The fundamental role of pH in CH4 bioconversion into polyhydroxybutyrate in mixed methanotrophic cultures

Climate change and plastic pollution are likely the most relevant challenges for the environment in the 21st century. Developing cost-effective technologies for the bioconversion of methane (CH4) into polyhydroxyalkanoates (PHAs) could simultaneously mitigate CH4 emissions and boost the commercialization of biodegradable polymers. Despite the fact that the role of temperature, nitrogen deprivation, CH4:O2 ratio or micronutrients availability on the PHA accumulation capacity of methanotrophs has been carefully explored, there is still a need for optimization of the CH4-to-PHA bioconversion process prior to becoming a feasible platform in future biorefineries. In this study, the influence of different cultivation broth pH values (5.5, 7, 8.5 and 10) on bacterial biomass growth, CH4 bioconversion rate, PHA accumulation capacity and bacterial community structure was investigated in a stirred tank bioreactor under nitrogen deprivation conditions. Higher CH4 elimination rates were obtained at increasing pH, with a maximum value of 50.4 ± 2.7 g CH4·m-3·h-1 observed at pH 8.5. This was likely mediated by an increased ionic strength in the mineral medium, which enhanced the gas-liquid mass transfer. Interestingly, higher PHB accumulations were observed at decreasing pH, with the highest PHB contents recorded at a pH 5.5 (43.7 ± 3.4 %w·w-1). The strong selective pressure of low pH towards the growth of Type II methanotrophic bacteria could explain this finding. The genus Methylocystis increased its abundance from 34 % up to 85 and 90 % at pH 5.5 and 7, respectively. On the contrary, Methylocystis was less abundant in the community enriched at pH 8.5 (14 %). The accumulation of intracellular PHB as energy and carbon storage material allowed the maintenance of high CH4 biodegradation rates during 48 h after complete nitrogen deprivation. The results here obtained demonstrated for the first time a crucial and multifactorial role of pH on the bioconversion performance of CH4 into PHA.

Microbially synthesized poly(hydroxybutyrate-co-hydroxyhexanoate) with low to moderate hydroxyhexanoate content: Properties and applications

Plastic pollution is the biggest environmental concern of our time. Breakdown products like micro- and nano-plastics inevitably enter the food chain and pose unprecedented health risks. In this scenario, bio-based and biodegradable plastic alternatives have been given a momentum aiming to bridge a transition towards a more sustainable future. Polyhydroxyalkanoates (PHAs) are one of the few thermoplastic polymers synthesized 100 % via biotechnological routes which fully biodegrade in common natural environments. Poly(hydroxybutyrate-co-hydroxyhexanoate) [P(HB-co-HHx)] is a PHA copolymer with great potential for the commodity polymers industry, as its mechanical properties can be tailored through fine-tuning of its molar HHx content. We have recently developed a strategy that enables for reliable tailoring of the monomer content of P(HB-co-HHx). Nevertheless, there is often a lack of comprehensive investigation of the material properties of PHAs to evaluate whether they actually mimic the functionalities of conventional plastics. We present a detailed study of P(HB-co-HHx) copolymers with low to moderate hydroxyhexanoate content to understand how the HHx monomer content influences the thermal and mechanical properties and to link those to their abiotic degradation. By increasing the HHx fractions in the range of 2 - 14 mol%, we impart an extension of the processing window and application range as the melting temperature (Tm) and glass temperature (Tg) of the copolymers decrease from Tm 165 °C to 126 °C, Tg 4 °C to -5.9 °C, accompanied by reduced crystallinity from 54 % to 20 %. Elongation at break was increased from 5.7 % up to 703 % at 14 mol% HHx content, confirming that the range examined was sufficiently large to obtain ductile and brittle copolymers, while tensile strength was maintained throughout the studied range. Finally, accelerated abiotic degradation was shown to be slowed down with an increasing HHx fraction decreasing from 70 % to 55 % in 12 h.

Relevance of lymphocyte proliferation to PHA in severe combined immunodeficiency (SCID) and T cell lymphopenia

Severe combined immunodeficiency (SCID) is characterized by a severe deficiency in T cell numbers. We analyzed data collected (n = 307) for PHA-based T cell proliferation from the PIDTC SCID protocol 6901, using either a radioactive or flow cytometry method. In comparing the two groups, a smaller number of the patients tested by flow cytometry had <10% of the lower limit of normal proliferation as compared to the radioactive method (p = 0.02). Further, in patients with CD3+ T cell counts between 51 and 300 cells/μL, there was a higher proliferative response with the PHA flow assay compared to the 3H-T assay (p < 0.0001), suggesting that the method of analysis influences the resolution and interpretation of PHA results. Importantly, we observed many SCID patients with profound T cell lymphopenia having normal T cell proliferation when assessed by flow cytometry. We recommend this test be considered only as supportive in the diagnosis of typical SCID.

Tobacco and nicotine use among active component U.S. military service members: a comparison of 2018 estimates from the Health Related Behaviors Survey and the Periodic Health Assessment

This study compared estimates of the prevalence of and risk factors for tobacco and nicotine use obtained from the 2018 Health Related Behaviors Survey (HRBS) and Periodic Health Assessment (PHA) survey. The HRBS and the PHA are important Department of Defense sources of data on health behavior collected from U.S. military service members. While their collection methods differ, some survey questions are similar, which provides an opportunity to compare survey estimates. Active duty service members consistently reported a much lower prevalence of all types of tobacco and nicotine use on the PHA compared to the HRBS: cigarettes (11.1% vs. 18.4%), e-cigarettes (7.3% vs. 16.2%), chewing tobacco (9.7% vs. 13.4%), any tobacco or nicotine use (25.3% vs. 37.8%), and use of 2 or more tobacco or nicotine products (5.8% vs. 17.4%). Associations between tobacco and nicotine use as well as demographic and other behavioral variables were fairly similar, including age, sex, education, race and ethnicity, rank, and alcohol use. The associations with service branch, body mass index, and sleep were inconsistent. This results of this study suggest that the PHA can provide timely information on trends in military tobacco and nicotine use over time, but much higher estimates from the confidential, voluntary HRBS reported in this study suggest that the command-directed PHA may substantially underestimate the prevalence of all types of tobacco and nicotine use.

Bioaugmentation of Thauera mechernichensis TL1 for enhanced polyhydroxyalkanoate production in mixed microbial consortia for wastewater treatment

Polyhydroxyalkanoate (PHA) is a fully biodegradable bioplastic. To foster a circular economy, the integration of PHA production into wastewater treatment facilities can be accomplished using mixed microbial consortia. The effectiveness of this approach relies greatly on the enrichment of PHA-accumulating microorganisms. Hence, our study focused on bioaugmenting Thauera mechernichensis TL1 into mixed microbial consortia with the aim of enriching PHA-accumulating microorganisms and enhancing PHA production. Three sequencing batch reactors-SBRctrl, SBR2.5%, and SBR25%-were operated under feast/famine conditions. SBR2.5% and SBR25% were bioaugmented with T. mechernichensis TL1 at 2.5%w/w of mixed liquor volatile suspended solids (MLVSS) and 25%w/w MLVSS, respectively, while SBRctrl was not bioaugmented. SBR2.5% and SBR25% achieved maximum PHA accumulation capacities of 56.3 %gPHA/g mixed liquor suspended solids (MLSS) and 50.2 %gPHA/gMLSS, respectively, which were higher than the 25.4 %gPHA/gMLSS achieved by SBRctrl. The results of quantitative polymerase chain reaction targeting the 16S rRNA gene specific to T. mechernichensis showed higher abundances of T. mechernichensis in SBR2.5% and SBR25% compared with SBRctrl in the 3rd, 17th, and 31st cycles. Fluorescence in situ hybridization, together with fluorescent staining of PHA with Nile blue A, confirmed PHA accumulation in Thauera spp. The study demonstrated that bioaugmentation of T. mechernichensis TL1 at 2.5%w/w MLVSS is an effective strategy to enhance PHA accumulation and facilitate the enrichment of PHA-accumulating microorganisms in mixed microbial consortia. The findings could contribute to the advancement of PHA production from wastewater, enabling the transformation of wastewater treatment plants into water and resource recovery facilities.

Ectoine hyperproduction by engineered Halomonas bluephagenesis

Ectoine, a crucial osmoprotectant for salt adaptation in halophiles, has gained growing interest in cosmetics and medical industries. However, its production remains challenged by stringent fermentation process in model microorganisms and low production level in its native producers. Here, we systematically engineered the native ectoine producer Halomonas bluephagenesis for ectoine production by overexpressing ectABC operon, increasing precursors availability, enhancing product transport system and optimizing its growth medium. The final engineered H. bluephagenesis produced 85 g/L ectoine in 52 h under open unsterile incubation in a 7 L bioreactor in the absence of plasmid, antibiotic or inducer. Furthermore, it was successfully demonstrated the feasibility of decoupling salt concentration with ectoine synthesis and co-production with bioplastic P(3HB-co-4HB) by the engineered H. bluephagenesis. The unsterile fermentation process and significantly increased ectoine titer indicate that H. bluephagenesis as the chassis of Next-Generation Industrial Biotechnology (NGIB), is promising for the biomanufacturing of not only intracellular bioplastic PHA but also small molecular compound such as ectoine.

