Model Study To Assess Softwood Hemicellulose Hydrolysates as the Carbon Source for PHB Production in Paraburkholderia sacchari IPT 101

Impact of Acetic Acid Supplementation in Polyhydroxyalkanoates Production by Cupriavidus necator Using Mixture-Process Design and Artificial Neural Network

The trend in bioplastic application has increased over the years where polyhydroxyalkanoates (PHAs) have emerged as a potential candidate with the advantage of being bio-origin, biodegradable, and biocompatible. The present study aims to understand the effect of acetic acid concentration (in combination with sucrose) as a mixture variable and its time of addition (process variable) on PHA production by Cupriavidus necator. The addition of acetic acid at a concentration of 1 g l-1 showed a positive influence on biomass and PHA yield; however, the further increase had a reversal effect. The addition of acetic acid at the time of incubation showed a higher PHA yield, whereas maximum biomass was achieved when acetic acid was added after 48 h. Genetic algorithm (GA) optimized artificial neural network (ANN) was used to model PHA concentration from mixture-process design data. Fitness of the GA-ANN model (R2: 0.935) was superior when compared to the polynomial model (R2: 0.301) from mixture design. Optimization of the ANN model projected 2.691 g l-1 PHA from 7.245 g l-1 acetic acid, 12.756 g l-1 sucrose, and the addition of acetic acid at the time of incubation. Sensitivity analysis indicates the inhibitory effect of all the predictors at higher levels. ANN model can be further used to optimize the variables while extending the bioprocess to fed-batch operation.

The potential of Burkholderia thailandensis E264 for co-valorization of C5 and C6 sugars into multiple value-added bio-products

Despite known metabolic versatility of Burkholderia spp., sugar metabolism and end-product synthesis patterns in Burkholderia thailandensis have been poorly characterized. This work has demonstrated that B. thailandensis is capable of simultaneously uptaking glucose and xylose and accumulating up to 64% of its dry mass as poly(3-hydroxyalkanoate) (PHA) biopolymers, resulting in a PHA titer of up to 3.8 g L-1 in shake flasks. Rhamnolipids - mainly (68-75%) in the form of Rha-Rha-C14-C14 - were produced concomitantly with a titer typically in the range of 0.2-0.4 g L-1. Gluconic and xylonic acids were also detected in titers of up to 5.3 g L-1, and while gluconic acid appeared to be back consumed, xylonic acid formed as a major end product. This first example of co-production of three products from mixed sugars using B. thailandensis paves the way for improving biorefinery economics.

Biotransformation of d-Xylose-Rich Rice Husk Hydrolysate by a Rice Paddy Soil Bacterium, Priestia sp. Strain JY310, to Low Molecular Weight Poly(3-hydroxybutyrate)

Poly(3-hydroxybutyrate) (PHB) is a versatile thermoplastic with superior biodegradability and biocompatibility that is intracellularly accumulated by numerous bacterial and archaeal species. Priestia sp. strain JY310 that was able to efficiently biotransform reducing sugars in d-xylose-rich rice husk hydrolysate (reducing sugar_RHH) to PHB was isolated from the soil of a rice paddy. Reducing sugar_RHH including 12.5% d-glucose, 75.3% d-xylose, and 12.2% d-arabinose was simply prepared using thermochemical hydrolysis of 3% H₂SO₄-treated rice husk for 15 min at 121 °C. When cultured with 20 g/L reducing sugar_RHH under optimized culture conditions in a batch bioreactor, Priestia sp. strain JY310 could produce PHB homopolymer up to 50.4% of cell dry weight (6.2 g/L). The melting temperature, heat of fusion, and thermal decomposition temperature of PHB were determined to be 167.9 °C, 92.1 J/g, and 268.1 °C, respectively. The number average and weight average molecular weights of PHB with a broad polydispersity index value (4.73) were estimated to be approximately 16.2 and 76.8 kg/mol, respectively. The findings of the present study suggest that Priestia sp. strain JY310 can be exploited as a good candidate for the low-cost production of low molecular weight PHB with improved biodegradability and reduced brittleness from inexpensive agricultural waste hydrolysates.

Engineering Burkholderia sacchari to enhance poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] production from xylose and hexanoate

Burkholderia sacchari LFM101 LMG19450^T is a Brazilian bacterium isolated from sugarcane crops soil and a promising biotechnological platform for bioprocesses. It is an efficient producer of poly(3-hydroxybutyrate) from carbohydrates including xylose. In the present work, the expression of B. sacchari xylose consumption genes (xylA, xylB and tktA) was combined with the expression of Aeromonas sp. phaC (PHA synthase), aiming to increase both the growth rates in xylose and the 3-hydroxyhexanoate (3HHx) molar fractions in the produced PHA. Genes were cloned into pBBR1MCS-2 vectors and then expressed in the B. sacchari PHA- mutant LFM344. Maximum specific growth rates on xylose and PHA accumulation capacity of all recombinants were evaluated. In bioreactor experiments, up to 55.5 % CDW was accumulated as copolymer, hexanoate conversion to 3HHx raised from 2 % to 54 % of the maximum theoretical value, compared to wild type. 3HHx mol% ranged from 8 to 35, and molecular weights were between 111 and 220 kg/mol. Thermal analysis measurement showed a decrease in T_g and T_m values with higher 3HHx fraction, indicating improved thermomechanical characteristics. Recombinants construction and bioreactor strategies allowed the production of P(3HB-co-3HHx) with controlled monomeric composition from xylose and hexanoate, allowing its application in diverse fields, including the medical area.

