Pseudomonas putida KT2442 cultivated on glucose accumulates poly(3-hydroxyalkanoates) consisting of saturated and unsaturated monomers

Constant fed-batch cultivation with glucose and propionate as co-substrate: A strategy to fine-tune polyhydroxyalkanoates monomeric composition in Pseudomonas spp

Pseudomonas sp. LFM693 is a 2-methylisocitrate lyase (prpB) disrupted mutant. This enzyme catalyzes a step in the 2-methylcitrate cycle, the only known and described pathway for propionate oxidation in this organism. The affected mutants can efficiently produce PHA containing even and odd-chain length hydroxyalkanoates (HAeven/odd) in the presence of propionate and glucose. In this study, a constant fed-batch configuration was utilized to control the composition of PHA and decrease the toxicity of propionate. The incorporation of HAodd into the copolymer was linear, ranging from 7 to approximately 30 %, and correlated directly with the propionate/glucose molar ratio in the feeding solution. This allowed for the molecular composition of the mclPHA to be fine-tuned with minimum process monitoring and control. The average PHA content was 52 % cell dry weight with a molar composition that favored 3-hydroxyalkanoates containing C8, C9, and C10. The conversion factor of propionate to HAodd varied between 0.36 and 0.53 mol·mol-1 (YHAodd/prop.), which are significantly lower than the theoretical maximum efficiency (1.0 mol·mol-1). These results along with the lack of 2-methylisocitrate as a byproduct provides further support for the evidence that the mutant prpB- is still capable of oxidizing propionate.

Polyhydroxyalkanoate production in Pseudomonas putida from alkanoic acids of varying lengths

Many studies have been conducted to produce microbial polyhydroxyalkanoates (PHA), a biopolymer, from Pseudomonas sp. fed with various alkanoic acids. Because this previous data was collected using methodologies that varied in critical aspects, such as culture media and size range of alkanoic acids, it has been difficult to compare the results for a thorough understanding of the relationship between feedstock and PHA production. Therefore, this study utilized consistent culture media with a wide range of alkanoic acids (C7-C14) to produce medium chain length PHAs. Three strains of Pseudomonas putida (NRRL B-14875, KT2440, and GN112) were used, and growth, cell dry weight, PHA titer, monomer distribution, and molecular weights were all examined. It was determined that although all the strains produced similar PHA titers using C7-C9 alkanoic acids, significant differences were observed with the use of longer chain feedstocks. Specifically, KT2440 and its derivative GN112 produced higher PHA titers compared to B-14875 when fed longer chain alkanoates. We also compared several analytical techniques for determining amounts of PHA and found they produced different results. In addition, the use of an internal standard had a higher risk of calculating inaccurate concentrations compared to an external standard. These observations highlight the importance of considering this aspect of analysis when evaluating different studies.

Novel Anti-Acetylcholinesterase Effect of Euonymus laxiflorus Champ. Extracts via Experimental and In Silico Studies

Alzheimer's disease (AD) is the most common form of dementia, which is recorded as a global health issue. Natural acetylcholinesterase inhibitors (AChEIs) are considered a helpful therapy for the management of symptoms of patients with mild-to-moderate AD. This work aimed to investigate and characterize Euonymus laxiflorus Champ. (ELC) as a natural source of AChEIs compounds via in vitro and virtual studies. The screening parts used, including the leaves, heartwood, and trunk bark of ELC, revealed that the trunk bark extract possessed the highest activity, phenolics and flavonoid content. The in vitro anti-Alzheimer activity of ELC trunk bark was notably reclaimed for the first time with comparable effect (IC₅₀ = 0.332 mg/mL) as that of a commercial AChEI, berberine chloride (IC₅₀ = 0.314 mg/mL). Among various solvents, methanol was the most suitable to extract ELC trunk bark with the highest activity. Twenty-one secondary metabolites (1-21) were identified from ELC trunk bark extract, based on GCMS and UHPLC analyses. Of these, 10 volatile compounds were identified from this herbal extract for the first time. One phenolic (11) and seven flavonoid compounds (15-21) were also newly found in this herbal extract. Of the identified compounds, chlorogenic acid (11), epigallocatechin gallate (12), epicatechin (13), apigetrin (18), and quercetin (20) were major compounds with a significant content of 395.8-2481.5 μg/g of dried extract. According to docking-based simulation, compounds (11-19, and 21) demonstrated more effective inhibitory activity than berberine chloride, with good binding energy (DS values: -12.3 to -14.4 kcal/mol) and acceptable RMSD values (0.77-1.75 Å). In general, these identified compounds processed drug properties and were non-toxic for human use, based on Lipinski's rule of five and ADMET analyses.

Medium chain length polyhydroxyalkanoate produced from ethanol by Pseudomonas putida grown in liquid obtained from acidogenic digestion of organic municipal solid waste

Production of medium chain length polyhydroxyalkanoate (mcl-PHA) up to about 6 g.L^-1 was obtained by feeding ethanol to Pseudomonas putida growing in liquid obtained from acidogenic digestion of organic municipal solid waste. Washing the wet, heat-inactivated Pseudomonas cells at the end of the fermentation with ethanol obviated the need of drying the biomass and enabled the removal of contaminating lipids before solvent-mediated extraction of PHA. Using 'green' solvents, 90 to near 100% of the mcl-PHA was extracted and purities of 71-78% mcl-PHA were reached already by centrifugation and decantation without further filtration for biomass removal. The mcl-PHA produced in this way consists of 10-18% C8, 72-78% C10 and 8-12% C12 chains (entirely medium chain length), has a crystallinity and melting temperature of ∼13% and ∼49 °C, respectively, and is a stiff rubberlike, colourless material at room temperature.

Methods of Analyses for Biodegradable Polymers: A Review

Biodegradable polymers are materials that can decompose through the action of various environmental microorganisms, such as bacteria and fungi, to form water and carbon dioxide. The biodegradability characteristics have led to a growing demand for the accurate and precise determination of the degraded polymer composition. With the advancements in analytical product development, various analytical methods are available and touted as practical and preferable methods of bioanalytical techniques, which enable the understanding of the complex composition of biopolymers such as polyhydroxyalkanoates and poly(lactic acid). The former part of this review discusses the definition and examples of biopolymers, followed by the theory and instrumentation of analytical methods applicable to the analysis of biopolymers, such as physical methods (SEM, TEM, weighing analytical balance, etc.), chromatographic methods (GC, THM-GC, SEC/GPC), spectroscopic methods (NMR, FTIR, XRD, XRF), respirometric methods, thermal methods (DSC, DTA, TGA), and meta-analysis. Special focus is given to the chromatographic methods, because this is the routine method of polymer analysis. The aim of this review is to focus on the recent developments in the field of biopolymer analysis and instrument application to analyse the various types of biopolymers.

