Stress-responsive indole-3-acetic acid biosynthesis by Azospirillum brasilense SM and its ability to modulate plant growth

Plant growth promotion by Azospirillum brasilense SM has been attributed to its indole-3-acetic acid (IAA) production. Analysis of IAA biosynthesis by this strain under nutrient stresses, likely environmental fluctuations and long-term batch cultures suggested that they significantly influenced this function, with some conditions (fluctuations in temperature) triggering IAA accumulation. In long-term batch cultures (of 30 days), the bacterial population was maintained at a specific cell density and produced IAA even after a sharp decline in population size, albeit fluctuations were observed in both the parameters. Long-term bacterial cultures under nitrogen starvation showed the same trend in cell viability; however, a continuous increase in IAA accumulation was seen over time. This study has shown that A. brasilense strain SM has the potential to be a competent rhizospheric bacterium as it can beneficially influence the growth of sorghum. Further, it also has the ability to promote the growth of a number of other plants like mung bean, maize, and wheat. The benefit of this characteristic of strain SM can be directly accrued to a range of plants with which it may associate so as to improve their yield.