Mixed Microbial Consortium Research Articles

English

The potential of poly(hydroxyalkanoates) (PHAs) to replace conventional plastic materials justifies the increasing attention they have drawn both at lab-scale and in industrial biotechnology. The improvement of large-scale productivity and biochemical/genetic properties of producing strains requires mathematical modeling and process/strain optimization procedures. Current models dealing with structurally diversified PHAs, both structured and unstructured, can be divided into formal kinetic, low-structured, dynamic, metabolic (high-structured), cybernetic, neural networks and hybrid models; these attempts are summarized in this review. Characteristic properties of specific groups of models are stressed in light of their benefit to the better understanding of PHA biosynthesis, and their applicability for enhanced productivity. Unfortunately, there is no single type of mathematical model that expresses exactly all the characteristics of producing strains and/or features of industrial-scale plants; in addition, the different requirements for modelling of PHA production by pure cultures or mixed microbial consortia have to be addressed. Therefore, it is crucial to sophisticatedly adapt and fine-tune the modelling approach accordingly to actual processes, as the case arises. For “standard microbial cultivations and everyday practices”, formal kinetic models (for simple cases) and “low-structured” models will be appropriate and of great benefit. They are relatively simple and of low computational demand. To overcome the specific weaknesses of different established model types, some authors use hybrid models. Here, satisfying compromises can be achieved by combining mechanistic, cybernetic, and neural and computational fluid dynamics (CFD) models. Therefore, this hybrid modelling approach appears to constitute the most promising solution to generate a holistic picture of the entire PHA production process, encompassing all the benefits of the original modelling strategies. Complex growth media require a higher degree of model structuring. For scientific purposes and advanced development of industrial equipment in the future, real systems will be modelled by highly organized hybrid models. All solutions related to modelling PHA production are discussed in this review.

Generation of bioethanol and VFA through anaerobic acidogenic fermentation route with press mud obtained from sugar mill as a feedstock

Acidogenic anaerobic fermentation route was explored for the production of bioethanol and volatile fatty acids (VFA) from the press mud (PM) obtained from sugar mill. Slurry was prepared from PM having 10% of total solids and the same was hydrolyzed under acidic thermal conditions. Both press mud slurry (PMS) and pre-treated press mud slurry (PTPMS) was used as feedstock with mixed microbial consortia (MMC) and enriched mixed microbial consortia (EMMC). Mix of bioethanol and VFA were obtained in all the four cases (PMS-MMC, PMS-EMMC, PTPMS-EMC and PTPMS-EMMC), but, bioethanol and VFA yield of 0.04g/g and 0.27g/g, respectively obtained from PTPMS with EMMC was found to be comparatively higher. Control experiments carried out with glucose yielded bioethanol and VFA of 0.042g/g and 0.28g/g, respectively demonstrating that the organism was using reducible sugars in the feedstock for the generation of bioethanol by simultaneously producing the VFA from COD.

Draft Genome Sequence of Clostridium beijerinckii Ne1, Clostridia from an Enrichment Culture Obtained from Australian Subterranean Termite, Nasutitermes exitiosus.

The draft genome of Clostridium beijerinckii strain Ne1 was reconstructed from the metagenomic sequence of a mixed-microbial consortium that produced commercially significant quantities of hydrogen from xylan as a sole feedstock. The organism possesses relatively limited hemicellulolytic capacity and likely requires the action of other organisms to completely degrade xylan.

Start-up, performance and optimization of a compost biofilter treating gas-phase mixture of benzene and toluene

The performance of a compost biofilter inoculated with mixed microbial consortium was optimized for treating a gas-phase mixture of benzene and toluene. The biofilter was acclimated to these VOCs for a period of ∼18d. The effects of concentration and flow rate on the removal efficiency (RE) and elimination capacity (EC) were investigated by varying the inlet concentration of benzene (0.12–0.95g/m3), toluene (0.14–1.48g/m3) and gas-flow rate (0.024–0.072m3/h). At comparable loading rates, benzene removal in the mixture was reduced in the range of 6.6–41% in comparison with the individual benzene degradation. Toluene removal in mixture was even more affected as observed from the reductions in REs, ranging from 18.4% to 76%. The results were statistically interpreted by performing an analysis of variance (ANOVA) to elucidate the main and interaction effects.

