From Organic Wastes and Hydrocarbons Pollutants to Polyhydroxyalkanoates: Bioconversion by Terrestrial and Marine Bacteria

Abstract

The use of fossil-based plastics has become unsustainable because of the polluting production processes, difficulties for waste management sectors, and high environmental impact. Polyhydroxyalkanoates (PHA) are bio-based biodegradable polymers derived from renewable resources and synthesized by bacteria as intracellular energy and carbon storage materials under nutrients or oxygen limitation and through the optimization of cultivation conditions with both pure and mixed culture systems. The PHA properties are affected by the same principles of oil-derived polyolefins, with a broad range of compositions, due to the incorporation of different monomers into the polymer matrix. As a consequence, the properties of such materials are represented by a broad range depending on tunable PHA composition. Producing waste-derived PHA is technically feasible with mixed microbial cultures (MMC), since no sterilization is required; this technology may represent a solution for waste treatment and valorization, and it has recently been developed at the pilot scale level with different process configurations where aerobic microorganisms are usually subjected to a dynamic feeding regime for their selection and to a high organic load for the intracellular accumulation of PHA. In this review, we report on studies on terrestrial and marine bacteria PHA-producers. The available knowledge on PHA production from the use of different kinds of organic wastes, and otherwise, petroleum-polluted natural matrices coupling bioremediation treatment has been explored. The advancements in these areas have been significant; they generally concern the terrestrial environment, where pilot and industrial processes are already established. Recently, marine bacteria have also offered interesting perspectives due to their advantageous effects on production practices, which they can relieve several constraints. Studies on the use of hydrocarbons as carbon sources offer evidence for the feasibility of the bioconversion of fossil-derived plastics into bioplastics.

Living in mangroves: a syntrophic scenario unveiling a resourceful microbiome

“…It has been reported that native mangrove microbial communities may have the potential to degrade petroleum hydrocarbons, even in pristine mangroves [ 155 ]. Coupled with beta-oxidation, most genes required for the synthesis of poly-beta-hydroxybutyrate (PHB) were identified in PO, which showed the three reaction steps catalyzed by acetyl-CoA acetyltransferase (ACAT), acetoacetyl-CoA reductase and PHA synthase (PhaC) [ 156 , 157 ]. The metabolic capability described for the Pseudomonadales MAGs seems to be more suitable for transient microaerobic/aerobic conditions, generating energy mostly from fatty acid degradation to acetyl-CoA, channeled through glyoxylate cycle, oxidative TCA and electron transport chain, with higher ATP yielding when oxygen is available.…”

Sustainable bioconversion of synthetic plastic wastes to polyhydroxyalkanoate (PHA) bioplastics: recent advances and challenges

“…134,135 PHA are produced by pure and mixed microbial cultures or genetically modified strains using costly substrates, carbon sources represent 40-50% of total production cost. 136,137 High production costs of PHA in comparison to petrochemical plastics limits their commercialization. 138 The bioplastics market represents about 1% of the total global plastic produced.…”