Polyhydroxyalkanoate bio-production and its rise as biomaterial of the future

The first observation of a polyhydroxyalkanoate (PHA) aggregate was in 1888 by Beijenrinck. Despite polyhydroxybutyrate (PHB) being the first type of PHA discovered, it was not extracted and characterized until 1925 by Maurice Lemoigne in France, even before the concept of "macromolecules" was known. After more than 30 years, in 1958, Wilkinson and co-workers rediscovered PHB and its metabolic role in the cells as storage compound. PHB started to be appealing to the industry in the 1980s, when a few companies started to commercialize microbially produced PHAs. During the 1990 s, the focus was on reducing production costs to make PHA production economically feasible, for instance by genetically modified microorganisms and even plants. Since then, many advances have been made: diverse wastes as feedstock, different production processes, and tailored design of biopolymers. This paper summarizes the scientific and technological development of PHAs from their discovery in 1888 until their latest applications and current commercial uses. Future perspectives have been devised too based on the current bottlenecks.

Streamlining of a synthetic co-culture towards an individually controllable one-pot process for polyhydroxyalkanoate production from light and CO2

Rationally designed synthetic microbial consortia carry a vast potential for biotechnological applications. The application of such a consortium in a bioprocess, however, requires tight and individual controllability of the involved microbes. Here, we present the streamlining of a co-cultivation process consisting of Synechococcus elongatus cscB and Pseudomonas putida for the production of polyhydroxyalkanoates (PHA) from light and CO₂. First, the process was improved by employing P. putida cscRABY, a strain with a higher metabolic activity towards sucrose. Next, the individual controllability of the co-culture partners was addressed by providing different nitrogen sources, each exclusively available for one strain. By this, the growth rate of the co-culture partners could be regulated individually, and defined conditions could be set. The molC/molN ratio, a key value for PHA accumulation, was estimated from the experimental data, and the necessary feeding rates to obtain a specific ratio could be predicted. This information was then implemented in the co-cultivation process, following the concept of a DBTL-cycle. In total, the streamlining of the process resulted in an increased maximal PHA titer of 393 mg/L and a PHA production rate of 42.1 mg/(L•day).

A Critical Review on the Economically Feasible and Sustainable Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate) Production from Alkyl Alcohols

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) is the most studied short-chain-length polyhydroxyalkanoates (PHA) with high application importance in various fields. The domination of high-cost propionate and valerate over other 3-hydroxyvalerate (3HV) precursors owing to their wide preference among PHA-producing bacteria has hindered the development of diverse production processes. As alkyl alcohols are mainly produced from inexpensive starting materials through oxo synthesis, they contribute a cost-effective advantage over propionate and valerate. Moreover, alkyl alcohols can be biosynthesized from natural substrates and organic wastes. Despite their great potential, their toxicity to most PHA-producing bacteria has been the major drawback for their wide implementation as 3HV precursors for decades. Although the standard PHA-producing bacteria Cupriavidus necator showed promising alcohol tolerance, the 3HV yield was discouraging. Continuous discovery of alkyl alcohols-utilizing PHA-producing bacteria has enabled broader choices in 3HV precursor selection for diverse P(3HB-co-3HV) production processes with higher economic feasibility. Besides continuous effort in searching for promising wild-type strains, genetic engineering to construct promising recombinant strains based on the understanding of the mechanisms involved in alkyl alcohols toxicity and tolerance is an alternative approach. However, more studies are required for techno-economic assessment to analyze the economic performance of alkyl alcohol-based production compared to that of organic acids.

The Production and Analysis of Biodegradable Polymers of Type of Medium-Chain-Length Polyhydroxyalkanoates (mcl-PHA) by Pseudomonas putida Strain for the Biomedical Engineering

BACKGROUND

Polyhydroxyalkanoates (PHAs) are bacteria-synthetized biopolymers under unbalanced growth conditions. These biopolymers are considered potential biomaterials for future applications for their biocompatibility and biodegradable features and potential biomaterials for future applications for their biocompatibility and biodegradable characteristics and their ability to be quickly produced and functionalize with strong mechanical resistance. This article is intended to perform microbial fermentation using Pseudomonas putida strain to show the amount of biopolymers of the type polyhydroxyalkanoates with medium-chain-length (mcl-PHA) obtained depending on the type and quantity of added precursors (glucose and fatty acids).

METHODS

It is important to understand the microbial interaction and mechanism involved in PHA biosynthetis.For these, several methods were used, such as: obtaining microbial biomass by using a Pseudomonas putida strain able of PHA-producing, analysis of biopolymer production by acetone extraction following the Soxhlet method, purification of biopolymer by methanol-ethanol treatment, followed by the estimation of biomass by spectrophotometric analysis and the measurement of the dry weight of cells and the quantification of the amount of biopolymer produced following the gas chromatographic method (GC).

RESULTS

The highest PHA yield was obtained using octanoic (17 mL in 2000 mL medium) and hexanoic acids (14 mL in 2000 mL medium) as precursors. Consequently, octanoic acid - octanoic acid, heptanoic acid - nonanoic acid, and octanoic acid - hexanoic acid were the mix of precursors that supported the amount of PHA obtained.

CONCLUSION

Of the 4 types of structurally related substrate, the strain Pseudomonas putida ICCF 319 prefers the C8 sublayer for an elastomeric PHA's biosynthesis with a composition in which the C8 monomer predominates over C6 and C10.

Comprehensive optimization of tropical biomass hydrolysis for nitrogen-limited medium-chain polyhydroxyalkanoate synthesis

Expanding the use of tropical biomass wastes for nitrogen-limited fermentation was investigated, specifically, the production of medium chain length polyhydroxyalkanoates. Comprehensive central composite design was conducted to assess pH, temperature, biomass solid loading, cellulase loading and amylase loading and their impact on the hydrolysis of palm, coconut and cassava wastes. Glucose yields of 33.3, 31.7 and 79.0% wt. with respect to total glucose were found for palm, coconut and cassava, respectively. Importantly, the impact on the total nitrogen derived during enzymatic hydrolysis of these tropical biomass was described for the first time. The level of nitrogen needs to be properly controlled as high nitrogen would result in low carbon to nitrogen ratio leading to low polyhydroxyalkanoates accumulation, but low nitrogen would hinder growth of the biopolymer producer. Maximum hydrolysate nitrogen, were 1.80, 1.55 and 0.871 g/l for palm, coconut and cassava, respectively. Using the surface responses, biomass media designed for high carbon-to-nitrogen were produced and validated using Pseudomonas putida. Low glucose-carbon to nitrogen were found for palm and coconut after scale-up, leading to the majority of their polyhydroxyalkanoates not being biomass-derived. However, cassava-derived biopolymers were successfully accumulated at 9.01 and 7.13% wt. for total medium chain length polyhydroxyalkanoates and 10-carbon polyhydroxyalkanoates, respectively. This study provides an important foundation for the expansion of tropical biomass wastes for biopolymer production and other nitrogen-limited applications in general.

Enhancement of polyhydroxyalkanoate production by co-feeding lignin derivatives with glycerol in Pseudomonas putida KT2440

BACKGROUND

Efficient utilization of all available carbons from lignocellulosic biomass is critical for economic efficiency of a bioconversion process to produce renewable bioproducts. However, the metabolic responses that enable Pseudomonas putida to utilize mixed carbon sources to generate reducing power and polyhydroxyalkanoate (PHA) remain unclear. Previous research has mainly focused on different fermentation strategies, including the sequential feeding of xylose as the growth stage substrate and octanoic acid as the PHA-producing substrate, feeding glycerol as the sole carbon substrate, and co-feeding of lignin and glucose. This study developed a new strategy-co-feeding glycerol and lignin derivatives such as benzoate, vanillin, and vanillic acid in Pseudomonas putida KT2440-for the first time, which simultaneously improved both cell biomass and PHA production.

