Effect of Cultivation Conditions on Poly(3-hydroxybutyrate) Synthesis by Nodule Bacteria Rhizobium phaseoli

Abstract

The synthesis of poly(3-hydroxybutyric acid) (PHB) in nodule bacteria Rhizobium phaseoli grown in submerged culture was studied. The Law method for the determination of PHB was modified, which made it possible to isolate the polymer and to carry out its quantitative assessment directly in the biomass. Only S forms of R. phaseoli cells could synthesize PHB. Its accumulation was more active on carbon-rich medium (by ~50%), and the polymer granules were more clearly visible. The PHB synthesis increased with a decrease in aeration, and the maximum content was reached after 35−40 h of growth. The effect of the oxidative stress caused by t-butyl hydroperoxide and benzyl viologen on the growth of PHB-synthesizing bacteria was studied. Both compounds negatively affected bacterial growth. The growth was reactivated only in PHB-synthesizing S forms. We can conclude that PHB is a protector for nodule bacteria under the conditions of oxidative stress. The maximal PHB content in R. phaseoli cells reached 54% of the dry cell weight, which exceeded the values previously described for rhizobia. This value is close to those reported for the bacterial strains producing the polymer and used in biotechnology. We can conclude that rhizobia grown in the submerged culture can be potential producers of PHB and other polyhydroxyalkanoates.