Evaluation of simultaneous nutrient and COD removal with polyhydroxybutyrate (PHB) accumulation using mixed microbial consortia under anoxic condition and their bioinformatics analysis.

Simultaneous nitrate-N, phosphate and COD removal was evaluated from synthetic waste water using mixed microbial consortia in an anoxic environment under various initial carbon load (ICL) in a batch scale reactor system. Within 6 hours of incubation, enriched DNPAOs (Denitrifying Polyphosphate Accumulating Microorganisms) were able to remove maximum COD (87%) at 2g/L of ICL whereas maximum nitrate-N (97%) and phosphate (87%) removal along with PHB accumulation (49 mg/L) was achieved at 8 g/L of ICL. Exhaustion of nitrate-N, beyond 6 hours of incubation, had a detrimental effect on COD and phosphate removal rate. Fresh supply of nitrate-N to the reaction medium, beyond 6 hours, helped revive the removal rates of both COD and phosphate. Therefore, it was apparent that in spite of a high carbon load, maximum COD and nutrient removal can be maintained, with adequate nitrate-N availability. Denitrifying condition in the medium was evident from an increasing pH trend. PHB accumulation by the mixed culture was directly proportional to ICL; however the time taken for accumulation at higher ICL was more. Unlike conventional EBPR, PHB depletion did not support phosphate accumulation in this case. The unique aspect of all the batch studies were PHB accumulation was observed along with phosphate uptake and nitrate reduction under anoxic conditions. Bioinformatics analysis followed by pyrosequencing of the mixed culture DNA from the seed sludge revealed the dominance of denitrifying population, such as Corynebacterium, Rhodocyclus and Paraccocus (Alphaproteobacteria and Betaproteobacteria). Rarefaction curve indicated complete bacterial population and corresponding number of OTUs through sequence analysis. Chao1 and Shannon index (H’) was used to study the diversity of sampling. “UCI95” and “LCI95” indicated 95% confidence level of upper and lower values of Chao1 for each distance. Values of Chao1 index supported the results of rarefaction curve.

Bio-removal of diesel oil through a microbial consortium isolated from a polluted environment

Cultures were selected to form a consortium, and were submitted to essays in flasks according to a complete factorial design 2³ in order to determine temperature, inoculum concentration and C:N ratio conditions more favorable to biodegradation, which were used later in the experiment conducted in a bioreactor. The micro-organisms with the greatest potentiality to degrade diesel oil, without developing antagonistic activity, were identified as Staphylococcus saprophyticus, Serratia marcescens, Rhodotorula aurantiaca and Candida ernobii, which formed a mixed microbial consortium, consisting of bacteria and yeasts. The C:N ratio and temperature were the factors that displayed significant effect on the bioprocess. The increased C:N ratio and the amount of inoculum yielded a positive effect while the increase of the temperature caused a negative effect on biodegradation. In the seven-day trial in a bioreactor was verified an increase of biomass, decrease in surface tension, reduction of all n-alkanes belonging to the range of C9 to C21 and decreased toxicity for vegetable seeds. The tested mixed microbial consortium present high ability to degrade diesel oil constituents and the maintenance of appropriate conditions leads to transformation of this oily source into less toxic compounds.

Chemical and thermal characterization of potato peel waste and its fermentation residue as potential resources for biofuel and bioproducts production.

The growing demand for renewable fuels has driven the interest in the utilization of alternative waste materials such as potato peel waste (PPW) which contains fermentable carbohydrate. Fermentation of PPW using a mixed microbial consortium yielded about 60% unreacted PPW fermentation residue (PPW-FR). The PPW and PPW-FR were characterized by a combination of Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies, gas chromatography-mass spectrometry (GC-MS), and thermogravimetric analysis (TGA) to quantify changes after fermentation. Fermentation of PPW resulted in fermentation of starch and concentrating lignin plus suberin and lipids in PPW-FR. TGA analysis showed that decomposition peaks differed for PPW (423 °C) and PPW-FR (457 °C). Pyrolysis-GC/MS showed an increase in phenolic and long chain fatty acid compounds with a concomitant decrease in carbohydrate derived compounds in the PPW after fermentation. Both the PPW and PPW-FR have shown potential based on properties to be converted into crude biofuel via thermochemical processes.

