Fermentation optimization and mathematical modeling of glycerol-based microbial poly(3-hydroxybutyrate) production

Synergistic approach for enhanced production of polyhydroxybutyrate by Bacillus pseudomycoides SAS-B1: Effective utilization of glycerol and acrylic acid through fed-batch fermentation and its environmental impact assessment

The continual rise in the consumption of petroleum-based synthetic polymers raised a significant environmental concern. Bacillus pseudomycoides SAS-B1 is a gram-positive rod-shaped halophilic bacterium capable of accumulating Polyhydroxybutyrate (PHB)-an intracellular biodegradable polymer. In the present study, the optimal conditions for cell cultivation in the seed media were developed. The optimal factors included a preservation age of 14 to 21 days (with 105 to 106 cells/mL), inoculum size of 0.1 % (w/v), 1 % (w/v) glucose, and growth temperature of 30 °C. The cells were then cultivated in a two-stage fermentation process utilizing glycerol and Corn Steep Liquor (CSL) as carbon and nitrogen sources, respectively. PHB yield was effectively increased from 2.01 to 9.21 g/L through intermittent feeding of glycerol and CSL, along with acrylic acid. FTIR, TGA, DSC, and XRD characterization studies were employed to enumerate the recovered PHB and determine its physicochemical properties. Additionally, the study assessed the cradle-to-gate Life Cycle Assessment (LCA) of PHB production, considering net CO2 generation and covering all major environmental impact categories. The production of 1000 kg of PHB resulted in lower stratospheric ozone depletion and comparatively reduced carbon dioxide emissions (2022.7 kg CO2 eq.) and terrestrial ecotoxicity (9.54 kg 1,4-DCB eq.) than typical petrochemical polymers.

Production of polyhydroxyalkanoates from hydrolysed rapeseed meal by Haloferax mediterranei

Rapeseed meal (RSM) hydrolysate is a potential low-cost feedstock for the production of polyhydroxyalkanoates (PHAs) by the archaea, Haloferax mediterranei. Acidic and enzymatic hydrolysis were carried out to compare effectiveness. Enzymatic hydrolysis is more effective than acidic hydrolysis for fermentation substrate leading to increased PHA productivity. H. mediterranei didn't grow or produce PHA when acid hydrolysed RSM medium was present in proportions greater than 25% (vol.), potentially due to the effect of inhibitors such as furfural, hydroxymethylfurfural (HMF), etc. However, H. mediterranei was able to grow and produce PHA when using enzymatically hydrolysed RSM medium. The maximum PHA concentration of 0.512 g/L was found at 75% (vol.) in enzymatic RSM hydrolysate medium. The biopolymer obtained had improved thermal and mechanical properties compared to PHB homopolymer. RSM's potential as a low-cost alternative feedstock for improved PHA production under non-sterile conditions was successfully demonstrated, and its usage should be further explored.

Utilizing microalgal hydrolysate from dairy wastewater-grown Chlorella sorokiniana SU-1 as sustainable feedstock for polyhydroxybutyrate and β-carotene production by engineered Rhodotorula glutinis #100-29

The objective of this study was to explore the potential of utilizing Chlorella sorokiniana SU-1 biomass grown on dairy wastewater-amended medium as sustainable feedstock for the biosynthesis of β-carotene and polyhydroxybutyrate (PHB) by Rhodotorula glutinis #100-29. To break down the rigid cell wall, 100 g/L of microalgal biomass was treated with 3% sulfuric acid, followed by detoxification using 5% activated carbon to remove the hydroxymethylfurfural inhibitor. The detoxified microalgal hydrolysate (DMH) was used for flask-scale fermentation, which yielded a maximum biomass production of 9.22 g/L, with PHB and β-carotene concentration of 897 mg/L and 93.62 mg/L, respectively. Upon scaling up to a 5-L fermenter, the biomass concentration increased to 11.2 g/L, while the PHB and β-carotene concentrations rose to 1830 mg/L and 134.2 mg/L. These outcomes indicate that DMH holds promise as sustainable feedstock for the production of PHB and β-carotene by yeast.

