Pseudomonas otitidis as a potential biocatalyst for polyhydroxyalkanoates (PHA) synthesis using synthetic wastewater and acidogenic effluents

Experimental and Computational Insights into Polyurethane Plastic Waste Conversion to Microbial Bioplastic

In this study, a seven-factor Hoke experimental design and the response surface methodology were used to optimize the fermentation conditions for the maximum polyhydroxyalkanoates (PHA) yield using polyurethane plastic waste (PUPW) as a source of carbon and energy for the microbial growth and biobased polyester production. The highest PHA yield (0.80 g/L ± 0.01) was obtained under a pH of 8; a temperature of 35 °C; a NaCl concentration of 5%; a PUPW concentration of 1%; an inoculum size of 15%, a monoculture of Pseudomonas rhizophila S211; and an incubation time of 6 days. The response values predicted by the Hoke design model at each combination of factor levels aligned with the experimental results, and the analysis of variance demonstrated the predictability and accuracy of the postulated model. In addition to the experimental evidences, P. rhizophila genome was explored to predict the PUPW-degrading enzymes and the associated protein secretion systems. Moreover, physicochemical properties, phylogenetic analysis, and 3D structure of S211 LipA2 polyurethanase were elucidated through an in-silico approach. Taken all together, integrated experimental tests and computational modeling suggest that P. rhizophila S211 has the necessary enzymatic machinery to effectively convert the non-biodegradable PUPW into PHA bioplastics.

Utilization of Crab Shell Waste for Value-Added Bioplastics by Pseudomonas-Based Microbial Cell Factories

With the development of the aquatic products processing industry, 6-8 million tons of shrimp and crab shell waste are produced globally annually, but, due to the lack of high-value conversion technology, crab shells are often discarded in large quantities as a by-product of processing. Pseudomonas-based microbial cell factories are capable of biosynthesis of high-value products using a wide range of substrates; however, there is currently no reliable fermentation model for producing high-value chemicals using crab shell waste by Pseudomonas strains. In this study, we first explored the culture conditions of shell fermentation using KT2440 through single-factor and orthogonal experiments, and the optimized fermentation parameters obtained are given as follows: a temperature of 30 °C, fermentation time of 42 h, substrate solid-liquid ratio of 7%, and rotational speed of 200 rpm. After optimization, the maximum cell growth was increased by 64.39% from 350.67 × 108 CFU/mL to 576.44 × 108 CFU/mL. Combined with engineering modification, two engineered strains, KT+IV and KT+lasBT, expressing exogenous proteases, were obtained, and the maximum growth was increased from 316.44 × 108 CFU/mL to 1268.44 × 108 CFU/mL and 616.89 × 108 CFU/mL, which were 300.84% and 94.94% higher, respectively. In addition, the engineered strain KT+NtrcT-D55E, which regulates nitrogen metabolism, was obtained, and the accumulation of intracellular polyhydroxy fatty acid esters (PHA) was increased from 20.00 mg/L to 78.58 mg/L, which was a significant increase of 292.93% relative to the control group. This study provides a theoretical basis and technical support for the high-value utilization of shrimp and crab shell resources and the development of environmentally friendly bioproducts.

Production of polyhydroxyalkanoate (PHA) copolymer from food waste using mixed culture for carboxylate production and Pseudomonas putida for PHA synthesis

Production of polyhydroxyalkanoates (PHAs) with high concentration of carboxylate, that was accumulated from solid state fermentation (SSF) of food waste (FW), was tested using Pseudomonas putida strain KT2440. Mixed-culture SSF of FW supplied in a high concentration of carboxylate, which caused a high PHA production of 0.56 g PHA/g CDM under nutrients control. Interestingly, this high PHA fraction in CDM was almost constant at 0.55 g PHA/g CDM even under high nutrients concentration (25 mM NH₄⁺), probably due to high reducing power maintained by high carboxylate concentration. PHA characterization indicated that the dominant PHA building block produced was 3-hydroxybutyrate, followed by 3-hydroxy-2-methylvalerate and 3-hydroxyhenxanoate. Carboxylate profiles before and after PHA production suggested that acetate, butyrate, and propionate were the main precursors to PHA via several metabolic pathways. Our result support that mixed culture SSF of FW for high concentration carboxylate and P. putida for PHA production enables sustainable production of PHA in cost-effective manners.

