Diversity and isolation of potassium solubilizing bacteria in tobacco rhizosphere soils

The concentration of soluble K in soils is usually very low which implies that a higher proportion of soil K occurs as insoluble rock, minerals and other deposits. K solubilizing bacteria have been noted to dissolve K from insoluble minerals, increase available K content in soils and stimulate plant growth. Application of K solubilizing bacteria may relieve K fertilizer shortage in China. In this research, K solubilizing bacteria were isolated in selective medium from tobacco rhizosphere soils sampled from tobacco areas in Sichuan, Hubei and Shangdong Provinces, and the diversity of the bacteria isolates analyzed using the 16S rDNA sequence. 27 K solubilizing bacteria strains were isolated and all the isolated bacteria strains solubilized powdered feldspar in solid and liquid media. The range of the zone of solubilization diameter formed by the strains was 0.11~0.30 cm on the agar medium. All the strains were able to release K (0.59~4.40 mg·L^-1 K of the fermentation broth) and plant-promoting effects (plant height and longest leaf length respectively increased by 0.97%~38.64% and 4.40%~31.02%). Strains XF11, GM2, JM19 and GL7 were high-efficient strains for K release and plant growth promotion and had high application potential. The strains were identified through comparisons of 16S ribosomal DNA sequences. There were 85.18% Gammaproteo-bacteria, 3.70% Alphaproteo-bacteria, 3.70% Betaproteo-bacteria, 3.70% Actins-bacteria and 3.70% Bacteroidetes. Among the isolated strains, the dominant bacteria were the strains for the genera Klebsiella bacteria in tobacco rhizosphere soil. Further studies were necessary into the effects of the bacterial strains on mobilizing K-bearing minerals under field conditions.