RESULTS

Co-feeding lignin derivatives (i.e. benzoate, vanillin, and vanillic acid) and glycerol to P. putida KT2440 was shown for the first time to simultaneously increase cell dry weight (CDW) by 9.4-16.1% and PHA content by 29.0-63.2%, respectively, compared with feeding glycerol alone. GC-MS results revealed that the addition of lignin derivatives to glycerol decreased the distribution of long-chain monomers (C10 and C12) by 0.4-4.4% and increased the distribution of short-chain monomers (C6 and C8) by 0.8-3.5%. The ¹H-¹³C HMBC, ¹H-¹³C HSQC, and ¹H-¹H COSY NMR analysis confirmed that the PHA monomers (C6-C14) were produced when glycerol was fed to the bacteria alone or together with lignin derivatives. Moreover, investigation of the glycerol/benzoate/nitrogen ratios showed that benzoate acted as an independent factor in PHA synthesis. Furthermore, ¹H, ¹³C and ³¹P NMR metabolite analysis and mass spectrometry-based quantitative proteomics measurements suggested that the addition of benzoate stimulated oxidative-stress responses, enhanced glycerol consumption, and altered the intracellular NAD⁺/NADH and NADPH/NADP⁺ ratios by up-regulating the proteins involved in energy generation and storage processes, including the Entner-Doudoroff (ED) pathway, the reductive TCA route, trehalose degradation, fatty acid β-oxidation, and PHA biosynthesis.

CONCLUSIONS

This work demonstrated an effective co-carbon feeding strategy to improve PHA content/yield and convert lignin derivatives into value-added products in P. putida KT2440. Co-feeding lignin break-down products with other carbon sources, such as glycerol, has been demonstrated as an efficient way to utilize biomass to increase PHA production in P. putida KT2440. Moreover, the involvement of aromatic degradation favours further lignin utilization, and the combination of proteomics and metabolomics with NMR sheds light on the metabolic and regulatory mechanisms for cellular redox balance and potential genetic targets for a higher biomass carbon conversion efficiency.

Engineering Native and Synthetic Pathways in Pseudomonas putida for the Production of Tailored Polyhydroxyalkanoates

Growing environmental concern sparks renewed interest in the sustainable production of (bio)materials that can replace oil-derived goods. Polyhydroxyalkanoates (PHAs) are isotactic polymers that play a critical role in the central metabolism of producer bacteria, as they act as dynamic reservoirs of carbon and reducing equivalents. PHAs continue to attract industrial attention as a starting point toward renewable, biodegradable, biocompatible, and versatile thermoplastic and elastomeric materials. Pseudomonas species have been known for long as efficient biopolymer producers, especially for medium-chain-length PHAs. The surge of synthetic biology and metabolic engineering approaches in recent years offers the possibility of exploiting the untapped potential of Pseudomonas cell factories for the production of tailored PHAs. In this article, an overview of the metabolic and regulatory circuits that rule PHA accumulation in Pseudomonas putida is provided, and approaches leading to the biosynthesis of novel polymers (e.g., PHAs including nonbiological chemical elements in their structures) are discussed. The potential of novel PHAs to disrupt existing and future market segments is closer to realization than ever before. The review is concluded by pinpointing challenges that currently hinder the wide adoption of bio-based PHAs, and strategies toward programmable polymer biosynthesis from alternative substrates in engineered P. putida strains are proposed.

Polyhydroxyalkanoates: Next generation natural biomolecules and a solution for the world's future economy

Petrochemical plastics have become a cause of pollution for decades and finding alternative plastics that are environmental friendly. Polyhydroxyalkanoate (PHA), a biopolyester produced by microbial cells, has characteristics (biocompatible, biodegradable, non-toxic) that make it appropriate as a biodegradable plastic substance. The different forms of PHA make it suitable to a wide choice of products, from packaging materials to biomedical applications. The major challenge in commercialization of PHA is the cost of manufacturing. There are a lot of factors that could affect the efficiency of a development method. The development of new strategic parameters for better synthesis, including consumption of low cost carbon substrates, genetic modification of PHA-producing strains, and fermentational strategies are discussed. Recently, many efforts have been made to develop a method for the cost-effective production of PHAs. The isolation, analysis as well as characterization of PHAs are significant factors for any developmental process. Due to the biodegradable and biocompatible properties of PHAs, they are majorly used in biomedical applications such as vascular grafting, heart tissue engineering, skin tissue repairing, liver tissue engineering, nerve tissue engineering, bone tissue engineering, cartilage tissue engineering and therapeutic carrier. The emerging and interesting area of research is the development of self-healing biopolymer that could significantly broaden the operational life and protection of the polymeric materials for a broad range of uses. Biodegradable and biocompatible polymers are considered as the green materials in place of petroleum-based plastics in the future.

Cyanobacterial Polyhydroxyalkanoates: A Sustainable Alternative in Circular Economy

Conventional petrochemical plastics have become a serious environmental problem. Its unbridled use, especially in non-durable goods, has generated an accumulation of waste that is difficult to measure, threatening aquatic and terrestrial ecosystems. The replacement of these plastics with cleaner alternatives, such as polyhydroxyalkanoates (PHA), can only be achieved by cost reductions in the production of microbial bioplastics, in order to compete with the very low costs of fossil fuel plastics. The biggest costs are carbon sources and nutrients, which can be appeased with the use of photosynthetic organisms, such as cyanobacteria, that have a minimum requirement for nutrients, and also using agro-industrial waste, such as the livestock industry, which in turn benefits from the by-products of PHA biotechnological production, for example pigments and nutrients. Circular economy can help solve the current problems in the search for a sustainable production of bioplastic: reducing production costs, reusing waste, mitigating CO2, promoting bioremediation and making better use of cyanobacteria metabolites in different industries.

High titer methyl ketone production with tailored Pseudomonas taiwanensis VLB120

Methyl ketones present a group of highly reduced platform chemicals industrially produced from petroleum-derived hydrocarbons. They find applications in the fragrance, flavor, pharmacological, and agrochemical industries, and are further discussed as biodiesel blends. In recent years, intense research has been carried out to achieve sustainable production of these molecules by re-arranging the fatty acid metabolism of various microbes. One challenge in the development of a highly productive microbe is the high demand for reducing power. Here, we engineered Pseudomonas taiwanensis VLB120 for methyl ketone production as this microbe has been shown to sustain exceptionally high NAD(P)H regeneration rates. The implementation of published strategies resulted in 2.1 g L_aq^-1 methyl ketones in fed-batch fermentation. We further increased the production by eliminating competing reactions suggested by metabolic analyses. These efforts resulted in the production of 9.8 g L_aq^-1 methyl ketones (corresponding to 69.3 g L_org^-1 in the in situ extraction phase) at 53% of the maximum theoretical yield. This represents a 4-fold improvement in product titer compared to the initial production strain and the highest titer of recombinantly produced methyl ketones reported to date. Accordingly, this study underlines the high potential of P. taiwanensis VLB120 to produce methyl ketones and emphasizes model-driven metabolic engineering to rationalize and accelerate strain optimization efforts.