Influence of Electrospinning Parameters on the Morphology of Electrospun Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Fibrous Membranes and Their Application as Potential Air Filtration Materials

A large number of non-degradable materials have severely damaged the ecological environment. Now, people are increasingly pursuing the use of environmentally friendly materials to replace traditional chemical materials. Polyhydroxyalkonates (PHAs) are receiving increasing attention because of the unique biodegradability and biocompatibility they offer. However, the applications of PHAs are still limited due to high production costs and insufficient study. This project examines the optimal electrospinning parameters for the production of PHA-based fibrous membranes for air filtration. A common biodegradable polyester, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), was electrospun into a nanofibrous membrane with a well-controlled surface microstructure. In order to produce smooth, bead-free fibers with micron-scale diameters, the effect of the process parameters (applied electric field, solution flow rate, inner diameter of hollow needle, and polymer concentration) on the electrospun fiber microstructure was optimized. The well-defined fibrous structure was optimized at an applied electric field of 20 kV, flow rate of 0.5 mL/h, solution concentration of 12 wt.%, and needle inner diameter of 0.21 mm. The morphology of the electrospun PHBV fibrous membrane was observed by scanning electron microscopy (SEM). Fourier transform infrared (FTIR) and Raman spectroscopy were used to explore the chemical signatures and phases of the electrospun PHBV nanofiber. The ball burst strength (BBS) was measured to assess the mechanical strength of the membrane. The small pore size of the nanofiber membranes ensured they had good application prospects in the field of air filtration. The particle filtration efficiency (PFE) of the optimized electrospun PHBV fibrous membrane was above 98% at standard atmospheric pressure.

Metabolic engineering of Halomonas bluephagenesis for production of five carbon molecular chemicals derived from L-lysine

5-Aminovaleric acid (5-AVA), 5-hydroxyvalerate (5HV), copolymer P(3HB-co-5HV) of 3-hydroxybutyrate (3HB) and 5HV were produced from L-lysine as a substrate by recombinant Halomonas bluephagenesis constructed based on codon optimization, deletions of competitive pathway and L-lysine export protein, and three copies of davBA genes encoding L-lysine monooxygenase (DavB) and 5-aminovaleramide amidohydrolase (DavA) inserted into its genome to form H. bluephagenesis YF117ΔgabT1+2, which produced 16.4 g L-1 and 67.4 g L-1 5-AVA in flask cultures and in 7 L bioreactor, respectively. It was able to de novo synthesize 5-AVA from glucose by L-lysine-overproducing H. bluephagenesis TD226. Corn steep liquor was used instead of yeast extract for cost reduction during the 5-AVA production. Using promoter engineering based on Pporin mutant library for downstream genes, H. bluephagenesis YF117 harboring pSEVA341-Pporin42-yqhDEC produced 6 g L-1 5HV in shake flask growth, while H. bluephagenesis YF117 harboring pSEVA341-Pporin42-yqhDEC-Pporin278-phaCRE-abfT synthesized 42 wt% P(3HB-co-4.8 mol% 5HV) under the same condition. Thus, H. bluephagenesis was successfully engineered to produce 5-AVA and 5HV in supernatant and intracellular P(3HB-co-5HV) utilizing L-lysine as the substrate.

Integrated selection of PHA-storing biomass and nitrogen removal via nitrite from sludge reject water: a mathematical model

One of the most recent innovations to promote a circular economy during wastewater treatment is the production of biopolymers. It has recently been demonstrated that it is possible to integrate the production of biopolymers in the form of polyhydroxyalkanoates (PHA) with nitrogen removal via nitrite during the treatment of sludge reject water. In the present study, simulation of a new process for bioresource recovery was conducted by an appropriate modification of the Activated Sludge Model 3. The process consists of the integrated nitrogen removal via nitrite from sludge reject water and the selection of PHA-storing biomass by inducing a feast and famine regime under aerobic and anoxic conditions. According to the results, it is anticipated that simulation data matched very satisfactorily with the experimental data and confirmed the main experimental observation, showing that during the famine period the PHA depletion was almost complete due to the availability of nitrite as the electron acceptor. Simulation results indicate that the selection of the volumetric organic loading rate and of the relative duration of the aerobic feast/anoxic famine duration is critical in order to allow for the effective denitritation of the internally stored PHA during the famine phase.

Copolymers and Blends Based on 3-Hydroxybutyrate and 3-Hydroxyvalerate Units

This review presents a comprehensive update of the biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), emphasizing its production, properties, and applications. The overall biosynthesis pathway of PHBV is explored in detail, highlighting recent advances in production techniques. The inherent physicochemical properties of PHBV, along with its degradation behavior, are discussed in detail. This review also explores various blends and composites of PHBV, demonstrating their potential for a range of applications. Finally, the versatility of PHBV-based materials in multiple sectors is examined, emphasizing their increasing importance in the field of biodegradable polymers.

Polyhydroxybutyrate synthesis in Camelina: Towards coproduction of renewable feedstocks for bioplastics and fuels

Plant-based co-production of polyhydroxyalkanoates (PHAs) and seed oil has the potential to create a viable domestic source of feedstocks for renewable fuels and plastics. PHAs, a class of biodegradable polyesters, can replace conventional plastics in many applications while providing full degradation in all biologically active environments. Here we report the production of the PHA poly[(R)-3-hydroxybutyrate] (PHB) in the seed cytosol of the emerging bioenergy crop Camelina sativa engineered with a bacterial PHB biosynthetic pathway. Two approaches were used: cytosolic localization of all three enzymes of the PHB pathway in the seed, or localization of the first two enzymes of the pathway in the cytosol and anchoring of the third enzyme required for polymerization to the cytosolic face of the endoplasmic reticulum (ER). The ER-targeted approach was found to provide more stable polymer production with PHB levels up to 10.2% of the mature seed weight achieved in seeds with good viability. These results mark a significant step forward towards engineering lines for commercial use. Plant-based PHA production would enable a direct link between low-cost large-scale agricultural production of biodegradable polymers and seed oil with the global plastics and renewable fuels markets.

Exploring Bacillus amyloliquefaciens strain OM81 for the production of polyhydroxyalkanoate (PHA) bioplastic using olive mill wastewater

In this study, bacterial strains isolated from olive oil mill wastewater assigned to Bacillus (n = 4) and Klebsiella (n = 1) genera, were evaluated for their ability to accumulate intracellular PHA granules using Sudan Black staining. A maximum PHA production of 0.14 g/L (i.e., 30.2% wt./wt. in dry biomass) was observed in Bacillus amyloliquefaciens strain OM81 after 72 h of incubation in the presence of 2% glucose (synthetic medium). To reduce bioplastic production costs and recover a polluting product, olive mill wastewater was tested as a carbon source. In this context, the maximum growth (1.45 g/L) was observed in the presence of 50% olive mill wastewater. After extracting the biopolymers with chloroform, quantitative and qualitative analyses were conducted using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). FTIR showed an absorption band at 1730 cm-1 assigned to the elongation of the PHB carbonyl groups. This approach offers a dual benefit of reducing pollution and bioplastic production costs. The Bacillus amyloliquefaciens strain OM81 showed promising results for PHAs production, making it a potential candidate for further investigation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03808-4.

Approaches to Control Crazing Deformation of PHA-Based Biopolymeric Blends

The mechanical behavior of polymer materials is heavily influenced by a phenomenon known as crazing. Crazing is a precursor to damage and leads to the formation of cracks as it grows in both thickness and tip size. The current research employs an in situ SEM method to investigate the initiation and progression of crazing in all-biopolymeric blends based on Polyhydroxyalkanoates (PHAs). To this end, two chemically different grades of PHA, namely poly(hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV), were melt-blended with polybutyrate adipate terephthalate (PBAT). The obtained morphologies of blends, the droplet/fibrillar matrix, were highly influenced by the plasticity of the matrices as well as the content of the minor phase. Increasing the concentration of PBAT from 15 to 30 wt.% resulted in the brittle to ductile transition. It changed the mechanism of plastic deformation from single craze-cracking to homogeneous and heterogeneous intensified crazing for PHB and PHBHV matrices, respectively. Homogeneous tensile crazes formed perpendicularly to the draw direction at the initial stages of deformation, transformed into shear crazes characterized by oblique edge propagation for the PHBHV/PBAT blend. Such angled crazes suggested that the displacement might be caused by shear localized deformation. The crazes' strength and the time to failure increased with the minor phase fibers. These fibers, aligned with the tensile direction and spanning the width of the crazes, were in the order of a few micrometers in diameter depending on the concentration. The network of fibrillar PBAT provided additional integrity for larger plastic deformation values. This study elucidates the mechanism of crazing in PHA blends and provides strategies for controlling it.

