Mixed Microbial Culture Research Articles

Biodegradation of glucose and paracetamol and process optimisation with open mixed microbial cultures in lab-scale sequencing batch reactors

In the context of biological wastewater treatment, this study investigated xenobiotics (man-made chemicals) biodegradation and process optimisation to maximise sustainability. Lab-scale sequencing batch reactors (SBRs) fed with paracetamol (model xenobiotic) and glucose (model biogenic substrate) each as only carbon source (feed concentration 1 g L−1) were run in a range of HRTs (hydraulic retention time, range 0.5–2 d) and SRTs (solids retention time, range 1–28 d). For both substrates, the removal of COD (chemical oxygen demand) increased as the SRT increased, reaching 97 % for glucose and 86 % for paracetamol. At the lowest HRT, the high solid losses with the effluent caused a reduction in the SRT with worse substrate removal. The fraction of the removed COD which was converted into biomass increased for lower SRT and overall the best performance for sustainability (compromise between substrate removal, energy consumption and plant footprint) was observed with HRT 1 d and SRT 11–12 d. The experimental data were modelled using two different approaches: linearisation of a continuous-flow model and non-linear parameter fitting with a periodic steady-state SBR model. The results indicated faster growth rate and slightly higher growth yield for glucose than for paracetamol.

Polyhydroxyalkanoates production from cheese whey under near-seawater salinity conditions

Treating saline streams presents considerable challenges due to their adverse effects on conventional biological processes, thereby leading to increased expenses in managing those side streams. With this in consideration, this study explores into the potential for valorizing fermented cheese whey (CW), a by-product of the dairy industry, into polyhydroxyalkanoates (PHA) using mixed microbial cultures (MMC) under conditions of near-seawater salinity (30 gNaCl/L). The selection of a PHA-accumulating MMC was successfully achieved using a sequential batch reactor operated under a feast and famine regime, with a hydraulic retention time of 14.5 h, a variable solids retention time of 3 and 4.5 days, and an organic loading rate (OLR) of 60 Cmmol/(L d). The selected culture demonstrated efficient PHA production rates and yields, maintaining robust performance even under high salinity conditions. During PHA accumulation, a maximum PHA content in biomass of 56.4 % wt. was achieved for a copolymer P(3HB-co-3HHx) with a 3HHx content of 7 %. Additionally, to asses the capacity of the culture to produce polymers with different compositions, valeric acid was supplemented to the real fermented feedstock which resulted in the production of terpolymers P(3HB-co-3HV-co-3HHx) with varied monomeric content and a higher maximum PHA content of 62 % wt. Additionally, this study highlights the potential utilization of seawater as alternative to freshwater for PHA production, thereby enhancing circular economy principles and promoting environmental sustainability.

Antioxidant capacity of fermented corn gluten meal in broiler chickens: a solid-state approach with mixed microbial fermentation

Fermentation of feed with probiotic and biofunctional properties has gained global attention for its potential to enhance digestive absorption and improve overall functional quality. This study investigates the antioxidant capacity and expression of antioxidant-related genes in broiler chickens fed with fermented corn gluten meal (FCGM) containing mixed microbial cultures. Seventy-two male Yellow-Feathered broiler chickens were randomly assigned to 2 groups, each consisting of 3 replicates, and were fed experimental diets containing either corn gluten meal or FCGM for 42 d. The antioxidant capacity of FCGM was assessed in vivo. Chickens fed with FCGM exhibited significant increases in serum glutathione concentration, as well as enhanced activities of total superoxide dismutase, glutathione peroxidase, and catalase (CAT) in their serum. Similar trends were observed in the liver, specifically in the activities of glutathione peroxidase and CAT. Additionally, the expression levels of key antioxidant-related genes in the liver, such as glutathione synthase, superoxide dismutase 1, superoxide dismutase 2, CAT, and glutathione peroxidase 1, were examined. The results indicated that FCGM significantly enhanced antioxidant capacity in broiler chickens. This study highlights the potential benefits of utilizing solid-state fermentation with mixed microbial cultures to improve the antioxidant properties of corn gluten meal, thereby contributing to the overall health and well-being of broiler chickens.