Electrospun poly(3-hydroxybutyrate-co-3-hydroxyvalerate) scaffolds - a step towards ligament repair applications

The incidence of anterior cruciate ligament (ACL) ruptures is approximately 50 per 100,000 people. ACL rupture repair methods that offer better biomechanics have the potential to reduce long term osteoarthritis. To improve ACL regeneration biomechanically similar, biocompatible and biodegradable tissue scaffolds are required. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with high 3-hydroxyvalerate (3HV) content, based scaffold materials have been developed, with the advantages of traditional tissue engineering scaffolds combined with attractive mechanical properties, e.g., elasticity and biodegradability. PHBV with 3HV fractions of 0 to 100 mol% were produced in a controlled manner allowing specific compositions to be targeted, giving control over material properties. In conjunction electrospinning conditions were altered, to manipulate the degree of fibre alignment, with increasing collector rotating speed used to obtain random and aligned PHBV fibres. The PHBV based materials produced were characterised, with mechanical properties, thermal properties and surface morphology being studied. An electrospun PHBV fibre mat with 50 mol% 3HV content shows a significant increase in elasticity compared to those with lower 3HV content and could be fabricated into aligned fibres. Biocompatibility testing with L929 fibroblasts demonstrates good cell viability, with the aligned fibre network promoting fibroblast alignment in the axial fibre direction, desirable for ACL repair applications. Dynamic load testing shows that the 50 mol% 3HV PHBV material produced can withstand cyclic loading with reasonable resilience. Electrospun PHBV can be produced with low batch variability and tailored, application specific properties, giving these biomaterials promise in tissue scaffold applications where aligned fibre networks are desired, such as ACL regeneration.   .

Utilization of Agave durangensis leaves by Bacillus cereus 4N for polyhydroxybutyrate (PHB) biosynthesis

Lignocellulosic wastes may provide a means to economize polyhydroxybutyrate (PHB) production. This study has proposed the use of Agave durangensis leaves obtained from the artisanal mezcal industry as a novel substrate for this aim. Results revealed an increase in PHB biosynthesis (0.32 g/L) and improvement in %PHB (16.79-19.51%) by Bacillus cereus 4N when A. durangensis leaves used as carbon source were physically pre-treated by ultrasound for 30 min (ADL + US30') and thermally pre-treated (ADL + Q). Chemical analyses and SEM studies revealed compositional and morphological changes when A. durangensis leaves were physically pre-treated. Also, elemental analysis of growth media showed that carbon/nitrogen ratios of 14-21, and low nitrogen, hydrogen, and protein content were well-suited for PHB biosynthesis. Confocal microscopy revealed morphological changes in the bacterial cell and carbonosome structure under the influence of different substrates. Finally, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) analyses showed that homopolymeric PHB with a high thermal-resistance (271.94-272.89 °C) was produced. Therefore, the present study demonstrates the potential use of physically pre-treated A. durangensis leaves to produce PHB. These results promote the development of a circular economy in Mexico, where lignocellulosic wastes can be employed to produce value-added biotechnological products.

Critical overview of biomass feedstocks as sustainable substrates for the production of polyhydroxybutyrate (PHB)

Polyhydroxybutyrates (PHBs) are a class of biopolymers produced by different microbial species and are biodegradable and biocompatible in nature as opposed to petrochemically derived plastics. PHBs have advanced applications in medical sector, packaging industries, nanotechnology and agriculture, among others. PHB is produced using various feedstocks such as glycerol, dairy wastes, agro-industrial wastes, food industry waste and sugars. Current focus on PHB research has been primarily on reducing the cost of production and, on downstream processing to isolate PHB from cells. Recent advancements to improve the productivity and quality of PHB include genetic modification of producer strain and modification of PHB by blending to develop desirable properties suited to diversified applications. Selection of feedstock plays a critical role in determining the economic feasibility and sustainability of the process. This review provides a bird's eye view of the suitability of different waste resources for producing polyhydroxybutyrate; providing state-of the art information and analysis.