Biotransformation of toxic lignin and aromatic compounds of lignocellulosic feedstock into eco-friendly biopolymers by Pseudomonas putida KT2440

Lignin and its derivatives are the most neglected compounds in bio-processing industry due to their toxic and recalcitrant nature. Considering this, the present study aimed at valorizing these toxic compounds by employing Pseudomonas putida KT2440. Acclimatization resulted in improved tolerance with considerable lag phase reduction and aromatics degradation. Glucose as co-substrate enhanced growth and degradation in the toxic environment. The strain was able to degrade 30 % (1.60 g·L^-1) lignin, 45 mM benzoate, 40 mM p-coumarate, 35 mM ferulate, 10 mM phenol, 10 mM pyrocatechol and 8 mM aromatics mixture. The strain synthesized biopolymers using these compounds under feast and famine conditions. Characterization using GC-MS, FT-IR, H¹ NMR revealed them to be Polyhydroxyalkanoate (PHA) heteropolymers. All the analyzed PHAs contained versatile monomers with Hexadecanoic acid being the major one. This is a novel attempt towards lignin and aromatics degradation coupled with biopolymers synthesis without any genetic manipulation of the strain.

Effect of short- and medium-chain fatty acid mixture on polyhydroxyalkanoate production by Pseudomonas strains grown under different culture conditions

Short- and medium-chain fatty acids (SMCFAs) derived from the acidogenic anaerobic mixed culture fermentation of acid whey obtained from a crude cheese production line and their synthetic mixture that simulates a real SMCFA-rich stream were evaluated for polyhydroxyalkanoate (PHA) production. Three individual Pseudomonas sp. strains showed different capabilities of growing and producing PHAs in the presence of a synthetic mixture of SMCFAs. Pseudomonas sp. GL06 exhibited the highest SMCFA tolerance and produced PHAs with the highest productivity (2.7 mg/L h). Based on these observations, this strain was selected for further investigations on PHA production in a fed-batch bioreactor with a SMCFA-rich stream extracted from the effluent. The results showed that PHA productivity reached up to 4.5 mg/L h at 24 h of fermentation together with the ammonium exhaustion in the growth medium. Moreover, the PHA monomeric composition varied with the bacterial strain and the type of the growth medium used. Furthermore, a differential scanning calorimetric and thermogravimetric analysis showed that a short- and medium-chain-length PHA copolymer made of 3-hydroxybutyric, -hexanoic, -octanoic, -decanoic, and -dodecanoic has promising properties. The ability of Pseudomonas sp. to produce tailored PHA copolymers together with the range of possible applications opens new perspectives in the development of PHA bioproduction as a part of an integrated valorization process of SMCFAs derived from waste streams.

Conversion of Short and Medium Chain Fatty Acids into Novel Polyhydroxyalkanoates Copolymers by Aeromonas sp. AC_01

Polyhydroxyalkanoates (PHAs) production by Aeromonas sp. AC_01 was investigated using synthetic and waste derived short and medium chain fatty acids (SMCFAs). The obtained results revealed that the analyzed bacterial strain was able to grow and synthesize PHAs using SMCFAs. The highest PHA productivity was observed in the cultivation supplemented with a mixture of acetic acid and butyric acid (3.89 mg/L·h). Furthermore, SMCFAs-rich stream, derived from acidogenic mixed culture fermentation of acid whey, was found to be less beneficial for PHA productivity than its synthetic mixture, however the PHA production was favored by the nitrogen-limited condition. Importantly, Aeromonas sp. AC_01 was capable of synthesizing novel scl-mcl copolymers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 3-hydroxytridecanoate (3HtriD) and/or 3-hydroxytetradecaonate (3HTD) with high 3HB and 3HV fractions. They were identified with alterable monomers composition depending on the culture conditions used. Moreover, in-depth thermal analyses proved that they are highly resistant to thermal degradation regardless of their monomeric composition. The obtained results confirm that Aeromonas sp. AC_01 is a promising candidate for the biotechnological production of PHAs from SMCFAs with thermal properties that can be tuned together with their chemical composition by the corresponding adjustment of the cultivation process.

