The alpine soil environments are characterized by a dramatic seasonal shift in physical and biochemical properties due to intermittent snow cover and fluctuating subfreezing temperatures in winter and intense desiceating sunshine punctuated by infrequent rains during summer. The bacteria, which are adapted to live in cold environments, are called as Psychrotrophs or cold tolerant bacteria. A number of such bacteria have been known from the Arctic region. Such temporal and climatic selection processes are bound to help in the evolution of a variety of living organisms that are highly adapted to changing extremities of weather. Since microorganisms are an important component of the soil and influence the soil health through their beneficial or detrimental activities, it is imperative to study the existence of cold adapted bacterial strains with beneficial traits in the soils of the subalpine regions for use a plant growth promoting bioinoculants.
The Indian Himalayas are a rich repository of cold adapted bacteria of agriculture importance. The North West Himalayan region of India comprises of several alpine and sub alpine tracts and is known to harbor a variety of useful bacteria. Several microbes promote plant growth by the solubilization of phosphates in the rhizosphere. Though plenty of work has been done the world over on the solubilization of phosphates, little information is available on the ability of bacteria to solubilize phosphate under suboptimal temperature conditions. The first report of phosphate solubilization at low temperature was made in the year 2003 and was observed phosphate solubilization by pseudomonas mutants under low temperature conditions. Reports were also there relating phosphate solubilizing and plant growth promoting activities by cold tolerant mutants of pseudomonas fluorescens.
The mountain aspect influence on the microbial diversity of fourteen cold tolerant phosphate solubilizing Pseudomonas and its effect on the phosphate solubilization at three different incubation temperatures. Another finding introduces Pantoea dispersa strain 1A is a gram negative rod-shaped, yellow pigmented bacterium isolated on nutrient agar plates incubated at 4°C. It is capable of growing at temperatures ranging from 4 to 40°C, but maximum growth is observed at 30°C. It is endowed with multiple plant growth promotion attributes such as phosphate solubilization, IAA production, siderophore production and HCN production which are expressed differentially at sub-optimal temperatures (15 and 4°C). Another novel finding by our group was Pseudomonas fragi CS11RH1 has been described as cold tolerant phosphate solubilizing bacteria isolated from the rhizosphre of garlic grown at a high altitude location (1800 above mean sea level) in Chamoli district (30024' N and 790 21'E) of the north western Indian himalayas. Pseudomonas fragi CS11RH1 isolated from a high altitude significantly increased the percent germination, rate of germination plant biomass and nutrient uptake of wheat seedlings. Plate based assays for screening of PSM showing activity at lower temperatures revealed that 69 bacteria solubilize phosphate at 4°C, solubilization efficiency varied from 25.8 to 375.4 and 31.7 to 456.5 at 4 and 10°C, respectively. Various species of Pseudomonas have been isolated from higher altitudes and sites experiencing low temperatures. An author reported nineteen efficient phosphates solubilizing fluorescent Pseudomonas from the cold desert of the Trans Himalayas were temperature plummet to -40ºC during winters, decrease in pH during phosphate solubilization indicated production of organic acids by the bacterial strains under desiccation condition, moreover even belonged to the same phylogenetic group, they exhibited distinctive tolerance to stress parameters and in solubilizing TCP under stress conditions. On the other hand Exiguobacterium acetylicum strain 1P isolated from high altitude soil in the N.W. Indian Himalayas has ability to produce siderophore and found to inhibit the growth and development of Rhizoctonia solani, Sclerotium rolfsii, Phythium and Fusarium oxysporium. Exiguobacterium acetylicum strain 1P is isolated at 4°C and is able to grow at temperatures ranging from 4 to 40°C and possessed antagonistic properties it would be appropriate to call it "cold tolerant antagonistic bacterium".
Thus there is the great need to explore such agricultural important phosphate solubilizing microbes from such a extreme conditions and to explore the mechanism which support their PGPR properties to sustain even in cold stress.
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Research Fellow & Phd.scholar