Recent advances in polyhydroxyalkanoate production: Feedstocks, strains and process developments

Polyhydroxyalkanoates (PHAs) have been actively studied in academia and industry for their properties comparable to petroleum-derived plastics and high biocompatibility. However, the major limitation for commercialization is their high cost. Feedstock costs, especially carbon costs, account for the majority of the final cost. Finding cheap feedstocks for PHA production and associated process development are critical for a cost-effective PHA production. In this study, waste materials from different sources, particularly lignocellulosic biomass, were proposed as suitable feedstocks for PHA production. Strains involved in the conversion of these feedstocks into PHA were reviewed. Newly isolated strains were emphasized. Related process development, including the factors that affect PHA production, fermentation modes and downstream processing, was elaborated upon.

Engineering a defined culture medium to grow Piscirickettsia salmonis for its use in vaccine formulations

Piscirickettsia salmonis is a facultative Gram-negative intracellular bacterium that produces piscirickettsiosis, disease that causes a high negative impact in salmonid cultures. The so-far-unidentified nutritional requirements have hindered its axenic culture at laboratory and industrial scales for the formulation of vaccines. The present study describes the development of a defined culture medium for P. salmonis. The culture medium was formulated through rational design involving auxotrophy test and statistical designs of experiments, considering the genome-scale metabolic reconstruction of P. salmonis reported by our group. The whole optimization process allowed for a twofold increase in biomass and a reduction of about 50% of the amino acids added to the culture medium. The final culture medium contains twelve amino acids, where glutamic acid, threonine and arginine were the main carbon and energy sources, supporting 1.65 g/L of biomass using 6.5 g/L of amino acids in the formulation. These results will contribute significantly to the development of new operational strategies to culture this bacterium for the production of vaccines.

Production of polyhydroxyalkanoates and enrichment of associated microbes in bioreactors fed with rice winery wastewater at various organic loading rates

This study aimed to explore the production of polyhydroxyalkanoates (PHA) and selection of PHA-accumulating microorganisms in bioreactors fed with rice winery wastewater at various organic loading rates (OLRs). The substrate utilization, sludge properties, PHA synthesis and microbial community structure of three sequencing batch reactors were monitored. The results show the highest PHA yield (0.23 g/g) was achieved in one of the three reactors with an OLR of 2.4 g COD/L/d, in which Zoogloea was the most dominant PHA-accumulating microorganism. To quantify the PHA production and track the population changing profiles of the PHA-accumulating microorganisms in the long-term reactor operation, the Activated Sludge Model No. 3 was modified with two different heterotrophic microorganisms responding differently with the same substrate. The modeling results indicate that a moderate OLR (>2.4 gCOD/L/d) was beneficial for PHA production. The results are useful for understanding the PHA production from industrial wastewaters and selection of PHA-accumulating microorganisms.

Molecular mechanism of acetoacetyl-CoA enhanced kinetics for increased bioplastic production from Cupriavidus necator 428

Polyhydroxyalkanoates are gaining importance due to their biodegradable nature and close analogy to plastics. Polyhydroxybutyrate (PHB) is the most widely used bioplastic from polyalkanoate family, which is produced by a legion of bacterial species via phbCAB operon encoding β-ketothiolase (PhaA), NADPH-dependent acetoacetyl-coenzyme A (acetoacetyl-CoA) reductase (PhaB) and polyhydroxyalkanoate synthase (PhaC). Augmentation in the activity of these enzymes is promising for increased PHB production which is achieved by enzyme engineering strategies including non-structural and structural approaches. Our study is deployed on directed evolution-based experimentally reported mutants of PhaB enzyme with increased efficiency due to impact on critical structural factors. We have analyzed and compared the native PhaB with two of its variants Q47L and T173S in complex with their cofactor i.e. NADPH as well as the substrate i.e. acetoacetyl-CoA, via long range molecular dynamics simulations. Interaction profile, MMPBSA, essential dynamics, and free energy landscape analysis revealed that the enzyme efficiency is critically affected by cofactor interactions. It was also observed that mutants have higher equilibrium constant with lesser but optimal affinity for substrate and cofactor than the wild type, which might be the reason for increased efficiency of the mutants via enhanced substrate and cofactor exchange rate. Our study provides insights into the cofactor and substrate binding affinities to PhaB enzyme at atomistic level, which will facilitate designing of highly efficient PhaB enzymes for increased PHB production. Communicated by Ramaswamy H. Sarma.