Polyhydroxyalkanoates production from short and medium chain carboxylic acids by Paracoccus homiensis

The aim of this study was to evaluate an effect of short and medium chain carboxylic acids (CAs) rich stream derived from acidogenic mixed culture fermentation of acid whey on polyhydroxyalkanoates (PHAs) synthesis by Paracoccus homiensis and compare it with the impact of individual synthetic CAs. The obtained results confirmed that the analyzed bacterium is able to metabolize synthetic CAs as the only carbon sources in the growth medium with maximum PHAs production yields of 26% of cell dry mass (CDM). The replacement of the individual CAs by a CAs-rich residual stream was found to be beneficial for the Paracoccus homiensis growth. The highest biomass concentration reached about 2.5 g/L with PHAs content of 17% of CDM. The purified PHAs were identified as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by applying gas chromatography coupled with mass spectrometry, Fourier transform infrared spectroscopic spectra and UV-Vis spectra. Furthermore, a differential scanning calorimetric, thermogravimetric and water contact angle analysis proved that the extracted copolymers have useful properties. The obtained data are promising in the perspective of developing a microbial PHAs production as a part of an integrated valorization process of high CAs content waste-derived streams.

Simultaneous biosynthesis of bacterial polyhydroxybutyrate (PHB) and extracellular polymeric substances (EPS): Process optimization and Scale-up

Owing to their biodegradability and renewability, biopolymers are being employed in industrial and bio-medical sectors as sustainable alternatives to chemical based polymers. In the present study, isolated Providencia sp. depicted dual production of intra and extracellular biopolymers, polyhydroxybutyrate (PHB) and extracellular polymeric substances (EPS), respectively. The polymer production process was optimised by varying process parameters such as carbon load (20, 30 and 40 g L^-1) and pH (6, 7 and 8) for enhancing PHB and EPS productivity. Maximum yield of both PHB (2.62 g L^-1) and EPS (3.92 g L^-1) was observed with carbon load of 30 g L^-1 at pH 7. Scale-up studies were performed with optimized conditions and PHB and EPS production of 2.62 g L^-1 and 3.91 g L^-1, respectively was observed. The extracted EPS and PHB were characterized using FT-IR, FE-SEM-EDX, H¹ and C¹³ NMR and fluorescence microscopy.

Recent developments in Polyhydroxyalkanoates (PHAs) production - A review

Polyhydroxyalkanoates (PHAs) are inevitably a key biopolymer that has the potential to replace the conventional petrochemical based plastics that pose jeopardy to the environment globally. Even then the reach of PHA in the common market is so restricted. The economy of PHA is such that, even after several attempts the overall production cost seems to be high and this very factor surpasses PHAs usage when compared to the conventional polymers. The major focus of the review relies on the synthesis of PHA from Mixed Microbial Cultures (MMCs), through a 3-stage process most probably utilizing feedstocks from waste streams or models that mimic them. Emphasis was given to the works carried out in the past decade and their coherence with each and every individual criteria (Aeration, Substrate and bioprocess parameters) such that to understand their effect in enhancing the overall production of PHA.

Bioconversion of waste (water)/residues to bioplastics- A circular bioeconomy approach

Research insight into the technical challenges of bioplastics production has revealed their confoundedness in their niche markets and struggles to enter the mainstream. There is an increasing problem of waste disposal and high cost of pure substrates in polyhydroxyalkanoates (PHA) production. This has led to the future need of upgrading the waste streams from different industries into the role of feedstocks for production of PHA. The review covers the latest developments in using wastes and surplus materials for PHA production. In addition to inexpensive carbon sources, efficient upstream and downstream processes and recycling of waste streams within the process are required to maintain the circularity in the entire process. A view on the link between circular bioeconomy and PHA production process covering the techno-economic, life cycle assessment and environmental aspects has also been provided. Furthermore, the future perspectives related to the topic have also been discussed.

Production of feather oligopeptides by a newly isolated bacterium Pseudomonas otitis H11

Oligopeptides usually have high nutritive value and multiple physiological functions. To achieve the highly efficient utilization of feather waste, a feather-degrading bacterium, Pseudomonas otitis, was isolated and used for production of feather oligopeptides. The production potential and characteristics of the produced oligopeptides by H11 were also investigated. The results demonstrated that the optimal initial pH, temperature, fermentation time, and sterilization conditions were 11, 40°C, 24 h, and 121°C for 20 min, respectively. After 24 h of fermentation under the optimal conditions, the feathers were almost completely degraded. Correspondingly, 35.37% oligopeptides (accounting for 69.70% of the total soluble peptides) and varieties of essential amino acids (valine, isoleucine, leucine, phenylalanine, methionine, threonine, and lysine) were obtained. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis indicated that the produced oligopeptides were mainly low molecular weight (below 1600 Da) and rich in branched-chain amino acids. Also, the oligopeptide-enriched hydrolysate displayed good antioxidant activity with 83% 2,2-diphenyl-1-picrylhydrazyl (DPPH•) scavenging ability and 53% superoxide anion (O2•-) scavenging activity. This study demonstrated that the hydrolysate of feathers was abundant in oligopeptide fractions with 5-10amino acid residues and possessed good antioxidant activity. This oligopeptide-enriched hydrolysate could be used as a functional feed supplement and as a source for functional oligopeptide extraction.

