Production of poly(3-hydroxybutyrate) by Halomonas boliviensis in an air-lift reactor

Abstract

BackgroundMicrobial polyesters, also known as polyhydroxyalkanoates (PHAs), closely resemble physical and mechanical features of petroleum derived plastics. Recombinant Escherichia coli strains are being used in industrial production of PHAs in Stirred Tank Bioreactors (STRs). However, use of Air-Lift Reactors (ALRs) has been known to offer numerous technical operating options over STRs, and as such has been successfully implemented in many bioprocesses. Halomonas boliviensis is a halophilic bacterium that is known to assimilate various carbohydrates and convert them into a particular type of PHA known as poly(3-hydroxybutyrate) (PHB). Owing to this capability, it has been used to synthesize the polyester using hydrolysates of starch or wheat bran in stirred tank bioreactors.ResultsThis research article firstly describes the production of PHB in shake flasks by H. boliviensis using different combinations of carbohydrates and partially hydrolyzed starch as carbon sources. The highest PHB yields, between 56 and 61 % (wt.), were achieved when either starch hydrolysate or a mixture of glucose and xylose were used as carbon sources. The starch hydrolysate obtained in this study was then used as carbon source in an ALR. The largest amount of PHB, 41 % (wt.), was attained after 24 hrs of cultivation during which maltose in the hydrolysate was assimilated more rapidly than glucose during active cell growth; however, the rate of assimilation of both the carbohydrates was found to be similar during synthesis of PHB. An incomplete pentose phosphate pathway, which lacks 6-phosphogluconate dehydrogenase, was deduced from the genome sequence of this bacterium and may result in the characteristic assimilation of glucose and maltose by the cells.ConclusionsThis study showed that the production of PHB by H. boliviensis using cheap substrates such as starch hydrolysate in a simple production system involving an ALR is feasible. Both maltose and glucose in the hydrolysate induce cell growth and PHB synthesis; most likely the cells balance adequately CoA and NAD(P)H during the assimilation of these carbohydrates. The combination of cheap substrates, simple production systems and the use of non-strict sterile conditions by the halophile H. boliviensis are desirable traits for large scale production of PHB, and should lead to a competitive bioprocess.Electronic supplementary materialThe online version of this article (doi:10.1186/s40709-015-0031-6) contains supplementary material, which is available to authorized users.

Recent strategies for efficient production of polyhydroxyalkanoates by micro-organisms

“…Air‐Lift Reactors (ALRs), which can offer lots of technical options over Stirred‐Tank Reactors (STRs), has been successfully used for PHAs production, and leading to a competitive bioprocess (Rivera‐Terceros et al . ). Using multistage system composed of series of two or more continuous stirred‐tank reactors (CSTRs) considered to be more perfect as the present fermentation system (Amulya et al .…”

“…In some cases, PHAs weight content obtained from continuing cultivation gave much improved biomass and PHAs production compared to batch cultivation (Kanjanachumpol et al 2013). Air-Lift Reactors (ALRs), which can offer lots of technical options over Stirred-Tank Reactors (STRs), has been successfully used for PHAs production, and leading to a competitive bioprocess (Rivera-Terceros et al 2015). Using multistage system composed of series of two or more continuous stirred-tank reactors (CSTRs) considered to be more perfect as the present fermentation system (Amulya et al 2015;Marang et al 2015).…”

Current developments on polyhydroxyalkanoates synthesis by using halophiles as a promising cell factory

“…Additionally, SSF mode required less inoculum volume, single reaction vessel and moreover, saved 47% of the overall processing time. In 2015, Air-Lift Reactors (ALR) was successfully employed to produce 41% (wt) PHB from H. boliviensis by using starch hydrolysate and monosodium glutamate as the respective carbon and nitrogen source [93]. Although the obtained PHB content was lower compared to fed-batch reactors, ALR has the advantages of reduced construction and operational costs.…”

The composition analysis and preliminary cultivation optimization of a PHA-producing microbial consortium with xylose as a sole carbon source

“…On the other hand, xylose is nearly the most highest content in lignocellulose hydrolysates (Jian and Stahl, 2008;Pan et al, 2012), and is the second most abundant sugar in nature (Lopes et al, 2009); besides, it is half the price of glucose (Koller et al, 2010), thus researches on xylose utilization lay the foundation for the application of sugar mixture (hexose and pentose) (Rivera-Terceros et al, 2015), lignocellulose hydrolysates (Davis et al, 2013), etc., which will greatly reduce the cost of substrates. Recent studies (Ferreira et al, 2015;Meur et al, 2012) proved that xylose could be a potential and promising substrate to produce PHA.…”