Properties of Degradable Polyhydroxyalkanoates Synthesized from New Waste Fish Oils (WFOs)

The synthesis of PHA was first investigated using WFOs obtained from smoked-sprat heads, substandard fresh sprats, and fresh mackerel heads and backbones. All the WFOs ensured the growth of the wild-type strain Cupriavidus necator B-10646 and the synthesis of PHA, regardless of the degree of lipid saturation (from 0.52 to 0.65) and the set and ratio of fatty acids (FA), which was represented by acids with chain lengths from C14 to C24. The bacterial biomass concentration and PHA synthesis were comparable (4.1-4.6 g/L and about 70%) when using WFO obtained from smoked-sprat heads and fresh mackerel, and it was twice as high as the bacterial biomass concentration from the fresh sprat waste. This depended on the type of WFO, the bacteria synthesized P(3HB) homopolymer or P(3HB-co-3HV-co-3HHx) copolymer, which had a lower degree of crystallinity (Cx 71%) and a lower molecular weight (Mn 134 kDa) compared to the P(3HB) (Mn 175-209 kDa and Cx 74-78%) at comparable temperatures (Tmelt and Tdegr of 158-168 °C and 261-284 °C, respectively). The new types of WFO, studied for the first time, are suitable as a carbon substrates for PHA synthesis. The WFOs obtained in the production of canned Baltic sprat and Baltic mackerel can be considered a promising and renewable substrate for PHA biosynthesis.

Inactivation of poly(3-hydroxybutyrate) (PHB) biosynthesis in 'Knallgas' bacterium Xanthobacter sp. SoF1

Aerobic hydrogen-oxidizing 'Knallgas' bacteria are promising candidates for microbial cell factories due to their ability to use hydrogen and carbon dioxide as the sole energy and carbon sources, respectively. These bacteria can convert atmospheric CO₂ to chemicals which could help to mitigate climate change by replacing fossil fuel-based chemicals. A known method to enhance the product yield is to disrupt competing metabolic pathways in the host organism. One such pathway in many 'Knallgas' bacteria is polyhydroxybutyrate (PHB) biosynthesis. In this study, the PHB biosynthesis genes of a non-model 'Knallgas' bacterium Xanthobacter sp. SoF1 were identified. Consequently, the phaA, phaB and phaC genes were individually deleted and the resulting knockouts were evaluated for their ability to produce PHB in autotrophic shake flask and small-scale bioreactor cultivations. The results demonstrate that PHB production was inactivated in the phaC1 knockout strain, which advances the development of Xanthobacter sp. SoF1 as a production host.

Degradation Behavior of Biodegradable Man-Made Fibers in Natural Soil and in Compost

In open environment applications, fibers are increasingly being used that are expected to biodegrade in the soil after their desired service life. Biodegradable polymer fibers are a versatile alternative to natural fibers. In this study, the degradation behavior of fibers made from polylactic acid (PLA) and a polyhydroxy alkanoate (PHA) blend with PLA, as well as a bicomponent fiber (BICO) made from polybutylene succinate (PBS) and PLA, was investigated. The fibers were stored in topsoil at 23 °C for 12 weeks. In addition, fibers were stored in compost at 58 °C for 4 weeks to investigate the degradation behavior in an industrial composting plant. Reference materials were also stored without substrate under the same temperatures and humidity conditions. Samples were taken regularly, and mechanical testing, scanning electron microscopy (SEM), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and infrared spectroscopy (IR) were used to study the degradation of the fibers. After 12 weeks in soil at ambient temperatures, the PLA and BICO fibers showed no degradation. The PHA fibers showed cracks in SEM, a decrease in molecular weight, and changes in the IR spectrum. No evidence of biological influence (bacteria or fungi) was found. Under industrial composting conditions, all fibers showed a decrease in strength and molecular weight. For the BICO and the PHA fibers, the SEM images show significant changes. Especially in the PHA fibers, fungal mycelia can be seen. The studies provide a better insight into the processes involved in the degradation behavior under different environmental conditions.

Tailoring the HHx monomer content of P(HB-co-HHx) by flexible substrate compositions: scale-up from deep-well-plates to laboratory bioreactor cultivations

The enhanced material properties exhibited by the microbially synthetized polyhydroxyalkanoate (PHA) copolymer poly(hydroxybutyrate-co-hydroxyhexanoate) [P(HB-co-HHx)] evidence that this naturally biodegrading biopolymer could replace various functionalities of established petrochemical plastics. In fact, the thermal processability, toughness and degradation rate of P(HB-co-HHx) can be tuned by modulating its HHx molar content enabling to manufacture polymers à-la-carte. We have developed a simple batch strategy to precisely control the HHx content of P(HB-co-HHx) to obtain tailor-made PHAs with defined properties. By adjusting the ratio of fructose to canola oil as substrates for the cultivation of recombinant Ralstonia eutropha Re2058/pCB113, the molar fraction of HHx in P(HB-co-HHx) could be adjusted within a range of 2-17 mol% without compromising polymer yields. The chosen strategy proved to be robust from the mL-scale in deep-well-plates to 1-L batch bioreactor cultivations.

Impact of the anaerobic feeding mode on substrate distribution in aerobic granular sludge

There is a growing interest to implement aerobic granular sludge (AGS) in existing conventional activated sludge (CAS) systems with a continuous flow-through configuration. The mode of anaerobic contact of raw sewage with the sludge is an important aspect in the adaptation of CAS systems to accommodate AGS. It remains unclear how the distribution of substrate over the sludge by a conventional anaerobic selector compares to the distribution via bottom-feeding applied in sequencing batch reactors (SBRs). This study investigated the effect of the anaerobic contact mode on the substrate (and storage) distribution by operating two lab-scale SBRs; one with the traditional bottom-feeding through a settled sludge bed similar to full-scale AGS systems, and one where the synthetic wastewater was fed as a pulse at the start of the anaerobic phase while the reactor was mixed through sparging of nitrogen gas (mimicking a plug-flow anaerobic selector in continuous flow-through systems). The distribution of the substrate over the sludge particle population was quantified via PHA analysis, combined with the obtained granule size distribution. Bottom-feeding was found to primarily direct substrate towards the large granular size classes (i.e. large volume and close to the bottom), while completely mixed pulse-feeding gives a more equal distribution of substrate over all granule sizes (i.e. surface area dependant). The anaerobic contact mode directly controls the substrate distribution over the different granule sizes, irrespective of the solids retention time of a granule as an entity. Preferential feeding of the larger granules will enhance and stabilise the granulation compared to pulse-feeding, certainly under less advantageous conditions imposed by real sewage.

Immune genotypes, immune responses, and survival in a wild bird population

Individuals vary in their immune genotype, inbreeding coefficient f, immune responses, survival to adulthood, and adult longevity. However, whether immune genes predict survival or longevity, whether such relationships are mediated through immune responses, and how f affects immune genotype remain unclear. We use a wild song sparrow (Melospiza melodia) population in which survival to adulthood, adult longevity, and f were measured precisely, and in which immune responses have previously been assessed. We investigate four toll-like receptor (TLR) and the major histocompatibility complex (MHC) class IIB exon 2 genes. We test whether immune genes predict fitness (survival to adulthood or adult longevity); whether immune genes predict immune response; whether immune response predicts fitness and whether fitness, immune responses, or immune genotypes are correlated with f. We find that survival to adulthood is not associated with immune gene variation, but adult longevity is decreased by high MHC allele diversity (especially in birds that were relatively outbred), and by the presence of a specific MHC supertype. Immune responses were affected by specific immune genotypes. Survival to adulthood and adult longevity were not predicted by immune response, implying caution in the use of immune response as a predictor for fitness. We also found no relationship between f and immune genotype. This finding indicates that immune gene associations with longevity and immune response are not artefacts of f, and suggests that pathogen-mediated selection at functional loci can slow the loss of genetic variation arising from genetic drift and small population size.

