Biosynthesis of Polyhydroxyalkanoates (PHAs) by the Valorization of Biomass and Synthetic Waste

Abstract

Synthetic pollutants are a looming threat to the entire ecosystem, including wildlife, the environment, and human health. Polyhydroxyalkanoates (PHAs) are natural biodegradable microbial polymers with a promising potential to replace synthetic plastics. This research is focused on devising a sustainable approach to produce PHAs by a new microbial strain using untreated synthetic plastics and lignocellulosic biomass. For experiments, 47 soil samples and 18 effluent samples were collected from various areas of Punjab, Pakistan. The samples were primarily screened for PHA detection on agar medium containing Nile blue A stain. The PHA positive bacterial isolates showed prominent orange-yellow fluorescence on irradiation with UV light. They were further screened for PHA estimation by submerged fermentation in the culture broth. Bacterial isolate 16a produced maximum PHA and was identified by 16S rRNA sequencing. It was identified as Stenotrophomonas maltophilia HA-16 (MN240936), reported first time for PHA production. Basic fermentation parameters, such as incubation time, temperature, and pH were optimized for PHA production. Wood chips, cardboard cutouts, plastic bottle cutouts, shredded polystyrene cups, and plastic bags were optimized as alternative sustainable carbon sources for the production of PHAs. A vital finding of this study was the yield obtained by using plastic bags, i.e., 68.24 ± 0.27%. The effective use of plastic and lignocellulosic waste in the cultivation medium for the microbial production of PHA by a novel bacterial strain is discussed in the current study.

Keywords: bacterial bioplastic; biodegradation; biological materials; biomass valorization; biomaterials; bioplastic; biopolymer; eco-friendly materials; microbial polymers; plastic bag.

Figure 1

PHA producing samples inoculated on PHA detecting agar, exhibiting fluorescence under UV light. (A) Shows a petri plate of sample 8 and (B) shows growth on the petri plate by sample 16.

Figure 2

Nucleotide Basic Local Alignment Search Tool (BLAST) results for the isolated strain: 16a. The first ten homologues were selected for phylogenetic tree construction.

Figure 3

An illustration of the neighbor-joining phylogenetic tree of identified isolate 16a: Stenotrophomonas maltophilia strain IAM 12423. The numbers indicate the evolutionary distance, whereas the labels at the end of the arms represent the accession numbers of the BLAST homologues. The blue pointers indicate nodes.

Figure 4

FTIR peaks for the extracted polymer within the transmittance range of 400–4000 cm⁻¹. The labels indicate the peaks through which functional groups are analyzed and compared with the peaks of the standard polymer, in this case, PHB.

Figure 5

Optimization of time of incubation for PHA production by S. maltophilia HA-16 with glucose as a carbon source.

Figure 6

Optimization of the temperature of incubation for PHA production by S. maltophilia HA-16 with glucose as a carbon source.

Figure 7

Optimization pH of fermentation medium for PHA production by S. maltophilia HA-16 with glucose as carbon source.

Figure 8

Optimization waste agro-industrial carbon sources for PHA production by S. maltophilia HA-16 with glucose as carbon source.

Figure 9

Brittle and Fragile film of extracted polymer.

Figure 10

Photographs of carbon sources used for optimization of PHA production. (A) Plastic cutouts of a plastic bottle, (B) shredded waste polystyrene cups, (C) shredded plastic bag, (D) cardboard carton cutouts, (E) wood chips.