Potential growth-promoting metabolites were assayedin vitrofor each of these strains, and data examined for correlates with growth enhancement. The metabolites evaluated were (i)
phosphate solubilizing agents, (ii) siderophores capable of converting ferric iron to soluble forms, and (iii) indole-3-acetic acid (IAA)
and auxin analogues. Phosphate solubilizing agents can stimulate
plant growth where phosphates are limiting, especially in acid soils
in which phosphorus is rapidly immobilized after addition to the
soil as a soluble fertilizer becoming unavailable for assimilation
by plants