Bin Lian

The Up-regulation of Carbonic Anhydrase Genes of Bacillus mucilaginosus under Soluble Ca2+ Deficiency and the Heterologously Expressed Enzyme Promotes Calcite Dissolution

Molecular mechanisms and gene regulation are of interest in the area of geomicrobiology in which the interaction between microbes and minerals is studied. This paper focuses on the regulation of the expression of carbonic anhydrase (CA) genes in Bacillus mucilaginosus and the effects of the expression product of the B. mucilaginosus CA gene in Escherichia coli on calcite weathering. Real-time fluorescent quantitative PCR (RT-qPCR) was used to explore the relationship between CA gene expression in B. mucilaginosus and promotion of calcite dissolution under condition of Ca2+ deficiency. The results showed that adding calcite to the medium, which lacks Ca2+, can up-regulate the expression of the bacterial CA genes to accelerate calcite dissolution for bacterial growth. CA genes from B. mucilaginosus were transferred into E. coli by cloning. We then employed crude enzyme extract from the resultant E. coli strain in calcite dissolution experiments. The enzyme extract promoted calcite dissolution. These findings provide direct evidence for the role of microbial CA on mineral weathering and mineral nutrition release.

A feasible way to increase carbon sequestration by adding dolomite and K-feldspar to soil

Abstract In recent years, many researchers have explored various possible ways to slow down the increase in atmospheric CO2 concentration as this process poses a serious threat to mankind’s survival. Mineral weathering is one possible way. Silicate weathering, for example, causes net carbon sequestration and carbonate weathering occurs relatively rapidly. In this study, dolomite and K-feldspar were added to soil to investigate if these minerals can increase carbon sequestration and also improve the available potassium content. The carbon content of amaranth, the organic and inorganic carbon content of the soil, two kinds of enzymes (polyphenol oxidase and urease), and the available potassium content were all tested. The experimental results show that the minerals accelerate the fixation of organic and inorganic carbon in the soil and also promote amaranth growth. Moreover, the available potassium content was increased when K-feldspar was added. Taken together, adding moderate amounts of carbonate and silicate minerals into the soil is found to be an attemptable way of accelerating CO2 fixation and improving the potassium content of soil.

An RNA-Sequencing Study of the Genes and Metabolic Pathways Involved in Aspergillus niger Weathering of Potassium Feldspar

Microbial transformation of potassium feldspar to produce organic composite potassium fertilizer is recognized to be an important method of effective use of the huge reserves of low grade K+-bearing rock in China. The mechanism underlying microbial weathering of silicate minerals is still unclear, and this is an obstacle to practical methods of application. To thoroughly understand the molecular mechanism responsible for the weathering of potassium feldspar by Aspergillus niger at a molecular level, high-throughput RNA-sequencing (RNA-seq) and treatment with different potassium sources (cultured in Czapek medium with soluble K+ or potassium feldspar) were used to investigate the differentially expressed genes of A. niger associated with potassium feldspar weathering and the related metabolic pathways. A series of differentially expressed genes related to the synthesis and transportation of organic acids, polysaccharides, and proteins (enzymes) were found to be closely associated with the K+ released from minerals through bioinformatic analysis. In addition, 12 genes that showed apparent expression differences by RNA-seq analysis and are relevant to organic acid synthesis, protein modification, maintenance of cellular homeostasis, and material transportation, were selected to be further verified using RT-qPCR. Compared to the fungal samples cultured with soluble K+, those with potassium feldspar have certain genes that are more up-regulated, such as the genes for Na+,K+-ATPase (447.6 multiples), cystathionine beta-synthase (5.6 multiples), cysteine synthase (9 multiples), and glutathione synthase (3.5 multiples). The analysis indicates that A. niger weathering of potassium feldspar is due to the synergistic effect of many factors including the up-regulation of certain genes and activation of related metabolite pathways. The research improves our understanding of the mechanisms of microbial weathering of silicate minerals.

