Palm oil mill effluent treatment by a tropical marine yeast

Durable Nano-Flower Structured Foam Coupled with Electrically-Driven in Situ Aeration Enable High-Flux Oil/Water Emulsion Separation with Dynamic Antifouling Ability

The conventional membranes used for separating oil/water emulsions are typically limited by the properties of the membrane materials and the impact of membrane fouling, making continuous long-term usage unachievable. In this study, a filtering electrode with synchronous self-cleaning functionality is devised, exhibiting notable antifouling ability and an extended operational lifespan, suitable for the continuous separation of oil/water emulsions. Compared with the original Ti foam, the in situ growth of NiTi-LDH (Layered double hydroxide) nano-flowers endows the modified Ti foam (NiTi-LDH/TF) with exceptional superhydrophilicity and underwater superoleophobicity. Driven by gravity, a rejection rate of over 99% is achieved for various emulsions containing oil content ranging from 1% to 50%, as well as oil/seawater emulsions. The flux recovery rate exceeds 90% after one hundred cycles and a 4-h filtration period. The enhanced separation performance is realized through the "gas bridge" effect during in situ aeration and electrochemical anodic oxidation. The internal aeration within the membrane pores contributes to the removal of oil foulants. This study underscores the potential of coupling foam metal filtration materials with electrochemical technology, providing a paradigm for the exploration of novel oil/water separation membranes.

Yeast-driven valorization of agro-industrial wastewater: an overview

The intensive industrial and agricultural activities currently on-going worldwide to feed the growing human population have led to significant increase in the amount of wastewater produced. These effluents are high in phosphorus (P), nitrogen (N), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and heavy metals. These compounds can provoke imbalance in the ecosystem with grievous consequences to both the environment and humans. Adequate treatment of these wastewaters is therefore of utmost importance to humanity. This can be achieved through valorization of these waste streams, which is based on biorefinery idea and concept of reduce, reuse, and recycle for sustainable circular economy. This concept uses innovative processes to produce value-added products from waste such as wastewater. Yeast-based wastewater treatment is currently on the rise given to the many characteristics of yeast cells. Yeasts are generally fast growing, and they are robust in terms of tolerance to stress and inhibitory compounds, in addition to their ability to metabolize a diverse range of substrates and create a diverse range of metabolites. Therefore, yeast cells possess the capacity to recover and transform agro-industrial wastewater nutrients into highly valuable metabolites. In addition to remediating the wastewater, numerous value-added products such as single cell oil (SCO), single cell proteins (SCPs), biofuels, organic acid, and aromatic compounds amongst others can be produced through fermentation of wastewater by yeast cells. This work thus brings to limelight the potential roles of yeast cells in reducing, reusing, and recycling of agro-industrial wastewaters while proffering solutions to some of the factors that limit yeast-mediated wastewater valorization.

Circular Economy Indicators for the Assessment of Waste and By-Products from the Palm Oil Sector

A circular economy (CE) promotes the reuse, reincorporation and valuation of waste and by-products under the framework of sustainable development through models and indicators that evaluate scenarios of second use and reduction in non-incorporated outputs to reduce negative externalities and pressures on the dimensions of development. A CE model applied to the transformation process of RFF in agro-industries is developed, which consists in the identification of the residue coefficients of EFB (22.48% ± 0.8), fiber (15.58% ± 0.49), husk (6.03% ± 0.66) and ash (0.55% ± 1.67). Subsequently, the valuation trends of potential second use were verified through a systematic review, which allowed the construction of the scenario of avoided costs of USD 678,721.5, a product of the total use of the outputs under bioenergy and nutrient source approaches. Finally, the RRSFM indicator was constructed, which can reach the level of 72% and a degree of improvement of 26% by 2026. In parallel, the HCRRS indicator revealed a reduction of 57.1%, 59.6% and 82.8% in emissions of t CO2-eq product in the comparison of scenarios for the use of residues and by-products of palm oil from agro-industries in the Casanare Department.

Yeasts Inhabiting Extreme Environments and Their Biotechnological Applications

Yeasts are microscopic fungi inhabiting all Earth environments, including those inhospitable for most life forms, considered extreme environments. According to their habitats, yeasts could be extremotolerant or extremophiles. Some are polyextremophiles, depending on their growth capacity, tolerance, and survival in the face of their habitat’s physical and chemical constitution. The extreme yeasts are relevant for the industrial production of value-added compounds, such as biofuels, lipids, carotenoids, recombinant proteins, enzymes, among others. This review calls attention to the importance of yeasts inhabiting extreme environments, including metabolic and adaptive aspects to tolerate conditions of cold, heat, water availability, pH, salinity, osmolarity, UV radiation, and metal toxicity, which are relevant for biotechnological applications. We explore the habitats of extreme yeasts, highlighting key species, physiology, adaptations, and molecular identification. Finally, we summarize several findings related to the industrially-important extremophilic yeasts and describe current trends in biotechnological applications that will impact the bioeconomy.

