A potassium solubilizing bacterial strain des- ignated EGT, which is tolerant of high temperature, was isolated from an earthworm＇s gut to obtain a bacterium that can weather potassium-bearing rock effectively through solid-state fermentation. Molecular phylogeny and 16S rRNA gene sequence analysis demonstrated the bacterial strain was a member of the Streptomyces genus. To assess its potential to release potassium from silicate minerals, this strain was used to degrade potassium-bearing rock powder by solid-state fermentation. After fermentation, the amount of water-soluble A1, Fe and K of the substrate with active inoculum was higher than those of the control, which had autoclaved inoculum, and those of the fresh substrate. The result indicated that the strain had the ability to weather potassium-bearing rock and could be used as an inoculum in the production of potassium bio-fertilizer, due to its potassium release activity from rock and tolerance to high temperature.
This study analyzes the biotransformation of earthworms on K in potassium-bearing mineral powder （PBMP） under different PBMP recruitments. A mixture of PBMP （10% to 60% mass fraction） and decaying cow dung was used as feed for breeding the earthworms to study the potassium-releasing ability of earthworms on PBMP in soil. The mixture containing 20% and 30% PBMP resulted in good growth and propagation of the earthworms as well as higher conversion rates of potassium. Therefore, the optimum recruitments of mineral powder are 20% and 30%. The mixture of cow dung and PBMP was compared with the mixture of cow dung and corresponding proportions of quartz powder to analyze the conversion rate of earthworms on PBMP in different combinations. After the earthworms were raised with the mixture of cow dung and PBMP （8 ： 2 and 7 ： 3） for 30 d, the contents of rapidly available K and effective K were 10 824.3±35.9 and 11 688.4±16.1 mg.k-1 as well as 10 079.6±62.2 and 10 247.5±172.7 mg.kg-1, respectively. After the earthworms were raised with the mixture of cow dung and quartz powder （8 ： 2 and 7 ： 3） for 30 d, the contents of rapidly available K and effective K were 10 623.3±41.1 and 11 385.5±13.5 mg.kg-1 as well as 9 834.2±51.8 and 9 907.6±11.4 mg.kg-1, respectively. Thus, the contents of rapidly available K and effective K in the mixture of cow dung and PBMP were significantly higher compared with those in the mixture of cow dung and quartz powder （P〈0.05）. The increment contents of rapidly available K and effective K were 201.0 and 302.9 mg.kg1 as well as 245.4 and 339.9 mg-kg1, respectively. Therefore, earthworms can activate and trans-form K into effective K through feeding, digestion, absorption, and excretion. The results pro- vided a new idea of using earthworms to release potassium in low-grade potassium-bearing rocks and obtain the rapidly available K and effective K needed by plants.
We investigated the differences in the gene expression of carbonic anhydrase （CA） and cysteine synthase （CysM） between two weathering conditions, with either soluble potassium or insoluble potassium. We cultured a strain of A. niger by adopting a variant Czapek medium （using NazHPO4 as a substitute for KzHPO4） in two groups, Group A （containing silicate minerals bearing potassium but without KC1） and Group B （with KCI） . We extracted the mRNAs of CA and CysM from these two groups and performed real-time quantitative polymerase chain reactions （RT-qPCR）. We constructed relative standard curves by using glyceraldehyde-3-phosphate dehydrogenase （GAPDH） as the reference to confirm a consistent amplification effi- ciency of the target genes （CA and CysM） and the reference gene and quantified the gene expression of the targets in a relative manner. Our results showed that CA and CysM in Group A were upregulated for 1.7 times and 11.7 times, respectively, com- pared with those in Group B. Furthermore, we also analyzed some metabolic pathways and functions of the A. niger-induced weathering of potassium-bearing minerals, which involved the synthesizing of these two enzymes. Thus our work provides materials for further study of the roles of A. niger in the metabolic regulation during the weathering process of potassi- um-beating minerals.
SUN LeiLeiXIAO LeiLeiXIAO BoWANG WeiYingPAN ChenWANG ShiJieLIAN Bin
