Fourier Transform Infrared Spectroscopic Analysis of Poly-3-Hydroxybutyrate Accumulation by Azospirillum brasilense Cells at Various Cultivation Periods and Ammonium Concentrations in the Culture Medium
Many bacteria, in response to unfavourable environmental conditions, can synthesise polyesters of the polyhydroxyalkanoate (PHA) class. These biopolymers, accumulating intracellularly in the form of granules, help the bacteria to cope with negative environments and are utilised as reserve sources of carbon and energy. Rhizobacteria of the species Azospirillum brasilense synthesise a single type of PHA, poly-3-hydroxybutyrate (PHB), in response to stress factors. Knowledge of the principles and conditions of PHB synthesis is of importance both for understanding the subsistence of azospirilla in their natural habitats and for their use as biofertilisers, to preserve their viability. In this work, Fourier transform infrared (FTIR) spectroscopy was used to study PHB accumulation by cells of Azospirillum brasilense strains Sp7 и Sp245 during growth of the bacteria for 6 days in standard malate salt medium containing various concentrations of ammonium chloride (0.05, 0.10 and 0.21 g/l). Comparative analysis of FTIR spectra of the bacterial biomass samples showed that, at suboptimal initial concentrations of bound nitrogen in the medium, PHB accumulation after 1 to 6 days of cultivation was more intensive in A. brasilense strain Sp7 than in strain Sp245. Maximum relative amounts of PHB were accumulated by biomass of A. brasilense Sp7 grown for 3 days at the initial NH4Cl concentration in the culture medium 0.10 g/l.
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