Recent Developments in Biological Processing Technology for Palm Oil Mill Effluent Treatment-A Review

Simple Summary

Palm oil mill effluent (POME) requires treatment prior to discharge to the environment. Biological processing technology is highly preferable due to its advantages of environmentally friendliness, cost effectiveness, and practicality. These methods utilized various designs and modifications of bioreactors fostering effective fermentation technology in the presence of fungi, bacteria, microalgae, and a consortium of microorganisms. This review highlights the recent biological processing technology for POME treatment as a resource utilization.

Abstract

POME is the most voluminous waste generated from palm oil milling activities. The discharge of POME into the environment without any treatment processing could inflict an undesirable hazard to humans and the environment due to its high amount of toxins, organic, and inorganic materials. The treatment of POME prior to discharge into the environment is utmost required to protect the liability for human health and the environment. Biological treatments are preferable due to eco-friendly attributes that are technically and economically feasible. The goal of this review article is to highlight the current state of development in the biological processing technologies for POME treatment. These biological processing technologies are conducted in the presence of fungi, bacteria, microalgae, and a consortium of microorganisms. Numerous microbes are listed to identify the most efficient strain by monitoring the BOD, COD, working volume of the reactor, and treatment time. The most effective processing technology for POME treatment uses an upflow anaerobic sludge blanket reactor with the COD value of 99%, hydraulic retention time of 7.2 days, and a working volume of 4.7 litres. Biological processing technologies are mooted as an efficient and sustainable management practice of POME waste.

High-performance biological treatment of tuna wash processing wastewater using Yarrowia lipolytica

It is well known that the lack of an effective treatment of tuna wash processing wastewater may pose substantial environmental and public health hazards. The present work investigates the performance of biological treatment of tuna wash processing wastewater (TWPW) by using Yarrowia lipolytica. Under optimized experimental conditions (pH "6.40-6.50" and 29 °C), Y. lipolytica reduced the pollution level of the crude and the diluted TWPW after only 7 days of incubation. The Yarrowia treatment leaded to a reduction of 66% chemical oxygen demand, 69.8% total organic carbon, 66% salinity, and phosphorus total (100%) removal of the crude TWPW, while the treated-diluted TWPW revealed significant reductions in chemical oxygen demand and total organic carbon (75% and 74%, respectively), as well as salinity (68%). Interestingly, a total removal of nitrogen and phosphorus from the diluted TWPW was obtained. Under high salinity, an important Y. lipolytica biomass of 5 g L^-1 is produced with high levels of lipids and protein contents at around 336 ± 12.2 mg g^-1 and 302.15 ± 5.44 mg g^-1, respectively. The phytotoxicity assessment of the treated TWPW on fenugreek seeds shows promising results, which reveals the good performance of Yarrowia treatment in reducing the toxicity of this wastewater.

Biodegradation of phenolic compounds present in palm oil mill effluent as single and mixed substrates by Trametes hirsuta AK04

The ability of white-rot fungus, Trametes hirsuta AK04, to utilize phenolics as single and mixed substrates was determined in mineral medium and palm oil mill effluent (POME). The strain AK04 was able to rapidly metabolize all ten phenolics as single and mixed substrates at all test concentrations. With single substrates, between 78 and 98% removal was achieved within seven days. The biomass yield increased with increasing concentration from 100 to 500 mg L^-1 but slightly decreased when the concentration was increased up to 1,000 mg L^-1. When fitted to a Haldane model, the groups of benzoic and cinnamic acid derivatives gave significantly higher maximum specific growth rates than other phenolics. Phenol exhibited the lowest affinity and highest inhibitory effects on fungal metabolism. In mixed substrates, the total concentration ranges of phenolics mixtures between 1,000 and 6,000 mg L^-1 did not affect the fungal growth rate and the strain AK04 showed a high degree of resistance to their toxic effects. The addition of glucose and yeast extract enhanced the degradation rates of individual phenolics in the substrate mixtures, demonstrating the advantage of this strain for treating complex media, such as industrial wastewater.