Treatment of simulated biomass gasification wastewater of varying strength in a three stage rotating biological contactor

Abstract Wastewater generated during wet scrubbing of producer gas formed in biomass gasifiers consist mainly of phenolics, heterocyclics, mono and polynuclear aromatic hydrocarbons (PAHs). The concentration of organics in such wastewater is reported to vary over a wide range depending on gasifier operating conditions and water recycling practices. Such variations may impact the performance of biological treatment processes due to the toxic nature of constituents. Treatment of simulated biomass gasification wastewater of varying strength in a rotating biological contactor (RBC), bioaugmented with a novel bacteria, Exiguobacterium aurantiacum, and operated at constant hydraulic retention time (HRT) of 24 h revealed consistently high removal efficiency in the range of 91–92% for organic loading rate (OLR) of 6.7–16.1 g-COD/m2/d. Increase in OLR to 39.5 g-COD/m2/d caused a marked drop in COD removal efficiency (83%). Greater than 74% removal was observed for all the components although the influent concentration of phenolics and heterocyclics were much higher compared to the PAHs. Abiotic loss in absence of the biofilm was consistently low (12–20% COD removal). Treatment was accompanied by significant reduction in acute toxicity. The biofilm consisting of E. aurantiacum and mixed microbial consortium thus have a good potential for removal of these toxic constituents.

Performance assessment and hydrodynamic analysis of a submerged membrane bioreactor for treating dairy industrial effluent

Submerged membrane bioreactor (SMBR) is a relatively advanced technology for waste water treatment that involves integrated aerobic and anaerobic biological processes with membrane filtration. In the present investigation, hydrophobic polyvinylidene fluoride (PVDF) and hydrophilic polyacrylonitrile (PAN) hollow fiber (HF) membranes were tested in an indigenously fabricated SMBR for dairy effluent treatment under aerobic conditions using mixed microbial consortia. Effect of operating parameters such as suction pressure, degree of aeration and trans-membrane pressure (TMP) on membrane performance in terms of flux, rejection of turbidity, BOD and COD besides fouling characteristics was investigated. The observed optimum permeabilities of PVDF and PAN HF membranes were approximately 108 and 115LMHbar−1 with high extent of impurity removal. The rejection of COD was found to be 93% for PVDF and 91% for PAN HF membranes whereas corresponding rejection of BOD was observed to be 92% and 86%. A two-dimensional comprehensive model was developed to predict the hydrodynamic profile inside the module. Regression analysis revealed that the simulation results agreed well with experimental data.

New insights into Dehalococcoides mccartyi metabolism from a reconstructed metabolic network-based systems-level analysis of D. mccartyi transcriptomes.

Organohalide respiration, mediated by Dehalococcoides mccartyi, is a useful bioremediation process that transforms ground water pollutants and known human carcinogens such as trichloroethene and vinyl chloride into benign ethenes. Successful application of this process depends on the fundamental understanding of the respiration and metabolism of D. mccartyi. Reductive dehalogenases, encoded by rdhA genes of these anaerobic bacteria, exclusively catalyze organohalide respiration and drive metabolism. To better elucidate D. mccartyi metabolism and physiology, we analyzed available transcriptomic data for a pure isolate (Dehalococcoides mccartyi strain 195) and a mixed microbial consortium (KB-1) using the previously developed pan-genome-scale reconstructed metabolic network of D. mccartyi. The transcriptomic data, together with available proteomic data helped confirm transcription and expression of the majority genes in D. mccartyi genomes. A composite genome of two highly similar D. mccartyi strains (KB-1 Dhc) from the KB-1 metagenome sequence was constructed, and operon prediction was conducted for this composite genome and other single genomes. This operon analysis, together with the quality threshold clustering analysis of transcriptomic data helped generate experimentally testable hypotheses regarding the function of a number of hypothetical proteins and the poorly understood mechanism of energy conservation in D. mccartyi. We also identified functionally enriched important clusters (13 for strain 195 and 11 for KB-1 Dhc) of co-expressed metabolic genes using information from the reconstructed metabolic network. This analysis highlighted some metabolic genes and processes, including lipid metabolism, energy metabolism, and transport that potentially play important roles in organohalide respiration. Overall, this study shows the importance of an organism's metabolic reconstruction in analyzing various “omics” data to obtain improved understanding of the metabolism and physiology of the organism.

