Polyhydroxyalkanoate Synthesis by Burkholderia glumae into a Sustainable Sugarcane Biorefinery Concept

Production of polyhydroxyalkanoate (PHA) biopolymer from crop residue using bacteria as an alternative to plastics: a review

Growing environmental concerns and the pressing need to combat plastic pollution have led to extensive research on sustainable alternatives to traditional plastics. Human blood sample analysis discovered microplastics which has caused health concerns regarding their influence on proper functioning of the human body. The compound polyhydroxyalkanoate (PHA) has gained popularity due to its comparable structure with synthetic polymers like polypropylene because it belongs to the category of biodegradable alternatives. Different PHA molecules have distinct properties because of their composition of monomers and production parameters. The current market offers an array of biopolymers but they do not satisfy industrial requirements regarding thermostability. The industrial heat-stability of materials comes from green biomass-derived polyethylene and extrudable cellulose biopolymers. The research analyses PHAs' suitability as synthetic plastic substitutes and addresses barriers to their industrial production and proposes modifications to improve performance. It underscores the importance of harnessing crop residue streams to produce valuable biopolymers, promoting resource efficiency and mitigating the environmental impact of plastic waste. This work aligns with the UN's sustainability goals, including SDG 3 good health, SDG 11 sustainable cities, SDG 12 responsible consumption, SDG 13 climate action, and SDG 14 sea and ocean protection.

Structure analysis and thermal stability of PHB recovered from sugar industry waste

The current article emphasized on cultural conditions for Alcaligenes sp. NCIM 5085 to synthesize Polyhydroxybutyrate (PHB) from sugar industry waste during batch fermentation. Alcaligenes sp. NCIM 5085 was found to grow best in conditions that included 40 g l-1 of cane molasses, 1 g l-1 of ammonium sulphate, 10% inoculum with neutral pH and 48 h of incubation time. Sudan Black B staining was employed to verify the PHB synthesis initially, and further TEM analysis was performed to confirm it. The structural analysis of recovered PHB was carried out by using GC-MS, FTIR, 1H NMR and 13C NMR analysis. The absorption peak at 1724.56 cm-1 revealed the presence of C=O (carbonyl) group by FTIR, which is an indicator of PHB presence. Furthermore, results of NMR and GC-MS analysis confirmed the recovered polymer was PHB. The thermal properties of recovered polymer were analyzed by TGA, DTG and DSC and showed thermal stability of PHB. The observed glass transient temperature (Tg) -2.8°C was within the normal PHB range of Tg. However, melting temperature of recovered PHB was 161.7°C, where the degree of crystallinity was lower than standard PHB that widens the application possibilities.

Electrochemical detection of poly(3-hydroxybutyrate) production from Burkholderia glumae MA13 using a molecularly imprinted polymer-reduced graphene oxide modified electrode

The development and application of an electrochemical sensor is reported for detection of poly(3-hydroxybutyrate) (P3HB) - a bioplastic derived from agro-industrial residues. To overcome the challenges of molecular imprinting of macromolecules such as P3HB, this study employed methanolysis reaction to break down the P3HB biopolymer chains into methyl 3-hydroxybutyrate (M3HB) monomers. Thereafter, M3HB were employed as the target molecules in the construction of molecularly imprinted sensors. The electrochemical device was then prepared by electropolymerizing a molecularly imprinted poly (indole-3-acetic acid) thin film on a glassy carbon electrode surface modified with reduced graphene oxide (GCE/rGO-MIP) in the presence of M3HB. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy with field emission gun (SEM-FEG), Raman spectroscopy, attenuated total reflection Fourier-transform infrared (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS) were employed to characterize the electrode surface. Under ideal conditions, the MIP sensor exhibited a wide linear working range of 0.1 - 10 nM and a detection limit of 0.3 pM (n = 3). The sensor showed good repeatability, selectivity, and stability over time. For the sensor application, the bioproduction of P3HB was carried out in a bioreactor containing the Burkholderia glumae MA13 strain and sugarcane byproducts as a supplementary carbon source. The analyses were validated through recovery assays, yielding recovery values between 102 and 104%. These results indicate that this MIP sensor can present advantages in the monitoring of P3HB during the bioconversion process.

