M. Sudhakara Reddy

Biosolubilization of poorly soluble rock phosphates by Aspergillus tubingensis and Aspergillus niger.

Three isolates of Aspergillus tubingensis and two isolates of Aspergillus niger isolated from rhizospheric soils were tested on solubilization of different rock phosphates. All the isolates of Aspergillus were capable of solubilizing all the natural rock phosphates. A. tubingensis (AT1) showed maximum percent solubilization in all the rock phosphates tested in this study when compared to other isolates. This isolate also showed highest phosphorus (P) solubilization when grown in the presence of 2% of rock phosphate. A. tubingensis (AT1) seems to be more efficient in solubilization of rock phosphates compared to other isolates reported elsewhere. This is the first report of rock phosphate solubilization by A. tubingensis and might provide an efficient large scale biosolubilization of rock phosphates intended for P fertilizer.

Strain improvement of Sporosarcina pasteurii for enhanced urease and calcite production

Phenotypic mutants of Sporosarcina pasteurii (previously known as Bacillus pasteurii) (MTCC 1761) were developed by UV irradiation to test their ability to enhance urease activity and calcite production. Among the mutants, Bp M-3 was found to be more efficient compared to other mutants and wild-type strain. It produced the highest urease activity and calcite production compared to other isolates. The production of extracellular polymeric substances and biofilm was also higher in this mutant than other isolates. Microbial sand plugging results showed the highest calcite precipitation by Bp M-3 mutant. Scanning electron micrography, energy-dispersive X-ray and X-ray diffraction analyses evidenced the direct involvement of bacteria in CaCO3 precipitation. This study suggests that calcite production by the mutant through biomineralization processes is highly effective and may provide a useful strategy as a sealing agent for filling the gaps or cracks and fissures in any construction structures.

ITS-RFLP and ITS sequence analysis of a foliar endophytic Phyllosticta from different tropical trees

Different isolates of a foliar endophytic species of Phyllosticta were isolated from different tropical tree species in India to examine genetic variation among the isolates. Internal transcribed spacer-restriction fragment length polymorphism (ITS-RFLP) analysis did not detect any variation among the isolates, suggesting that they all belong to the same species. Sequence data of the ITS region of ribosomal DNA (ITS1 and ITS2, including 5.8S rDNA) supported the identity of the present fungal isolates as P. capitalensis. These results show that P. capitalensis (teleomorph Guignardia endophyllicola?) is an ubiquitous foliar endophyte that can infect tree hosts from different families and habitats.

Effect of Carbon and Nitrogen Sources on Phosphate Solubilization by a Wild-Type Strain and UV-Induced Mutants of Aspergillus tubingensis

The mechanisms of action of phosphate solubilization were studied in the wild-type strain Aspergillus tubingensis and the phenotypic mutants derived from it. The P solubilization activities of these isolates were measured in liquid media using different carbon and nitrogen sources. All the mutants showed higher P solubilization compared to the wild type. Glucose and sucrose significantly promoted P solubilization compared to fructose, lactose, galactose, and xylose. Potassium nitrate significantly increased P solubilization compared to other nitrogen sources such as ammonium sulfate, ammonium nitrate, aspargine, and tryptophan. The P solubilization activity was strongly associated with the production of organic acids, especially succinic acid and acetic acid. The enzyme activities such as acid phosphatase and phytase also increased significantly in mutants compared to the wild type. These results suggested the role of these enzymes in P solubilization apart from the organic acid exudation and H+ pump in A. tubingensis.

Coinoculation efficacy of ectomycorrhizal fungi on Pinus patula seedlings in a nursery

Abstract The coinoculation efficacy of the ectomycorrhizal fungi Laccaria laccata and Thelephora terrestris on the growth and mycorrhizal development of Pinus patula seedlings was studied and compared to individual inoculation of these fungi in a nursery. The total number of mycorrhizas was higher in seedlings inoculated with the combined inoculum than with the individual inocula. The colonization by T. terrestris was higher than L. laccata when the seedlings were inoculated with the two fungi simultaneously. Coinoculation significantly increased the height and dry weight of the seedlings compared with individual inoculation, both in steam-sterilized and unsterilized soil.

Application of calcifying bacteria for remediation of stones and cultural heritages.