Bioenergy for a Cleaner Future: A Case Study of Sustainable Biogas Supply Chain in the Malaysian Energy Sector

A life cycle assessment (LCA)-based environmental sustainability evaluation conceptual framework of biogas production has been proposed to improve the sustainability of biogas supply chains. The conceptual framework developed in this study can be used as a guideline for the related stakeholders and decision makers to improve the quality and enhance the sustainability of biogas production in Malaysia as well as promoting biogas as a clean, reliable and secure energy. A case study on an LCA analysis of a zero waste discharge treatment process has been conducted. In the zero discharge treatment system, biogas can be produced with a maximum water recycle and reuse. It was indicated that the biogas production and zero discharge treatment of a palm oil mill effluent were environmentally sustainable as the system utilized organic waste to produce bioenergy and achieved zero discharge. However, there were other aspects that should be taken into consideration, particularly regarding the sources of electricity and upstream activity, to ensure the sustainability of the system holistically.

Bioaugmentation coupled with phytoremediation for the removal of phenolic compounds and color from treated palm oil mill effluent

The potential for coupling bioaugmentation with phytoremediation to simultaneously treat and utilize treated palm oil mill effluent (TPOME) in animal feed production was determined from a reduction in phenolic compounds and color in soil leachates, as well as from an increased yield of pasture grass. Two phenol-degrading bacteria-Methylobacterium sp. NP3 and Acinetobacter sp. PK1-were inoculated into the Brachiaria humidicola rhizosphere before the application of TPOME. A pot study showed that the soil with both grass and inoculated bacteria had the highest dephenolization and decolorization efficiencies, with a maximum capability of removing 70% from 587 mg total phenolic compounds added and 73% from 4438 color units during ten TPOME application cycles. The results corresponded to increases in the number of phenol-degrading bacteria and the grass yield. In a field study, this treatment was able to remove 46% from 21,453 mg total phenolic compounds added, with a maximum color removal efficiency of 52% from 5105 color units, while the uninoculated plots removed about 24-39% and 29-46% of phenolic compounds and color, respectively. The lower treatment performance was probably due to the increased TPOME concentrations. Based on the amounts of phenolic compounds, protein, and crude fiber in the grass biomass, the inoculated TPOME-treated grass had a satisfactory nutritional quality and digestibility for use as animal feed.

Prospective Application of Palm Oil Mill Boiler Ash as a Biosorbent: Effect of Microwave Irradiation and Palm Oil Mill Effluent Decolorization by Adsorption

Common conventional biological treatment methods fail to decolorize palm oil mill effluent (POME). The present study focused on using the abundant palm oil mill boiler (POMB) ashes for POME decolorization. The POMB ashes were subjected to microwave irradiation and chemical treatment using H₂SO₄. The resultant adsorbents were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Brunauer–Emmett–Teller (BET) analyses. The adsorption efficiency was evaluated at various pH levels (2–8.5), adsorption dosages (3–15 g) in 200 mL, and contact times (1–5 h). The microwave-irradiated POMB-retained ash recorded the highest color removal of 92.31%, for which the best conditions were pH 2, 15 g adsorbent dosage in 200 mL, and 5 h of contact time. At these best treatment conditions, the color concentration of the treated effluent was analyzed using the method proposed by the American Dye Manufacturers Institute (ADMI). The color concentration was 19.20 ADMI, which complies with the Malaysia discharge standard class A. The Freundlich isotherm model better fit the experimental data and had a high R² of 0.9740. Based on these results, it can be deduced that microwave-irradiated POMB-retained ash has potential applications for POME decolorization via a biosorption process.

Bioremediation of palm oil mill effluent (POME) using indigenous Meyerozyma guilliermondii

Despite being a key Malaysian economic contributor, the oil palm industry generates a large quantity of environmental pollutant known as palm oil mill effluent (POME). Therefore, the need to remediate POME has drawn a mounting interest among environmental scientists. This study has pioneered the application of Meyerozyma guilliermondii with accession number (MH 374161) that was isolated indigenously in accessing its potential to degrade POME. This strain was able to treat POME in shake flask experiments under aerobic condition by utilising POME as a sole source of carbon. However, it has also been shown that the addition of suitable carbon and nitrogen sources has significantly improved the degradation potential of M. guilliermondii. The remediation of POME using this strain resulted in a substantial reduction of chemical oxygen demand (COD) of 72%, total nitrogen of 49.2% removal, ammonical nitrogen of 45.1% removal, total organic carbon of 46.6% removal, phosphate of 60.6% removal, and 92.4% removal of oil and grease after 7 days of treatment period. The strain also exhibited an extracellular lipase activity which promotes better wastewater treatment. Additionally, Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) analyses have specifically shown that M. guilliermondii strain can degrade hydrocarbons, fatty acids, and phenolic compounds present in the POME. Ultimately, this study has demonstrated that M. guilliermondii which was isolated indigenously exhibits an excellent degrading ability. Therefore, this strain is suitable to be employed in the remediation of POME, contributing to a safe discharge of the effluent into the environment.