Polyhydroxyalkanoates production in biorefineries: A review on current status, challenges and opportunities

The need for a sustainable and circular bioeconomy model is imperative due to petroleum non-renewability, scarcity and environmental impacts. Biorefineries systems explore biomass to its maximum, being an important pillar for the development of circular bioeconomy. Polyhydroxyalkanoates (PHAs) can take advantage of biorefineries, as they can be produced using renewable feedstocks, and are potential substitutes for petrochemical plastics. The present work aims to evaluate the current status of the industrial development of PHAs production in biorefineries and PHAs contributions to the bioeconomy, along with future development points. Advancements are noticed when PHA production is coupled in wastewater treatment systems, when residues are used as substrate, and also when analytical methodologies are applied to evaluate the production process, such as the Life Cycle and Techno-Economic Analysis. For the commercial success of PHAs, it is established the need for dedicated investment and policies, in addition to proper collaboration of different society actors.

Polyhydroxyalkanoate (PHA) Biopolymer Synthesis by Marine Bacteria of the Malaysian Coral Triangle Region and Mining for PHA Synthase Genes

Polyhydroxyalkanoate (PHA), a biodegradable and plastic-like biopolymer, has been receiving research and industrial attention due to severe plastic pollution, resource depletion, and global waste issues. This has spurred the isolation and characterisation of novel PHA-producing strains through cultivation and non-cultivation approaches, with a particular interest in genes encoding PHA synthesis pathways. Since sea sponges and sediment are marine benthic habitats known to be rich in microbial diversity, sponge tissues (Xestospongia muta and Aaptos aaptos) and sediment samples were collected in this study from Redang and Bidong islands located in the Malaysian Coral Triangle region. PHA synthase (phaC) genes were identified from sediment-associated bacterial strains using a cultivation approach and from sponge-associated bacterial metagenomes using a non-cultivation approach. In addition, phylogenetic diversity profiling was performed for the sponge-associated bacterial community using 16S ribosomal ribonucleic acid (16S rRNA) amplicon sequencing to screen for the potential presence of PHA-producer taxa. A total of three phaC genes from the bacterial metagenome of Aaptos and three phaC genes from sediment isolates (Sphingobacterium mizutaii UMTKB-6, Alcaligenes faecalis UMTKB-7, Acinetobacter calcoaceticus UMTKB-8) were identified. Produced PHA polymers were shown to be composed of 5C to nC monomers, with previously unreported PHA-producing ability of the S. mizutaii strain, as well as a 3-hydroxyvalerate-synthesising ability without precursor addition by the A. calcoaceticus strain.

Enhanced production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer by endophytic Bacillus cereus RCL 02 utilizing sugarcane molasses as sole source of carbon: a statistical optimization approach

Polymers of biological origin have become a topic of interest due to growing concerns about the environmental impact of the disposal of plastics. In recent years, the production of ecobenign microbial polymer polyhydroxyalkanoates (PHAs) using inexpensive and renewable resources has gained significant interest as these compounds are highly biodegradable, biocompatible, and sustainable. This study used leaf endophytic isolate Bacillus cereus RCL 02, obtained from the oil-yielding plant Ricinus communis L., to achieve statistical optimization of culture variables for the enhanced production of PHAs utilizing sugarcane molasses as the sole carbon source. A three-level and four-factor Box-Behnken design of response surface methodology was implemented to optimize the process variables, namely molasses (carbon substrate), ammonium sulfate (nitrogen source), initial pH, and incubation period, for improved biomass formation and PHA production. The highest growth (14.8 g/l) and PHA production (85.2%, dry cell weight) by the isolate were observed with 47 g/l molasses, 3 g/l ammonium sulfate, an initial pH of 6.7, and 62 h of incubation. Statistical optimization of the process allowed achieving a 1.6-fold increase in the PHA yield (7.8-12.6 g/l) compared with the conventional single-factor system of analysis. The biopolymer thus produced was confirmed as a copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate [P(3HB-co-3HV)] using ¹H nuclear magnetic resonance spectroscopic analysis and was found to contain 7.8 mol% 3-hydroxyvalerate. These findings clearly indicate the efficacy of the B. cereus RCL 02 isolate in the biotransformation of raw sugarcane molasses to P(3HV-co-3HV), without the need for supplementation with high-cost precursors.

