Growth Enhancement of Arabidopsis (Arabidopsis thaliana) and Onion (Allium cepa) With Inoculation of Three Newly Identified Mineral-Solubilizing Fungi in the Genus Aspergillus Section Nigri

Some soil fungi play an important role in supplying elements to plants by the solubilizing of insoluble minerals in the soil. The present study was conducted to isolate the mineral-solubilizing fungi from rhizosphere soil in some agricultural areas in northern Thailand. Seven fungal strains were obtained and identified using a polyphasic taxonomic approach with multilocus phylogenetic and phenotypic (morphology and extrolite profile) analyses. All obtained fungal strains were newly identified in the genus Aspergillus section Nigri, Aspergillus chiangmaiensis (SDBR-CMUI4 and SDBR-CMU15), Aspergillus pseudopiperis (SDBR-CMUI1 and SDBR-CMUI7), and Aspergillus pseudotubingensis (SDBR-CMUO2, SDBR-CMUO8, and SDBR-CMU20). All fungal strains were able to solubilize the insoluble mineral form of calcium, copper, cobalt, iron, manganese, magnesium, zinc, phosphorus, feldspar, and kaolin in the agar plate assay. Consequently, the highest phosphate solubilization strains (SDBR-CMUI1, SDBR-CMUI4, and SDBR-CMUO2) of each fungal species were selected for evaluation of their plant growth enhancement ability on Arabidopsis and onion in laboratory and greenhouse experiments, respectively. Plant disease symptoms were not found in any treatment of fungal inoculation and control. All selected fungal strains significantly increased the leaf number, leaf length, dried biomass of shoot and root, chlorophyll content, and cellular inorganic phosphate content in both Arabidopsis and onion plants under supplementation with insoluble mineral phosphate. Additionally, the inoculation of selected fungal strains also improved the yield and quercetin content of onion bulb. Thus, the selected strains reveal the potential in plant growth promotion agents that can be applied as a biofertilizer in the future.

Study on Conditions Optimization of Surplus Sludge and Nutrient Soil Co-Composting

In order to test the feasibility of co-composting for surplus sludge and garbage RD thermal decompositing nutrient soil, the mid-temperature composting experiments for the optimized conditions such as bacteria inoculating mode, initial moisture and pH were carried. The results showed that:(1) K-bacteria isolated from soil had a ability of decompositing insoluble mineral potassium to soluble forms at a rate of 9.20 μgK/200ml.h, and a decomposing ratio of 7.83% for potassium feldspar in liquid batch culturing. Moreover, after liquid enlargement culturing for 32h, the quantity of bacteria spores reached its climax, which ensured the high survival rate of K-bacteria. (2) The pre-compost inoculating mode (M1) was superior to post-compost (5th d M2) based on available nutrient or K-bacteria quantity increasing;(3) Through optimizing experiments, the best initial moisture of 50-60% and pH of 6.5 were determined with an ideal available nutrients and K-bacteria quantity in compost; (4) The inoculating of K-bacteria could increase the microbial quantity and activity, which may increase the heavy metal activity in compost, so the further researches on heavy metal passivation should be considered.

Mn oxide as a contaminated-land remediation product

Natural Mn oxides are an important component of biogeochemical cycles in many environmental settings. Mn oxides are strong oxidizing agents, facilitating the breakdown of organic contaminants and enhancing humification of soil organic matter. Interactions with metals and radionuclides, including surface adsorption, sequestration and oxidation can lead to incorporation of metals into insoluble mineral phases and a consequent reduction in bioavailability of toxic contaminants. Because of these properties, addition of Mn oxides may prove an effective treatment method for land contaminated by a range of organic and inorganic contaminants.

Biogenic Mineral Formation by Iron Reducing Bacteria

Dissimilatory iron reducing bacteria have been extensively studied for their ability to reduce ferric iron Fe(III) to ferrous iron Fe(II), as well as several multivalent heavy metals and radionuclides as a mode of energy-yielding respiration. Shewanella putrefaciens strain CN32 was used to investigate the mechanism of biogenic metal reduction in systems simulating conditions of natural anaerobic iron reducing environments in the subsurface contaminated with U and Tc as a possible strategy for bioremediation of soils containing these contaminants. As previously reviewed, U(VI) is soluble in most groundwaters, while U(VI) generally precipitates as the insoluble mineral uraninite. Formation of bioreduced minerals can lead to immobilization of these contaminants in the subsurface, which might be a very useful strategy for in situ bioremediation.To determine the metal reduction and the formation of biogenic Fe(II), U(IV) and Tc(IV) minerals, experiments with CN32 exposed to well-defined aqueous solutions were conducted. Metal reduction was measured with time, and the resulting solids were analyzed by X-ray diffraction, scanning electron microscopy (SEM) and energydispersive X-ray spectroscopy (EDS).