Adsorption of hexavalent chromium onto organic bentonite modified by the use of iron(III) chloride

The adsorption of hexavalent chromium (Cr(VI)) was improved by using organic bentonite (OB) modified with iron(III) chloride. The adsorption mechanisms and characteristics of OB and organic bentonite modified by FeCl3 (FMOB) were studied by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy (EDS). It was found that hydroxyl-iron replaced some of the calcium and magnesium contained in the FMOB, but no significant change in its structure was shown even though the adsorption experiments proved that FMOB had a better Cr(VI) adsorption ability compared to OB. The coated material was prepared by mixing FMOB and 4A molecular sieves in a coated pot for the adsorption experiments in the test column. The relevant results showed that the adsorption of the coated material retained its high adsorption ability and maintained that ability after desorption and regeneration, which implied a potential for further application.

A practical soil management to improve soil quality by applying mineral organic fertilizer

Heavy use of chemical fertilizer causes increasing soil and environmental crisis, and the use of organic fertilizer increases obvious in recent years. In this study, mineral organic fertilizer (MOF) and compound fertilizer (CF) were applied in amaranth culture to explore the effects of these two kinds of fertilizers on soil quality and the potential function for CO2 fixation. Some soil parameters were tested, e.g. pH value, organic carbon content, microbial biomass, urease activity, and available potassium content. In addition, some parameters of soil infiltration water were also determined, such as pH and HCO3− concentration. Experimental results showed that MOF improved soil quality and amaranth biomass and increased possible soil carbon sink. On the contrary, the utilization of CF worsened soil quality and made the soil acidize. These results suggested that MOF can partially replace CF to improve plant growth, soil quality and possible CO2 sink.

The Release of Phosphorus from Sediment to Lake Water Induced by Cyanobacterial Blooms and Phosphorus Removal by Cell Harvesting

ABSTRACT To investigate the influence of cyanobacterial blooms on phosphorus release across the sediment-water interface and the repair mechanisms of internal phosphorus by harvesting of cyanobacteria, a series of laboratory-based experiments were conducted. Microcystis aeruginosa was cultured in phosphorus-free BG11 medium containing sediments from different eutrophic water bodies. The culture solution was removed and the same volume of phosphorus-free BG11 medium was put into the system until the M. aeruginosa had died. Cyanobacterial density, pH and different phosphorus forms in culture solution and sediments after culturing M. aeruginosa were determined. The results showed that cyanobacterial blooms stimulated phosphorus release from the sediment to the overlying water for the sediment in the eutrophic water body. Phosphorus released from the sediment was assimilated by M. aeruginosa and no increase in water-soluble phosphorus was observed. Cyanobacterial blooms caused sharp increases in different phosphorus fractions of sediment with the exception of the phosphorite-type (Ca10-P). Cyanobacterial blooms decomposed iron minerals in the sediment yet there was no clear evidence to demonstrate a positive correlation between water-soluble phosphorus in the overlying water and iron bound phosphorus (Fe-P) in the sediment. These results indicated that harvesting of cyanobacteria might be a suitable method to eradicate cyanobacterial blooms and to limit phosphorus pollution under controlled external nutrient loads.

Microbial flocculant combined ferric trichloride facilitates floating aggregation of Microcystis aeruginosa for efficient removal

AbstractA combination of microbial flocculant (MBF) and ferric trichloride (FeCl3) was applied to aggregate and harvest algae. The orthogonal experiment was designed to optimize conditions of flocculation. Mechanism of flocculation was observed through determining the zeta potential and observing the morphology of algal floc using stereo and scanning electron microscope. The results showed that the optimum combination of flocuulants was 0.175xa0g of FeCl3 with 10xa0mLxa0MBF per liter, which exhibited the highest flocculation efficacy (95.12%) and lowest chemical oxygen demand (10.44xa0mg/L). The flocculation mechanism was charge neutralization, where the MBF first adhered and coated algae. Due to its high affinity to iron-hydroxy ions and long-chain molecules, the MBF attracted positively charged hydroxyl irons generated by FeCl3 hydrolysis and interacted with the iron-hydroxy ions to form a larger floc by bridging. The coat made of MBF formed a thin film which protected algae from being destroyed, and trapped th...

