Poly-3-hydroxybutyrate synthesis by different Azospirillum brasilense strains under varying nitrogen deficiency: A comparative in-situ FTIR spectroscopic analysis

Monitoring of poly-3-hydroxybutyrate accumulation and changes in its relative contents in biomass of the plant-growth-promoting bacteria Azospirillum brasilense (strains Sp7, Cd and Sp245) was performed during aerobic cultivation for 1 to 8 days at various initial concentrations of bound nitrogen (0.1 to 0.5 g∙L–1 NH4Cl) in the culture medium using in-situ transmission FTIR spectroscopy. A methodology has been proposed based on calculating band areas in FTIR spectra (instead of band intensities commonly used earlier) for determining relative contents of PHB in dry bacterial biomass, using the ester ν(C=O) band as a PHB marker (in the region 1750–1720 cm−1) and amide II band of cellular proteins (at ca. 1540 cm−1). Differences in PHB accumulation levels and their changes in the course of cultivation under various trophic stress for the three strains are discussed in relation to their different ecological niches which they occupy in the rhizosphere.