Relationships between hormone levels, metabolism and immune response in toads from a semi-arid region

Steroid hormones (e.g. androgens [AN] and corticosterone [CORT]) modulate complex physiological functions such as reproduction, energy mobilization, metabolism, and immunity. Fluctuations in environmental resource availability along with other factors, such as parasitism, can interact with the effects of these steroids, modifying aspects of immunocompetence and its metabolic costs. To understand these possible interactions, we studied AN and CORT, immune response [swelling response to phytohemagglutinin (PHA) injection and bacterial killing ability (BKA)], parasite load, resting metabolic rate (RMR) and rates of oxygen consumption after PHA injection, in two different phases of the annual cycle of a toad (Rhinella jimi) from a highly seasonal environment (Brazilian semi-arid, Caatinga). We observed increased rates of O₂ consumption after both PHA and the control (saline) injection, indicating a metabolic response to adverse stimuli but not the immune challenge. Toads showing higher RMR and VO₂ after the adverse stimuli (PHA/saline injection) had lower field AN and CORT plasma levels, suggesting these hormones might mediate a metabolic energy conservation strategy both at baseline levels and after adverse stimuli. Parasite load seem to impose an energetic constrain to the metabolic response to PHA and saline injection. Also, individuals showing higher PHA swelling response had higher field CORT plasma levels (particularly when males are breeding) which opposes the idea of a possible trade-off between reproductive activity and other physiological traits and indicate the immunoenhancing effects CORT elevated at physiological levels. BKA did not show a seasonal variation or correlation with body condition nor hormone levels, indicating that the immune surveillance mediated by the complement remains constant despite other ecological and physiological changes.

Anaerobic Biodegradability of Commercial Bioplastic Products: Systematic Bibliographic Analysis and Critical Assessment of the Latest Advances

Bioplastics have entered everyday life as a potential sustainable substitute for commodity plastics. However, still further progress should be made to clarify their degradation behavior under controlled and uncontrolled conditions. The wide array of biopolymers and commercial blends available make predicting the biodegradation degree and kinetics quite a complex issue that requires specific knowledge of the multiple factors affecting the degradation process. This paper summarizes the main scientific literature on anaerobic digestion of biodegradable plastics through a general bibliographic analysis and a more detailed discussion of specific results from relevant experimental studies. The critical analysis of literature data initially included 275 scientific references, which were then screened for duplication/pertinence/relevance. The screened references were analyzed to derive some general features of the research profile, trends, and evolution in the field of anaerobic biodegradation of bioplastics. The second stage of the analysis involved extracting detailed results about bioplastic degradability under anaerobic conditions by screening analytical and performance data on biodegradation performance for different types of bioplastic products and different anaerobic biodegradation conditions, with a particular emphasis on the most recent data. A critical overview of existing biopolymers is presented, along with their properties and degradation mechanisms and the operating parameters influencing/enhancing the degradation process under anaerobic conditions.

Simultaneous production of renewable biohydrogen, biobutanol and biopolymer from phytogenic CoNPs-assisted Clostridial fermentation for sustainable energy and environment

Considering the environmental impacts, rapid fossil fuel depletion and production costs, sustainable production of clean biofuels from alternative sources is required to meet the increasing demand for energy while avoiding environmental pollution. In this study, phytogenic cobalt nanoparticles (CoNPs)-assisted dark fermentation process was developed for the simultaneous production of biohydrogen, biobutanol and biopolymer from glucose using Clostridium acetobutylicum NCIM 2337. The maximum biohydrogen yield of 2.89 mol H₂/mol glucose was achieved at 1.5 mg of CoNPs, which is 1.6 folds higher than that of the control experiment. The high level of soluble metabolites, specifically acetate and butyrate, confirmed the production of biohydrogen through acetate/butyrate pathways. The modified Gompertz model fitted well with experimental results of CoNPs-assisted biohydrogen production. The CoNPs could act as an electron carrier in intracellular metabolism to enhance the activity of ferredoxin and hydrogenase enzymes, thus improving biohydrogen production. Furthermore, biobutanol and biopolymer yields of 975 ± 2.5 mg/L and 1182 ± 1.4 mg/L were achieved, with 2.0 mg and 2.5 mg of CoNP, respectively, which were 1.27 and 1.19 folds higher than the control values. Hence, the inclusion of CoNPs in the fermentation medium seems to be a promising technique for the enhanced simultaneous production of biohydrogen, biobutanol and biopolymer. The environmental perspectives of the obtained renewable biohydrogen, biobutanol and biopolymer are also discussed.

Trends and challenges in the valorization of kitchen waste to polyhydroxyalkanoates

Kitchen waste (KW) is frequently available for free or with a negative cost due to its huge production. It contains a large proportion of organic substances, especially fermentable sugars, which can be used for bioplastic (polyhydroxyalkanoates or PHA) synthesis. Nevertheless, due to the difficulties in processing, various pre-treatments of KW are being investigated to enhance the concentration of simple sugars released during its hydrolysis. The effective use of KW will help in minimizing the issues of its inappropriate disposal. However, the review on KW to bioplastic synthesis is rarely reported in the literature. Hence, this particular review provides a comprehensive summary of the updated research developments in KW valorization and its potency as a feedstock for PHAs synthesis. Additionally, the impacts of KW, its availability, the necessary pre-treatments for the biopolymerization process, as well as the prospects and challenges for industrially generating sustainable PHAs, are critically discussed.

Mechanistic insights into polyhydroxyalkanoate-enhanced denitrification capacity of microbial community: Evolution of community structure and intracellular electron transfer of nitrogen metabolism

Denitrification is the key driving force of nitrogen cycle in surface water and plays an important role in eutrophication water remediation. Compared with some other common carbon sources, such as glucose and sodium acetate, polyhydroxyalkanoates (PHAs) were found to have the distinguished advantages in screening specific denitrifying bacteria of natural surface water bodies. In this study, the large ensembles of taxa were obtained from surface water samples and then sub-cultured with PHA or glucose as the sole carbon source. The microbial community that could be screened by PHA was identified, and the environmental functions of these bacteria were analyzed. At the genus level, the main communities regulated by PHA included Pseudomonas (56.30 %), Acinetobacter (27.75 %), Flavobacterium (10.19 %) and Comamonas (3.14 %), which all had good denitrification ability. The changes in carbon source, nitrogen source and biomass (expressed by DNA) were simultaneously monitored when culturing the model strain (P. stuzeri) with PHA or glucose. Compared with the glucose group, less PHA was consumed to remove the same amount of nitrate within a shorter incubation time, and there was no significant difference in bacterial growth with PHA or glucose as the carbon source (glucose:ΔN:ΔC:ΔDNA = 1:18:0.072; PHA:ΔN:ΔC:ΔDNA = 1:11:0.063). PHA improved the denitrification efficiency by increasing the expression of NarGHI, NirB, NirK and NorB, i.e., the key enzymes in the denitrification process. In addition, PHA accelerated the assimilating rate of extracellular nitrate by bacteria through increasing the expression of NarK. Finally, PHA-regulated electron transfer during denitrification was studied by observing the changes in NADH and NAD⁺. PHA could use a large proportion of NADH to offer electrons for denitrification, which increased the rate of denitrification. Improved mechanistic insights into the PHA-enhanced denitrification capacity of the microbial community can provide novel options for the in-situ remediation of eutrophic surface water.

Formation of polyhydroxyalkanoates using agro and industrial waste as a substrate - a review

In the present scenario, rising environmental concerns of non-biodegradable plastic pollution and depletion of petroleum based raw materials lead to the development of biopolymers. The biodegradability of biopolymers gives them a specific advantage for the environmental concerns. Polyhydroxyalkanoates (PHAs) are a type of biopolymers which are synthesized by microorganisms. Although there are different substrates available in pure forms which are currently used in the production of PHA, 40% of production cost depends on the expensive substrate which is a major disadvantage and make it far from many applications. The use of an inexpensive carbon source which is high in organic matter content such as waste streams of process industries can make this process viable and diminish PHA production cost. This study explores the current research initiatives on various agricultural and industrial waste feedstocks, formulations and processing conditions for producing PHA in a way that is both inexpensive and beneficial to the environment. The creation of fermentation conditions and metabolic engineering techniques for promoting microbial growth and PHA synthesis were also discussed in the review.

Multifunctional Electrospinning Polyhydroxyalkanoate Fibrous Scaffolds with Antibacterial and Angiogenesis Effects for Accelerating Wound Healing

To treat large-scale wounds or chronic ulcers, it is highly desirable to develop multifunctional wound dressings that integrate antibacterial and angiogenic properties. While many biomaterials have been fabricated as wound dressings for skin regeneration, few reports have addressed the issue of complete skin regeneration due to the lack of vasculature and hair follicles. Herein, an instructive poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) fibrous wound dressing that integrates an antibacterial ciprofloxacin (CIP) and pro-angiogenic dimethyloxalylglycine (DMOG) is successfully prepared via electrospinning. The resultant dressings exhibit suitable flexibility with tensile strength and elongation at break up to 4.08 ± 0.18 MPa and 354.8 ± 18.4%, respectively. The in vitro results revealed that the groups of P34HB/CIP/DMOG dressings presented excellent biocompatibility on cell proliferation and significantly promote the spread and migration of L929 cells in both transwell and scratch assays. Capillary-like tube formation is also significantly enhanced in the P34HB/CIP/DMOG group dressings. Additionally, dressings from the P34HB/CIP and P34HB/CIP/DMOG groups show a broad spectrum of antimicrobial action against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. In vivo studies further demonstrated that the prepared dressings in the P34HB/CIP/DMOG group not only improved wound closure, increased re-epithelialization and collagen formation, as well as reduced inflammatory response but also increased angiogenesis and remodeling, resulting in complete skin regeneration and hair follicles. Collectively, this work provides a simple but efficient approach for the design of a versatile wound dressing with the potential to have a synergistic effect on the rapid stimulation of angiogenesis as well as antibacterial activity in full-thickness skin repair.