Pseudomonas putida KT2440 is naturally endowed to withstand industrial-scale stress conditions

Pseudomonas putida is recognized as a very promising strain for industrial application due to its high redox capacity and frequently observed tolerance towards organic solvents. In this research, we studied the metabolic and transcriptional response of P. putida KT2440 exposed to large-scale heterogeneous mixing conditions in the form of repeated glucose shortage. Cellular responses were mimicked in an experimental setup comprising a stirred tank reactor and a connected plug flow reactor. We deciphered that a stringent response-like transcriptional regulation programme is frequently induced, which seems to be linked to the intracellular pool of 3-hydroxyalkanoates (3-HA) that are known to serve as precursors for polyhydroxyalkanoates (PHA). To be precise, P. putida is endowed with a survival strategy likely to access cellular PHA, amino acids and glycogen in few seconds under glucose starvation to obtain ATP from respiration, thereby replenishing the reduced ATP levels and the adenylate energy charge. Notably, cells only need 0.4% of glucose uptake to build those 3-HA-based energy buffers. Concomitantly, genes that are related to amino acid catabolism and β-oxidation are upregulated during the transient absence of glucose. Furthermore, we provide a detailed list of transcriptional short- and long-term responses that increase the cellular maintenance by about 17% under the industrial-like conditions tested.

Biotransformation of d-xylose to d-xylonate coupled to medium-chain-length polyhydroxyalkanoate production in cellobiose-grown Pseudomonas putida EM42

Co-production of two or more desirable compounds from low-cost substrates by a single microbial catalyst could greatly improve the economic competitiveness of many biotechnological processes. However, reports demonstrating the adoption of such co-production strategy are still scarce. In this study, the ability of genome-edited strain Pseudomonas putida EM42 to simultaneously valorize d-xylose and d-cellobiose - two important lignocellulosic carbohydrates - by converting them into the platform chemical d-xylonate and medium-chain-length polyhydroxyalkanoates, respectively, was investigated. Biotransformation experiments performed with P. putida resting cells showed that promiscuous periplasmic glucose oxidation route can efficiently generate extracellular xylonate with a high yield. Xylose oxidation was subsequently coupled to the growth of P. putida with cytoplasmic β-glucosidase BglC from Thermobifida fusca on d-cellobiose. This disaccharide turned out to be a better co-substrate for xylose-to-xylonate biotransformation than monomeric glucose. This was because unlike glucose, cellobiose did not block oxidation of the pentose by periplasmic glucose dehydrogenase Gcd, but, similarly to glucose, it was a suitable substrate for polyhydroxyalkanoate formation in P. putida. Co-production of extracellular xylose-born xylonate and intracellular cellobiose-born medium-chain-length polyhydroxyalkanoates was established in proof-of-concept experiments with P. putida grown on the disaccharide. This study highlights the potential of P. putida EM42 as a microbial platform for the production of xylonate, identifies cellobiose as a new substrate for mcl-PHA production, and proposes a fresh strategy for the simultaneous valorization of xylose and cellobiose.

A Nitrate-Blind P. putida Strain Boosts PHA Production in a Synthetic Mixed Culture

One of the major challenges for the present and future generations is to find suitable substitutes for the fossil resources we rely on today. In this context, cyanobacterial carbohydrates have been discussed as an emerging renewable feedstock in industrial biotechnology for the production of fuels and chemicals. Based on this, we recently presented a synthetic bacterial co-culture for the production of medium-chain-length polyhydroxyalkanoates (PHAs) from CO₂. This co-cultivation system is composed of two partner strains: Synechococcus elongatus cscB which fixes CO₂, converts it to sucrose and exports it into the culture supernatant, and a Pseudomonas putida strain that metabolizes this sugar and accumulates PHAs in the cytoplasm. However, these biopolymers are preferably accumulated under conditions of nitrogen limitation, a situation difficult to achieve in a co-culture as the other partner, at best, should not perceive any limitation. In this article, we will present an approach to overcome this dilemma by uncoupling the PHA production from the presence of nitrate in the medium. This is achieved by the construction of a P. putida strain that is no longer able to grow with nitrate as nitrogen source -is thus nitrate blind, and able to grow with sucrose as carbon source. The deletion of the nasT gene encoding the response regulator of the NasS/NasT two-component system resulted in such a strain that has lost the ability use nitrate, but growth with ammonium was not affected. Subsequently, the nasT deletion was implemented in P. putida cscRABY, an efficient sucrose consuming strain. This genetic engineering approach introduced an artificial unilateral nitrogen limitation in the co-cultivation process, and the amount of PHA produced from light and CO₂ was 8.8 fold increased to 14.8% of its CDW compared to the nitrate consuming reference strain. This nitrate blind strain, P. putidaΔnasT attTn7:cscRABY, is not only a valuable partner in the co-cultivation but additionally enables the use of other nitrate containing substrates for medium-chain-length PHA production, like for example waste-water.

Bioreactor Operating Strategies for Improved Polyhydroxyalkanoate (PHA) Productivity

Microbial polyhydroxyalkanoates (PHAs) are promising biodegradable polymers that may alleviate some of the environmental burden of petroleum-derived polymers. The requirements for carbon substrates and energy for bioreactor operations are major factors contributing to the high production costs and environmental impact of PHAs. Improving the process productivity is an important aspect of cost reduction, which has been attempted using a variety of fed-batch, continuous, and semi-continuous bioreactor systems, with variable results. The purpose of this review is to summarize the bioreactor operations targeting high PHA productivity using pure cultures. The highest volumetric PHA productivity was reported more than 20 years ago for poly(3-hydroxybutryate) (PHB) production from sucrose (5.1 g L⁻¹ h⁻¹). In the time since, similar results have not been achieved on a scale of more than 100 L. More recently, a number fed-batch and semi-continuous (cyclic) bioreactor operation strategies have reported reasonably high productivities (1 g L⁻¹ h⁻¹ to 2 g L⁻¹ h⁻¹) under more realistic conditions for pilot or industrial-scale production, including the utilization of lower-cost waste carbon substrates and atmospheric air as the aeration medium, as well as cultivation under non-sterile conditions. Little development has occurred in the area of fully continuously fed bioreactor systems over the last eight years.

Gas chromatography-mass spectrometry-based monomer composition analysis of medium-chain-length polyhydroxyalkanoates biosynthesized by Pseudomonas spp

Medium-chain-length (mcl)-polyhydroxyalkanoates (PHAs), elastomeric polyesters synthesized by Genus Pseudomonas bacteria, generally have many different monomer components. In this study, PHAs biosynthesized by four type strains of Pseudomonas (P. putida, P. citronellolis, P. oleovorans, and P. pseudoalcaligenes) and a typical PHA producer (P. putida KT2440) were characterized in terms of the monomer structure and composition by gas chromatography-mass spectrometry (GC-MS) analysis. With a thiomethyl pretreatment of PHA methanolysis derivatives, two unsaturated monomers, 3-hydroxy-5-dodecenoate (3H5DD) and 3-hydroxy-5-tetradecenoate (3H5TD), were identified in mcl-PHAs produced by P. putida and P. citronellolis. The quantitative analysis of PHA monomers was performed by employing GC-MS with methanolysis derivatives, and the results coincided with those obtained by performing nuclear magnetic resonance spectroscopy. Only poly(3-hydroxybutyrate) was detected from the P. oleovorans and P. pseudoalcaligenes type strains. These analytical results would be useful as a reference standard for phenotyping of new PHA-producing bacteria.