Since ages, architects and artists worldwide have focused on usage of durable stones as marble and limestone for construction of beautiful and magnificent historic monuments as European Cathedrals, Roman, and Greek temples, Taj Mahal etc. But survival of these irreplaceable cultural and historical assets is in question these days due to their degradation and deterioration caused by number of biotic and abiotic factors. These causative agents have affected not only the esthetic appearance of these structures, but also lead to deterioration of their strength and durability. The present review emphasizes about different causative agents leading to deterioration and application of microbially induced calcium carbonate precipitation as a novel and potential technology for dealing with these problems. The study also sheds light on benefits of microbial carbonate binders over the traditional agents and future directions.

Corrosion Prevention of Reinforced Concrete with Microbial Calcite Precipitation

The corrosion of steel and reinforcing bar in concrete structures is one the most common reasons for civil infrastructure failures, especially for structures located in coastal and marine environments. Microbially induced calcite precipitation (MICP) on concrete or mortar is an important area of research to enhance the durability of construction materials. The effectiveness of MICP in reducing reinforcement corrosion is investigated in this article. Reinforced concrete (RC) specimens were treated with the bacterial strain Bacillus sp. CT-5, isolated from the cement sample, and subjected to accelerated corrosion. The results showed that bacterial-treated RC specimens reduced the corrosion rate four times more than the control specimens. A considerable reduction in mass loss and increase in pullout strength is observed with MICP-treated specimens. Corn steep liquor, an industrial pollutant, was used as a nutrient source to grow the bacterial cells for MICP in cementitious structures. This is a step toward the development of microbial concrete that provides a greener and more ecofriendly option.

Role of phosphate-solubilizing bacteria in improving the soil fertility and crop productivity in organic farming

In the present study, two phosphate-solubilizing bacteria Pantoea cypripedii and Pseudomonas plecoglossicida isolated from an organic field were tested for their efficacy to solubilize rock phosphate (RP) and other plant growth-promoting activities such as nitrogen fixation and the production of indole acetic acid (IAA) and siderophores. Both of the bacteria effectively solubilized RP and released significant amount of phosphorous (up to 271 µg P ml–1) in the culture medium. These isolates produced IAA and siderophores and failed to fix nitrogen as determined by acetylene reduction. Two-year field study was conducted to test the efficacy of these bacteria on the growth and yield of maize and wheat crops grown in organic farm with and without RP. Field trials for both crops were conducted in a completely randomized block design consisting of six treatments and each treatment with triplicates. Significant increase in growth parameters, grain yield, total P uptake, and soil fertility in context of organic carbon, available P, total P, and enzyme activities were observed in inoculation treatments along with RP fertilization compared with control. This study suggested that P. cypripedii and P. plecoglossicida along with RP play an important role in improving crop productivity in organic farming.

Influence of arbuscular mycorrhizal fungi on the growth and nutrient status of bermudagrass grown in alkaline bauxite processing residue.

A nursery experiment was conducted to evaluate the potential role of arbuscular mycorrhizal (AM) fungi in encouraging the vegetation cover on bauxite residue (red mud) sites. An alkali tolerant bermudagrass (Cynodon dactylon) adapted to local conditions were grown in red mud with different amendments with and without AM fungi to assess mycorrhizal effects on plant growth, mineral nutrition, metal uptake and neutralization of bauxite residue. Inoculation of AM fungi significantly increased the plant growth, nutrient uptake and reduced Fe, Al accumulation in plant tissue and also improved the soil physico-chemical and biochemical properties. Gypsum and sludge amended treatments inoculated with AM fungi had maximum biomass, nutrient uptake and reduced accumulation of metals. The neutralization of red mud was significant in presence of AM fungi than control. The experiment provided evidence for the potential use of bermudagrass in combination with AM fungi for ecological restoration of bauxite residue sites.

Molecular characterization of Morchella species from the Western Himalayan region of India.

The molecular diversity of thirty-two different Morchella cultures/fruiting bodies, collected from the Western Himalayan region was studied in this investigation. Considerable taxonomic confusion exists regarding many species of Morchella. Although classical taxonomy is helpful in identification for many ascomycetes, morels exhibit considerable morphological diversity and there is disagreement in the identification of morel species. Phylogenetic analyses based on DNA sequences could help in sorting out morel taxonomy which is essential to better define the morel diversity. In this study, sequence analysis revealed that in the Western Himalayan region of India, both yellow (M. crassipes, M. spongiola) and black morels (M. elata, M. angusticeps, and M. gigas) were prominent along with two Verpa species. Phylogenetic analysis by maximum parsimony, maximum likelihood and Bayesian inference revealed two different clades and a clear distinction between yellow and black morels.