Biogeochemical properties of blue carbon sediments influence the distribution and monomer composition of bacterial polyhydroxyalkanoates (PHA)

Coastal wetlands are highly efficient 'blue carbon' sinks which contribute to mitigating climate change through the long-term removal of atmospheric CO₂ and capture of carbon (C). Microorganisms are integral to C sequestration in blue carbon sediments and face a myriad of natural and anthropogenic pressures yet their adaptive responses are poorly understood. One such response in bacteria is the alteration of biomass lipids, specifically through the accumulation of polyhydroxyalkanoates (PHAs) and alteration of membrane phospholipid fatty acids (PLFA). PHAs are highly reduced bacterial storage polymers that increase bacterial fitness in changing environments. In this study, we investigated the distribution of microbial PHA, PLFA profiles, community structure and response to changes in sediment geochemistry along an elevation gradient from intertidal to vegetated supratidal sediments. We found highest PHA accumulation, monomer diversity and expression of lipid stress indices in elevated and vegetated sediments where C, nitrogen (N), PAH and heavy metals increased, and pH was significantly lower. This was accompanied by a reduction in bacterial diversity and a shift to higher abundances of microbial community members favouring complex C degradation. Results presented here describe a connection between bacterial PHA accumulation, membrane lipid adaptation, microbial community composition and polluted C rich sediments.

GRAPHICAL ABSTRACT

Geochemical, microbiological and polyhydroxyalkanoate (PHA) gradient in a blue carbon zone.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10533-022-01008-5.

Unsterile production of a polyhydroxyalkanoate copolymer by Halomonas cupida J9

Microbial production of bioplastics polyhydroxyalkanoates (PHA) has opened new avenues to resolve "white pollution" caused by petroleum-based plastics. PHAs consisting of short- and medium-chain-length monomers, designated as SCL-co-MCL PHAs, exhibit much better thermal and mechanical properties than PHA homopolymers. In this study, a halophilic bacterium Halomonas cupida J9 was isolated from highly saline wastewater and proven to produce SCL-co-MCL PHA consisting of 3-hydroxybutyrate (3HB) and 3-hydroxydodecanoate (3HDD) from glucose and glycerol. Whole-genome sequencing and functional annotation suggest that H. cupida J9 may possess three putative PHA biosynthesis pathways and a class I PHA synthase (PhaC_J9). Interestingly, the purified His₆-tagged PhaC_J9 from E. coli BL21 (DE3) showed polymerizing activity towards 3HDD-CoA and a phaC_J9-deficient mutant was unable to produce PHA, which indicated that a low-substrate-specificity PhaC_J9 was exclusively responsible for PHA polymerization in H. cupida J9. Docking simulation demonstrated higher binding affinity between 3HB-CoA and PhaC_J9 and identified the key residues involved in hydrogen bonds formation between 3-hydroxyacyl-CoA and PhaC_J9. Furthermore, His489 was identified by site-specific mutagenesis as the key residue for the interaction of 3HDD-CoA with PhaC_J9. Finally, PHA was produced by H. cupida J9 from glucose and glycerol in shake flasks and a 5-L fermentor under unsterile conditions. The open fermentation mode makes this strain a promising candidate for low-cost production of SCL-co-MCL PHAs. Especially, the low-specificity PhaC_J9 has great potential to be engineered for an enlarged substrate range to synthesize tailor-made novel SCL-co-MCL PHAs.

PHA stimulated denitrification through regulation of preferential cofactor provision and intracellular carbon metabolism at different dissolved oxygen levels by Pseudomonas stutzeri

Denitrification, a typical biological process mediated by complex environmental factors, i.e., carbon sources and dissolved oxygen (DO), has attracted great attention due to its contribution to the control of eutrophication and the biochemical cycling of nitrogen. However, the effects of carbon source on electron distribution and enzyme expression for enhanced denitrification under competition of electron acceptors (DO and nitrate) remain unclear. Here, we profile the carbon metabolic pathway of polyhydroxybutyrate (PHB) and glucose (Glu) at high and low DO levels (50% and 10% saturated DO, respectively). It was found that PHB enhanced the growth of Pseudomonas stutzeri (model denitrifying bacterium) and improved the specific nitrogen removal rate (SNRR) at all DO levels. The functional proteins had a better affinity for the cofactor nicotinamide-adenine dinucleotide (NADH) than for nicotinamide adenine dinucleotide phosphate (NADPH); thus, more electrons were involved in nitrogen reduction and intracellular PHB production in the PHB groups than in the Glu groups. Furthermore, the expression difference of enzymes in glucose and PHB metabolism was demonstrated by metaproteomic and target protein analysis, implying that PHB-driven intracellular carbon accumulation could optimize the intracellular electron allocation and correspondingly promote nitrogen metabolism. Our work integrated the mechanisms of intracellular carbon metabolism with preferences for electron transfer pathways in denitrification, providing a new perspective on how the selective parameters regulated microbial functions involved in denitrification.

Closing the Gap between Bio-Based and Petroleum-Based Plastic through Bioengineering

Bioplastics, which are plastic materials produced from renewable bio-based feedstocks, have been investigated for their potential as an attractive alternative to petroleum-based plastics. Despite the harmful effects of plastic accumulation in the environment, bioplastic production is still underdeveloped. Recent advances in strain development, genome sequencing, and editing technologies have accelerated research efforts toward bioplastic production and helped to advance its goal of replacing conventional plastics. In this review, we highlight bioengineering approaches, new advancements, and related challenges in the bioproduction and biodegradation of plastics. We cover different types of polymers, including polylactic acid (PLA) and polyhydroxyalkanoates (PHAs and PHBs) produced by bacterial, microalgal, and plant species naturally as well as through genetic engineering. Moreover, we provide detailed information on pathways that produce PHAs and PHBs in bacteria. Lastly, we present the prospect of using large-scale genome engineering to enhance strains and develop microalgae as a sustainable production platform.

Halomonas spp., as chassis for low-cost production of chemicals

Halomonas spp. are the well-studied platform organisms or chassis for next-generation industrial biotechnology (NGIB) due to their contamination-resistant nature combined with their fast growth property. Several Halomonas spp. have been studied regarding their genomic information and molecular engineering approaches. Halomonas spp., especially Halomonas bluephagenesis, have been engineered to produce various biopolyesters such as polyhydroxyalkanoates (PHA), proteins including surfactants and enzymes, small molecular compounds including amino acids and derivates, as well as organic acids. This paper reviews all the progress reported in the last 10 years regarding this robust microbial cell factory. KEY POINTS: • Halomonas spp. are robust chassis for low-cost production of chemicals • Genomic information of some Halomonas spp. has been revealed • Molecular tools and approaches for Halomonas spp. have been developed • Halomonas spp. are becoming more and more important for biotechnology.

Production of biopolymers from food waste: Constrains and perspectives

Food is an essential commodity for the survival of any form of life on earth. Yet generation of plethora of food waste has significantly elevated the global concern for food scarcity, human and environment deterioration. Also, increasing use of polymers derived from petroleum hydrocarbons has elevated the concerns towards the depletion of this non-renewable resource. In this review, the use of waste food for the production of bio-polymers and their associated challenges has been thoroughly investigated using scientometric analysis. Various categories of food waste including fruit, vegetable, and oily waste can be employed for the production of different biopolymers including polyhydroxyalkanoates, starch, cellulose, collagen and others. The advances in the production of biopolymers through chemical, microbial or enzymatic process that increases the acceptability of these biopolymers has been reviewed. The comprehensive compiled information may assist researchers for addressing and solving the issues pertaining to food wastage and fossil fuel depletion.