Engineering sucrose metabolism in Pseudomonas putida highlights the importance of porins

Using agricultural wastes as a substrate for biotechnological processes is of great interest in industrial biotechnology. A prerequisite for using these wastes is the ability of the industrially relevant microorganisms to metabolize the sugars present therein. Therefore, many metabolic engineering approaches are directed towards widening the substrate spectrum of the workhorses of industrial biotechnology like Escherichia coli, yeast or Pseudomonas putida. For instance, neither xylose or arabinose from cellulosic residues, nor sucrose, the main sugar in waste molasses, can be metabolized by most E. coli and P. putida wild types. We evaluated a new, so far uncharacterized gene cluster for sucrose metabolism from Pseudomonas protegens Pf‐5 and showed that it enables P. putida to grow on sucrose as the sole carbon and energy source. Even when integrated into the genome of P. putida, the resulting strain grew on sucrose at rates similar to the rate of the wild type on glucose – making it the fastest growing, plasmid‐free P. putida strain known so far using sucrose as substrate. Next, we elucidated the role of the porin, an orthologue of the sucrose porin ScrY, in the gene cluster and found that in P. putida, a porin is needed for sucrose transport across the outer membrane. Consequently, native porins were not sufficient to allow unlimited growth on sucrose. Therefore, we concluded that the outer membrane can be a considerable barrier for substrate transport, depending on strain, genotype and culture conditions, all of which should be taken into account in metabolic engineering approaches. We additionally showed the potential of the engineered P. putida strains by growing them on molasses with efficiencies twice as high as obtained with the wild‐type P. putida. This can be seen as a further step towards the production of low‐value chemicals and biofuels with P. putida from alternative and more affordable substrates in the future.

Carbon flux to growth or polyhydroxyalkanoate synthesis under microaerophilic conditions is affected by fatty acid chain-length in Pseudomonas putida LS46

Economical production of medium-chain length polyhydroxyalkanoates (mcl-PHA) is dependent on efficient cultivation processes. This work describes growth and mcl-PHA synthesis characteristics of Pseudomonas putida LS46 when grown on medium-chain length fatty acids (octanoic acid) and lower-cost long-chain fatty acids (LCFAs, derived from hydrolyzed canola oil) in microaerophilic environments. Growth on octanoic acid ceased when the oxygen uptake rate was limited by the oxygen transfer rate, and mcl-PHA accumulated to 61.9% of the cell dry mass. From LCFAs, production of non-PHA cell mass continued at a rate of 0.36 g L^-1 h^-1 under oxygen-limited conditions, while mcl-PHA accumulated simultaneously to 31% of the cell dry mass. The titer of non-PHA cell mass from LCFAs at 14 h post-inoculation was double that obtained from octanoic acid in bioreactors operated with identical feeding and aeration conditions. While the productivity for octanoic acid was higher by 14 h, prolonged cultivation on LCFAs achieved similar productivity but with twice the PHA titer. Simultaneous co-feeding of each substrate demonstrated the continued cell growth under microaerophilic conditions characteristic of LCFAs, and the resulting polymer was dominant in C8 monomers. Furthermore, co-feeding resulted in improved PHA titer and volumetric productivity compared to either substrate individually. These results suggest that LCFAs improve growth of P. putida in oxygen-limited environments and could reduce production costs since more non-PHA cell mass, the cellular factories required to produce mcl-PHA and the most oxygen-intensive cellular process, can be produced for a given oxygen transfer rate.

Transcriptome remodeling of Pseudomonas putida KT2440 during mcl-PHAs synthesis: effect of different carbon sources and response to nitrogen stress

Bacterial response to environmental stimuli is essential for survival. In response to fluctuating environmental conditions, the physiological status of bacteria can change due to the actions of transcriptional regulatory machinery. The synthesis and accumulation of polyhydroxyalkanoates (PHAs) are one of the survival strategies in harsh environments. In this study, we used transcriptome analysis of Pseudomonas putida KT2440 to gain a genome-wide view of the mechanisms of environmental-friendly biopolymers accumulation under nitrogen-limiting conditions during conversion of metabolically different carbon sources (sodium gluconate and oleic acid). Transcriptomic data revealed that phaG expression is associated with medium-chain-length-PHAs' synthesis not only on sodium gluconate but also on oleic acid, suggesting that PhaG may play a role in this process, as well. Moreover, genes involved in the β-oxidation pathway were induced in the PHAs production phase when sodium gluconate was supplied as the only carbon and energy source. The transition from exponential growth to stationary phase caused a significant expression of genes involved in nitrogen metabolism, energy supply, and transport system. In this study, several molecular mechanisms, which drive mcl-PHAs synthesis, have been investigated. The identified genes may provide valuable information to improve the efficiency of this bioprocess and make it more economically feasible.

Recovery of polyhydroxyalkanoates from municipal secondary wastewater sludge

In the current study, the feasibility of utilizing municipal secondary wastewater sludge for Polyhydroxyalkanoate (PHA) extraction was improved by optimization of various parameters (temperature, duration and concentration of sludge solids). Optimized process parameters resulted in PHA recovery of 0.605 g, significantly higher than un-optimized conditions. The characterization of PHA was carried out by GC-MS, FT-IR and NMR (¹H and ¹³C) spectroscopy. The PHA profile was found to be dominated by mcl PHA (58%) along with other diverse PHA. The results of the present study show rich diversity of PHA extracted from a raw material which is readily available at minimal cost. In conclusion, exploring the potential of wastes for production of bioplastics not only reduces the cost of bioplastic production, but also provides a sustainable means for waste management.

Co-production of fully renewable medium chain α-olefins and bio-oilviahydrothermal liquefaction of biomass containing polyhydroxyalkanoic acid

Medium chain-length linear α-olefins (mcl-LAO) are versatile precursors to commodity products such as synthetic lubricants and biodegradable detergents, and have been traditionally produced from ethylene oligomerization and Fischer–Tropsch synthesis. Medium chain-length polyhydroxyalkanoic acid (mcl-PHA) can be produced by some microorganisms as an energy storage. In this study, Pseudomonas putida biomass that contained mcl-PHA was used in HTL at 300 °C for 30 min, and up to 65 mol% of mcl-PHA was converted into mcl-LAO. The yield and quality of the bio-oil co-produced in the HTL was remarkably improved with the biomass rich in mcl-PHA. Experiments with extracted mcl-PHA revealed the degradation mechanism of mcl-PHA in HTL. Overall, this work demonstrates a novel process to co-produce mcl-LAO and bio-oil from renewable biomass.

Co-production of fully renewable medium chain α-olefins and bio-oil by hydrothermal liquefaction.

