Establishment of Azotobacter on plant roots: chemotactic response, development and analysis of root exudates of cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.)

Abstract

Biofertilizers contribute in N(2) fixation, P solubilization, phytohormone production and thus enhance plant growth. Beneficial plant-microbe interactions and the stability and effectiveness of biofertilizer depend upon the establishment of bacterial strains in the rhizosphere of the plant. This interaction depends upon many factors, one of them being plant exudates. Root exudates are composed of small organic molecules like carbonic acids, amino acids or sugars etc., which are released into the soil and bacteria can be attracted towards these exudates due to chemotaxis. The chemotactic behaviour of Azotobacter strains was studied using cotton (Desi HD 123 and American H 1098) and wheat (WH 711) seedlings and the root exudates of these two plants were chemically characterized. Analysis of the root exudates revealed the presence of sugars and simple polysaccharides (glucose), amino acids (glutamate, lysine) and organic acids (citric acid, succinic acid, maleic acid, malonic acid). Differences between cotton cultivars in root exudates were observed which influenced chemotactic response in Azotobacter. These results indicate colonization with rhizobacteria which implies that optimal symbionts, on the sides of both plant cultivar and bioinoculant bacteria can lead to better plant growth under cultivation conditions.

Influence of plant-growth-promoting bacteria on germination, growth and nutrients’ uptake ofOnobrychis sativaL. under drought stress

“…ACC-deaminase enzyme bacteria are able to use ACC as the only source of nitrogen and, by reducing ethylene concentration and preventing the accumulation of this material under drought stress, can control the negative effects on root growth and, therefore, protect it (Glick et al 2007). Cotton and wheat seeds inoculated with growth promoters increased shoot and root height (Narula et al 2005;Kumar et al 2007). An increased height of Z. mays.…”

Azotobacter-enriched organic manures to increase nitrogen fixation and crop productivity

“…However, the use of selected N 2 -fixing bacteria and arbuscular mycorrhizal fungi alone or in combination have shown slight to moderate benefits in increasing crop productivity and a modest capability to reduce the use of mineral fertilizers (El-Sirafy et al, 2006;Aseri et al, 2008;Gupta and Aggarwal, 2008;Jahan et al, 2013;Ansari et al, 2015). The greater benefits to crop growth seem to occur when an inoculant containing N 2 -fixing bacteria and other beneficial microorganisms is mixed with organic substrates (Nuruzzaman et al, 2003;Kumar et al, 2007;Singh et al, 2013;Kumar et al, 2014). Kumar et al (2015) showed that using a biofertilizer in the form of a super granule, containing Azotobacter chroococcum and Bacillus subtilis entrapped in an organic matrix [consisting of cow dung, rice bran, dried powder of neem leaves, and clay soil in 1:1:1:1 ratio and 25% (w/w) saresh (plant gum of Acacia sp.…”

Gene Deletions Resulting in Increased Nitrogen Release by Azotobacter vinelandii: Application of a Novel Nitrogen Biosensor

“…The development of biological approaches to improve biofertilizers represents a unique opportunity for future generations to lower the potential economic costs and environmental impacts of current fossil-fuel-dependent industrial methods for the production of ammonia-derived fertilizers (4)(5)(6). Various laboratories have been investigating the potential of Azotobacter species to provide nitrogen to specific crops for many years, with various degrees of success (5)(6)(7)(8)(9)(10)(11).…”

“…Various laboratories have been investigating the potential of Azotobacter species to provide nitrogen to specific crops for many years, with various degrees of success (5)(6)(7)(8)(9)(10)(11). Although many nitrogen-fixing bacteria produce nitrogen in environments requiring very low oxygen, Azotobacter vinelandii has evolved the capability of fixing nitrogen as a free-living aerobe, despite the fact that nitrogenase is inherently sensitive to oxygen.…”

“…Biological assimilation of nutrients in addition to timed-release of nitrogen compounds would mitigate issues associated with agricultural residue runoff from excessive application of industrial fertilizers, leading to eutrophication of nearby water supplies and streams. Both higher land plants and microalgae are known to produce extracellular carbon as a potential source of fixed carbon to support beneficial heterotrophs that make up part of the rhizosphere (5,(12)(13)(14)(15).…”