Burkholderia sacchari (synonym Paraburkholderia sacchari): An industrial and versatile bacterial chassis for sustainable biosynthesis of polyhydroxyalkanoates and other bioproducts

This is the first review presenting and discussing Burkholderia sacchari as a bacterial chassis. B. sacchari is a distinguished polyhydroxyalkanoates producer strain, with low biological risk, reaching high biopolymer yields from sucrose (0.29 g/g), and xylose (0.38 g/g). It has great potential for integration into a biorefinery using residues from biomass, achieving 146 g/L cell dry weight containing 72% polyhydroxyalkanoates. Xylitol (about 70 g/L) and xylonic acid [about 390 g/L, productivity 7.7 g/(L.h)] are produced by the wild-type B. sacchari. Recombinants were constructed to allow the production and monomer composition control of diverse tailor-made polyhydroxyalkanoates, and some applications have been tested. 3-hydroxyvalerate and 3-hydroxyhexanoate yields from substrate reached 80% and 50%, respectively. The genome-scale reconstruction of its metabolic network, associated with the improvement of tools for genetic modification, and metabolic fluxes understanding by future research, will consolidate its potential as a bioproduction chassis.

Genome-Wide Metabolic Reconstruction of the Synthesis of Polyhydroxyalkanoates from Sugars and Fatty Acids by Burkholderia Sensu Lato Species

Burkholderia sensu lato (s.l.) species have a versatile metabolism. The aims of this review are the genomic reconstruction of the metabolic pathways involved in the synthesis of polyhydroxyalkanoates (PHAs) by Burkholderia s.l. genera, and the characterization of the PHA synthases and the pha genes organization. The reports of the PHA synthesis from different substrates by Burkholderia s.l. strains were reviewed. Genome-guided metabolic reconstruction involving the conversion of sugars and fatty acids into PHAs by 37 Burkholderia s.l. species was performed. Sugars are metabolized via the Entner-Doudoroff (ED), pentose-phosphate (PP), and lower Embden-Meyerhoff-Parnas (EMP) pathways, which produce reducing power through NAD(P)H synthesis and PHA precursors. Fatty acid substrates are metabolized via β-oxidation and de novo synthesis of fatty acids into PHAs. The analysis of 194 Burkholderia s.l. genomes revealed that all strains have the phaC, phaA, and phaB genes for PHA synthesis, wherein the phaC gene is generally present in ≥2 copies. PHA synthases were classified into four phylogenetic groups belonging to class I II and III PHA synthases and one outlier group. The reconstruction of PHAs synthesis revealed a high level of gene redundancy probably reflecting complex regulatory layers that provide fine tuning according to diverse substrates and physiological conditions.

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.

Efficient Enzymatic Hydrolysis of Biomass Hemicellulose in the Absence of Bulk Water

Current enzymatic methods for hemicellulosic biomass depolymerization are solution-based, typically require a harsh chemical pre-treatment of the material and large volumes of water, yet lack in efficiency. In our study, xylanase (E.C. 3.2.1.8) from Thermomyces lanuginosus is used to hydrolyze xylans from different sources. We report an innovative enzymatic process which avoids the use of bulk aqueous, organic or inorganic solvent, and enables hydrolysis of hemicellulose directly from chemically untreated biomass, to low-weight, soluble oligoxylosaccharides in >70% yields.

Use of agro-industrial residue from the canned pineapple industry for polyhydroxybutyrate production by Cupriavidus necator strain A-04

BACKGROUND

Pineapple is the third most important tropical fruit produced worldwide, and approximately 24.8 million tons of this fruit are produced annually throughout the world, including in Thailand, which is the fourth largest pineapple producer in the world. Pineapple wastes (peel and core) are generated in a large amount equal to approximately 59.36% based on raw material. In general, the anaerobic digestion of pineapple wastes is associated with a high biochemical oxygen demand and high chemical oxygen demand, and this process generates methane and can cause greenhouse gas emissions if good waste management practices are not enforced. This study aims to fill the research gap by examining the feasibility of pineapple wastes for promoting the high-value-added production of biodegradable polyhydroxybutyrate (PHB) from the available domestic raw materials. The objective of this study was to use agro-industrial residue from the canned pineapple industry for biodegradable PHB production.

RESULTS

The results indicated that pretreatment with an alkaline reagent is not necessary. Pineapple core was sized to - 20/+ 40 mesh particle and then hydrolyzed with 1.5% (v/v) H₂SO₄ produced the highest concentration of fermentable sugars, equal to 0.81 g/g dry pineapple core, whereas pineapple core with a + 20 mesh particle size and hydrolyzed with 1.5% (v/v) H₃PO₄ yielded the highest concentration of PHB substrates (57.2 ± 1.0 g/L). The production of PHB from core hydrolysate totaled 35.6 ± 0.1% (w/w) PHB content and 5.88 ± 0.25 g/L cell dry weight. The use of crude aqueous extract (CAE) of pineapple waste products (peel and core) as a culture medium was investigated. CAE showed very promising results, producing the highest PHB content of 60.00 ± 0.5% (w/w), a cell dry weight of 13.6 ± 0.2 g/L, a yield ( YP/S ) of 0.45 g PHB/g PHB substrate, and a productivity of 0.160 g/(L h).

CONCLUSIONS

This study demonstrated the feasibility of utilizing pineapple waste products from the canned pineapple industry as lignocellulosic feedstocks for PHB production. C. necator strain A-04 was able to grow on various sugars and tolerate levulinic acid and 5-hydroxymethyl furfural, and a detoxification step was not required prior to the conversion of cellulose hydrolysate to PHB. In addition to acid hydrolysis, CAE was identified as a potential carbon source and offers a novel method for the low-cost production of PHB from a realistic lignocellulosic biomass feedstock.