Utilization of the siderophores FOB and pseudobactin by rhizosphere microorganisms of cotton plants

Abstract

The hydroxamate siderophores ferrioxamine B (FOB) and the pseudobactin siderophores st3 (PSB_st3) and 7NSK₂ (PSB_7nsk2) were evaluated as iron (Fe) sources to cotton (Gossypium herbeceum) rhizosphere bacteria. About 13% of the total bacterial CFUs were able to utilize FeFOB as the sole Fe source in an Fe‐deficient medium, as compared to 1.6 and 2.6% being able to utilize the chelated Fe supplied as Fe‐pseudobactins St3 and 7NSK₂, respectively. Cotton plants grown in soil amended with ⁵⁵Fe‐EDDHA had about ten times more Fe in their leaves than when supplied with ⁵⁵Fe‐PSB_st3. In a treatment in which the cells of strain 3 (St3) were added to the soil, about twice as much radioactivity was associated with the roots (on a gram fresh weight basis) of plants irrigated with PSB_st3 than in the non‐inoculated control treatment. These data suggest that pseudobactin is intrisincally a less available source of Fe to microbes than FOB and that the composition of the bacterial population of the rhizosphere may play an important role in transport and mobilization of Fe in this environment.