Microbiota of Palm Oil Mill Wastewater in Malaysia

This study was aimed at identifying indigenous microorganisms from palm oil mill effluent (POME) and to ascertain the microbial load. Isolation and identification of indigenous microorganisms was subjected to standard microbiological methods and sequencing of the 16S rRNA and 18S rRNA genes. Sequencing of the 16S rRNA and 18S rRNA genes for the microbial strains signifies that they were known as Micrococcus luteus 101PB, Stenotrophomonas maltophilia 102PB, Bacillus cereus 103PB, Providencia vermicola 104PB, Klebsiella pneumoniae 105PB, Bacillus subtilis 106PB, Aspergillus fumigatus 107PF, Aspergillus nomius 108PF, Aspergillus niger 109PF and Meyerozyma guilliermondii 110PF. Results revealed that the population of total heterotrophic bacteria (THB) ranged from 9.5 × 10⁵ - 7.9 × 10⁶ cfu/mL. The total heterotrophic fungi (THF) ranged from 2.1 × 10⁴ - 6.4 × 10⁴ cfu/mL. Total viable heterotrophic indigenous microbial population on CMC agar ranged from 8.2 × 10⁵ - 9.1 × 10⁶ cfu/mL and 1.4 × 10³ - 3.4 × 10³ cfu/mL for bacteria and fungi respectively. The microbial population of oil degrading bacteria (ODB) ranged from 6.4 × 10⁵ - 4.8 × 10⁶ cfu/mL and the oil degrading fungi (ODF) ranged from 2.8 × 10³ - 4.7 × 10⁴ cfu/mL. The findings revealed that microorganisms flourish well in POME. Therefore, this denotes that isolating native microorganisms from POME is imperative for effectual bioremediation, biotreatment and biodegradation of industrial wastewaters.

Trend and current practices of palm oil mill effluent polishing: Application of advanced oxidation processes and their future perspectives

Palm oil processing is a multi-stage operation which generates large amount of effluent. On average, palm oil mill effluent (POME) may contain up to 51, 000 mg/L COD, 25,000 mg/L BOD, 40,000 TS and 6000 mg/L oil and grease. Due to its potential to cause environmental pollution, palm oil mills are required to treat the effluent prior to discharge. Biological treatments using open ponding system are widely used for POME treatment. Although these processes are capable of reducing the pollutant concentrations, they require long hydraulic retention time and large space, with the effluent frequently failing to satisfy the discharge regulation. Due to more stringent environmental regulations, research interest has recently shifted to the development of polishing technologies for the biologically-treated POME. Various technologies such as advanced oxidation processes, membrane technology, adsorption and coagulation have been investigated. Among these, advanced oxidation processes have shown potentials as polishing technologies for POME. This paper offers an overview on the POME polishing technologies, with particularly emphasis on advanced oxidation processes and their prospects for large scale applications. Although there are some challenges in large scale applications of these technologies, this review offers some perspectives that could help in overcoming these challenges.

The expression of the Cuphea palustris thioesterase CpFatB2 in Yarrowia lipolytica triggers oleic acid accumulation

The conversion of industrial by-products into high-value added compounds is a challenging issue. Crude glycerol, a by-product of the biodiesel production chain, could represent an alternative carbon source for the cultivation of oleaginous yeasts. Here, we developed five minimal synthetic glycerol-based media, with different C/N ratios, and we analyzed the production of biomass and fatty acids by Yarrowia lipolytica Po1g strain. We identified two media at the expense of which Y. lipolytica was able to accumulate ∼5 g L(-1) of biomass and 0.8 g L(-1) of fatty acids (0.16 g of fatty acids per g of dry weight). These optimized media contained 0.5 g L(-1) of urea or ammonium sulfate and 20 g L(-1) of glycerol, and were devoid of yeast extract. Moreover, Y. lipolytica was engineered by inserting the FatB2 gene, coding for the CpFatB2 thioesterase from Cuphea palustris, in order to modify the fatty acid composition towards the accumulation of medium-chain fatty acids. Contrary to the expected, the expression of the heterologous gene increased the production of oleic acid, and concomitantly decreased the level of saturated fatty acids.