Synthesis of polyhydroxyalkanoates (PHAs) from vegetable oils and free fatty acids by wild-type and mutant strains of Pseudomonas chlororaphis

Pseudomonas chlororaphis PA23 was isolated from soybean roots as a plant-growth-promoting rhizobacterium. This strain secretes a wide range of compounds, including the antibiotics phenazine-1-carboxylic acid (PCA), pyrrolnitrin, and 2-hydroxyphenazine. We have determined that P. chlororaphis PA23 can synthesize medium-chain-length polyhydroxyalkanoate (PHA) polymers utilizing free fatty acids, such as octanoic acid and nonanoic acid, as well as vegetable oils as sole carbon sources. Genome analysis identified a pha operon containing 7 genes in P. chlororaphis PA23 that were highly conserved. A nonpigmented strain that does not synthesize PCA, P. chlororaphis PA23-63, was also studied for PHA production. Pseudomonas chlororaphis PA23-63 produced 2.42–5.14 g/L cell biomass and accumulated PHAs from 11.7% to 32.5% cdm when cultured with octanoic acid, nonanoic acid, fresh canola oil, waste canola fryer oil, or biodiesel-derived waste free fatty acids under batch culture conditions. The subunit composition of the PHAs produced from fresh canola oil, waste canola fryer oil, or biodiesel-derived free fatty acids did not differ significantly. Addition of octanoic acid and nonanoic acid to canola oil cultures increased PHA production, but addition of glucose did not. PHA production in the phz mutant, P. chlororaphis PA23-63, was greater than that in the parent strain.

Pathway-Consensus Approach to Metabolic Network Reconstruction for Pseudomonas putida KT2440 by Systematic Comparison of Published Models

Over 100 genome-scale metabolic networks (GSMNs) have been published in recent years and widely used for phenotype prediction and pathway design. However, GSMNs for a specific organism reconstructed by different research groups usually produce inconsistent simulation results, which makes it difficult to use the GSMNs for precise optimal pathway design. Therefore, it is necessary to compare and identify the discrepancies among networks and build a consensus metabolic network for an organism. Here we proposed a process for systematic comparison of metabolic networks at pathway level. We compared four published GSMNs of Pseudomonas putida KT2440 and identified the discrepancies leading to inconsistent pathway calculation results. The mistakes in the models were corrected based on information from literature so that all the calculated synthesis and uptake pathways were the same. Subsequently we built a pathway-consensus model and then further updated it with the latest genome annotation information to obtain modelPpuQY1140 for P. putida KT2440, which includes 1140 genes, 1171 reactions and 1104 metabolites. We found that even small errors in a GSMN could have great impacts on the calculated optimal pathways and thus may lead to incorrect pathway design strategies. Careful investigation of the calculated pathways during the metabolic network reconstruction process is essential for building proper GSMNs for pathway design.

Synthesis Gas (Syngas)-Derived Medium-Chain-Length Polyhydroxyalkanoate Synthesis in Engineered Rhodospirillum rubrum

The purple nonsulfur alphaproteobacterium Rhodospirillum rubrum S1 was genetically engineered to synthesize a heteropolymer of mainly 3-hydroxydecanoic acid and 3-hydroxyoctanoic acid [P(3HD-co-3HO)] from CO- and CO₂-containing artificial synthesis gas (syngas). For this, genes from Pseudomonas putida KT2440 coding for a 3-hydroxyacyl acyl carrier protein (ACP) thioesterase (phaG), a medium-chain-length (MCL) fatty acid coenzyme A (CoA) ligase (PP_0763), and an MCL polyhydroxyalkanoate (PHA) synthase (phaC1) were cloned and expressed under the control of the CO-inducible promoter P_cooF from R. rubrum S1 in a PHA-negative mutant of R. rubrum P(3HD-co-3HO) was accumulated to up to 7.1% (wt/wt) of the cell dry weight by a recombinant mutant strain utilizing exclusively the provided gaseous feedstock syngas. In addition to an increased synthesis of these medium-chain-length PHAs (PHA_MCL), enhanced gene expression through the P_cooF promoter also led to an increased molar fraction of 3HO in the synthesized copolymer compared with the P_lac promoter, which regulated expression on the original vector. The recombinant strains were able to partially degrade the polymer, and the deletion of phaZ2, which codes for a PHA depolymerase most likely involved in intracellular PHA degradation, did not reduce mobilization of the accumulated polymer significantly. However, an amino acid exchange in the active site of PhaZ2 led to a slight increase in PHA_MCL accumulation. The accumulated polymer was isolated; it exhibited a molecular mass of 124.3 kDa and a melting point of 49.6°C. With the metabolically engineered strains presented in this proof-of-principle study, we demonstrated the synthesis of elastomeric second-generation biopolymers from renewable feedstocks not competing with human nutrition.

IMPORTANCE

Polyhydroxyalkanoates (PHAs) are natural biodegradable polymers (biopolymers) showing properties similar to those of commonly produced petroleum-based nondegradable polymers. The utilization of cheap substrates for the microbial production of PHAs is crucial to lower production costs. Feedstock not competing with human nutrition is highly favorable. Syngas, a mixture of carbon monoxide, carbon dioxide, and hydrogen, can be obtained by pyrolysis of organic waste and can be utilized for PHA synthesis by several kinds of bacteria. Up to now, the biosynthesis of PHAs from syngas has been limited to short-chain-length PHAs, which results in a stiff and brittle material. In this study, the syngas-utilizing bacterium Rhodospirillum rubrum was genetically modified to synthesize a polymer which consisted of medium-chain-length constituents, resulting in a rubber-like material. This study reports the establishment of a microbial synthesis of these so-called medium-chain-length PHAs from syngas and therefore potentially extends the applications of syngas-derived PHAs.

Bacterial polyhydroxyalkanoates: Still fabulous?

Bacterial polyhydroxyalkanoates (PHA) are polyesters accumulated as carbon and energy storage materials under limited growth conditions in the presence of excess carbon sources. They have been developed as biomaterials with unique properties for the past many years being considered as a potential substitute for conventional non-degradable plastics. Due to the increasing concern towards global climate change, depleting petroleum resource and problems with an utilization of a growing number of synthetic plastics, PHAs have gained much more attention from industry and research. These environmentally friendly microbial polymers have great potential in biomedical, agricultural, and industrial applications. However, their production on a large scale is still limited. This paper describes the backgrounds of PHAs and discussed the current state of knowledge on the polyhydroxyalkanoates. Ability of bacteria to convert different carbon sources to PHAs, the opportunities and challenges of their introduction to global market as valuable renewable products have been also discussed.

Microbial production of polyhydroxyalkanoates (PHAs) and its copolymers: A review of recent advancements

Traditional mineral oil based plastics are important commodity to enhance the comfort and quality of life but the accumulation of these plastics in the environment has become a major universal problem due to their low biodegradation. Solution to the plastic waste management includes incineration, recycling and landfill disposal methods. These processes are very time consuming and expensive. Biopolymers are important alternatives to the petroleum-based plastics due to environment friendly manufacturing processes, biodegradability and biocompatibility. Therefore use of novel biopolymers, such as polylactide, polysaccharides, aliphatic polyesters and polyhydroxyalkanoates is of interest. PHAs are biodegradable polyesters of hydroxyalkanoates (HA) produced from renewable resources by using microorganisms as intracellular carbon and energy storage compounds. Even though PHAs are promising candidate for biodegradable polymers, however, the production cost limit their application on an industrial scale. This article provides an overview of various substrates, microorganisms for the economical production of PHAs and its copolymers. Recent advances in PHAs to reduce the cost and to improve the performance of PHAs have also been discussed.

