Phosphate-solubilising Microorganisms as Potential Biofertilizer: A Review

After the nitrogen phosphorus is the second most important plant nutrient to necessary for plant development and growth. The use of excess phosphate fertilizers potentially causes surface and ground water pollutions and soil fertility depletation and accumulation of phosphate in soil which is unavailable for plant. Biofertilizers play a very significant role in improving soil fertility by fixing atmospheric nitrogen, both, in association with plant roots and without it, solubilized insoluble soil phosphates and produces plant growth substances in the soil. There have been a number of reports on plant growth promotion by microorganisms that have the ability to solubilize inorganic and organic P from soil. There is a dynamic and complex relationship among the different forms of P involving soil, plant and microorganisms. Microorganisms can enhance the capacity of plants to acquire P from soil through various mechanisms. They are able to solubilize unavailable form of unsolubilized phosphate in available form. Purpose of this review is to focuses on the understanding of the mechanism of phosphate solubilisation their role of PSMs(phosphate solubilizing microorganisms) in crop production as biofertilizers.

Study of tolerance ability in phosphate solubilising microorganisms isolated from tea plantations soil of lower Darjeeling hills

Background Tea is an important plantation crop in India and world. Introduction of fertilisers and pesticides for better production polluted tea garden soils. Phosphates in agricultural soils are converted into soluble forms by phosphate solubilising microorganisms (PSMs). Consortium of PSM having high tolerance level is an attractive option for bioremediation of degraded tea plantation soils. This research initiative was to isolate PSM from tea plantation soil and detect their tolerance against pesticide, antibiotic and antifungal. Results Isolated consortia from organic and inorganic tea plantation soils of Darjeeling showing halo was considered for tolerance study. Phorate was most and Deltamethrin was the least tolerant pesticide for the isolated PSM consortia. So, Phorate may be considered as most used or most accumulated pesticide. Erythromycin was most and Ofloxacin was the least tolerant antibiotic while Fluconazole was most and Itraconazole was the least tolerant antifungal agent for the isolated PSM consortia. It was noted that there was no or partial inhibition of PSM growth by some pesticide, antibiotic and antifungal agents. In all the three tolerance studies it was observed that there is no relation between collection sites but in all the assays average inhibition zones were more in organic plantations than inorganic plantations. Conclusions Thus, it may be said that inorganic practice induces tolerance to microbes. So, other than cultural practice use of chemicals, micro-ecosystem and antibiosis exhibited by microbes do play a role in conferring tolerance.

PHOSPHATE SOLUBILIZING MICROORGANISM CONSORTIUM OF VIRGIN TIGER HILL FOREST SOIL SHOWS HIGH LEVEL TOLERANCE TO PESTICIDE, ANTIBIOTIC, ANTIFUNGAL AND HEAVY METALS

Tiger Hill, a notified reserve forest is the highest point around Darjeeling town in Eastern Himalayan Hotspot. Soil nutrition of this forest area depends on nutrient recycling where phosphate solubilising microorganisms (PSM) has crucial role to play as it solubilises insoluble phosphorus salt to soluble forms. But, with rise in use of toxic chemicals these microbes are at threat. This research initiative explores isolation of PSM from Tiger hill forest soil to detect pesticide, antibiotic, antifungal and heavy metal tolerance. Soil sample from tiger hill has moisture (18.55%), pH (3.87), organic carbon (1.187%), total Nitrogen (1.02%) and Phosphorus in P2O5 form (10ppm). Isolation and screening of PSM were conducted on Pikovskaya’s agar medium. In vitro tolerance assay was performed to detect degree of tolerance in isolated PSM-consortium (PSMC). Pesticides like Fipronil, Thiomethoxame, Emamectin benzoate, Deltamethrin, Flubendiamide, Spiromesifen, Fenazaquin and Phorate exhibited complete to high degree of tolerance. PSMC was fully tolerant to antibiotic like Augmentin, Erythromycin, Chloramphenicol, Ofloxacin, Co-Trimoxazole, Cefotaxime; antifungal Itraconazole and Fluconazole. Mild tolerance towards heavy metal salts like As2O3, SnCl2, CdCl2, CuCl2, CdSO4 and CuSO4 were detected. Synergestic effect of cells present in the isolated PSMC may also be an added advantageous property to tolerate pesticides, antibiotic, antifungal and heavy metal salts.