Achieving Metabolic Flux Analysis for S. cerevisiae at a Genome-Scale: Challenges, Requirements, and Considerations

Recent advances in 13C-Metabolic flux analysis (13C-MFA) have increased its capability to accurately resolve fluxes using a genome-scale model with narrow confidence intervals without pre-judging the activity or inactivity of alternate metabolic pathways. However, the necessary precautions, computational challenges, and minimum data requirements for successful analysis remain poorly established. This review aims to establish the necessary guidelines for performing 13C-MFA at the genome-scale for a compartmentalized eukaryotic system such as yeast in terms of model and data requirements, while addressing key issues such as statistical analysis and network complexity. We describe the various approaches used to simplify the genome-scale model in the absence of sufficient experimental flux measurements, the availability and generation of reaction atom mapping information, and the experimental flux and metabolite labeling distribution measurements to ensure statistical validity of the obtained flux distribution. Organism-specific challenges such as the impact of compartmentalization of metabolism, variability of biomass composition, and the cell-cycle dependence of metabolism are discussed. Identification of errors arising from incorrect gene annotation and suggested alternate routes using MFA are also highlighted.

Conventional methods and emerging wastewater polishing technologies for palm oil mill effluent treatment: a review

The Malaysian palm oil industry is a major revenue earner and the country is ranked as one of the largest producers in the world. However, growth of the industry is synonymous with a massive production of agro-industrial wastewater. As an environmental protection and public health concern, the highly polluting palm oil mill effluent (POME) has become a major attention-grabber. Hence, the industry is targeting for POME pollution abatement in order to promote a greener image of palm oil and to achieve sustainability. At present, most palm oil mills have adopted the ponding system for treatment. Due to the successful POME pollution abatement experiences, Malaysia is currently planning to revise the effluent quality standards towards a more stringent discharge limits. Hence, the current trend of POME research focuses on developing tertiary treatment or polishing systems for better effluent management. Biotechnologically-advanced POME tertiary (polishing) technologies as well as other physicochemical methods are gaining much attention as these processes are the key players to push the industry towards the goal of environmental sustainability. There are still ongoing treatment technologies being researched and the outcomes maybe available in a while. However, the research completed so far are compiled herein and reported for the first time to acquire a better perspective and insight on the subject with a view of meeting the new standards. To this end, the most feasible technology could be the combination of advanced biological processes (bioreactor systems) with extended aeration, followed by solids separation prior to discharge. Chemical dosing is favoured only if effluent of higher quality is anticipated.

Treatment and Valorization of Palm Oil Mill Effluent through Production of Food Grade Yeast Biomass

Palm oil mill effluent (POME) is high strength wastewater derived from processing of palm fruit. It is generated in large quantities in all oil palm producing nations where it is a strong pollutant amenable to microbial degradation being rich in organic carbon, nitrogen, and minerals. Valorization and treatment of POME with seven yeast isolates was studied under scalable conditions by using POME to produce value-added yeast biomass. POME was used as sole source of carbon and nitrogen and the fermentation was carried out at 150 rpm, 28 ± 2°C using an inoculum size of 1 mL of 106 cells. Yeasts were isolated from POME, dump site, and palm wine. The POME had chemical oxygen demand (COD) 114.8 gL−1, total solid 76 gL−1, total suspended solid (TSS) 44 gL−1 and total lipid 35.80 gL−1. Raw POME supported accumulation of 4.42 gL−1 dry yeast with amino acid content comparable or superior to the FAO/WHO standard for feed use SCP. Peak COD reduction (83%) was achieved with highest biomass accumulation in 96 h using Saccharomyces sp L31. POME can be used as carbon source with little or no supplementation to achieve waste-to-value by producing feed grade yeast with reduction in pollution potential.

Marine yeast isolation and industrial application

Over the last century, terrestrial yeasts have been widely used in various industries, such as baking, brewing, wine, bioethanol and pharmaceutical protein production. However, only little attention has been given to marine yeasts. Recent research showed that marine yeasts have several unique and promising features over the terrestrial yeasts, for example higher osmosis tolerance, higher special chemical productivity and production of industrial enzymes. These indicate that marine yeasts have great potential to be applied in various industries. This review gathers the most recent techniques used for marine yeast isolation as well as the latest applications of marine yeast in bioethanol, pharmaceutical and enzyme production fields.