Microstructural Behaviors of Matrices Based on Polylactic Acid and Polyhydroxyalkanoates

Individual films of polyhydroxyalkanoates (PHA) and polylactic acid (PLA) and their blends were developed by solvent casting. PHA was obtained from activated sludges from a wastewater-treatment system at a laboratory scale. This work focused on analyzing the microstructural properties and thermal behaviors of individual films of PHA and PLA as well as those of their blends. The behaviors of the biodegradation processes of the individual films and blends were examined from a microstructural point of view. ATR-FTIR spectra indicated the existence of weak molecular interactions between the polymers. The formulation of blend films improved the crystallinity of PLA; additionally, it induced the polymer-recrystallization phenomenon, because crystallized PHA acted as a PLA-nucleating agent. This phenomenon explains the improvements in the films' water-vapor-barrier properties. The blends exposed to a biodegradation process showed an intermediate behavior between PLA and PHA, leading to a consistent basis for designing systems tailored to a particular purpose.

Anaerobic accumulation of short-chain fatty acids from algae enhanced by damaging cell structure and promoting hydrolase activity

Short-chain fatty acid (SCFAs) produced from harvested algae by anaerobic fermentation with uncontrolled pH was limited due to the solid cell structure of algae. This study, therefore, was undertaken to enhance the generation of SCFAs from algae by controlling the fermentation pH. pH influenced not only the total SCFAs production, but the percentage of individual SCFA. The maximal yield of SCFAs occurred at pH 10.0 and fermentation time of 6 d (3161 mg COD/L), which mainly contained acetic and iso-valeric acids and was nearly eight times that at uncontrolled pH (392 mg COD/L). Mechanism exploration revealed at alkaline pH, especially at pH 10.0, not only the cell structure of algae was damaged effectively, but also activities and relative quantification of hydrolases as well as the abundance of microorganisms responsible for organics hydrolysis and SCFAs production were improved. Also, the released microcystins from algae were removed efficiently during alkaline anaerobic fermentation.

Statistical Design of Experimental and Bootstrap Neural Network Modelling Approach for Thermoseparating Aqueous Two-Phase Extraction of Polyhydroxyalkanoates

At present, polyhydroxyalkanoates (PHAs) have been considered as a promising alternative to conventional plastics due to their diverse variability in structure and rapid biodegradation. To ensure cost competitiveness in the market, thermoseparating aqueous two-phase extraction (ATPE) with the advantages of being mild and environmental-friendly was suggested as the primary isolation and purification tool for PHAs. Utilizing two-level full factorial design, this work studied the influence and interaction between four independent variables on the partitioning behavior of PHAs. Based on the experimental results, feed forward neural network (FFNN) was used to develop an empirical model of PHAs based on the ATPE thermoseparating input-output parameter. In this case, bootstrap resampling technique was used to generate more data. At the conditions of 15 wt % phosphate salt, 18 wt % ethylene oxide–propylene oxide (EOPO), and pH 10 without the addition of NaCl, the purification and recovery of PHAs achieved a highest yield of 93.9%. Overall, the statistical analysis demonstrated that the phosphate concentration and thermoseparating polymer concentration were the most significant parameters due to their individual influence and synergistic interaction between them on all the response variables. The final results of the FFNN model showed the ability of the model to seamlessly generalize the relationship between the input–output of the process.

The link of feast-phase dissolved oxygen (DO) with substrate competition and microbial selection in PHA production