Metabolomics ravels flavor compound formation and metabolite transformation in rapid fermentation of salt-free fish sauce from catfish frames induced by mixed microbial cultures

This study demonstrates that the co-inoculation with Lactiplantibacillus plantarum, Pichia fermentans and Staphylococcus saprophyticus accelerates catfish frame fish sauce fermentation. Over a 3-day period, significant changes occurred in physicochemical properties, microbial profiles, flavor compounds, and metabolomic spectra. Notable increases in acidity coupled with decreases in glucose underscored the robust environmental adaptability of the employed microorganisms. A reduction in total amino acids, alongside a rise in umami amino acids, suggested flavor enhancement. GC–MS analysis identified 40 key volatile compounds, with esters and aldehydes crucial for aroma development. UPLC-QTOF-MS-based untargeted analysis identified 934 metabolites, with 377 differential metabolites being vital (VIP > 1.5, P < 0.05), including amino acids, peptides, organic acids, nucleic acids, and fatty acids. Metabolites linked to amino acid metabolism, particularly phenylalanine and arginine, were associated with fermentation duration. These findings offer a theoretical basis for optimizing flavor and quality in fish sauces from fish by-products through accelerated fermentation.

13C-Labelled Glucose Reveals Shifts in Fermentation Pathway During Cathodic Electro-Fermentation with Mixed Microbial Culture.

Cathodic Electro-Fermentation (CEF) is an innovative approach to manage the spectrum of products deriving from anaerobic fermentation. Herein, mixed microbial culture fermentation using a ternary mixture containing labelled 13C glucose and non-labelled acetate and ethanol was studied to identify the role of polarization on the metabolic pathways of glucose fermentation. CEF at an applied potential of -700 mV (vs. SHE, Standard Hydrogen Electrode) enhanced the production yield of acetate, propionate, and butyrate (0.90±0.10, 0.22±0.03, and 0.34±0.05 mol/mol; respectively) compared to control tests performed at open circuit potential (OCP) (0.54±0.09, 0.15±0.04, and 0.20±0.001 mol/mol, respectively). Results indicate that CEF affected the 13C labelled fermented product levels and their fractional 13C enrichments, allowing to establish metabolic pathway models. This work demonstrates that, under cathodic polarization, the abundance of both fully 13C labelled propionate and butyrate isotopomers increased compared to control tests. The effect of CEF is mainly due to intermediates initially produced from the glucose metabolic transformation in the presence of non-labelled acetate and ethanol as external substrates. These findings represent a significant advancement in current knowledge of CEF, which offers a promising tool to control mixed cultures bioprocesses.

Advanced Bioconversion of sugary wastewater: Integrated polyhydroxybutyrate and hydrogen productions in a continuous airlift two-chamber bioreactor

This study utilized a novel Continuous Airlift Two-chamber Bioreactor (CATBR) for the co-production of hydrogen and polyhydroxybutyrate (PHB) from mixed microbial cultures in sugary wastewater. Hydrogen generation was investigated in a defined bacterial consortium that contained mainly Clostridium species, and diverse microbial communities were studied in relation to PHB production, demonstrating the ability of diverse microbial communities to form stable microbial consortia. The impact of hydraulic retention time (HRT), pH, and air flow rate on PHB production was evaluated with special emphasis on volatile suspended solids (VSS).Optimal conditions for hydrogen and PHB production were established at a pH of 5.5, an aeration rate of 1500 mL/h, and an HRT of two days. Hydrogen yield was determined to be 3.14 ± 0.92 mL/g COD, and PHB yield was 31.32% (g PHB/g VSS). Production rates for hydrogen and PHB peaked at 0.23 ± 0.07 L/L.d and 0.64 g PHB/L.d, respectively, with a COD removal efficiency of 85 ± 0.67%. At an HRT of two days, the PHB generation rate was found to be 6–10 times higher than previously reported rates. The application of immobilized cell technology effectively prevented bacterial washout from the reactor, thereby ensuring stable operational conditions.

Biodegradation of DDT using multi-species mixtures: Fromgenome-mining prediction to practical assessment.

DDT (dichlorodiphenyltrichloroethane) is a commonly used insecticide that is recalcitrant and highly stable in the environment. Currently, DDT residue contamination, especially in agricultural soil, is still a concern in many countries, threatening human health and the environment. Among the approaches to resolve such an issue, novel biodegradation-based methods are now preferred to physicochemical methods, due to the sustainability and the effectiveness of the former. In this study, we explored the possibility of building mixed microbial cultures that can offer improved DDT-degrading efficiencies and be more environmentally transilient, based on genome annotation using the KEGG database and prediction of interactions between single strains using the obtained metabolic maps. We then proposed 10 potential DDT-degrading mixed cultures of different strain combinations and evaluated their DDT degradation performances in liquid, semi-solid and solid media. The results demonstrated the superiority of the mixtures over the single strains in terms of degrading DDT, particularly in a semi-solid medium, with up to 40-50% more efficiency. Not only did the mixed cultures degrade DDT more efficiently, but they also adapted to broader spectra of environmental conditions. The three best DDT-degrading and transilient mixtures were selected, and it turned out that their component strains seemed to have more metabolic interactions than those in the other mixtures. Thus, our study demonstrates the effectiveness of exploiting genome-mining techniques and the use of constructed mixed cultures in improving biodegradation.