Yarrowia lipolytica and pollutants: Interactions and applications

Yarrowia lipolytica is a dimorphic, non-pathogenic, ascomycetous yeast species with distinctive physiological features and biochemical characteristics that are significant in environment-related matters. Strains naturally present in soils, sea water, sediments and waste waters have inherent abilities to degrade hydrocarbons such as alkanes (short and medium chain) and aromatic compounds (biphenyl and dibenzofuran). With the application of slow release fertilizers, design of immobilization techniques and development of microbial consortia, scale-up studies and in situ applications have been possible. In general, hydrocarbon uptake in this yeast is mediated by attachment to large droplets (via hydrophobic cell surfaces) or is aided by surfactants and emulsifiers. Subsequently, the internalized hydrocarbons are degraded by relevant enzymes innately present in the yeast. Some wild-type or recombinant strains also detoxify nitroaromatic (2,4,6-trinitrotoluene), halogenated (chlorinated and brominated hydrocarbons) and organophosphate (methyl parathion) compounds. The yeast can tolerate some metals and detoxify them via different biomolecules. The biomass (unmodified, in combination with sludge, magnetically-modified and in the biofilm form) has been employed in the biosorption of hexavalent chromium ions from aqueous solutions. Yeast cells have also been applied in protocols related to nanoparticle synthesis. The treatment of oily and solid wastes with this yeast reduces chemical oxygen demand or value-added products (single cell oil, single cell protein, surfactants, organic acids and polyalcohols) are obtained. On account of all these features, the microorganism has established a place for itself and is of considerable value in environment-related applications.

Decolorization of palm oil mill effluent using growing cultures of Curvularia clavata

Agricultural wastewater that produces color are of environmental and health concern as colored effluent can produce toxic and carcinogenic by-products. From this study, batch culture optimization using response surface methods indicated that the fungus isolated from the pineapple solid waste, Curvularia clavata was able to decolorize sterile palm oil mill effluent (POME) which is mainly associated with polyphenol and lignin. Results showed successful decolorization of POME up to 80 % (initial ADMI [American Dye Manufacturing Index] of 3,793) with 54 % contributed by biosorption and 46 % by biodegradation after 5 days of treatment. Analysis using HPLC and GC-MS showed the degradation of color causing compound such as 3-methoxyphenyl isothiocynate and the production of new metabolites. Ecotoxicity test indicated that the decolorized effluent is safe for discharge. To determine the longevity of the fungus for a prolonged decolorization period, sequential batch decolorization studies were carried out. The results showed that lignin peroxidase and laccase were the main ligninolytic enzymes involved in the degradation of color. Carboxymethyl cellulase (CMCase) and xylanase activities were also detected suggesting possible roles of the enzymes in promoting growth of the fungus which consequently contributed to improved decolorization of POME. In conclusion, the ability of C. clavata in treating color of POME indicated that C. clavata is of potential use for decolorization and degradation of agricultural wastewater containing polyphenolic compounds.

Morphological and metabolic shifts of Yarrowia lipolytica induced by alteration of the dissolved oxygen concentration in the growth environment

Yarrowia lipolytica, an ascomycete with biotechnological potential, is able to form either yeast cells or hyphae and pseudohyphae in response to environmental conditions. This study shows that the morphology of Y. lipolytica, cultivated in batch cultures on hydrophilic (glucose and glycerol) and hydrophobic (olive oil) media, was not affected by the nature of the carbon source, nor by the nature or the concentration of the nitrogen source. By contrast, dissolved oxygen concentration (DOC) should be considered as the major factor affecting yeast morphology. Specifically, when growth occurred at low or zero DOC the mycelial and/or pseudomycelial forms predominated over the yeast form independently of the carbon and nitrogen sources used. Experimental data obtained from a continuous culture of Y. lipolytica on glycerol, being used as carbon and energy source, demonstrated that the mycelium-to-yeast form transition occurs when DOC increases from 0.1 to 1.5 mg l(-1). DOC also affected the yeast physiology, as the activity of enzymes implicated in lipid biosynthesis (i.e. ATP-citrate lyase, malic enzyme) was upregulated at high DOC whereas the activity of enzymes implicated in glycerol assimilation (such as glycerol dehydrogenase and kinase) remained fundamentally unaffected in the cell-free extract.

