A Mesorhizobium huakuii strain HN3015 was isolated from Astragalus sinicus in a rice-growing field of Southern China. Strain HN3015 contained three large plasmids. The three indigenous plasmids, named as pMhHN3015a, pMhHN3015b and pMhHN3015c of M. huakuii HN3015, were, respectively, cured by Tn5-sacB insertion. The mutant strain HN3015-1 cured with its largest plasmid pMhHN3015c formed only white null nodules. Mutant HN3015-3 cured with its smallest plasmid pMhHN3015a could form pink effective nodules. However, mutant HN3015-2 cured of the second largest plasmid pMhHN3015b lost nodulation ability. Furthermore, curing of pMhHN3015a had enhanced competitive nodulation ability and symbiotic efficiency of HN3015-3. The results from acidity tolerance assays indicated that the three plasmids in M. huakuii HN3015 had a positive control effect on acidity tolerance of HN3015, and all indigenous plasmids of M. huakuii HN3015 had a negative control effect on the alkali tolerance capacity of HN3015. Surprisingly, all plasmids in M. huakuii HN3015 had also a negative control effect on its growth rate. The results showed an interactive and functional complexity of plasmids in strain HN3015.

This paper explored the effects of Tween 80 on the biomass, intracellular polysaccharide (IPS) content, fermentation parameters, the pellets size of mycelium, and the antioxidant activity of IPS in liquid fermentation. With adding to Tween 80, the outputs of biomass and IPS increased during the fermentation, respectively, while the reducing sugar content was decreased, as well as, the time courses of pH value were different. It was also shown that the addition of Tween 80 could protect the intact of pellets from breaking down. The effects of Tween 80 on the main structure of IPS were no obvious, and the IPS were revealed similar infrared spectrum, as was indicated by the infrared spectrum analysis. Improvements in the scavenging capacity of DPPH radicals of IPS were observed in Tween 80 treated group compared with the control group. Tween 80 exerts impacts on the liquid fermentation of .

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