In silico identification of bacterial seaweed-degrading bioplastic producers

There is an urgent need to replace petroleum-based plastic with bio-based and biodegradable alternatives. Polyhydroxyalkanoates (PHAs) are attractive prospective replacements that exhibit desirable mechanical properties and are recyclable and biodegradable in terrestrial and marine environments. However, the production costs today still limit the economic sustainability of the PHA industry. Seaweed cultivation represents an opportunity for carbon capture, while also supplying a sustainable photosynthetic feedstock for PHA production. We mined existing gene and protein databases to identify bacteria able to grow and produce PHAs using seaweed-derived carbohydrates as substrates. There were no significant relationships between the genes involved in the deconstruction of algae polysaccharides and PHA production, with poor to negative correlations and diffused clustering suggesting evolutionary compartmentalism. We identified 2 987 bacterial candidates spanning 40 taxonomic families predominantly within Alphaproteobacteria, Gammaproteobacteria and Burkholderiales with enriched seaweed-degrading capacity that also harbour PHA synthesis potential. These included highly promising candidates with specialist and generalist specificities, including Alteromonas, Aquisphaera, Azotobacter, Bacillus, Caulobacter, Cellvibrionaceae, Duganella, Janthinobacterium, Massilia, Oxalobacteraceae, Parvularcula, Pirellulaceae, Pseudomonas, Rhizobacter, Rhodanobacter, Simiduia, Sphingobium, Sphingomonadaceae, Sphingomonas, Stieleria, Vibrio and Xanthomonas. In this enriched subset, the family-level densities of genes targeting green macroalgae polysaccharides were considerably higher (n=231.6±68.5) than enzymes targeting brown (n=65.34±13.12) and red (n=30.5±10.72) polysaccharides. Within these organisms, an abundance of FabG genes was observed, suggesting that the fatty acid de novo synthesis pathway supplies (R)-3-hydroxyacyl-CoA or 3-hydroxybutyryl-CoA from core metabolic processes and is the predominant mechanism of PHA production in these organisms. Our results facilitate extending seaweed biomass valorization in the context of consolidated biorefining for the production of bioplastics.

Polyhydroxyalkanoate recovery from newly screened Bacillus sp. LPPI-18 using various methods of extraction from Loktak Lake sediment sample

BACKGROUND

Nowadays, the conventional plastic wastes are very challenging to environments and its production cost also creates an economic crisis due to petrochemical-based plastic. In order to solve this problem, the current studies were aimed at screening and characterizing these polyhydroxyalkanoate (PHA)-producing isolates and evaluating the suitability of some carbon source for newly screened PHA-producing isolates.

MATERIAL AND METHODS

Some carbon sources such as D-fructose, glucose, molasses, D-ribose and sucrose were evaluated for PHA production. Data were analyzed using SPSS version 20. The 16SrRNA gene sequence of these isolates was performed. These newly isolated taxa were related to Bacillus species. It was designated as Bacillus sp. LPPI-18 and affiliated Bacillus cereus ATCC 14577^T (AE01687) (99.10%). Paenibacillus sp. 172 (AF273740.1) was used as an outgroup.

RESULTS

Bacillus sp. LPPI-18 is a gram-positive, rod-shaped, endospore former, and citrate test positive. This isolate showed positive for amylase, catalase, pectinase, and protease test. They produced intracellular PHA granules when this isolate was stained with Sudan Black B (SBB) and Nile blue A (NBA) preliminary and specific staining dyes, respectively. Both temperature and pH used to affect polyhydroxyalkanoates (PHA) productivity. Bacteria are able to reserve PHA in the form of granules during stress conditions. This isolate produces only when supplied with carbon sources. More PHA contents (PCs) were obtained from glucose, molasses, and D-fructose. In this regard, the maximum mean value of PC was obtained from glucose (40.55±0.7%) and the minimum was obtained from D-ribose (12.4±1.4%). Great variations (P≤0.05) of PCs were observed among glucose and sucrose, molasses and sucrose, and D-fructose and sucrose carbon sources for PHA productivity (PP) of cell dry weight (CDW) g/L. After extraction, PHA film was produced for this typical isolate using glucose as a sole carbon source. Fourier transform infrared spectrum was performed for this isolate and showed the feature of polyester at 1719.64 to 1721.16 wavelengths for these extracted samples. The peak of fingerprinting (band of carboxylic acid group) at this wavelength is a characteristic feature of polyhydroxybutyrate (PHB) and corresponds to the ester functional group (C=O).

CONCLUSION

In this study, newly identified Bacillus sp. LPPI-18 is found to be producing biodegradable polymers that are used to replace highly pollutant conventional plastic polymers. This isolate is also used to employ certain cost-effective carbon sources for the production of PHA polymers.

Bacterial growth in multicellular aggregates leads to the emergence of complex life cycles

Facultative multicellular behaviors expand the metabolic capacity and physiological resilience of bacteria. Despite their ubiquity in nature, we lack an understanding of how these behaviors emerge from cellular-scale phenomena. Here, we show how the coupling between growth and resource gradient formation leads to the emergence of multicellular lifecycles in a marine bacterium. Under otherwise carbon-limited growth conditions, Vibrio splendidus 12B01 forms clonal multicellular groups to collectively harvest carbon from soluble polymers of the brown-algal polysaccharide alginate. As they grow, groups phenotypically differentiate into two spatially distinct sub-populations: a static "shell" surrounding a motile, carbon-storing "core." Differentiation of these two sub-populations coincides with the formation of a gradient in nitrogen-source availability within clusters. Additionally, we find that populations of cells containing a high proportion of carbon-storing individuals propagate and form new clusters more readily on alginate than do populations with few carbon-storing cells. Together, these results suggest that local metabolic activity and differential partitioning of resources leads to the emergence of reproductive cycles in a facultatively multicellular bacterium.

Novel thermophilic polyhydroxyalkanoates producing strain Aneurinibacillus thermoaerophilus CCM 8960

Aneurinibacillus thermoaerophilus CCM 8960 is a thermophilic bacterium isolated from compost in Brno. The bacterium accumulates polyhydroxyalkanoates (PHAs), a biodegradable and renewable alternative to petrochemical polymers. The bacterium reveals several features that make it a very interesting candidate for the industrial production of PHA. At first, due to its thermophilic character, the bacterium can be utilized in agreement with the concept of next-generation industrial biotechnology (NGIB), which relies on extremophiles. Second, the bacterium is capable of producing PHA copolymers containing a very high portion of 4-hydroxybutyrate (4HB). Such materials possess unique properties and can be advantageously used in multiple applications, including but not limited to medicine and healthcare. Therefore, this work focuses on the in-depth characterization of A. thermoaerophilus CCM 8960. In particular, we sequenced and assembled the genome of the bacterium and identified its most important genetic features, such as the presence of plasmids, prophages, CRISPR arrays, antibiotic-resistant genes, and restriction-modification (R-M) systems, which might be crucial for the development of genome editing tools. Furthermore, we focused on genes directly involved in PHA metabolism. We also experimentally studied the kinetics of glycerol and 1,4-butanediol (1,4BD) utilization as well as biomass growth and PHA production during cultivation. Based on these data, we constructed a metabolic model to reveal metabolic fluxes and nodes of glycerol and 1,4BD concerning their incorporation into the poly(3-hydroxybutyrate-co-4-hydroxybutyrate (P(3HB-co-4HB)) structure. KEY POINTS: • Aneurinibacillus sp. H1 was identified as Aneurinibacillus thermoaerophilus. • PHA metabolism pathway with associated genes was presented. • Unique monomer composition of produced PHAs was reported.

Engineering Halomonas bluephagenesis via small regulatory RNAs

Halomonas bluephagenesis, a robust and contamination-resistant microorganism has been developed as a chassis for "Next Generation Industrial Biotechnology". The non-model H. bluephagenesis requires efficient tools to fine-tune its metabolic fluxes for enhanced production phenotypes. Here we report a highly efficient gene expression regulation system (PrrF1-2-HfqPa) in H. bluephagenesis, small regulatory RNA (sRNA) PrrF1 scaffold from Pseudomonas aeruginosa and a target-binding sequence that downregulate gene expression, and its cognate P. aeruginosa Hfq (HfqPa), recruited by the scaffold to facilitate the hybridization of sRNA and the target mRNA. The PrrF1-2-HfqPa system targeting prpC in H. bluephagenesis helps increase 3-hydroxyvalerate fraction in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) to 21 mol% compared to 3.1 mol% of the control. This sRNA system repressed phaP1 and minD simultaneously, resulting in large polyhydroxybutyrate granules. Further, an sRNA library targeting 30 genes was employed for large-scale target identification to increase mevalonate production. This work expands the study on using an sRNA system not based on Escherichia coli MicC/SgrS-Hfq to repress gene expression, providing a framework to exploit new powerful genome engineering tools based on other sRNAs.

Role of carbon-dioxide sequestering bacteria for clean air environment and prospective production of biomaterials: a sustainable approach

The increase in demand of fossil fuel uses for developmental activity and manufacturing of goods have resulted a huge emission of global warming gases (GWGs) in the atmosphere. Among all GWGs, CO₂ is the major contributor that inevitably causes global warming and climate change. Mitigation strategies like biological CO₂ capture through sequestration and their storage into biological organic form are used to minimize the concentration of atmospheric CO₂ with the goal to control climate change. Since increasing atmospheric CO₂ level supports microbial growth and productivity thus microbial-based CO₂ sequestration has remarkable advantages as compared to plant-based sequestration. This review focuses on CO₂ sequestration mechanism in bacteria through different carbon fixation pathways, involved enzymes, their role in calcite, and other environmentally friendly biomaterials such as biofuel, bioplastic, and biosurfactant.