Polyhydroxyalkanoates (PHAs) are biobased and biodegradable polyesters with the potential to replace conventional plastics. Aeration requires large amounts of energy in PHA production by mixed microbial cultures (MMCs), particularly during the feast phase due to substrate uptake. The objective of this study was to investigate the impact of DO concentrations on microbial selection, substrate competition and PHA production performance by MMCs. This represents the first study investigating DO impact on PHA production while feeding the multiple volatile fatty acids (VFAs) typically encountered in real fermented feedstocks, as well as the substrate preferences at different DO levels. Efficient microbial cultures were enriched under both high (3.47 ± 1.12 mg/L) and low (0.86 ± 0.50 mg/L) DO conditions in the feast phase containing mostly the same populations but with different relative abundance. The most abundant microorganisms in the two MMCs were Plasticicumulans, Zoogloea, Paracoccus, and Flavobacterium. Butyrate and valerate were found to be the preferred substrates as compared to acetate and propionate regardless of DO concentrations. In the accumulation step, the PHA storage capacity and yield were less affected by the change of DO levels when applying the culture selected under low DO in the feast phase (PHA storage capacity >60% and yield > 0.9 Cmol PHA/Cmol VFA). A high DO level is required for maximal PHA accumulation rates with the four VFAs (acetate, propionate, butyrate and valerate) present, due to the lower specific uptake rates of acetate and propionate under low DO conditions. However, butyrate and valerate specific uptake rates were less impacted by DO levels and hence low DO for PHA accumulation may be effective when feed is composed of these substrates only.

Cloud-point extraction of green-polymers from Cupriavidus necator lysate using thermoseparating-based aqueous two-phase extraction

Polyhydroxyalkanoates (PHAs), a class of renewable and biodegradable green polymers, have gained attraction as a potential substitute for the conventional plastics due to the increasing concern towards environmental pollution as well as the rapidly depleting petroleum reserve. Nevertheless, the high cost of downstream processing of PHA has been a bottleneck for the wide adoption of PHAs. Among the options of PHAs recovery techniques, aqueous two-phase extraction (ATPE) outshines the others by having the advantages of providing a mild environment for bioseparation, being green and non-toxic, the capability to handle a large operating volume and easily scaled-up. Utilizing unique properties of thermo-responsive polymer which has decreasing solubility in its aqueous solution as the temperature rises, cloud point extraction (CPE) is an ATPE technique that allows its phase-forming component to be recycled and reused. A thorough literature review has shown that this is the first time isolation and recovery of PHAs from Cupriavidus necator H16 via CPE was reported. The optimum condition for PHAs extraction (recovery yield of 94.8% and purification factor of 1.42 fold) was achieved under the conditions of 20 wt/wt % ethylene oxide-propylene oxide (EOPO) with molecular weight of 3900 g/mol and 10 mM of sodium chloride addition at thermoseparating temperature of 60°C with crude feedstock limit of 37.5 wt/wt %. Recycling and reutilization of EOPO 3900 can be done at least twice with satisfying yield and PF. CPE has been demonstrated as an effective technique for the extraction of PHAs from microbial crude culture.

Production of poly-3-hydroxybutyrate (P3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) from synthetic wastewater using Hydrogenophaga palleronii

In the present study, synthetic wastewater (SW) was used for production of poly-3-hydroxybutyrate (P3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) using the bacteria Hydrogenophaga palleronii. SW at various volatile fatty acids concentrations (5-60g/l) was evaluated for the growth and biopolymer production using H. palleronii. Substrate degradation was analyzed using total organic carbon (TOC) analyzer and high pressure liquid chromatography (HPLC). H. palleronii showed highest and lowest removal of TOC at 5g/l (88±4%) and 60g/l (15±6%) respectively. Among all the concentrations evaluated, bacteria showed highest biopolymer production with 20g/l (63±5%), followed by 30g/l (58±3%) and 40g/l (56±2%). Lowest biopolymer production was observed at 5g/l concentration (21±3%). Structure, molecular weight, and thermal properties of the produced biopolymer were analyzed. These results denoted that the strain H. palleronii can be used for degradation of high concentration of volatile fatty acids persistent in wastewaters and their subsequent conversion into useable biopolymers.

Poly-3-hydroxybutyrate (PHB) production from alkylphenols, mono and poly-aromatic hydrocarbons using Bacillus sp. CYR1: A new strategy for wealth from waste

In the present study five different types of alkylphenols, each of the two different types of mono and poly-aromatic hydrocarbons were selected for degradation, and conversion into poly-3-hydroxybutyrate (PHB) using the Bacillus sp. CYR1. Strain CYR1 showed growth with various toxic organic compounds. Degradation pattern of all the organic compounds at 100 mg/l concentration with or without addition of tween-80 were analyzed using high pressure liquid chromatography (HPLC). Strain CYR1 showed good removal of compounds in the presence of tween-80 within 3 days, but it took 6 days without addition of tween-80. Strain CYR1 showed highest PHB production with phenol (51 ± 5%), naphthalene (42 ± 4%), 4-chlorophenol (32 ± 3%) and 4-nonylphenol (29 ± 3%). The functional groups, structure, and thermal properties of the produced PHB were analyzed. These results denoted that the strain Bacillus sp. CYR1 can be used for conversion of different toxic compounds persistent in wastewaters into useable biological polyesters.

