hydrogen oxidizing bacteria can significant promote and protective effect on Pak choi seedlings growth, Pak choi seedlings inoculated with these bacterias grown in 200g sterile soil added to Cr6+(10μM,50 μM,150 μM), according to the physiological index of Pak choi seedlings further selected a hydrogen oxidizing bacteria strain that promotion and protection of Pak choi seedlings growth under heavy metal stress.32 strains of bacteria were isolated. Among them,11 strains had stronger ability to oxidizing hydrogen and could grow chemolithoautotrophically. The results of the growth promoting properties show that 8 strains produce ACC deaminase, the highest activity reached at 79.27±3.42 μMol mg-1 h-1; 8 strains produce IAA, concentration is 4.29 to 119.28 mg L-1; The ACC deaminase and IAA hydrogen oxidizing bacteria accounted for 72.7% of total strain; 2 strains of hydrogen oxidizing bacteria have phosphate-solubilizing ability,1 strain of hydrogen oxidizing bacteria produces HCN, the range of hydrogen oxidizing bacteria tolerance of Cr6+ is 200-1000μM. Physiological test and 16s rDNA sequence analysis results show that zx-1, zw-17, zw-25 belong to Pseudomonas; zw-13, zw-35 belong to SphingobacteriμM; zw-28-1 belong to Stenotrophomonas. The growth promotion test results of Pak choi seedlings in the Hoagland semi solid showed that 5 strains of hydrogen oxidizing bacteria (zw-13, zw-23, zw-26, zw-28-1, zw-35) have significant effect compared with the control group to promote the growth of Pak choi seedlings root length, increased respectively 17.1%,23.2%,34.2%,48.7%,35.4%. In the 150μM treated soil, only zw-35 has a promoting effect to the Pak choi seedlings stem, increased by 11.9% compared with the control group. In the 150μM treated soil, Four strains (zw-13, zw-26, zw-35, zw-28-1) has a promoting effect on the elongation of Pak choi seedlings root length, compared with the control group increased by 33.3%,76.1%,119.2%,81.9%. Among them, zw-35 promote the root length increased by 119.2%. In the 150μM treated soil, Both zw-13 and zw-35 advance the Pak choi seedlings fresh weight increased, compared with the control group respectively increased by 19.6%,10.7%; In 150 μM treatment of soil, zw-26, zw-35, zw-28-1 can push the Pak choi seedlings fresh weight increased, compared with the control group respectively increased by 16.3%,49.0%,69.4%.The results show that:the roots growth of Pak choi seedlings susceptible to influenced by the metal Cr6+, which influence along with the metal concentrations increasing will be more obvious. At different concentration and different culture substrates, the physiological indexes of Pak choi seedlings inoculated four hydrogen oxidizing bacteria showed that inoculated with hydrogen oxidizing bacteria is beneficial to plant growth and root length, compared with the group without inoculation of hydrogen oxidizing bacteria. In different concentration of Cr+, the root length of Pak choi seedlings vaccinated zw-13, zw-28-1 has little scope to reduce, compared with the control group. In the same concentration of Cr6+, inoculated with zw-26, zw-35 is conducive to the growth of plant root. In high concentration (150 uM), the root length of Pak choi seedlings that inoculated with (zw-13 zw-26, zw-35, zw-28-1) were increased by 33.3%,76.1%,119.2%,81.9%, compared with the control group. The stem length of Pak choi seedlings inoculated with zw-35 were increased by 11.9%, other three strains of hydrogen oxidizing bacteria had no significant promoting effect on the growth of Pak choi seedlings shoot length. The fresh weight of Pak choi seedlings that inoculated with (zw-26, zw-35, zw-28-1) were increased by 16.3%,49%,69.4%. Zw-35 promoted Pak choi seedlings dry weight increased by 18.5%. The above data are sufficient to prove that whether at the concentration of 10μM, or 50μM, 100μM, or 150μM concentration, SphingobacteriμM.sp of zw-35 on plant growth promoting is better than the other strains. Under Cr6+ stress not only can promote the growth of Pak choi seedlings but also protect plants against heavy metal toxicity. To analyze and study the population structure hydroxide bacteria provides important experimental basis, For the protection and promotion of plant seedlings by hydroxide bacteria grows laid a solid foundation. |
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