Poly(3-hydroxybutyrate) production in an integrated electromicrobial setup: Investigation under stress-inducing conditions

Abstract

Poly(3-hydroxybutyrate) (PHB), a biodegradable polymer, can be produced by different microorganisms. The PHB belongs to the family of polyhydroxyalkanoate (PHA) that mostly accumulates as a granule in the cytoplasm of microorganisms to store carbon and energy. In this study, we established an integrated one-pot electromicrobial setup in which carbon dioxide is reduced to formate electrochemically, followed by sequential microbial conversion into PHB, using the two model strains, Methylobacterium extorquens AM1 and Cupriavidus necator H16. This setup allows to investigate the influence of different stress conditions, such as coexisting electrolysis, relatively high salinity, nutrient limitation, and starvation, on the production of PHB. The overall PHB production efficiency was analyzed in reasonably short reaction cycles typically as short as 8 h. As a result, the PHB formation was detected with C. necator H16 as a biocatalyst only when the electrolysis was operated in the same solution. The specificity of the source of PHB production is discussed, such as salinity, electricity, concurrent hydrogen production, and the possible involvement of reactive oxygen species (ROS).

From CO2 to Bioplastic – Coupling the Electrochemical CO2 Reduction with a Microbial Product Generation by Drop‐in Electrolysis

“…[23] Furthermore, it has to be mentioned that contrary to the results reported by Al Rowaihi et al, within this study the conversion of formate to PHB could also be shown without the application of electrolysis and the consequently assumed presence of reactive oxygen species. [23] However, when evaluating the PHB concentration, the starting biomass concentration and substrate availability also have to be taken into account. It is assumed that with a higher amount of resting cells and constant substrate feed significantly higher product concentrations are feasible.…”

“…[12,19] When combining electroreduction to form intermediates with bioproduction, different approaches are feasible (Scheme 1). One promising option are secondary microbial electrochemical technologies (MET), locating the initial electrochemical reduction in-situ to the microbial biosynthesis, [20,21] as it has already been shown for formate [22,23] and H 2 . [24] However, scale-up issues and non-ideal conditions of the electrochemical set up pose major challenges for establishing in-situ production with direct bioconversion in industrial scale.…”

Changes in Cell Size and Shape During 50,000 Generations of Experimental Evolution with Escherichia coli

“…14). These dots are reminiscent of the polyhydroxyalkanoate storage granules that some bacterial species produce under conditions where their growth is unbalanced (56,57) or when cells are otherwise stressed (58,59). It is also possible that these dots comprise the nucleoid or some other remnant of a leaky cytoplasm.…”

Switching from petro-plastics to microbial polyhydroxyalkanoates (PHA): the biotechnological escape route of choice out of the plastic predicament?

“…More recently, the scientific community revealed the significant protective role of PHA against a number of stress factors, which are harmful or even lethal for PHA-free microbial cells (53). In this context, it was demonstrated that presence of PHA exerts a protective effect against the impact of elevated temperature (54), attenuates the destructive impact of excessive UV-irradiation by scattering light (55), helps to repair damage caused by repeated freezing-and-thawing cycles (56) or sudden osmotic imbalances (57), and elevates the burdens caused by chemical oxidants in general (58), and by sudden generation of reactive oxygen species (ROS) in particular (59). Regarding elevated salt concentrations (hyperosmotic conditions), presence of PHA granules in living microbes turned out to support the cells to better survive the harmful effects of osmotic up-shock; this also clarifies why PHA granules are found in so many haloarchaeal species isolated up to date from extremely saline ecological niches (57).…”