Acidogenic fermentation of food waste for volatile fatty acid production with co-generation of biohydrogen

Fermentation experiments were designed to elucidate the functional role of the redox microenvironment on volatile fatty acid (VFA, short chain carboxylic acid) production and co-generation of biohydrogen (H2). Higher VFA productivity was observed at pH 10 operation (6.3g/l) followed by pH 9, pH 6, pH 5, pH 7, pH 8 and pH 11 (3.5 g/l). High degree of acidification, good system buffering capacity along with co-generation of higher H2 production from food waste was also noticed at alkaline condition. Experiments illustrated the role of initial pH on carboxylic acids synthesis. Alkaline redox conditions assist solubilization of carbohydrates, protein and fats and also suppress the growth of methanogens. Among the carboxylic acids, acetate fraction was higher at alkaline condition than corresponding neutral or acidic operations. Integrated process of VFA production from waste with co-generation of H2 can be considered as a green and sustainable platform for value-addition.

Applied potentials regulate recovery of residual hydrogen from acid-rich effluents: Influence of biocathodic buffer capacity over process performance

An absolute biological microbial electrolysis cell (MEC) was operated for a prolonged period under different applied potentials (Eapp, -0.2V to -1.0V) and hydrogen (H2) production was observed using acid-rich effluent. Among these potentials, an optimal voltage of -0.6 V influenced the biocathode by which maximum H2 production of 120 ± 9 ml was noticed. This finding was corroborated with dehydrogenase activity (1.8 ± 0.1 μg/ml) which is the key enzyme for H2 production. The in situ biocathode regulated buffer overpotentials which was remarkably observed by the change in peak heights of dissociation value (pKa) from the titration curve. Substrate degradation analysis gave an estimate of coulombic efficiency of about 72 ± 5% when operated at optimal voltage. Evidently, the electron transfer from solid carbon electrode to biocathode was analyzed by cyclic voltammetry and its derivatives showed the involvement of redox mediators. Despite, the MEC endures certain activation overpotentials which were estimated from the Tafel slope analysis.

Sustainable multistage process for enhanced productivity of bioplastics from waste remediation through aerobic dynamic feeding strategy: Process integration for up-scaling

Polyhydroxyalkanoates (PHA) production was evaluated in a multistage operation using food waste as a renewable feedstock. The first step involved the production of bio-hydrogen (bio-H2) via acidogenic fermentation. Volatile fatty acid (VFA) rich effluent from bio-H2 reactor was subsequently used for PHA production, which was carried out in two stages, Stage II (culture enrichment) and Stage III (PHA production). PHA-storing microorganisms were enriched in a sequencing batch reactor (SBR), operated at two different cycle lengths (CL-24; CL-12). Higher polymer recovery as well as VFA removal was achieved in CL-12 operation both in Stage II (16.3% dry cell weight (DCW); VFA removal, 84%) and Stage III (23.7% DCW; VFA removal, 88%). The PHA obtained was a co-polymer [P(3HB-co-3HV)] of PHB and PHV. The results obtained indicate that this integrated multistage process offers new opportunities to further leverage large scale PHA production with simultaneous waste remediation in the framework of biorefinery.

Systematic approach to assess biohydrogen potential of anaerobic sludge and soil rhizobia as biocatalysts: Influence of crucial factors affecting acidogenic fermentation

A systematic protocol was designed to enumerate the variation in biohydrogen production with two different biocatalysts (sludge and soil) under different pH and organic loads. Both the biocatalysts showed cumulatively higher H2 production under acidogenic condition (pH 6) than at neutral pH condition. The cumulative hydrogen production was non-linearly fitted with modified Gompertz model and statistically validated. Pretreated soil biocatalyst showed relatively higher H2 production (OLR II, 142±5ml) than pretreated sludge (OLR I, 123±5ml); which was evidenced by substrate linked dehydrogenase activity and bio-electrochemical analysis. Experimental results revealed agricultural soil as a better biocatalyst than anaerobic sludge for all the operated process conditions. The voltammogram profiles and Tafel slopes revealed dominance of reductive catalytic activity of the pretreated inoculums substantiating dark-fermentation. Soil consortia showed low polarization resistance (2.24kΩ) and high reductive electron transfer efficiency (1.17 Vdec(-1)) at a high organic load; thus, rebating high H2 production.