Bioethanol Production from Glycerol by Mixed Culture System

Glycerol, a by-product from biodiesel industry, is a promising feedstock for subsequent bioconversion to higher-value products. Potential application of a mixed microbial consortium on the fermentative conversion of glycerol to ethanol was demonstrated in this study. Maximum ethanol concentration of 11.1 g l-1 was produced after 72 h fermentation from the initial pure glycerol concentration of 45 g l-1, at 30 ̊C, and pH 7 under anaerobic conditions, corresponding to the ethanol production rate and yield of 0.34 g l-1 h-1, and 0.81 mol ethanolmol-1 glycerol, respectively. The microbial consortium yielded lower ethanol concentration (6.5 g l-1) but similar ethanol yield (0.85 mol ethanol mol-1 glycerol) when crude glycerol of 45 g l-1 was fermented at the same condition. At the optimum fermentative condition of the pure glycerol, phylogenetic analysis of microbial consortium based on 16S rRNA gene sequences indicated that Gammaproteobacteria represented 95% of the microbial diversity in the consortium while the rest belonged to Betaproteobacteria. The consortium was dominated by bacteria closely related to genera Enterobacter and Klebsiella, which could play the role on conversion of glycerol to ethanol in this system.

Biohydrogen production using native carbon monoxide converting anaerobic microbial consortium predominantly Petrobacter sp.

In this study, anaerobic mixed microbial consortium isolated from a local sewage treatment plant in Guwahati, India, was used to convert carbon monoxide (CO) to hydrogen. The consortium was initially grown in acetate containing medium and later acclimatized to utilize CO as the sole carbon source for hydrogen production. By 16S rDNA analysis, the consortium was identified to be predominantly Petrobacter sp. Statistically designed experiments were then applied to optimize the CO conversion and hydrogen production by the anaerobic mixed consortium. To evaluate the significant factors that influenced the biohydrogen production, Plackett–Burman screening design of experiments was applied, which revealed that temperature and Fe2+ influenced the most on hydrogen production with P values less than 0.05 each. The effect due to pH and Ni2+ was less with P values 0.120 and 0.132, respectively. Concentration of Fe2+ and Ni2+ in the medium was then subsequently optimized by using Central Composite Design (CCD) of experiments followed by response surface methodology (RSM) which yielded the optimum value of 213 mg/L for Fe2+ and 2.2 mg/L for Ni2+. At these optimum conditions, 60.8 mol hydrogen production was achieved which was 8% higher than that observed from the screening experiment.

Growth kinetics of an indigenous mixed microbial consortium during methylene chloride degradation in a batch reactor

Biodegradation of methylene chloride by a mixed microbial culture, isolated from a common sewage treatment plant, was investigated in a batch system. Batch experiments were performed at room temperature (27 °C) and pH value of 7. The methylene chloride concentration in growth media varied from 25 mgl−1 to 250mgl−1. A maximum observed degradation was 1 mgl−1h−1 at 100 mgl−1 of methylene chloride. The culture followed substrate inhibition kinetics and specific growth rate were fitted to different substrate inhibition models (Haldane, Aiba and Edwards models) by MATLAB 7.1@. Among all models, Haldane was found to better fit with root mean square of 0.947. The biokinetic constants estimated using these models show good potential of the mixed microbial culture in methylene Chloride degradation. Escherichia coli and Staphylococcus aureus are predominant microbes present in the mixed culture.

