Effects of heavy metals on plant-associated rhizobacteria: Comparison of endophytic and non-endophytic strains of Azospirillum brasilense

Phytoextraction of soil cadmium and zinc by microbes-inoculated Indian mustard (Brassica juncea)

“…The substantial increase in bioavailabilty of Zn and Cd in response to bacterial and fungal inoculation, as observed in the present study, underlines the role of rhizospheric microbes in the synthesis of siderophores and chelators to solubilize and sequester metals from soil (Gadd 2004;Braud et al 2007). Microbial inoculation has also been observed to produce several organic acids and phytochelatins ensuring easy availability of metals to plants (Kamnev et al 2005), which in turn brings down the pH of soil towards acidic nature and thereby enhances metal bioavailability (Kunito et al 1998). Besides, the microbial inoculation is noticed to protect the plant against the toxic effects of heavy metals and other abiotic stresses (Belimov et al 2005).…”

New advances in plant growth-promoting rhizobacteria for bioremediation

“…The best known iPGPR are rhizobia, but they are restricted to nodules in leguminous plants (Sriprang et al, 2003). Kamnev et al (2005) studied a wild-type strain Sp245 of rhizobacterium Azospirillum brasilense, which has been proven to be capable of colonizing both interior and exterior of the plant root (i.e., a facultative endophyte), while other strains can colonize the root surface only. They compared the responses of Sp245 and other strains to several heavy metals (Co 2+ , Cu 2+ and Zn 2+ ).…”

Role of soil rhizobacteria in phytoremediation of heavy metal contaminated soils

“…It has been well documented that the biosynthesis of auxins with their excretion into soil makes a major contribution to the bacterial plantgrowth-promoting effect (Lambrecht et al, 2000;Kamnev, 2003;Steenhoudt and Vanderleyden, 2000). It has been found that Cu 2+ and Cd 2+ significantly suppressed the production of IAA (auxin) by nonendophytic and facultatively endophytic strains of A. brasilense (Sp7 and Sp245, respectively), which can directly affect the plant-growth-stimulating efficiency of associative plant-bacterial symbioses in heavymetal-polluted soils (Kamnev et al, 2005). Kamnev et al(2005) similarly discovered that both Cu 2+ and Cd 2+ ions significantly decreased the level of IAA production for strain Sp7, whereas the bacterial growth rate was virtually not affected.…”

“…It has been found that Cu 2+ and Cd 2+ significantly suppressed the production of IAA (auxin) by nonendophytic and facultatively endophytic strains of A. brasilense (Sp7 and Sp245, respectively), which can directly affect the plant-growth-stimulating efficiency of associative plant-bacterial symbioses in heavymetal-polluted soils (Kamnev et al, 2005). Kamnev et al(2005) similarly discovered that both Cu 2+ and Cd 2+ ions significantly decreased the level of IAA production for strain Sp7, whereas the bacterial growth rate was virtually not affected. In addition, some plant growth-promoting bacteria i.e., free-living soil bacteria that are involved in a beneficial association with plants, contain the enzyme ACC deaminase (Glick, 1995;Glick et al, 1995;Jacobson et al, 1994), which can cleave the plant ethylene precursor ACC and lower the level of ethylene in a developing or stressed plant.…”