Aerobic dynamic feeding as a strategy for in situ accumulation of polyhydroxyalkanoate in aerobic granules

Aerobic dynamic feeding (ADF) strategy was applied in sequencing batch reactor (SBR) to accumulate polyhydroxyalkanoate (PHA) in aerobic granules. The aerobic granules were able to remove 90% of the COD from palm oil mill effluent (POME). The volatile fatty acids (VFAs) in the POME are the sole source of the PHA accumulation. In this work, 100% removal of propionic and butyric acids in the POME were observed. The highest amount of PHA produced in aerobic granules was 0.6833mgPHA/mgbiomass. The PHA formed was identified as a P (hydroxybutyrate-co-hydroxyvalerate) P (HB-co-HV).

Acidogenic spent wash valorization through polyhydroxyalkanoate (PHA) synthesis coupled with fermentative biohydrogen production

The production of polyhydroxyalkanoates (PHAs) by Bacillus tequilensis biocatalyst using spent wash effluents as substrate was evaluated to increase the versatility of the existing PHA production process and reduce production cost. In this study, spent wash was used as a substrate for biohydrogen (H2) production and the resulting acidogenic effluents were subsequently employed as substrate for PHA production. Maximum H2 production of 39.8L and maximum PHA accumulation of 40% dry cell weight was attained. Good substrate removal associated with decrement in acidification (53% to 15%) indicates that the VFA generated were effectively utilized for PHA production. The PHA composition showed presence of copolymer [P (3HB-co-3HV)] with varying contents of hydroxybutyrate and hydroxyvalerate. The results obtained suggest that the use of spent wash effluents as substrate can considerably reduce the production cost of PHA with simultaneous waste valorization. PHA synthesis with B. tequilensis and spent wash effluents is reported for the first time.

Biotechnological Production of Polyhydroxyalkanoates: A Review on Trends and Latest Developments

Polyhydroxyalkanoates (PHA) producers have been reported to reside at various ecological niches which are naturally or accidently exposed to high organic matter or growth limited conditions such as dairy wastes, hydrocarbon contaminated sites, pulp and paper mill wastes, agricultural wastes, activated sludges of treatment plants, rhizosphere, and industrial effluents. Few among them also produce extracellular by-products like rhamnolipids, extracellular polymeric substances, and biohydrogen gas. These sorts of microbes are industrially important candidates for the reason that they can use waste materials of different origin as substrate with simultaneous production of valuable bioproducts including PHA. Implementation of integrated system to separate their by-products (intracellular and extracellular) can be economical in regard to production. In this review, we have discussed various microorganisms dwelling at different environmental conditions which stimulate them to accumulate carbon as polyhydroxyalkanoates granules and factors influencing its production and composition. A brief aspect on metabolites which are produced concomitantly with PHA has also been discussed. In conclusion, exploring of capabilities like of dual production by microbes and use of wastes as renewable substrate under optimized cultural conditions either in batch or continuous process can cause deduction in present cost of bioplastic production from stored PHA granules.

Relative effect of different inorganic acids on selective enrichment of acidogenic biocatalyst for fermentative biohydrogen production from wastewater

The effect of different inorganic acids viz., HNO3, HCl, H2SO4 and H3PO4 on inoculum pretreatment to selectively enrich hydrogen (H2) producing acidogenic bacteria was evaluated in anaerobic sequencing batch bioreactors. Relative positive efficiency of HNO3 pretreated consortia in enhancing H2 production (11.85 mol H2/kg CODR) was noticed compared to other acids (HCl, 5.64 mol H2/kg CODR; H2SO4, 7.65 mol H2/kg CODR; H3PO4, 6.90 mol H2/kg CODR) and untreated-parent consortia (control, 6.80 mol H2/kg CODR). On the contrary, substrate degradation (COD removal) was higher with the control operation (ξCOD, 66.3%; substrate degradation rate (SDR), 1.42 kg CODR/m(3)-day) compared to pre-treated culture. HNO3 pre-treatment resulted in a shift in the fermentation pathway towards more acetic acid production, while other acid pretreatment and untreated culture showed mixed type fermentation (acetic, butyric, propionic acids). The bio-electrochemical analysis and dehydrogenase activity supported the biocatalyst performance after HNO3 pretreatment with specific enrichment of Firmicutes and Bacillus.

