Carbon Sources for Polyhydroxyalkanoates and an Integrated Biorefinery

Abstract

Polyhydroxyalkanoates (PHAs) are a group of bioplastics that have a wide range of applications. Extensive progress has been made in our understanding of PHAs’ biosynthesis, and currently, it is possible to engineer bacterial strains to produce PHAs with desired properties. The substrates for the fermentative production of PHAs are primarily derived from food-based carbon sources, raising concerns over the sustainability of their production in terms of their impact on food prices. This paper gives an overview of the current carbon sources used for PHA production and the methods used to transform these sources into fermentable forms. This allows us to identify the opportunities and restraints linked to future sustainable PHA production. Hemicellulose hydrolysates and crude glycerol are identified as two promising carbon sources for a sustainable production of PHAs. Hemicellulose hydrolysates and crude glycerol can be produced on a large scale during various second generation biofuels’ production. An integration of PHA production within a modern biorefinery is therefore proposed to produce biofuels and bioplastics simultaneously. This will create the potential to offset the production cost of biofuels and reduce the overall production cost of PHAs.

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

“…Nevertheless, in order to make PHA production competitive also in economic terms, a number of process steps have to be optimized. Efforts in this direction are to an increasing extent devoted to the selection of inexpensive carbon feedstocks, which can replace costly raw materials typically used for biotechnological purposes, such as sugars or edible oils [11]. Among such inexpensive feedstocks, a number of [agro]industrial surplus materials was already investigated for PHA production, such as waste streams from dairy and cheese making industry [12,13], residues of the biodiesel and animal processing industry [14][15][16], or various abundant lignocellulosics [17], e.g., hydrolyzed bagasse and fruit peels [18], straw [19,20] or even spent coffee ground [21].…”

Advanced approaches to produce polyhydroxyalkanoate (PHA) biopolyesters in a sustainable and economic fashion

“…To address the use of inexpensive carbon sources, biorefinery concepts are developed these days, which resort to carbon-rich side streams of diverse (agro)industrial processes to be used as "2 nd -generation feedstocks" for PHA production (15,16). In this context, as the first core topic of this review, lactose-rich surplus whey from dairy industry is another viable feedstock for PHA production (17).…”

Biotic and Abiotic Synthesis of Renewable Aliphatic Polyesters from Short Building Blocks Obtained from Biotechnology

“…[316,317] Additionally,f or the same substrate, different bacterial strains can produce various PHAs.F or example, Pseudomonas strains can use glucosea nd other simples ugars to synthesize mcl-PHAs,s uch as P(3HHx), [318,319] whereas C. necator synthesizes only P(3HB)f rom glucose. [322] Most PHAsynthesizing bacteria can only use simple sugars;the use of triglycerides has only been reported for some microorganisms and hydrocarbon metabolism is more limited. Substrates can be generally divided into three categories with 1) carbohydrates (sugars), 2) triglycerides, and 3) hydrocarbons.…”

“…[320,321] Substrates for the bacterial production of PHAs are usually restricted to small molecules because large polymeric molecules cannotb et ransported into the cell. [322] Therefore, it is important to use cheap and widely availablecarbon sources. [322] Most PHAsynthesizing bacteria can only use simple sugars;the use of triglycerides has only been reported for some microorganisms and hydrocarbon metabolism is more limited.…”