Isolation, Mutagenesis, and Organic Acid Secretion of a Highly Efficient Phosphate-Solubilizing Fungus

The highly effective phosphate-solubilizing microorganisms are significant for making full use of the potential phosphorus resources in the soil and alleviating the shortage of phosphorus resources. In this study, a phosphate-solubilizing fungus was isolated from wheat and cotton rhizosphere soils in the lower reaches of the Yellow River in China and was identified as Penicillium oxalicum by morphological and ITS sequencing analysis. In order to obtain a fungus with more efficient phosphorus solubilization ability, we tested three positive mutant strains (P1, P2, and P3) and three negative mutant strains (N1, N2, and N3) through low-energy nitrogen ion implantation mutagenesis. Compared with the parental strain, the phosphate-solubilizing capacity of P1, P2, and P3 was enhanced by 56.88%, 42.26%, and 32.15%, respectively, and that of N1, N2, and N3 was weakened by 47.53%, 35.27%, and 30.86%, respectively. Compared with the parental strain, the total amount of organic acids secreted significantly increased in the three positive mutant strains and decreased in the negative mutant strains; the pH of culture medium was significantly lower in the positive mutant strains and higher in the negative mutant strains. The capacity of phosphate-solubilizing fungus to secrete organic acids and reduce the growth-medium pH was closely related to its phosphate-solubilizing ability. The changes in the amount of organic acids secreted by mutants can alter their acidification and phosphate-solubilizing capacity. In conclusion, this study offers a theoretical basis and strain materials for the exploration and application of phosphate-solubilizing fungi.

A comprehensive synthesis unveils the mysteries of phosphate-solubilizing microbes

Phosphate-solubilizing microbes (PSMs) drive the biogeochemical cycling of phosphorus (P) and hold promise for sustainable agriculture. However, their global distribution, overall diversity and application potential remain unknown. Here, we present the first synthesis of their biogeography, diversity and utility, employing data from 399 papers published between 1981 and 2017, the results of a nationwide field survey in China consisting of 367 soil samples, and a genetic analysis of 12986 genome-sequenced prokaryotic strains. We show that at continental to global scales, the population density of PSMs in environmental samples is correlated with total P rather than pH. Remarkably, positive relationships exist between the population density of soil PSMs and available P, nitrate-nitrogen and dissolved organic carbon in soil, reflecting functional couplings between PSMs and microbes driving biogeochemical cycles of nitrogen and carbon. More than 2704 strains affiliated with at least nine archaeal, 88 fungal and 336 bacterial species were reported as PSMs. Only 2.59% of these strains have been tested for their efficiencies in improving crop growth or yield under field conditions, providing evidence that PSMs are more likely to exert positive effects on wheat growing in alkaline P-deficient soils. Our systematic genetic analysis reveals five promising PSM genera deserving much more attention.

Genetically modified bacteria for targeted phototherapy of tumor

Live attenuated bacteria have been used as target vehicles for genetic therapy of malignant carcinoma because they can be reprogrammed by following simple genetic rules and have the ability to target tumor hypoxic region. In this research, noninvasive Escherichia coli (E. Coli) is genetically modified through the plasmid transfection to afford E. Coli(p) with overexpressed human catalase for catalyzing H₂O₂ into O₂ in the tumor site. The produced O₂ is consequently converted to cytotoxic ¹O₂ under near-infrared (NIR) light irradiation for photodynamic therapy. Chlorin e6 (Ce6) is chosen as the photosensitizer for its excellent photodynamic ability, and polydopamine (pDA) is employed to encapsulate Ce6 for its good biosafety, photothermal ability, and adhesion capacity with bacteria. Dopamine polymerizes in the presence of Ce6 to form pDA/Ce6, and then E. Coli(p) is coated with pDA/Ce6 to afford the final E. Coli(p)/pDA/Ce6. The obtained system is intravenously administrated for selective accumulation and replication in the hypoxic tumor. NIR light irradiation is introduced to enable photothermal and O₂-enhanced photodynamic therapy. On account of complementary combination, the system exhibits efficient antitumor effect in vitro and in vivo. Thus, the integration of genetically modified bacteria with pDA/Ce6 presents a promising application potential for precise tumor inhibition.

Screening of potential bioremediation enzymes from hot spring bacteria using conventional plate assays and liquid chromatography - Tandem mass spectrometry (Lc-Ms/Ms)

The search for an eco-friendly, non-toxic, economical and efficient means of cleaning water through bioremediation is not only more favourable but critical to maintaining water quality globally especially in water-scarce countries. Thermophilic bacteria including Bacillus species are an important source of novel enzymes for biotechnology applications. In this study, 56 bacterial isolates which were cultured from five hot springs in South Africa were identified predominantly as Bacillus sp. or Bacillus-related spp by 16S rDNA gene sequencing. These isolates were screened for potentially useful enzymes for water bioremediation. Using conventional agar plate assays, 56% (n = 43), 68% (n = 38) and 16% (n = 31) were positive for amylase, protease and bromothymol blue decolorisation respectively. In liquid starch culture, three amylase-positive isolates differentially degraded starch by 34% (isolate 20S) to 98% (isolate 9T). Phenol degradation revealed that five out of thirty reduced phenol up to 42% by colorimetric assay. A thermophilic strain of Anoxybacillus rupiensis 19S (optimal growth temperature of 50 °C), which degraded starch, protein and phenol, was selected for further analysis by tandem LC-MS/MS. This newer technique identified potential enzymes for water bioremediation relating to pollutants from the food industry (amylase, proteases), polyaromatic hydrocarbons and dye pollutants (catalase peroxidase, superoxide dismutase, azoreductase, quinone oxidoreductase), antibiotic residues (ribonucleases), solubilisation of phosphates (inorganic pyrophosphatase) and reduction of chromate and lead. In addition, potential enzymes for biomonitoring of environmental pollutants were also identified. Specifically, dehydrogenases were found to decrease as the level of inorganic heavy metals and petroleum increased in soil samples. This study concludes that bacteria found in South African hot springs are a potential source of novel enzymes with tandem LC-MS/MS revealing substantially more information compared with conventional assays, which can be used for various applications of water bioremediation.