Plasma treatment of electrodes significantly enhances the development of anodic electrochemically active biofilms

Surface modifications of electrode materials are important for improved performance of microbial bio-electrochemical systems. Here, we studied the effect of pre-treating both glassy carbon and graphite felt electrodes with either an oxygen or a nitrogen plasma before reactor inoculation with a mixed microbial consortia. The plasma produces chemical modifications at the electrode surface level. X-ray photoelectron spectroscopy and water contact angle analysis showed that the plasma removes surface contamination, produces ion implantation and renders the hydrophobic surfaces highly hydrophilic. Plasma pre-treatment considerably accelerated the generation of a bio-electrochemical anodic current after inoculation. Nitrogen plasma pre-treatment yielded the best performance, followed closely by oxygen plasma. Plasma pre-treated electrodes reached a plateau of maximum current density twice as fast as untreated electrodes. Analysis of the current development profiles suggests that the plasma pre-treatment is neither producing a preferential attachment of certain types of bacteria over others nor accelerating the extracellular electron transfer rate. The results indicate that the plasma treatment considerably enhances the initial cell adhesion, which results in subsequently faster biofilm development. Plasma pre-treatment of electrodes is an inexpensive, fast, safe and straightforward technique to achieve more rapid start-up of bio-electrochemical processes.

Community dynamics of cellulose‐adapted thermophilic bacterial consortia

Enzymatic hydrolysis of cellulose is a key process in the global carbon cycle and the industrial conversion of biomass to biofuels. In natural environments, cellulose hydrolysis is predominately performed by microbial communities. However, detailed understanding of bacterial cellulose hydrolysis is primarily confined to a few model isolates. Developing models for cellulose hydrolysis by mixed microbial consortia will complement these isolate studies and may reveal new mechanisms for cellulose deconstruction. Microbial communities were adapted to microcrystalline cellulose under aerobic, thermophilic conditions using green waste compost as the inoculum to study cellulose hydrolysis in a microbial consortium. This adaptation selected for three dominant taxa--the Firmicutes, Bacteroidetes and Thermus. A high-resolution profile of community development during the enrichment demonstrated a community transition from Firmicutes to a novel Bacteroidetes population that clusters in the Chitinophagaceae family. A representative strain of this population, strain NYFB, was successfully isolated, and sequencing of a nearly full-length 16S rRNA gene demonstrated that it was only 86% identical compared with other validated strains in the phylum Bacteroidetes. Strain NYFB grew well on soluble polysaccharide substrates, but grew poorly on insoluble polysaccharide substrates. Similar communities were observed in companion thermophilic enrichments on insoluble wheat arabinoxylan, a hemicellulosic substrate, suggesting a common model for deconstruction of plant polysaccharides. Combining observations of community dynamics and the physiology of strain NYFB, a cooperative successional model for polysaccharide hydrolysis by the Firmicutes and Bacteroidetes in the thermophilic cellulolytic consortia is proposed.

Characterization of polyhydroxybutyrate biosynthesized from crude glycerol waste using mixed microbial consortia

AbstractThis study focused on the characterization of polyhydroxybutyrate (PHB) produced from crude glycerol (CG) using mixed microbial consortia (MMC). PHB recovered from two biomass drying treatments (65°C oven drying and lyophilization) was characterized comparatively along with a commercially sourced PHB (PHB‐C). Characterization results showed that oven‐drying method caused PHB partial hydrolysis, as indicated by its lower molecular weight (Mw) (PHB‐O, 144,000 g mol−1), which further affected its physical and chemical properties. Lyophilization helped alleviate PHB hydrolysis during drying process, leading to PHB (PHB‐L) of higher Mw (309,000 g mol−1) and material properties comparable with commercial PHB. Furthermore, crystallization and morphological studies showed that PHB‐L featured faster crystallization rates and smaller spherulites as compared with PHB‐C, probably due to its lower Mw. In general, the results from this study suggested that CG‐MMC‐derived PHB‐L possessed material properties comparable with those of pure substrate/culture produced PHB. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Effect of pH and Fe(III) ions on chalcopyrite bioleaching by an adapted consortium from biogas sweetening

