Biosynthesis of PHB from a new isolated Bacillus megaterium strain: Outlook on future developments with endospore forming bacteria

Diverse Bacillus strains are known as producers of polyhydroxyalkanoates (PHAs) under nutrient-limiting conditions. However, these limiting conditions have the same nutritional characteristics that stimulate spore generation in Gram-positive microorganisms. In the present work, a new isolated Bacillus megaterium strain was characterized based on 16S rRNA gene sequences (1,411 bp) and studied in terms of its ability for producing polyhydroxybutyrate (PHB) by implementing different fermentation configurations on formulated media. The isolated strain was able to produce PHB up to 59 and 60% of its dry cell weight during bioreactor experiments employing glucose and glycerol as carbon source, respectively. The produced biopolymer was characterized and identified by using carbon-13 nuclear magnetic resonance (∨13C-NMR) and Fourier transform infrared (FTIR) techniques. In spite of the sporulation phenomenon existing in Bacillus strains, obtained results demonstrate that the new isolated strain has the potential of accumulating high levels of intracellular PHB. Supported by these experimental results and by those reported by other authors, the last section of this paper gives an outlook of future research topics on PHB and polyhydroxyalkanoate (PHA) copolymers production by Gram-positive bacteria. The importance of combining bioprocessing/biorefinering concepts with bioreactor optimization approaches is stressed and analyzed based on current PHAs research trends.