Medium chain length polyhydroxyalkanoates consisting primarily of unsaturated 3-hydroxy-5-cis-dodecanoate synthesized by newly isolated bacteria using crude glycerol

Background

Our study aimed to search for novel bacteria capable of producing polyhydroxyalkanoates (PHAs) using crude glycerol residue obtained from biodiesel production in which used cooking oils were the substrates.

Results

Newly isolated bacteria from soils in Thailand were screened for the efficient production of PHAs from crude glycerol. The bacterial strains were cultivated on glucose, refined glycerol, crude glycerol, or various cooking oils (canola oil, palm oil, soybean oil, sunflower oil, corn oil, grape seed oil, olive oil, rice bran oil, camellia seed oil) for growth and PHA production. The effects of the total organic carbon (TOC) concentration and the mole ratio of carbon to nitrogen were investigated in batch cultivation. ¹H NMR, two dimensional-¹H-correlation spectroscopy (2D-¹H-COSY) and ¹³C NMR analyses confirmed four bacterial strains were capable of producing medium-chain-length PHAs (mcl-PHAs), consisting of 3-hydroxyoctanoate (3HO) and 3-hydroxy-5-cis-dodecanoate (3H5DD), from crude glycerol. On the basis of phenotypic features and genotypic investigations, the bacterial strains were assigned as: ASC1, Acinetobacter genus (94.9 % similarity); ASC2, Pseudomonas genus (99.2 % similarity); ASC3, Enterobacter genus (99.2 % similarity); ASC4, Bacillus genus (98.4 % similarity). The highest amount of mcl-PHAs, 17.5 ± 0.8 g/L (content 61.8 ± 3.3 % wt), with 3HO (14.7 ± 2.2 mol %), 3H5DD (85.3 ± 2.2 mol %), and a total biomass of 32.3 ± 0.3 g/L, was obtained from Pseudomonas sp. ASC2 in batch cultivation after 36 h. The mcl-PHAs recovered had a number-average molecular weight (M_N) of 3.6 × 10⁴ Da. Homopolymeric 3H5DD was obtained when the cultivation time was prolonged to 96 h.

Conclusions

Novel PHA-producing strains were isolated and identified. These bacterial strains are able to produce mcl-PHAs from crude glycerol. The mcl-PHAs produced contained a high percentage of 3H5DD, which suggests their future application as softeners mixed with other biomaterials. The unsaturated side chain of 3H5DD monomers containing double bounds offers additional potential for improving the properties of the mcl-PHAs or extending their applications to the food industry.

Advanced functionalization of polyhydroxyalkanoate via the UV-initiated thiol-ene click reaction

Polyhydroxyalkanoates (PHAs) incorporating vinyl-bearing 3-hydroxyalkanoates were prepared in 8.5-12.9 g L(-1) yield. The molar ratios (0-16 mol%) of the vinyl-bearing 3-hydroxyalkanoate derivatives were controlled by the continuous feeding of undecylenate at various concentrations. Subsequently, the PHAs were functionalized by UV-initiated thiol-ene click reaction and chemical modification. (1)H NMR spectra suggested that 3-mercaptopropionic acid and 2-aminoethanethiol were successfully introduced into the vinyl-bearing PHA. Subsequently, chemical modification using fluorescein or a fibronectin active fragment (GRGDS) was attempted. The former yielded a PHA derivative capable of emitting fluorescence under UV irradiation, which was useful for determining the miscibility of PHA in a composite film comprising poly-ʟ-lactic acid (PLLA) and PHA. In the latter case, PHA bearing GRGDS peptides exhibited cell adhesiveness, suggesting that its biocompatibility was improved upon peptide introduction. Taken together, the UV-initiated thiol-ene click reaction was demonstrated to be useful in PHA modification.

Fed-batch production of poly-3-hydroxydecanoate from decanoic acid

Decanoic acid is an ideal substrate for the synthesis of medium-chain-length poly-3-hydroxyalkanoate (MCL-PHA), but its use for this purpose has only previously been studied in shake-flasks likely due to its surfactant properties, low aqueous solubility and high melting temperature. A fed-batch fermentation process was developed for the production of MCL-PHA from decanoic acid using Pseudomonas putida KT2440. Decanoic acid was kept in liquid form by heating or by mixing with acetic acid to prevent crystallization. Different ratios of decanoic acid:acetic acid:glucose (DA:AA:G) were fed to produce a specific growth rate of 0.15 h(-1). This method produced a maximum of 39 g L(-1) dry biomass containing 67% MCL-PHA when the DA:AA:G ratio was 5:1:4. However, a declining growth rate occurred in the late stage of fermentation, resulting in decanoic acid accumulation in the bioreactor leading to foaming. The duration of MCL-PHA production was extended by shifting from exponential to linear feeding before accumulation of decanoic acid. This resulted in 75 g L(-1) biomass containing 74% PHA and an overall PHA productivity of 1.16 g L(-1)h(-1) with the production of each gram of PHA requiring only 1.16 g of decanoic acid. The final PHA composition (on a molar basis) was 78% 3-hydroxydecanoate, 11% 3-hydroxyoctanoate and 11% 3-hydroxyhexanoate.

Exploring medium-chain-length polyhydroxyalkanoates production in the engineered yeast Yarrowia lipolytica

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are a large class of biopolymers that have attracted extensive attention as renewable and biodegradable bio-plastics. They are naturally synthesized via fatty acid de novo biosynthesis pathway or β-oxidation pathway from Pseudomonads. The unconventional yeast Yarrowia lipolytica has excellent lipid/fatty acid catabolism and anabolism capacity depending of the mode of culture. Nevertheless, it cannot naturally synthesize PHA, as it does not express an intrinsic PHA synthase. Here, we constructed a genetically modified strain of Y. lipolytica by heterologously expressing PhaC1 gene from P. aeruginosa PAO1 with a PTS1 peroxisomal signal. When in single copy, the codon optimized PhaC1 allowed the synthesis of 0.205 % DCW of PHA after 72 h cultivation in YNBD medium containing 0.1 % oleic acid. By using a multi-copy integration strategy, PHA content increased to 2.84 % DCW when the concentration of oleic acid in YNBD was 1.0 %. Furthermore, when the recombinant yeast was grown in the medium containing triolein, PHA accumulated up to 5.0 % DCW with as high as 21.9 g/L DCW, which represented 1.11 g/L in the culture. Our results demonstrated the potential use of Y. lipolytica as a promising microbial cell factory for PHA production using food waste, which contains lipids and other essential nutrients.

Comparison of mcl-Poly(3-hydroxyalkanoates) synthesis by different Pseudomonas putida strains from crude glycerol: citrate accumulates at high titer under PHA-producing conditions

BACKGROUND

Achieving a sustainable society requires, among other things, the use of renewable feedstocks to replace chemicals obtained from petroleum-derived compounds. Crude glycerol synthesized inexpensively as a byproduct of biodiesel production is currently considered a waste product, which can potentially be converted into value-added compounds by bacterial fermentation. This study aimed at evaluating several characterized P. putida strains to produce medium-chain-length poly(3-hydroxyalkanoates) (mcl-PHA) using raw glycerol as the only carbon/energy source.