Pseudomonas putida KT2442 as a platform for the biosynthesis of polyhydroxyalkanoates with adjustable monomer contents and compositions

The β-oxidation weakened Pseudomonas putida were established as a platform for the production of polyhydroxyalkanoates (PHA) with adjustable monomer compositions and micro-structures. When mutant P. putida KTOYO6ΔC (phaPCJA.c) was cultivated on mixtures of sodium butyrate and sodium hexanoate (C4:C6), random copolymers of P(3HB-co-3HHx) consisting of 3-hydroxybutyrate (3HB), 3-hydroxyhexanoate (3HHx), were accumulated with 3HHx content ranged from 19 mol% to 75 mol%. While recombinant P. putida KTQQ20 grown on mixtures of sodium hexanoate and decanoic acid (C6:C10), produced random copolymers of P(3HHx-co-3HD) consisting of 3-hydroxyhexanoate (3HHx) and 3-hydroxydecanoate (3HD), the monomer fraction of 3HHx ranged from 16 mol% to 63 mol%. The comonomer compositions were easily regulated by varying the fatty acid concentrations. P. putida KTQQ20 produced a novel diblock copolymer P3HHx-b-P(3HD-co-3HDD) consisting of 49 mol% P3HHx and 51 mol% P(3HD-co-3HDD) [35.25 mol% 3HDD (3-hydroxydodecanoate)], which was characterized by (13)C NMR, HMBC NMR, DSC, GPC and universal testing machine.

Enzymatic synthesis of S-phenyl-L-cysteine from keratin hydrolysis industries wastewater with tryptophan synthase

An economical method for production of S-phenyl-L-cysteine from keratin acid hydrolysis wastewater (KHW) containing L-serine was developed by recombinant tryptophan synthase. This study provides us with an alternative KHW utilization strategy to synthesize S-phenyl-L-cysteine. Tryptophan synthase could efficiently convert L-serine contained in KHW to S-phenyl-L-cysteine at pH 9.0, 40°C and Trion X-100 of 0.02%. In a scale up study, L-serine conversion rate reach 97.1% with a final S-phenyl-L-cysteine concentration of 38.6 g l(-1).

Biofilm-mediated enhanced crude oil degradation by newly isolated pseudomonas species

The bioavailability of organic contaminants to the degrading bacteria is a major limitation to efficient bioremediation of sites contaminated with hydrophobic pollutants. Such limitation of bioavailability can be overcome by steady-state biofilm-based reactor. The aim of this study was to examine the effect of such multicellular aggregation by naturally existing oil-degrading bacteria on crude oil degradation. Microorganisms, capable of utilizing crude oil as sole carbon source, were isolated from river, estuary and sea-water samples. Biochemical and 16S rDNA analysis of the best degraders of the three sources was found to belong to the Pseudomonas species. Interestingly, one of the isolates was found to be close to Pseudomonas otitidis family which is not reported yet as a degrader of crude oil. Biodegradation of crude oil was estimated by gas chromatography, and biofilm formation near oil-water interface was quantified by confocal laser scanning microscopy. Biofilm supported batches of the isolated Pseudomonas species were able to degrade crude oil much readily and extensively than the planktonic counterparts. Volumetric and topographic analysis revealed that biofilms formed in presence of crude oil accumulate higher biomass with greater thickness compared to the biofilms produced in presence of glucose as sole carbon source.

Optimization of critical factors to enhance polyhydroxyalkanoates (PHA) synthesis by mixed culture using Taguchi design of experimental methodology

Optimizing different factors is crucial for enhancement of mixed culture bioplastics (polyhydroxyalkanoates (PHA)) production. Design of experimental (DOE) methodology using Taguchi orthogonal array (OA) was applied to evaluate the influence and specific function of eight important factors (iron, glucose concentration, VFA concentration, VFA composition, nitrogen concentration, phosphorous concentration, pH, and microenvironment) on the bioplastics production. Three levels of factor (2(1) × 3(7)) variation were considered with symbolic arrays of experimental matrix [L(18)-18 experimental trails]. All the factors were assigned with three levels except iron concentration (2(1)). Among all the factors, microenvironment influenced bioplastics production substantially (contributing 81%), followed by pH (11%) and glucose concentration (2.5%). Validation experiments were performed with the obtained optimum conditions which resulted in improved PHA production. Good substrate degradation (as COD) of 68% was registered during PHA production. Dehydrogenase and phosphatase enzymatic activities were monitored during process operation.