Differences on carboxylic acids bioproduction from soluble carbohydrates or proteins in a sequencing batch reactor: Deciphering the influence of the volumetric and specific organic loading rate

Acidogenic fermentation (AF) has been extensively explored. However, the impact of operational parameters on AF has led to inconsistent results. In this work, AF experiments were performed in a sequencing batch reactor (SBR) using simulated wastewaters solely containing soluble carbohydrates or proteins as carbon sources to independently assess the impact of the volumetric organic loading rate (OLRv) and of the specific organic loading rate (OLRs). When only carbohydrates were used, the main effluent components were acetic and butyric acids at OLRv of 6.0 g COD L−1 d−1, while changing OLRv over 11.0 g COD L−1 d−1 gave acetic acid and ethanol as main components. Conversely, if the carbon source consisted solely of proteins, increasing the OLRv or the OLRs had minimal impact on the AF performance and on the effluent composition. Also, in the case of carbohydrate experiments, increasing the OLRs from 2.3 to 3.8 g COD g−1 VSS d−1 promoted chain elongation reactions, as caproic acid formation was also observed. Besides, at the highest OLRv tested in this work for protein experiments (18.5 g COD L−1 d−1), it was obtained the maximum isocaproic acid concentration using mixed microbial cultures and without adding any external electron donor. The SBR configuration proved to be an adequate system, especially when proteins were used as carbon source, since it makes possible to keep low the OLRs and to reduce the hydrolysis limitations. Finally, the bacterial genera detected in the reactors notably changed between both substrates. Future work must be focused on identifying carboxylic acid producing-genera from proteins.

Ex-situ single-culture biomethanation operated in trickle-bed configuration: Microbial H2 kinetics and stoichiometry for biogas conversion into renewable natural gas

Biomethanation converts carbon dioxide (CO2) emissions into renewable natural gas (RNG) using mixed microbial cultures enriched with hydrogenotrophic archaea. This study examines the performance of a single methanogenic archaeon converting biogas with added hydrogen (H2) into methane (CH4) using a trickle-bed bioreactor with enhanced gas–liquid mass transport. The process in continuous operation followed the theoretical reaction of hydrogenotrophic methanogenesis (CO2 + 4 H2 → CH4 + 2 H2O), producing RNG with over 99 % CH4 and more than 0.9 H2 conversion efficiency. The Monod constants of H2 uptake were experimentally determined using kinetic modelling. Also, a dimensionless parameter was used to quantify the ratio between the H2 mass transfer rate and the maximum attainable H2 consumption rate. Single-culture biomethanation averts the formation of secondary metabolites and bicarbonate buffer interferences, resulting in lower demands for H2 than mixed-culture biomethanation.

An engineered prodrug selectively suppresses β-lactam resistant bacteria in a mixed microbial setting.

The rise of β-lactam resistance necessitates new strategies to combat bacterial infections. We purposefully engineered the β-lactam prodrug AcephPT to exploit β-lactamase activity to selectively suppress resistant bacteria producing extended-spectrum-β-lactamases (ESBLs). Selective targeting of resistant bacteria requires avoiding interaction with penicillin-binding proteins, the conventional targets of β-lactam antibiotics, while maintaining recognition by ESBLs to activate AcephPT only in resistant cells. Computational approaches provide a rationale for structural modifications to the prodrug to achieve this biased activity. We show AcephPT selectively suppresses gram-negative ESBL-producing bacteria in clonal populations and in mixed microbial cultures, with effective selectivity for both lab strains and clinical isolates expressing ESBLs. Time-course NMR experiments confirm hydrolytic activation of AcephPT exclusively by ESBL-producing bacteria. In mixed microbial cultures, AcephPT suppresses proliferation of ESBL-producing strains while sustaining growth of β-lactamase-non-producing bacteria, highlighting its potential to combat β-lactam resistance while promoting antimicrobial stewardship.