Engineering an oleic acid-induced system for Halomonas, E. coli and Pseudomonas

Ligand-induced system plays an important role for microbial engineering due to its tunable gene expression control over timings and levels. An oleic acid (OA)-induced system was recently constructed based on protein FadR, a transcriptional regulator involved in fatty acids metabolism, for metabolic control in Escherichia coli. In this study, we constructed a synthetic FadR-based OA-induced systems in Halomonas bluephagenesis by hybridizing the porin promoter core region and FadR-binding operator (fadO). The dynamic control range was optimized over 150-fold, and expression leakage was significantly reduced by tuning FadR expression and positioning fadO, forming a series of OA-induced systems with various expression strengths, respectively. Additionally, ligand orthogonality and cross-species portability were also studied and showed highly linear correlation among Halomonas spp., Escherichia coli and Pseudomonas spp. Finally, OA-induced systems with medium- and small-dynamic control ranges were employed to dynamically control the expression levels of morphology associated gene minCD, and monomer precursor 4-hydroxybutyrate-CoA (4HB-CoA) synthesis pathway for polyhydroxyalkanoates (PHA), respectively, in the presence of oleic acid as an inducer. As a result, over 10 g/L of poly-3-hydroxybutyrate (PHB) accumulated by elongated cell sizes, and 6 g/L of P(3HB-co-9.57 mol% 4HB) were obtained by controlling the dose and induction time of oleic acid only. This study provides a systematic approach for ligand-induced system engineering, and demonstrates an alternative genetic tool for dynamic control of industrial biotechnology.

Rogue one: A plastic story

Plastic comprises of variety of polymers and has many applications, but the waste generated by plastic pose threat to environment and marine life. Plastic can be classified into two types: thermoplastics and thermosetting and are divided into 7 different categories: (Polyethylene Terephthalate [PETE], High-Density Polyethylene [HDPE], Polyvinyl Chloride [PVC], Low-Density Polyethylene [LDPE], Polypropylene [PP], Polystyrene or Styrofoam [PS] & Polycarbonate or ABS [others]). To curb the deleterious effects of plastic waste various methods have been devised and utilized that include chemical, physical and biological treatments. One of the aspects primarily focused by the researchers is the phenomenon of biodegradation and there are many microorganisms (bacteria) that have the ability to carry out this particular process. These bacteria assist biodegradation by production of several enzymes like PETases and MHETases. There are few microorganisms that have been listed which cannot be applied for industrial use due to its low biodegradation capacity. To overcome this problem, PHA is one of the alternatives to replace the synthetic plastic due to its high degrading capacity.

Induction of both local and systemic immunity by in vivo injection of PHA into ginbuna carp fin

Phytohemagglutinin (PHA) is a well-known mitogen inducing activation and proliferation of lymphocytes, particularly T lymphocytes in vitro. PHA has also been used in vivo for assessing cell-mediated immunity in non-mammalian vertebrates, particularly in birds. However, it has been suggested that local inflammation as a direct result of tissue damage could be responsible for skin swelling after PHA injection, in addition to induction of T lymphocyte mitogenesis. In order to understand the complex nature of this response in fish we investigated the accumulation of cell types chronologically in dorsal fin of ginbuna crucian carp Carassius auratus langsdorfii after PHA injection. Neutrophils appeared first and showed a peak response on day 1, decreasing gradually and followed by macrophages and blast cells while lymphocytes increased later with a peak response on day 5. The number of accumulated cells was significantly higher in PHA-injected fish than controls in most cases. Lymphocytes identified as CD4-1⁺and CD8α⁺ were significantly more abundant in PHA-injected fish than in control fish throughout the 7-day experimental period except on day 1, while the number of IgM⁺ lymphocytes was higher in PHA-injected fish only on day 1. In the blast cell fraction, the number of CD4-1⁺ lymphocytes was significantly higher in PHA-injected fish than in control fish throughout experimental period, except on day 1. We also document the migration of neutrophils from the kidney to the fin through blood, followed by granulopoiesis in the kidney. These results suggest that adaptive immunity as well as innate immunity was induced by in vivo stimulation with PHA.

Phosphorus recovery in the alternating aerobic/anaerobic biofilm system: Performance and mechanism

To balance the high phosphorus concentration in recirculated solution and the stability of biofilm system, this study explored the performance and mechanism of phosphorus uptake/release for recovering phosphorus from sewage when the phosphorus content in biofilm (P_biofilm) changed. The results showed that the maximum phosphorus concentration in the concentrated solution reached 171.2 ± 2.5 mg·L^-1 in harvest 1st-5th stages. Polyphosphate accumulating organisms (PAOs) performed a metabolic shift from glycogen accumulation metabolism (GAM) to polyphosphate accumulation metabolism (PAM) when P_biofilm increased at each phosphorus enrichment stage, and more phosphorus was absorbed/released by PAOs. Nevertheless, the release of poly-phosphate from PAOs was inhibited after phosphorus concentration stabilized, and PAOs were unable to absorb phosphorus from wastewater as it reached the phosphorus saturation stage. To maintain the stability of the system, phosphorus had to be harvested so that the saturated phosphorus in PAOs was easily released in a new recirculated solution, resulting in adequate storage space for PAOs to absorb phosphorus. Meanwhile, the ³¹P NMR analysis demonstrated that phosphorus was stored in EPS and cell of PAOs, whereas EPS played a significant role than cell at the anaerobic phase. Particularly, ortho-phosphate was the major component of phosphorus release by EPS and poly-phosphate was the major part of phosphorus release by cell. Furthermore, the change of P_biofilm had no impact on biofilm characteristics and microbial communities, whereas some PAOs would be enriched, and others that were not suitable for this process would be inhibited with repeated cycles of alternating aerobic/anaerobic operation.

Evaluation and Correlation of Rabies Vaccine Potency Using the National Institute of Health, Rapid Focus Fluorescent Inhibition, and Passive Hemagglutination Tests

Rabies vaccine preparations are quantitatively assayed for potency using the in-vivo challenge National Institute of Health (NIH), the main test that consumes a high number of animals, takes a long time, and has wide variability. The Rapid focus fluorescent inhibition (RFFIT) and the passive hemagglutination (PHA) tests, the two serologically based tests, were also used for such purpose. In this study, we aimed to evaluate and correlate the potency of the NIH, RFFIT, and PHA tests according to the World Health Organization (WHO) validity criteria, aiming to validate the use of RFFIT or PHA test as a substitute to the NIH test for determining the potency of commercially available Rabies vaccine preparations. The results showed that, the three tests can be successfully used; however, a higher correlation between RFFIT and NIH than PHA and NIH was recorded (Pearson correlation = 1). The potency of rabies vaccine preparations using NIH, RFFIT, and PHA were 3.73, 3.51, and 4.50, respectively. NIH is the main test for the determination of vaccine potency carried out by conducting 25 experiments and consuming about 5,000 mice compared to 1,200 mice used with RFFIT and 1,000 mice used with PHA test. Taken together, we concluded that (i) in some tested preparations, both RFFIT and PHA tests gave comparable results, and they can be used interchangeably; (ii) RFFIT could successfully replace NIH test, but not PHA; (iii) RFFIT and PHA tests are faster, more accurate, more economic, and more sensitive than NIH; nevertheless, PHA needs further investigations; and (iv) both RFFIT and NIH tests complement and reinforce each other as they provide a comprehensive picture of the product potency.

Enrichment of Methylocystis dominant mixed culture from rice field for PHB production

Presence of methanotrophs in diverse environmental habitats helps to reduce emissions of greenhouse gas like methane. Isolation and culture of undiscovered wealth of methanotrophic organisms can help in exploitation of these organisms in value added products. The present study focuses on the enrichment of methanotroph dominated mixed microbial community by use of three stage strategy of revival, proliferation, and segregation. During the enrichment process amplicon sequencing of 16 s rRNA V3-V4 region showed relative abundance of mixed culture comprising single methanotrophic species of Methylocystis genus (88.92%) along with only three other species. Methylocystis dominant mixed culture (MMI-11) was observed to produce polyhydroxyalkanoates (PHA). During studies to identify favourable culture conditions, nitrate was found to be preferred nitrogen source for growth and PHA production. Cell growth ability to produce PHA was also evaluated at 14 L fermentor by supplying gas using continuous bubbling and through pressurization in the headspace. The mixed methanotrophic culture was found to accumulate maximum of 22.20% polyhydroxybutyrate (PHB) under nitrate limited condition. The molecular weight of PHB was found to be 2.221 × 10⁵ g mol^-1 with polydispersity of 1.82.

