New PHB-producing Bacillus Strain from Environmental Samples

Abstract

Many microorganisms are known to synthesize poly[(R)-3-hydroxybutyrate] (PHB) from renewable resources. This biocompatible and biodegradable biopolyester possesses similar properties to some of the conventional plastics such as polypropylene. However, PHB is not competitive with the polymers from the oil industry so far due to its high production costs. An aproach to overcome this problem is to discover new microorganisms with higher polymer productivity. Therefore, the main objectives of this chapter are focused on finding a new PHB-producing bacterium from environmental samples capable of growing in different salts conditions, and on characterizing the biopolymer produced. A bacterial isolation process was carried out with environmental samples of water and mud from different Bolivian salt lakes. One bacterium from the Uyuni salt lake fulfilled the selection conditions and was consequently used in an initial fermentation to generate biopolymer in order to identify and characterize it via Fourier transform infrared microscopy (FTIR), nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DS) analyses. Then, the microorganism was tested in different fed-batch fermentation processes to determine its PHB production potential, and to analyse the influence of salt content in the medium on both, the cell growth and the PHB production. The selected biopolymer synthetised in a conventional medium used for industrial biopolymer production was identified as PHB homopolymer. Surprisingly, it featured several fractions of different molecular masses and thermal properties unusual for PHB. The results of fermentation in the 3L-bioreactor showed a high specific growth rate. The highest polymer content ever reached for the genus Bacillus was up to 70% PHB of cell dry mass. The strain turned out to be appealing not only due to its growth and PHB accumulation kinetics under the cultivation conditions investigated, but also due to the thermal properties of the PHB produced. Also, the strain shows a high adaptability to media with high salt concentrations, constantly synthesizing PHB. The strain was taxonomically identified by molecular processes as the novel strain of Bacillus megaterium uyuni S29. It is deposited in the Spanish Type Culture Collection and its nucleotide sequence is deposited at GenBank. The tolerance to the salt, together with the production of biopolymer, makes this strain viable for its utilization in the biotechnological production of PHA as well as for other applications such as the treatment of salty wastewater