Opportunities in the microbial valorization of sugar industrial organic waste to biodegradable smart food packaging materials

Many petroleum-derived plastics, including food packaging materials are non-biodegradable and designed for single-use applications. Annually, around 175 Mt. of plastic enters the land and ocean ecosystems due to mismanagement and lack of techno economically feasible plastic waste recycling technologies. Renewable sourced, biodegradable polymer-based food packaging materials can reduce this environmental pollution. Sugar production from sugarcane or sugar beet generates organic waste streams that contain fermentable substrates, including sugars, acids, and aromatics. Microbial metabolism can be leveraged to funnel those molecules to platform chemicals or biopolymers to generate biodegradable food packaging materials that have active or sensing molecules embedded in biopolymer matrices. The smart package can real-time monitor food quality, assure health safety, and provide economic and environmental benefits. Active packaging materials display functional properties such as antimicrobial, antioxidant, and light or gas barrier. This article provides an overview of potential biodegradable smart/active polymer packages for food applications by valorizing sugar industry-generated organic waste. We highlight the potential microbial pathways and metabolic engineering strategies to biofunnel the waste carbon efficiently into the targeted platform chemicals such as lactic, succinate, muconate, and biopolymers, including polyhydroxyalkanoates, and bacterial cellulose. The obtained platform chemicals can be used to produce biodegradable polymers such as poly (butylene adipate-co-terephthalate) (PBAT) that could replace incumbent polyethylene and polypropylene food packaging materials. When nanomaterials are added, these polymers can be active/smart. The process can remarkably lower the greenhouse gas emission and energy used to produce food-packaging material via sugar industrial waste carbon relative to the petroleum-based production. The proposed green routes enable the valorization of sugar processing organic waste into biodegradable materials and enable the circular economy.

Developing Microbial Co-Culture System for Enhanced Polyhydroxyalkanoates (PHA) Production Using Acid Pretreated Lignocellulosic Biomass

In the growing polymer industry, the interest of researchers is captivated by bioplastics production with biodegradable and biocompatible properties. This study examines the polyhydroxyalkanoates (PHA) production performance of individual Lysinibacillus sp. RGS and Ralstonia eutropha ATCC 17699 and their co-culture by utilizing sugarcane bagasse (SCB) hydrolysates. Initially, acidic (H₂SO₄) and acidified sodium chlorite pretreatment was employed for the hydrolysis of SCB. The effects of chemical pretreatment on the SCB biomass assembly and its chemical constituents were studied by employing numerous analytical methods. Acidic pretreatment under optimal conditions showed effective delignification (60%) of the SCB biomass, leading to a maximum hydrolysis yield of 74.9 ± 1.65% and a saccharification yield of 569.0 ± 5.65 mg/g of SCB after enzymatic hydrolysis. The resulting SCB enzymatic hydrolysates were harnessed for PHA synthesis using individual microbial culture and their defined co-culture. Co-culture strategy was found to be effective in sugar assimilation, bacterial growth, and PHA production kinetic parameters relative to the individual strains. Furthermore, the effects of increasing acid pretreated SCB hydrolysates (20, 30, and 40 g/L) on cell density and PHA synthesis were studied. The effects of different cost-effective nutrient supplements and volatile fatty acids (VFAs) with acid pretreated SCB hydrolysates on cell growth and PHA production were studied. By employing optimal conditions and supplementation of corn steep liquor (CSL) and spent coffee waste extracted oil (SCGO), the co-culture produced maximum cell growth (DCW: 11.68 and 11.0 g/L), PHA accumulation (76% and 76%), and PHA titer (8.87 and 8.36 g/L), respectively. The findings collectively suggest that the development of a microbial co-culture strategy is a promising route for the efficient production of high-value bioplastics using different agricultural waste biomass.