Mechanism of phosphate solubilization and antifungal activity of Streptomyces spp. isolated from wheat roots and rhizosphere and their application in improving plant growth

Abstract

The application of plant-growth-promoting rhizobacteria (PGPR) at field scale has been hindered by an inadequate understanding of the mechanisms that enhance plant growth, rhizosphere incompetence and the inability of bacterial strains to thrive in different soil types and environmental conditions. Actinobacteria with their sporulation, nutrient cycling, root colonization, bio-control and other plant-growth-promoting activities could be potential field bio-inoculants. We report the isolation of five rhizospheric and two root endophytic actinobacteria from Triticum aestivum (wheat) plants. The cultures exhibited plant-growth-promoting activities, namely phosphate solubilization (1916 mg l "1 ), phytase (0.68 U ml "1 ), chitinase (6.2 U ml ) was estimated in the culture supernatant of the highest phosphate solublizer, Streptomyces mhcr0816. The mechanism of malate overproduction was studied by gene expression and assays of key glyoxalate cycle enzymes -isocitrate dehydrogenase (IDH), isocitrate lyase (ICL) and malate synthase (MS). The significant increase in gene expression (ICL fourfold, MS sixfold) and enzyme activity (ICL fourfold, MS tenfold) of ICL and MS during stationary phase resulted in malate production as indicated by lowered pH (2.9) and HPLC analysis (retention time 13.1 min). Similarly, the secondary metabolites for chitinaseindependent biocontrol activity of Streptomyces mhcr0817, as identified by GC-MS and 1 H-NMR spectra, were isoforms of pyrrole derivatives. The inoculation of actinobacterial isolate mhce0811 in T. aestivum (wheat) significantly improved plant growth, biomass (33 %) and mineral (Fe, Mn, P) content in non-axenic conditions. Thus the actinobacterial isolates reported here were efficient PGPR possessing significant antifungal activity and may have potential field applications.

The Role of Soil Beneficial Bacteria in Wheat Production: A Review

“…Plant growth promotion can be achieved through solubilization of inorganic phosphates by these organic acids. de Werra et al showed that this happens with not only gluconate but also malate [42,43]. These results were consistent with earlier report on the P and Zn solubilizing properties of Acinetobacter sp.…”

“…Inoculation of efficient plant-growth-promoting actinobacterial Streptomyces species significantly improved the Fe, Mn and P content of wheat plants when compared with an uninoculated control [43,105]. Yasin et al investigated the effects of selenate fertilization and bacterial inoculation on Se uptake and plant growth [122].…”

“…Trials with rhizosphere-associated plant growth-promoting N 2 -fixing and P-solubilising Bacillus and other species indicated yield increases in many crops such as wheat [43,51,170,171]. In wheat, several rhizobacteria have been reported as improving grain yield, grain protein concentration or both [3,135,140,164,172].…”

PROFILING OF ANTI-FUNGAL ACTIVITY OF Trichoderma virens 159C INVOLVED IN BIOCONTROL ASSAY OF Ganoderma boninense

“…were implicated in anti-fungal activities by Jog et al (2014), where studies showed that Streptomyces strain that inhibits the growth of fungal pathogens produces this low molecular mass compound. However, compare to the GC-MSD profile of the Streptomyces strain in Jog et al (2014), the level of detection for pyrrolo (1, 2a) pyrazine, 1,4-dione hexahydro-3-(2 methylpropyl) is higher compared to T. virens 159c. Another compound known as dl-mevalonic acid lactone was identified in fraction 4.…”

Actinobactérias de biomas brasileiros: biodiversidade e potencial de uso na agricultura

“…Esses mecanismos de ação posicionam as Actinobactérias entre o grupo das Rizobactérias Promotoras do Crescimento em Plantas (RPCPs), mais importantes da rizosfera se destacando por estimular o crescimento vegetal e diminuir a invasão de microrganismos fitopatógenos nas plantas com as quais se associam (Beneduzi et al 2013). Dentre os mecanismos indiretos que podem exercer as Actinobactérias para o controle de microrganismos fitopatógenos, além da indução de resistência, encontra-se a solubilização de fósforo, principalmente associado à produção de ácidos orgânicos, como os ácidos cítrico, glucônico, láctico, málico e oxálico (Chen et al, 2006;Jog et al, 2014). A liberação desses ácidos já foi descrito para alguns gêneros de Actinobactéria, como é o caso de Streptomyces em solos com deficiência de fósforo em cultivos de trigo (Hamdali et al, 2008).…”