Treatment of Palm Oil Mill Effluent by a Microbial Consortium Developed from Compost Soils

A method for the aerobic treatment of palm oil mill effluent (POME) was investigated in shake-flask experiments using a consortium developed from POME compost. POME was initially centrifuged at 4,000 g for 15 min and the supernatant was enriched with (NH₄)₂SO₄ (0.5%) and yeast extract (0.25%) to boost its nitrogen content. At optimum pH (pH 4) and temperature (40°C) conditions, the chemical oxygen demand (COD) of the effluent decreased from 10,350 to 1,000 mg/L (90.3%) after 7 days. The total bacterial population determined by plate count enumeration was 2.4 × 10⁶ CFU/mL, while the fungal count was 1.8 × 10³ colonies/mL. Bacteria of the genera Pseudomonas, Flavobacterium, Micrococcus, and Bacillus were isolated, while the fungal genera included Aspergillus, Penicillium, Trichoderma, and Mucor. When the isolated species were each inoculated into separate batches of the raw effluent, both pH and COD were unchanged. However, at 75 and 50% POME dilutions, the COD dropped by 52 and 44%, respectively, while the pH increased from 4 to 7.53. POME treatment by aerobic method is sustainable and holds promising prospects for cushioning the environment from the problems associated with the use of anaerobic systems.

A novel multigene expression construct for modification of glycerol metabolism in Yarrowia lipolytica

BACKGROUND

High supply of raw, residual glycerol from biodiesel production plants promote the search for novel biotechnological methods of its utilization. In this study we attempted modification of glycerol catabolism in a nonconventional yeast species Yarrowia lipolytica through genetic engineering approach.

RESULTS

To address this, we developed a novel genetic construct which allows transferring three heterologous genes, encoding glycerol dehydratase, its reactivator and a wide-spectrum alcohol oxidoreductase under the control of glycerol-induced promoter. The three genes, tandemly arrayed in an expression cassette with a marker gene ura3, regulatory and targeting sequences (G3P dh promoter and XPR-like terminator, 28S rDNA as a target locus), were transferred into Yarrowia lipolytica cells. The obtained recombinant strain NCYC3825 was characterized at the molecular level and with respect to its biotechnological potential. Our experiments indicated that the novel recombinant strain stably borne one copy of the expression cassette and efficiently expressed heterologous alcohol oxidoreductase, while glycerol dehydratase and its reactivator were expressed at lower level. Comparative shake flask cultivations in glucose- and glycerol-based media demonstrated higher biomass production by the recombinant strain when glycerol was the main carbon source. During bioreactor (5 L) fed-batch cultivation in glycerol-based medium, the recombinant strain was characterized by relatively high biomass and lipids accumulation (up to 42 gDCW L(-1), and a peak value of 38%LIPIDS of DCW, respectively), and production of high titers of citric acid (59 g L(-1)) and 2-phenylethanol (up to 1 g L(-1) in shake flask cultivation), which are industrially attractive bioproducts.

CONCLUSIONS

Due to heterogeneous nature of the observed alterations, we postulate that the main driving force of the modified phenotype was faster growth in glycerol-based media, triggered by modifications in the red-ox balance brought by the wide spectrum oxidoreductase. Our results demonstrate the potential multidirectional use of a novel Yarrowia lipolytica strain as a microbial cell factory.

Optimization of decolorization of palm oil mill effluent (POME) by growing cultures of Aspergillus fumigatus using response surface methodology

The conventional treatment process of palm oil mill effluent (POME) produces a highly colored effluent. Colored compounds in POME cause reduction in photosynthetic activities, produce carcinogenic by-products in drinking water, chelate with metal ions, and are toxic to aquatic biota. Thus, failure of conventional treatment methods to decolorize POME has become an important problem to be addressed as color has emerged as a critical water quality parameter for many countries such as Malaysia. Aspergillus fumigatus isolated from POME sludge was successfully grown in POME supplemented with glucose. Statistical optimization studies were conducted to evaluate the effects of the types and concentrations of carbon and nitrogen sources, pH, temperature, and size of the inoculum. Characterization of the fungus was performed using scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and Brunauer, Emmet, and Teller surface area analysis. Optimum conditions using response surface methods at pH 5.7, 35 °C, and 0.57 % w/v glucose with 2.5 % v/v inoculum size resulted in a successful removal of 71 % of the color (initial ADMI of 3,260); chemical oxygen demand, 71 %; ammoniacal nitrogen, 35 %; total polyphenolic compounds, 50 %; and lignin, 54 % after 5 days of treatment. The decolorization process was contributed mainly by biosorption involving pseudo-first-order kinetics. FTIR analysis revealed that the presence of hydroxyl, C-H alkane, amide carbonyl, nitro, and amine groups could combine intensively with the colored compounds in POME. This is the first reported work on the application of A. fumigatus for the decolorization of POME. The present investigation suggested that growing cultures of A. fumigatus has potential applications for the decolorization of POME through the biosorption and biodegradation processes.