RESULTS

Among all tested strains, P. putida KT2440 most efficiently synthesized mcl-PHA under nitrogen-limiting conditions, amassing more than 34% of its cell dry weight as PHA. Disruption of the PHA depolymerase gene (phaZ) in P. putida KT2440 enhanced the biopolymer titer up to 47% PHA (%wt/wt). The low biomass and PHA titer found in the mutant strain and the wild-type strain KT2440 seems to be triggered by the high production of the side-product citrate during the fermentation process which shows a high yield of 0.6 g/g.

CONCLUSIONS

Overall, this work demonstrates the importance of choosing an appropriate microbe for the synthesis of mcl-PHA from waste materials, and a close inspection of the cell metabolism in order to identify undesired compounds that diminish the availability of precursors in the synthesis of biopolymers such as polyhydroxyalkanoates. Future metabolic engineering works should focus on reducing the production of citrate in order to modulate resource allocation in the cell's metabolism of P. putida, and finally increase the biopolymer production.

Growth kinetics, effect of carbon substrate in biosynthesis of mcl-PHA by Pseudomonas putida Bet001

Growth associated biosynthesis of medium chain length poly-3-hydroxyalkanoates (mcl-PHA) in Pseudomonas putida Bet001 isolated from palm oil mill effluent was studied. Models with substrate inhibition terms described well the kinetics of its growth. Selected fatty acids (C_8:0 to C_18:1) and ammonium were used as carbon and nitrogen sources during growth and PHA biosynthesis, resulting in PHA accumulation of about 50 to 69% (w/w) and PHA yields ranging from 10.12 g L⁻¹ to 15.45 g L⁻¹, respectively. The monomer composition of the PHA ranges from C4 to C14, and was strongly influenced by the type of carbon substrate fed. Interestingly, an odd carbon chain length (C7) monomer was also detected when C_18:1 was fed. Polymer showed melting temperature (T_m) of 42.0 (± 0.2) °C, glass transition temperature (T_g) of −1.0 (± 0.2) °C and endothermic melting enthalpy of fusion (ΔH_f) of 110.3 (± 0.1) J g⁻¹. The molecular weight (M_w) range of the polymer was relatively narrow between 55 to 77 kDa.

Isolation and characterization of a thermophilic Bacillus shackletonii K5 from a biotrickling filter for the production of polyhydroxybutyrate

Polyhydroxyalkanoates (PHAs) are aliphatic polyesters accumulated intracellularly by both Gram-negative and Gram-positive bacteria. However, compared to the PHAs of Gram-negative bacteria, few endotoxins (lipopolysaccharides, LPS), which would be co-purified with PHAs and cause immunogenic reactions, are found in the PHAs produced by Gram-positive bacteria. A thermophilic Gram-positive bacterium K5, which exhibited good growth and polyhydroxybutyrate (PHB)-accumulating ability, has been isolated and characterized from a biotrickling filter designed for the removal of NOx from flue gas in a coal-fired power plant in China. Based on the biochemical characterization and 16S rRNA gene sequence (Genbank accession no. JX437933), the strain K5 has been identified as Bacillus shackletonii, which has rarely been reported in the literature, and this report is the first time that B. shackletonii has been found to accumulate PHB. The strain K5 was able to utilize glucose as carbon source to synthesize PHB at a broad range of temperatures (from 35 to 50°C), and the ideal temperature was 45°C. The strain K5 could effectively yield PHB of up to 69.9% of its cell dry weight (CDW) (2.28 g/L) in flask experiments employing glucose as carbon source at 45°C, followed by 56.8% and 52.3% of its CDW when using sodium succinate and glycerol as carbon source, respectively. For batch cultivation, the strain K5 was able to produce PHB of up to 72.6% of its cell dry weight (9.76 g/L) employing glucose as carbon source at 45°C and pH7.0.

Production of medium chain length polyhydroxyalkanoate in metabolic flux optimized Pseudomonas putida

BACKGROUND

Pseudomnas putida is a natural producer of medium chain length polyhydroxyalkanoates (mcl-PHA), a polymeric precursor of bioplastics. A two-fold increase of mcl-PHA production via inactivation of the glucose dehydrogenase gene gcd, limiting the metabolic flux towards side products like gluconate was achieved before. Here, we investigated the overproduction of enzymes catalyzing limiting steps of mcl-PHA precursor formation.

RESULTS

A genome-based in silico model for P. putida KT2440 metabolism was employed to identify potential genetic targets to be engineered for the improvement of mcl-PHA production using glucose as sole carbon source. Here, overproduction of pyruvate dehydrogenase subunit AcoA in the P. putida KT2440 wild type and the Δgcd mutant strains led to an increase of PHA production. In controlled bioreactor batch fermentations PHA production was increased by 33% in the acoA overexpressing wild type and 121% in the acoA overexpressing Δgcd strain in comparison to P. putida KT2440. Overexpression of pgl-encoding 6-phosphoglucolactonase did not influence PHA production. Transcriptome analyses of engineered PHA producing P. putida in comparison to its parental strains revealed the induction of genes encoding glucose 6-phosphate dehydrogenase and pyruvate dehydrogenase. In addition, NADPH seems to be quantitatively consumed for efficient PHA synthesis, since a direct relationship between low levels of NADPH and high concentrations of the biopolymer were observed. In contrast, intracellular levels of NADH were found increased in PHA producing organisms.

CONCLUSION

Production of mcl-PHAs was enhanced in P. putida when grown on glucose via overproduction of a pyruvate dehydrogenase subunit (AcoA) in combination with a deletion of the glucose dehydrogenase (gcd) gene as predicted by in silico elementary flux mode analysis.

Production of scopularide A in submerged culture with Scopulariopsis brevicaulis

BACKGROUND

Marine organisms produce many novel compounds with useful biological activity, but are currently underexploited. Considerable research has been invested in the study of compounds from marine bacteria, and several groups have now recognised that marine fungi also produce an interesting range of compounds. During product discovery, these compounds are often produced only in non-agitated culture conditions, which are unfortunately not well suited for scaling up. A marine isolate of Scopulariopsis brevicaulis, strain LF580, produces the cyclodepsipeptide scopularide A, which has previously only been produced in non-agitated cultivation.

RESULTS

Scopulariopsis brevicaulis LF580 produced scopularide A when grown in batch and fed-batch submerged cultures. Scopularide A was extracted primarily from the biomass, with approximately 7% being extractable from the culture supernatant. By increasing the biomass density of the cultivations, we were able to increase the volumetric production of the cultures, but it was important to avoid nitrogen limitation. Specific production also increased with increasing biomass density, leading to improvements in volumetric production up to 29-fold, compared with previous, non-agitated cultivations. Cell densities up to 36 g L-1 were achieved in 1 to 10 L bioreactors. Production of scopularide A was optimised in complex medium, but was also possible in a completely defined medium.

CONCLUSIONS

Scopularide A production has been transferred from a non-agitated to a stirred tank bioreactor environment with an approximately 6-fold increase in specific and 29-fold increase in volumetric production. Production of scopularide A in stirred tank bioreactors demonstrates that marine fungal compounds can be suitable for scalable production, even with the native production organism.