Biodegradation and adsorption of benzo[a]pyrene by fungi-bacterial coculture

In this work, the relationship and kinetics of biodegradation and bio-adsorption of benzo[a]pyrene (BaP) by Bacillus and Ascomycota were explored, and the metabolites of BaP under mixed microbial coculture were analyzed and characterized. The results show that BaP was removed through both biosorption and biodegradation. Under mixed microbial coculture, biosorption played a significant role in the early stage and biodegradation was predominant in the later stage. During the removal of BaP, the fungi exhibited remarkable adsorption capabilities for BaP with an adsorption efficiency (AE) of 38.14 %, while bacteria had a best degradation for BaP with a degradation efficiency (DE) of 56.13 %. Under the mixed microbial culture, the removal efficiency (RE) of BaP by the synergistic action of fungi and bacteria reached up to 76.12 % within 15 days. Kinetics analysis illustrated that the degradation and adsorption process of BaP were well fit to the first-order and the pseudo-second-order kinetic models, respectively. The research on the relationship between degradation and adsorption during microbial removal of BaP, as well as the synergistic effects of fungi and bacteria, will provide a theoretical guidance for two or even synthetic microbial communities.

Multi-stage process for mixed microbial culture production of polyhydroxyalkanoates from sugarcane stillage: Assessment of external nutrient supplementation

Sugarcane stillage is an abundant wastewater from ethanol production. It has drawn considerable interest as a potential feedstock for biotechnological processes aiming at the recovery of energy and value-added products. In this study we explored the use of stillage for the production of polyhydroxyalkanoates (PHA), which are microbial bioplastics with potential to replace conventional plastics in specific applications. As stillage is nutrient deficient, we investigated the impact of external nutrient supplementation on the selection of PHA-producing mixed cultures. Cultures selected under four different total-chemical-oxygen-demand-to-nitrogen ratios (COD.t/N) (15, 30, 40 and 80) were evaluated according to their PHA production performance and microbial composition. The experimental results demonstrated that the most favorable PHA production was achieved for the biomass selected under strict carbon-limiting conditions, with a COD.t/N ratio of 15. This resulted in an overall PHA volumetric productivity of 2.10 g PHA L−1 d−1, a maximum intracellular PHA content of 0.65 g PHA g VSS−1 and a PHA storage yield of 0.71 g CODPHA g CODH.Org−1. The resulting PHA was a copolymer of 3-hydroxybutyrate (73 %mol) and 3-hydroxyvalerate (27 %mol) monomers. The microbial consortium was enriched by members of the Brevundimonas genus, known PHA producers, with a relative abundance of 26.4 %.

Harnessing Brewery Spent Grain for Polyhydroxyalkanoate Production

The utility of brewery spent grain (BSG), a byproduct of the beer production process, for the synthesis of polyhydroxyalkanoates (PHAs), is a significant advancement towards sustainable and cost−effective biopolymer production. This paper reviews the upcycling potential of BSG as a substrate for PHA production, utilizing various biotechnological approaches to convert this abundant waste material into high−value biodegradable polymers. Through a comprehensive review of recent studies, we highlight the biochemical composition of BSG and its suitability for microbial fermentation processes. This research delves into different methodologies for PHA production from BSG, including the use of mixed microbial cultures (MMCs) for the synthesis of volatile fatty acids (VFAs), a critical precursor in PHA production, and solid−state fermentation (SSF) techniques. We also examine the optimization of process parameters such as pH, temperature, and microbial concentration through the application of the Doehlert design, revealing the intricate relationships between these factors and their impact on VFA profiles and PHA yields. Additionally, this paper discusses challenges and future perspectives for enhancing the efficiency and economic viability of PHA production from BSG. By harnessing the untapped potential of BSG, this research contributes to the development of a circular economy model, emphasizing waste valorization and the creation of sustainable alternatives to conventional plastics.

