Isolation and characterization of halotolerant phosphate-solubilizing microorganisms from saline soils

Abstract

Halotolerant phosphate-solubilizing microorganisms (PSMs) capable of producing plant-growth-promoting traits were grown on salt medium containing Ca 3 (PO 4 ) 2 or egg yolk. The number of colonies on plates with Ca 3 (PO 4 ) 2 was higher than that on plates with egg yolk. Further, a total of 42 PSM isolates were purified. The majority were Bacillus spp., while one Providencia rettgeri strain was confirmed, for the first time, as a PSM. All PSMs had a phosphate-solubilizing index (PSI) between 1.1 and 2.58 and a strong capacity for dissolving calcium phosphate between 2.25 and 442 mg•L −1 . In contrast, these PSMs were less effective when dissolving aluminum phosphate, ferric phosphate and lecithin. Isolates were also tested for growth-promoting substances. The results showed that all isolates were able to secrete indole-3-acetic acid in amounts ranging from 2.7 to 31.8 mg•L −1 and exopolysaccharide within the range 74.3 and 225.7 mg•L −1 . Only 12 siderophore-producing strains with siderophore units of 1.9-42.1% were detected. Among them, ten isolates with solubilization rates greater than 200 mg•L −1 and relatively high NaCl tolerance (1.5 M) were classified as candidate PSMs. Eight different organic acids with different contents were detected in the culture filtrates, and propionic and oxalic acids have been proposed as the main mechanisms for solubilization. The ten isolates have the potential for use as bioinoculants to protect plants in saline environments.

Effect of Plant Growth Promoting Bacteria on the Growth of Wheat Seedlings Subjected to Phosphate Starvation

“…Phosphate-solubilizing microorganisms are a group of PGPB known to dissolve both, inorganic and organic P and to maintain soil nutrient levels [9]. Phosphate-solubilizing microorganisms are classified into P-solubilizing bacteria (PSB) and P-mineralizing bacteria (PMB) depending on the P sources utilized and the mechanisms leading to P availability for the plant; and P solubilization and mineralization activity could coexist in the same bacterial strain [17,18]. The inoculation of soil with microorganisms able to mobilize soil P through solubilization or mineralization, respectively, represents a promising strategy for the improvement of plant growth in soils with low Pi availability [19,20].…”

“…The main mechanism of microbial Pi solubilization is via the production of mineral-dissolving compounds, such as organic acids, siderophores, protons, hydroxyl ions and CO 2 [5,21]. Organic acids such as propionic and oxalic acid and their carboxyl and hydroxyl ions chelate cations and/or reduce the pH to release Pi [17,22]. Jiang et al [17] identified potential PSMs from saline soil and proposed that organic acid production was the main mechanism for Pi solubilization.…”

“…Organic acids such as propionic and oxalic acid and their carboxyl and hydroxyl ions chelate cations and/or reduce the pH to release Pi [17,22]. Jiang et al [17] identified potential PSMs from saline soil and proposed that organic acid production was the main mechanism for Pi solubilization. An alternative mechanism to organic acid production for solubilization of mineral P is the release of H + to the outer surface in exchange for cation uptake or with the help of H + translocating ATPase [5,21].…”

Harnessing Soil Microbes to Improve Plant Phosphate Efficiency in Cropping Systems

“…Each of these methods increases the levels of P i in the soil solution [141,142]. Soil bacteria can also solubilize inorganic sources of P by releasing inorganic acids, protons, hydroxyl ions, siderophores, and CO 2 [1,[143][144][145].…”

Improvement in Soil Characteristics of Sandy Loam Soil and Grain Quality of Spring Maize by Using Phosphorus Solublizing Bacteria

“…Moreover, phosphatases (e.g., acid and alkaline phosphatases) released from the cell (exo-enzymes) use organic phosphorus as a substrate and transform into inorganic forms of phosphorus [13]. However, negative or positive activities of microorganisms have direct or indirect effects on the soil health [14]. Rhizospheric microorganisms improve the soil quality by mediating the soil processes viz.…”