Bacterial diversity among the fruit bodies of ectomycorrhizal and saprophytic fungi and their corresponding hyphosphere soils

Macro-fungi play important roles in the soil elemental cycle in terrestrial ecosystems. Many researchers have focused on the interactions between mycorrhizal fungi and host plants, whilst comparatively few studies aim to characterise the relationships between macro-fungi and bacteria in situ. In this study, we detected endophytic bacteria within fruit bodies of ectomycorrhizal and saprophytic fungi (SAF) using high-throughput sequencing technology, as well as bacterial diversity in the corresponding hyphosphere soils below the fruit bodies. Bacteria such as Helicobacter, Escherichia-Shigella, and Bacillus were found to dominate within fruit bodies, indicating that they were crucial in the development of macro-fungi. The bacterial richness in the hyphosphere soils of ectomycorrhizal fungi (EcMF) was higher than that of SAF and significant difference in the composition of bacterial communities was observed. There were more Verrucomicrobia and Bacteroides in the hyphosphere soils of EcMF, and comparatively more Actinobacteria and Chloroflexi in the hyphosphere of SAF. The results indicated that the two types of macro-fungi can enrich, and shape the bacteria compatible with their respective ecological functions. This study will be beneficial to the further understanding of interactions between macro-fungi and relevant bacteria.

Redox of Fungal Multicopper Oxidase: A Potential Driving Factor for the Silicate Mineral Weathering

Abstract Microbial mineral weathering is ubiquitous in nature, but research related to the direct effect of oxidoreductase (e.g., fungal multicopper oxidase) on silicate mineral weathering is rare. This study uses genetic engineering technologies of heterologous expression and gene overexpression and electrochemical methods to examine the effects of multicopper oxidase (McoA) and its gene (mcoA) of Aspergillus niger in the weathering of K+-bearing silicate minerals (KBS). In the experiment of weathering KBS, the mcoA-overexpressed strain showed higher K+-release ability than the wild-type strain, and the heterologous-expressed McoA demonstrated a direct potential to weather KBS and release K+. The electrochemical results showed that the reduction potential of McoA was 0.302u2009V, and doubled the current of the KBS-modified electrode, meaning that McoA can enhance the electricity transfer in the experiment of weathering KBS. This study confirmed that McoA of A. niger can directly participate in the weathering of silicate minerals, which promotes electron transport at the instable edge of minerals to accelerate mineral weathering. The study will enable greater understanding of the role of oxidoreductase in the biochemical weathering of silicate minerals and identify a possible way to improve the microbial weathering capacity on minerals by genetic engineering manipulation.

Adsorption of Ni2+ and Cu2+ using Bio-Mineral: Adsorption Isotherms and Mechanisms

ABSTRACT Heavy metal pollution has become one of the most serious environmental pollution problems. This study aimed to determine the adsorption and desorption characteristics of Ni2+ and Cu2+ by bio-mineral which was induced by Bacillus subtilis, and to explore the effect of pH on adsorption characteristics. The results showed that the Langmuir model gave a better fit to the experimental data than the Freundlich model, which demonstrated the adsorption was of a single-molecule layer form. The maximum adsorption capacities of the bio-mineral for Ni2+ and Cu2+ were determined as 67.114 mg/g and 69.930 mg/g, respectively. The desorption rates of Ni2+ and Cu2+ were very low, especially for Ni2+ which was almost 0. Besides, the bio-mineral maintained high adsorption capability for metals ions within a wide pH range (pH ≥ 3). It did not show any new phases after adsorption of Ni2+ and Cu2+ tested by FTIR, indicating that the bio-mineral and heavy metal ions might mainly physically be adsorbed. The bio-mineral has a larger internal and external specific surface area, pore volume and colloidal properties which are beneficial for the adsorption of metals ions, but shows limits in desorption. This study provides a theoretical basis for the utilization of bio-mineral and opens a new perspective for the remediation of heavy metals pollution.