Food wastes for bioproduct production and potential strategies for high feedstock variability

Unavoidable food wastes could be an important feedstock for industrial biotechnology, while their valorization could provide added value for the food processor. However, despite their abundance and low costs, the heterogeneous/mixed nature of these food wastes produced by food processors and consumers leads to a high degree of variability in carbon and nitrogen content, as well as specific substrates, in food waste hydrolysate. This has limited their use for bioproduct synthesis. These wastes are often instead used in anaerobic digestion and mixed microbial culture, creating a significant knowledge gap in their use for higher value biochemical production via pure and single microbial culture. To directly investigate this knowledge gap, various waste streams produced by a single food processor were enzymatically hydrolyzed and characterized, and the degree of variability with regard to substrates, carbon, and nitrogen was quantified. The impact of hydrolysate variability on the viability and performance of polyhydroxyalkanoates biopolymers production using bacteria (Cupriavidus necator) and archaea (Haloferax mediterranei) as well as sophorolipids biosurfactants production with the yeast (Starmerella bombicola) was then elucidated at laboratory-scale. After which, strategies implemented during this experimental proof-of-concept study, and beyond, for improved industrial-scale valorization which addresses the high variability of food waste hydrolysate were discussed in-depth, including media standardization and high non-selective microbial organisms growth-associated product synthesis. The insights provided would be beneficial for future endeavors aiming to utilize food wastes as feedstocks for industrial biotechnology.

Simultaneous Removal of Setazol Navy Blue and Cr(VI) By Mixed Microbial Culture Isolated from the Çubuk Stream

Water samples taken from the Çubuk Stream (Ankara, Turkey) were inoculated into nutrient broth media containing Setazol Navy Blue SBG (SNB), an organic pollutant, and heavy metal Cr(VI), an inorganic pollutant, to obtain a pollutant-resistant mixed microbial culture. Experiments were conducted with this culture to remove SNB and heavy metal. The optimum conditions, where the mixed bacterial culture removed the pollutants most effectively, were determined, showing that the highest capacity for removal took place at pH 8 with removal percentages 96.3% for Cr(VI) and 78.5% for SNB. In media with 50.4 mg/L SNB and 9.7 mg/L Cr(VI), the SNB removal was 87.3%, and the Cr(VI) removal was 96.6% at the end of the 7-day incubation period. The highest removal was observed with a biomass concentration of 8% (v/v) of mixed culture [50 mg/L SNB dye+25 mg/L Cr(VI)]. The removal was 100% for both Cr(VI) and the SNB dye. The bacteria with the highest removal were isolated and identified using 16S rDNA gene sequence analysis as Microbacterium oxydans and Leucobacter aridicollis. The role of various functional groups and the structures of the microorganisms that might be involved in the removal mechanisms were discussed using their FTIR spectra. This report is the first study that investigates a mixed bacterial culture and pure cultures (M. oxydans and L. aridicollis) isolated from that mixed culture, removing both SNB and Cr(VI) simultaneously.

Potential of activated sludge-derived mixed microbial culture enriched on acetate to produce polyhydroxyalkanoates from various substrates

The use of waste activated sludge (WAS) as a biocatalyst to produce polyhydroxyalkanoates (PHA) from waste streams may help promote the beneficial use of WAS for low-carbon, sustainable wastewater treatment. However, it remains unclear which types of substrates can be used for efficient PHA production, and how the PHA production can be maximized. This study aimed to assess the substrate versatility of mixed microbial cultures (MMCs) constructed from WAS by enriching PHA-accumulating bacteria using an aerobic dynamic discharge (ADD) process fed with acetate. Twelve different substrates, including organic acids, saccharides, and alcohols, were selected as the test substrates. In single-batch assays, the highest PHA production (583–680 mg/L) was achieved using butyrate, acetate, and pyruvate. In fed-batch assays, > 30 wt% PHA content was achieved using acetate, butyrate, propionate, lactate, and ethanol, with the highest content (60.3 wt%) using acetate. These results indicate that acetate-fed MMC by the ADD process could efficiently produce PHA from volatile fatty acids, lactate, pyruvate, and ethanol. Polyhydroxybutyrate was preferentially produced from acetate, butyrate, pyruvate, lactate, and ethanol, whereas polyhydroxyvalerate was notably produced from propionate. The results suggest that PHA can be efficiently produced from a wide range of substrates using MMCs enriched on a single substrate.

Optimisation of the biological production of levulinic acid in a mixed microbial culture fed with synthetic grape pomace.

Levulinic acid (LA) is a polymer with a vast industrial application range and can be co-produced as a minor by-product during the biological production of polyhydroxyalkanoates (PHA). However, the influence of key parameters as tools for favouring the production of LA over PHA is still unclear. In this study, we investigated how several critical operational conditions, i.e., carbon-nitrogen ratio (C/N), organic loading rate (OLR) and airflow, can be optimised to favour LA accumulation over PHA production by a mixed microbial culture (MMC), using synthetic grape pomace (GP) hydrolysate as the substrate. The results showed that it was possible to direct the MMC towards LA accumulation instead of PHA. The maximum LA yield was 2.7 ± 0.2g LA/(L·d) using a C/N of 35, an airflow of 5L/min and an OLR of 4g sCOD/(L·d). The OLR and, to a lesser extent, the C/N ratio were the main factors significantly and positively correlated with the biological synthesis of LA.