MC34 and Cobetia marina DSM 4741T and in silico analyses of the genus specific PhaC2 polymerase variant

BACKGROUND

Several members of the bacterial Halomonadacea family are natural producers of polyhydroxyalkanoates (PHA), which are promising materials for use as biodegradable bioplastics. Type-strain species of Cobetia are designated PHA positive, and recent studies have demonstrated relatively high PHA production for a few strains within this genus. Industrially relevant PHA producers may therefore be present among uncharacterized or less explored members. In this study, we characterized PHA production in two marine Cobetia strains. We further analyzed their genomes to elucidate pha genes and metabolic pathways which may facilitate future optimization of PHA production in these strains.

RESULTS

Cobetia sp. MC34 and Cobetia marina DSM 4741T were mesophilic, halotolerant, and produced PHA from four pure substrates. Sodium acetate with- and without co-supplementation of sodium valerate resulted in high PHA production titers, with production of up to 2.5 g poly(3-hydroxybutyrate) (PHB)/L and 2.1 g poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/L in Cobetia sp. MC34, while C. marina DSM 4741T produced 2.4 g PHB/L and 3.7 g PHBV/L. Cobetia marina DSM 4741T also showed production of 2.5 g PHB/L from glycerol. The genome of Cobetia sp. MC34 was sequenced and phylogenetic analyses revealed closest relationship to Cobetia amphilecti. PHA biosynthesis genes were located at separate loci similar to the arrangement in other Halomonadacea. Further genome analyses revealed some differences in acetate- and propanoate metabolism genes between the two strains. Interestingly, only a single PHA polymerase gene (phaC2) was found in Cobetia sp. MC34, in contrast to two copies (phaC1 and phaC2) in C. marina DSM 4741T. In silico analyses based on phaC genes show that the PhaC2 variant is conserved in Cobetia and contains an extended C-terminus with a high isoelectric point and putative DNA-binding domains.

CONCLUSIONS

Cobetia sp. MC34 and C. marina DSM 4741T are natural producers of PHB and PHBV from industrially relevant pure substrates including acetate. However, further scale up, optimization of growth conditions, or use of metabolic engineering is required to obtain industrially relevant PHA production titers. The putative role of the Cobetia PhaC2 variant in DNA-binding and the potential implications remains to be addressed by in vitro- or in vivo methods.

Polyhydroxyalkanoates synthesis using acidogenic fermentative effluents

Polyhydroxyalkanoates (PHA) are natural polyesters synthesized by microbes which consume excess amount of carbon and less amount of nutrients. It is biodegradable in nature, and it synthesized from renewable resources. It is considered as a future polymer, which act as an attractive replacement to petrochemical based polymers. The main hindrance to the commercial application of PHA is the high manufacturing cost. This article provides an overview of different cost-effective substrates, their characteristics and composition, major strains involved in economical production of PHA and biosynthetic pathways leading to accumulation of PHA. This review also covers the operational parameters, various fermentative modes including batch, fed-batch, repeated fed-batch and continuous fed-batch systems, along with advanced feeding strategies such as single pulse carbon feeding, feed forward control, intermittent carbon feeding, feast famine conditions to observe their effects for improving PHA synthesis and associated challenges. In addition, it also presents the economic analysis and future perspectives for the commercialization of PHA production process thereby making the process sustainable and lucrative with the possibility of commercial biomanufacturing.

Ameliorating effect of nitrate on nitrite inhibition for denitrifying P-accumulating organisms

Lowered air supply and organic carbon need are the key factors to reduce wastewater treatment costs and thereby, avoid eutrophication. Denitrifying PO₄^3-- removal (DPR) process using nitrate instead of oxygen for PO₄^3- uptake was started up in the sequencing batch reactor (SBR) at a nitrate dosing rate of 20-25 mg N L^-1 d^-1. Operation with a real municipal wastewater supplied with CH₃COONa, K₂HPO₄ and KNO₃ succeeded in the cultivation of biomass containing denitrifying polyphosphate accumulating organisms (DPAOs). The durations of SBR process anaerobic/anoxic/oxic cycles were 1.5 h, 3.5 h and 1 h, respectively. SBR operation resulted in a maximum PO₄^3--P uptake of 17 mg PO₄^3--P g^-1 MLSS. The highest TN and PO₄^3- removal efficiencies were observed during the first half of reactor operation at 77 (±10) % and 71 (±5) %, respectively. An average COD removal rate of 172 (±98) mg g^-1 MLSS and a high average removal efficiency of 89 (±4) % were achieved. Nitrite effect with/without nitrate as DPR electron acceptor was investigated in batch-scale to show possibilities to use high nitrite and nitrate contents simultaneously as electron acceptors for the anoxic phosphate uptake. Nitrate attenuation against nitrite toxicity can be economically justified in full-scale treatment applications in which wastewater has a high nitrogen content. Nitrate attenuated nitrite toxicity (caused by nitrite content at 5-100 mg NO₂^--N L^-1) when using supplemental additions of nitrate (at concentrations of 45-200 mg NO₃^--N L^-1) in batch tests. Illumina sequencing emphasized that during biomass adaption microbial community changed by lowered aerobic cycle length and by lowered nitrate dosing towards representation of key DPAO/PAO- organisms, such as Candidatus Accumulibacter, Xanthomonadaceae, Comomonadaceae, Saprospiraceae and Rhodocyclaceae. This study showed that DPAO biomass adaption to nitrate maintained an efficient COD, nitrogen and phosphorus removal and the biomass can be applied for treatment of wastewater containing high nitrite and nitrate content.

3D Printing Optimization for Environmental Sustainability: Experimenting with Materials of Protective Face Shield Frames

The motivation for research on 3D printing of protective face shields was the urgent societal demand for healthcare in the fight against the spread of COVID19 pandemic. Research is based on a literature review that shows that objects produced by additive technologies do not always have consistent quality suitable for the given purpose of use. Besides, they have different effects on the environment and leave different footprints. The overall goal of the research was to find out the most suitable thermoplastic material for printing shield frames in terms of mechanical properties, geometric accuracy, weight, printing time, filament price, and environmental sustainability. Fused deposition modeling (FDM) technology was used for 3D printing, and three different filaments were investigated: polylactic acid (PLA), polyethylene terephthalate (PETG), and polyhydroxyalkanoate (PHA). The weighted sum method for multi-objective optimization was used. Finally, PHA material was chosen, mainly due to its environmental sustainability, as it has the most negligible impact on the environment.

T-cell dysregulation is associated with disease severity in Parkinson's Disease

The dysregulation of peripheral immunity in Parkinson’s Disease (PD) includes changes in both the relative numbers and gene expression of T cells. The presence of peripheral T-cell abnormalities in PD is well-documented, but less is known about their association to clinical parameters, such as age, age of onset, progression rate or severity of the disease. We took a detailed look at T-cell numbers, gene expression and activation in cross-sectional cohorts of PD patients and age-matched healthy controls by means of flow cytometry and NanoString gene expression assay. We show that the well-pronounced decrease in relative T-cell numbers in PD blood is mostly driven by a decrease of CD8⁺ cytotoxic T cells and is primarily associated with the severity of the disease. In addition, we demonstrate that the expression of inflammatory genes in T cells from PD patients is also associated with disease severity. PD T cells presented with increased activation upon stimulation with phytohemagglutinin that also correlated with disease severity. In summary, our data suggest that the consequences of disease severity account for the changes in PD T cells, rather than age, age of onset, duration or the disease progression rate.

CYR1

Cheese whey (CW) can be an excellent carbon source for polyhydroxyalkanoates (PHA)-producing bacteria. Most studies have used CW, which contains high amounts of lactose, however, there are no reports using raw CW, which has a relatively low amount of lactose. Therefore, in the present study, PHA production was evaluated in a two-stage process using the CW that contains low amounts of lactose. In first stage, the carbon source existing in CW was converted into acetic acid using the bacteria, Acetobacter pasteurianus C1, which was isolated from food waste. In the second stage, acetic acid produced in the first stage was converted into PHA using the bacteria, Bacillus sp. CYR-1. Under the condition of without the pretreatment of CW, acetic acid produced from CW was diluted at different folds and used for the production of PHA. Strain CYR-1 incubated with 10-fold diluted CW containing 5.7 g/L of acetic acid showed the higher PHA production (240.6 mg/L), whereas strain CYR-1 incubated with four-fold diluted CW containing 12.3 g/L of acetic acid showed 126 mg/L of PHA. After removing the excess protein present in CW, PHA production was further enhanced by 3.26 times (411 mg/L) at a four-fold dilution containing 11.3 g/L of acetic acid. Based on Fourier transform infrared spectroscopy (FT-IR), and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, it was confirmed that the PHA produced from the two-stage process is poly-β-hydroxybutyrate (PHB). All bands appearing in the FT-IR spectrum and the chemical shifts of NMR nearly matched with those of standard PHB. Based on these studies, we concluded that a two-stage process using Acetobacter pasteurianus C1 and Bacillus sp. CYR-1 would be applicable for the production of PHB using CW containing a low amount of lactose.