The 'LipoYeasts' project: using the oleaginous yeast Yarrowia lipolytica in combination with specific bacterial genes for the bioconversion of lipids, fats and oils into high-value products

The oleochemical industry is currently still dominated by conventional chemistry, with biotechnology only starting to play a more prominent role, primarily with respect to the biosurfactants or lipases, e.g. as detergents, or for biofuel production. A major bottleneck for all further biotechnological applications is the problem of the initial mobilization of cheap and vastly available lipid and oil substrates, which are then to be transformed into high-value biotechnological, nutritional or pharmacological products. Under the EU-sponsored LipoYeasts project we are developing the oleaginous yeast Yarrowia lipolytica into a versatile and high-throughput microbial factory that, by use of specific enzymatic pathways from hydrocarbonoclastic bacteria, efficiently mobilizes lipids by directing its versatile lipid metabolism towards the production of industrially valuable lipid-derived compounds like wax esters (WE), isoprenoid-derived compounds (carotenoids, polyenic carotenoid ester), polyhydroxyalkanoates (PHAs) and free hydroxylated fatty acids (HFAs). Different lipid stocks (petroleum, alkane, vegetable oil, fatty acid) and combinations thereof are being assessed as substrates in combination with different mutant and recombinant strains of Y. lipolytica, in order to modulate the composition and yields of the produced added-value products.

Quantitative study of lipase secretion, extracellular lipolysis, and lipid storage in the yeast Yarrowia lipolytica grown in the presence of olive oil: analogies with lipolysis in humans

Lipase secretion, extracellular lipolysis, and fatty acid uptake were quantified in the yeast Yarrowia lipolytica grown in the presence of olive oil and/or glucose. Specific lipase assays, Western blot analysis, and ELISA indicated that most of the lipase activity measured in Y. lipolytica cultures resulted from the YLLIP2 lipase. Lipase production was triggered by olive oil and, during the first hours of culture, most of the lipase activity and YLLIP2 immunodetection remained associated with the yeast cells. YLLIP2 was then released in the culture medium before it was totally degraded by proteases. Olive oil triglycerides were largely degraded when the lipase was still attached to the cell wall. The fate of lipolysis products in the culture medium and inside the yeast cell, as well as lipid storage, was investigated simultaneously by quantitative TLC-FID and GC analysis. The intracellular levels of free fatty acids (FFA) and triglycerides increased transiently and were dependent on the carbon sources. A maximum fat storage of 37.8% w/w of yeast dry mass was observed with olive oil alone. A transient accumulation of saturated FFA was observed whereas intracellular triglycerides became enriched in unsaturated fatty acids. So far, yeasts have been mainly used for studying the intracellular synthesis, storage, and mobilization of neutral lipids. The present study shows that yeasts are also interesting models for studying extracellular lipolysis and fat uptake by the cell. The quantitative data obtained here allow for the first time to establish interesting analogies with gastrointestinal and vascular lipolysis in humans.

Pollution control technologies for the treatment of palm oil mill effluent (POME) through end-of-pipe processes

Palm oil production is one of the major industries in Malaysia and this country ranks one of the largest productions in the world. In Malaysia, the total production of crude palm oil in 2008 was 17,734,441 tonnes. However, the production of this amount of crude palm oil results in even larger amounts of palm oil mill effluent (POME). In the year 2008 alone, at least 44 million tonnes of POME was generated in Malaysia. Currently, the ponding system is the most common treatment method for POME but other processes such as aerobic and anaerobic digestion, physicochemical treatment and membrane filtration may also provide the palm oil industries with possible insights into the improvement of POME treatment processes. Generally, open ponding offers low capital and operating costs but this conventional method is becoming less attractive because the methane produced is wasted to the atmosphere and the system can not be certified for Carbon Emission Reduction trading. On the other hand, anaerobic digestion of POME provides the fastest payback of investment because the treatment enables biogas recovery for heat generation and treated effluent for land application. Lastly, it is proposed herewith that wastewater management based on the promotion of cleaner production and environmentally sound biotechnologies should be prioritized and included as a part of the POME management in Malaysia for attaining sustainable development. This paper thus discusses and compares state-of-the-art POME treatment methods as well as their individual performances.