Comparative in vitro analysis of the antifungal activity of different calcium silicate-based endodontic sealers

Aim: This study aimed to perform an in vitro comparative analysis of the antifungal activity of different calcium silicate-based endodontic sealers against three fungal species. Methods: The antifungal properties of three calcium silicate-based sealers were tested: Bio-C Sealer, Cambiar a Sealer Plus BC, and MTA-Fillapex. Two commonly used sealers were used as controls: AH Plus and Endomethasone. An agar diffusion test was performed to analyze the antifungal activity of the sealers against Candida albicans, Candida glabrata, Candida tropicalis, and a mixed microbial culture medium. The results were analyzed using ANOVA (p &lt;0.05). Results: Endomethasone exhibited the highest inhibition against all strains examined, maintaining a consistent level of inhibition throughout 7 days. MTA-Fillapex demonstrated the best performance among the calcium silicate-based sealers for the three fungal species (p &lt; 0.05), maintaining stable values over the 7 days, surpassing that of Endomethasone. Nevertheless, MTA-Fillapex only exhibited antimicrobial effect against the mixed culture for the first 24 hours, and no antimicrobial activity was observed at 48 hours, being surpassed by all tested sealers (p &lt; 0.05). Conclusion: Of all silicate-based sealers tested, only MTA-Fillapex exhibited promising antifungal activity. Nevertheless, care must be taken when extrapolating these results, as MTA-Fillapex exhibited poor antimicrobial activity when tested in mixed microbial cultures.

Influence of Aeration Rate on Uncoupled Fed Mixed Microbial Cultures for Polyhydroxybutyrate Production

The use of residual streams as feedstock for the production of polyhydroxyalkanoates (PHAs) is growing steadily, as it allows the valorization of waste and nutrients otherwise disposed of and the potential production of a biodegradable bioplastic. To date, the environmental and economic costs associated with this process limit its scale-up, which is why it is important to identify possible solutions and optimize the costliest steps. With this in mind, a laboratory-scale sequenced batch reactor (SBR, 5 L) was constructed to allow the selection of a mixed microbial culture able to convert volatile fatty acids (VFAs) into PHA. The reactor is fed with synthetic water containing VFAs, ammonium, phosphate, and micronutrients, typical compounds of fermented streams of certain wastes, such as cheese whey, food waste, or wastewater sludge. The biomass selected and produced by this first reactor is sent to an accumulation reactor, which is fed with a solution rich in VFAs, allowing the accumulation of PHAs. The role of aeration and its impacts on the main process parameters were analyzed. Three scenarios corresponding to different aeration rates were analyzed: 0.08, 0.16, and 0.32 vvm. The SBR was operated at an organic load rate of 600 mgCOD L−1d−1, under a dynamic feeding regime (feast–famine) and a short hydraulic retention time (HRT; 1 day). The results obtained showed that a value of 0.32 enabled better selection and better settling of the sludge. Furthermore, a potential correlation between aeration rate and VFA and NH4+ consumption rates was identified. The resulting biomass was able to accumulate up to 0.15 ± 0.02 g PHAgVSS−1.

Dynamics in the profile of biopolymers produced by mixed microbial cultures from ethanol-rich feedstocks

The use of agro-industrial wastes as substrates for polyhydroxyalkanoate (PHA) production by mixed microbial cultures is an alternative to lower the price of these biopolymers. However, when submitting these wastes to pre-fermentation, lactate and ethanol can be produced in addition to volatile fatty acids (VFAs). In this study, the impact of ethanol on PHA storage and in the carbon flux of the process were assessed. The co-production of extracellular polymeric substances (EPS) and its impact on PHA production was investigated. PHA production yield showed a decrease from 0.92 ± 0.004–0.63 ± 0.002 Cmol-PHA.Cmol-S−1 with the increase of ethanol content from 5 to 20 Cmmol.L−1. EPS production was directly proportional to the ethanol’s fed, reaching a maximum EPS total content of 6.70 Cmmol for the maximum ethanol supplied. EPS acted as a protection strategy, which benefited PHA specific storage rate for the highest ethanol content tested. These results indicate that ethanol-rich feedstocks can be valorised through the simultaneous production of two value-added biopolymers.