Microbial Diversities During Bioconversion Of Potassium-bearing Rocks And Its Mechanisms

Potassium is the third major macro nutrient for plant growth, but China is deficient in potassium fertilizer resources. China is fortunate to have rich deposit of potassium-bearing rock (PBR). If PBR could be converted into potassium fertilizer, it will provide enough potassium resource for China’s agriculture. Microorganism play a key role during releasing potassium from PBR by bioconversion technology, so studying the bacterial diversities during bioconversion of PBR and understanding bio-weathering mechanism of PBR will be of benefit to improve bioconversion technology.Feeding experiments were conducted to examine the accelerated degradation of potassium-bearing rock powders (PBRP) induced by earthworm. Results indicated some elements such as K, Al, Fe and Ca were released from the PBRP upon digestion by earthworm, and the contents of water-soluble K, Al, Fe and Ca in the PBRP weathered by earthworm respectively increased by5.64%,20.25%,27.52%,17.21%and its HNO3-extractable K Al, Fe and Ca respectively increased by6.59%,3.94%,4.36%and8.49%, thereby enhancing the degradation of PBRP. The microbial communities in earthworm’s gut and the surrounding substrates including soil and PBRP were analyzed by ARDRA (Amplified Ribosomal DNA Restriction Analysis). The results indicated a higher bacterial diversity in the guts of the earthworms fed with PBRP and the PBRP fed to earthworm. The earthworms’gut and surrounding environment shared some bacteria, but bacterial communities showed very different in different stage. Some members from Gammaproteobacteria dominating in earthworm gut were likely to play an important role during degradation of mineral grains mediated by earthworm. The results also showed that the microbial communities relevant to mineral degradation varied with environmental conditions, but a large number of microorganisms played their role in the degradation process of PBRP.Composting is an efficient technique to transform the potassium in PRRP into bioactive forms. To obtain high effective microorganisms which can solubilizing potassium from PBRP in compost, bacteria, tolerating high temperature, were screened. One mineral solubilizing bacterial strain designated EGT, which can be tolerant to high temperature, was isolated from the earthworm fed with PBRP. The sequence similarities and phylogenetic relationships based on16S rRNA gene showed that the strain belonged to the group of the genus Streptomyces. The strain was used as the agent releasing potassium from PBRP under solid state fermentation. Comparing to fresh substrate, the contents of water-soluble Al, Fe and K from the substrate inocubated by the strain respectively increased by23.08%、123.19%and30.99%. Comparing to the substrate inocubated by autoclaved inoculum, their contents respectively increased by45.45%,52.48%and9.13%. The increase of water-soluble elements indicated that the strain could weather PBRP. It may be as an effective inoculum of the compost which comprise PBRP and organic matter such as straw and cotton seed hull to obtain potassium fertilizer by composting.The low-grade potassium-bearing rock powder (PBRP) was processed by composting to enhance the weathering of it for K-fertilizer’s production. After compost was finished, the compost was treated again with earthworms’feeding to further increase its available potassium. The results revealed that the two processing could effectively accelerate the degradation of PBRP and increase the compost’s available potassium. The dynamics of bacterial communities during composting and earthworm’s feeding was investigated using DGGE technique. The profile of DGGE showed that the bacterial community of compost had a large difference in the earlier stage, but had a little difference in the latter stage. The dominant species of bacteria largely varied in the earlier stage of composting, but they were stable in the latter stage. Only band12and14, which belonged to Alteromonas and Firmicutes respectively, had been dominant during the whole course of composting. None of special dominant bacteria appeared after the compost was fed to earthworm. Selected bands were cut from the DGGE gel and then were sequenced after recycling and purifying. The similarities and phylogeny of the16S rRNA sequences indicated that the bacteria which the thirteen dominant bands represented were attributed only to Proteobacteria and Firmicutes. Therefore, the two phyla of bacteria may play an important role during composting of the material enriched by potassium-bearing rock powder.The compost enriched by PBRP is abundant not only in bioactive potassium but also in nitrogen and phosphorus. Therefore, it would promote the growth of plants and affect its endophytic bacterial communities in root. The endophytic bacteria in plant root contributes to plant growth by dissolving soil mineral, providing nutrients for plant, protecting plant from disease and produing plant growth promoting molecules or substances. Amaranth (Amaranthus mangostanus L.) is a plant of rich potassium and might be effective in solubilizing mineral K of soil. Its endophytic bacteria in root may play an important role during amaranth releasing potassium from soil mineral. The compost enriched by PBRP was used as base fertilizer to amaranth which is a plant of rich potassium and might be effective in solubilizing mineral K of soil. The endophytic bacteria in amaranth root may play an important role during amaranth releasing potassium from soil mineral. The endophytic bacterial communities of amaranth’s root fertilized by the compost and its control to which no fertilizer was applied were investigated through16S rRNA gene cloning library technology and and ARDRA. The number of clones in two libraries were similar, but the number of endophytic bacteria from library of the amaranth without fertilizer were much higher than those of the amaranth fertilized by the compost enriched by PBRP. The result showed that the former’s endophytic bacteria were much richer than the latter’s. Comparing to those of the amaranth fertilized by compost, some bacteria from Gammaproteobacteria were dominant in the root of the amaranth no fertilizer was applied. Among these bacteria of Gammaproteobacteria, main members were from the genera Enterobacter, Pantoea and Pseudomonas. These bacteria may play an important role in promoting amaranth’s growth by releasing elements from soil, fixing nitrogen and producing growth hormones.These studies not only revealed the bacterial communities associated with weathering of PBRP and the dynamics of bacterial communities in the compost enriched by PBRP during composting and feeding earthworms, but also showed the changes of amaranth’s growth and its endophytic bacteria in root after providing the compost enriched by PBRP as a base fertilizer to it. The results will be useful in helping us improve the technology of bioconversion of PBRP, find new the resources of mineral potassium-solubilizing bacteria and produce more effective potassium bio-fertilizer for agriculture.