A Method for Detection of Pseudobactin, the Siderophore Produced by a Plant-Growth-Promoting Pseudomonas Strain, in the Barley Rhizosphere

Abstract

Detection in the rhizosphere of the siderophore produced by an inoculated microorganism is critical to determining the role of microbial iron chelators on plant growth promotion. We previously reported the development of monoclonal antibodies (MAb) to ferric pseudobactin, the siderophore of plant-growthpromoting Pseudomonas strain B10. One of these MAb reacted less strongly to pseudobactin than to ferric pseudobactin. The MAb reacted to Al(III), Cr(III), Cu(II), and Mn(II) complexes of pseudobactin at a level similar to the level at which it reacted to ferric pseudobactin and reacted less to the Zn(ll) complex, but these metals would make up only a small fraction of chelated pseudobactin in soil on the basis of relative abundance of metals and relative binding constants. Fourteen-day-old barley plants grown in limed and autoclaved soil were inoculated with 109 CFU of Pseudomonas strain Sml-3, a strain of Pseudomonas B10 Rif Nal' selected for enhanced colonization, and sampled 3 days later. Extraction and analysis of the roots and surrounding soil using the MAb in an immunoassay indicated a concentration of 3.5 x 1010 mol of ferric pseudobactin g-1 (wet weight). This is the first direct measurement of a pseudobactin siderophore in soil or rhizosphere samples.

Iron Stress and Pyoverdin Production by a Fluorescent Pseudomonad in the Rhizosphere of White Lupine (Lupinus albus L.) and Barley (Hordeum vulgare L.)

“…The estimated pyoverdin production by P. fluorescens Pf-5 (pvd-inaZ) in the rhizosphere (0.5 to 0.8 nmol g [dry weight] of root Ϫ1 [ Table 2]) is in the same range as in other studies on bacterial siderophores in the rhizosphere (5,20,23) but very low compared to the pyoverdin production measured in vitro under extreme Fe stress (18). The results of the present study suggest that pyoverdin production by a given strain may to be estimated by ice nucleation in the rhizosphere and the regression between ice nucleation and pyoverdin concentration obtained in vitro.…”

“…Using pyoverdin promoter-driven ice nucleation in combination with the filter paper technique provides a novel method to assess iron stress in the rhizosphere. In contrast to extraction of siderophores from entire root systems (5,20), our method allows nondestructive sampling of the same root system over time in different root zones and can therefore increase our knowledge of Fe stress and siderophore production on a microsite level. However, the filter paper lifts only cells that are easily removed from the root surface.…”

Native soil bacteria isolates in Mexico exhibit a promising antagonistic effect against Fusarium oxysporum f. sp. radicis‐lycopersici

“…To avoid and/or reduce FCRRT disease progression, plant growth promoting rhizobacteria (PGPR) populations in the soil may induce plant growth by assisting plant nutrition, either by solubilizing phosphorous from the soil and making it available to the plant, or by increasing the iron uptake via siderophores . Bacteria can also produce phytohormones such as IAA that can directly induce plant roots to develop faster or with a different architecture (i.e., lateral root patterning), leading to a larger root volume which is more resistant to fungal attack .…”

A Biological Sensor for Iron Available to Bacteria in Their Habitats on Plant Surfaces

“…(5,22) and ferric siderophores produced by members of diverse genera of bacteria and fungi (16). Pseudobactin, a pyoverdine produced by P. fluorescens B1O, was detected recently in a rhizosphere at a concentration of 3.5 x 10-' M by an immunoassay in which specific monoclonal antibodies were used (4). Because the transcriptional activity of the pvd promoter is proportional to pyoverdine production in Pseudomonas spp.…”