Particle size, pH and Fe(III) ions affect the process of bioleaching of copper from chalcopyrite ores. In the study presented herein a copper sulfide ore was subjected to bioleaching process using a mixed microbial consortium obtained from a biotrickling filter treating high loads of H2S at different mineral particle size, distinct medium pH and various additional Fe(III) ion concentrations as leaching agent. After 1300h of operation, the total copper recovery achieved a value of 50% in the most acidic conditions. A decrease of 2.5 units of pH implied an increase in the efficiency of 35%. It was also observed an optimal particle size (between 2 and 3mm), considerably higher than previous reported studies, meaning a decrease in operational cost to mill material. Finally, results indicate that there is a threshold concentration of ferric ion from which the system is not sensitive (500ppm).

Evaluation of Laminaria-based microbial fuel cells (LbMs) for electricity production

Marine algae represents a sustainable feedstock in microbial fuel cells (MFCs) due to its low water and energy requirements for cultivation, higher capacity to sequester carbondioxide, and high carbohydrate content. Two-compartment MFCs were evaluated under batch-fed mode using Laminaria saccharina as the model for algae-based electron donor, and mixed microbial consortia as the biocatalyst, in the anode compartment. The Laminaria-based MFCs (LBMs) were studied with three different pretreatment conditions for the L. saccharina: (i) autoclaving (Auto), (ii) microwave irradiation (Micro), and (iii) as received treatment (No-Treat). A control was setup to establish base line performance for two-compartment MFCs using glucose as the electron donor in the anode. The performance of LBMs (250mW/m2 and 900mA/m2) was on par with glucose-based MFCs. AC impedance analysis revealed that the charge transfer resistance was at least 50-fold higher than the corresponding ohmic losses in both LBMs and glucose-based MFCs.

Biodegradation of 4-bromophenol by Arthrobacter chlorophenolicus A6T in a newly designed packed bed reactor

Bromophenol is listed as a priority pollutant by the U.S. EPA. However, there has been no report on the removal of bromophenol in any biological system that is operated in a continuous mode. The efficiency of Arthrobacter chlorophenolicus A6(T) on the biodegradation of 4-bromophenol (4-BP) in a newly designed packed bed reactor (PBR) was evaluated with different influent 4-BP concentrations between 400mgl(-1) and 1200mgl(-1) and hydraulic retention times (HRTs) between 24h and 7.5h. The response of the PBR to 4-BP shock loadings was also tested, and the bioreactor was found to adequately handle these shock loadings. The percentage of effluent toxicity in the PBR was tested using mixed microbial consortia as the test species; this experiment was performed using a 4-BP influent concentration of 1200mgl(-1) and HRTs between 24h and 7.5h. A maximal 98% effluent toxicity removal was achieved when the PBR was operated at an HRT of 24h. In the present study, 4-BP was used as the sole source of carbon and energy, and the complete removal of 4-BP was achieved with 4-BP loading rates of up to 2277mgl(-1)day(-1).

Simultaneous co-metabolic decolourisation of azo dye mixtures and bio-electricity generation under thermophillic (50 °C) and saline conditions by an adapted anaerobic mixed culture in microbial fuel cells

In this study, azo dye adapted mixed microbial consortium was used to effectively remove colour from azo dye mixtures and to simultaneously generate bio-electricity using microbial fuel cells (MFCs). Operating temperature (20–50°C) and salinity (0.5–2.5%w/v) were varied during experiments. Reactor operation at 50°C improved dye decolourisation and COD removal kinetic constants by approximately 2-fold compared to the kinetic constants at 30°C. Decolourisation and COD removal kinetic constants remained high (0.28h−1 and 0.064h−1 respectively) at moderate salinity (1%w/v) but deteriorated approximately 4-fold when the salinity was raised to 2.5% (w/v). Molecular phylogenetic analysis of microbial cultures used in the study indicated that both un-acclimated and dye acclimated cultures from MFCs were predominantly comprised of Firmicutes bacteria. This study demonstrates the possibility of using adapted microbial consortia in MFCs for achieving efficient bio-decolourisation of complex azo dye mixtures and concomitant bio-electricity generation under industrially relevant conditions.