Lipid production in association of filamentous fungi with genetically modified cyanobacterial cells

Oleaginous fungi: a promising source of biofuels and nutraceuticals with enhanced lipid production strategies

Oleaginous fungi have attracted a great deal of interest for their potency to accumulate high amounts of lipids (more than 20% of biomass dry weight) and polyunsaturated fatty acids (PUFAs), which have a variety of industrial and biological applications. Lipids of plant and animal origin are related to some restrictions and thus lead to attention towards oleaginous microorganisms as reliable substitute resources. Lipids are traditionally biosynthesized intra-cellularly and involved in the building structure of a variety of cellular compartments. In oleaginous fungi, under certain conditions of elevated carbon ratio and decreased nitrogen in the growth medium, a change in metabolic pathway occurred by switching the whole central carbon metabolism to fatty acid anabolism, which subsequently resulted in high lipid accumulation. The present review illustrates the bio-lipid structure, fatty acid classes and biosynthesis within oleaginous fungi with certain key enzymes, and the advantages of oleaginous fungi over other lipid bio-sources. Qualitative and quantitative techniques for detecting the lipid accumulation capability of oleaginous microbes including visual, and analytical (convenient and non-convenient) were debated. Factors affecting lipid production, and different approaches followed to enhance the lipid content in oleaginous yeasts and fungi, including optimization, utilization of cost-effective wastes, co-culturing, as well as metabolic and genetic engineering, were discussed. A better understanding of the oleaginous fungi regarding screening, detection, and maximization of lipid content using different strategies could help to discover new potent oleaginous isolates, exploit and recycle low-cost wastes, and improve the efficiency of bio-lipids cumulation with biotechnological significance.

Erythromycin mediates co-flocculation between cyanobacterium Synechocystis sp. PCC 6803 and filamentous fungi in liquid cultivation without organic compounds

Photoautotrophic cyanobacteria assimilate the greenhouse gas carbon dioxide as their sole carbon source for producing useful bioproducts. However, harvesting the cells from their liquid media is a major bottleneck in the process. Thus, an easy-to-harvest method, such as auto-flocculation, is desirable. Here, we found that cyanobacterium Synechocystis sp. PCC 6803 co-flocculated with a natural fungal contamination in the presence of the antibiotic erythromycin (EM) but not without EM. The fungi in the co-flocculated biomass were isolated and found to consist of five species with the filamentous Purpureocillium lilacinum and Aspergillus protuberus making up 71% of the overall fungal population. The optimal co-cultivation for flocculation was an initial 5 mg (fresh weight) of fungi, an initial cell density of Synechocystis of 0.2 OD730, 10 µM EM, and 14 days of cultivation in 100 mL of BG11 medium with no organic compound. This yielded 248 ± 28 mg/L of the Synechocystis-fungi flocculated biomass from 560 ± 35 mg/L of total biomass, a 44 ± 2% biomass flocculation efficiency. Furthermore, the EM treated Synechocystis cells in the Synechocystis-fungi flocculate had a normal cell color and morphology, while those in the axenic suspension exhibited strong chlorosis. Thus, the occurrence of the Synechocystis-fungi flocculation was mediated by EM, and the co-flocculation with the fungi protected Synechocystis against the development of chlorosis. Transcriptomic analysis suggested that the EM-mediated co-flocculation was a result of down-regulation of the minor pilin genes and up-regulation of several genes including the chaperone gene for pilin regulation, the S-layer protein genes, the exopolysaccharide-polymerization gene, and the genes for signaling proteins involved in cell attachment and abiotic-stress responses. The CuSO4 stress can also mediate Synechocystis-fungi flocculation but at a lower flocculation efficiency than that caused by EM. The EM treatment may be applied in the co-culture between other cyanobacteria and fungi to mediate cell bio-flocculation.

Filamentous fungal pellets as a novel and sustainable encapsulation matrix for exogenous bioactive compounds

Edible filamentous fungi (FF) are considered sustainable food materials given their rich nutrient profile and low carbon and water footprints during production. The current study evaluated FF biomass as a natural encapsulation system for exogenous bioactive compounds and as a model system to investigate the complex food matrix-micronutrient interactions during in vitro digestion. Our objective was to compare the fungal pellet, as a multicellular encapsulation system, with single yeast cell-based carriers in terms of loading and release of curcumin, a model compound. The results suggest that the curcumin encapsulation efficiency was similar in single yeast cells and fungal hyphal cells. A vacuum treatment used to facilitate the infusion of curcumin into yeast or fungal cells also enabled rapid internalization of yeast cells into the fungal pellet matrix. Compared to the single-cell encapsulation system, the multicellular systems modified the release kinetics of curcumin during in vitro digestion by eliminating the initial rapid release and reducing the overall release rate of curcumin in the small intestinal phase. These results provide a deeper understanding of the effect of natural edible structures on the bioaccessibility of micronutrients, and demonstrate the potential of using FF biomass as functional food materials.

Metabolic Profiling of Endophytic Bacteria in Relation to Their Potential Application as Components of Multi-Task Biopreparations

Agricultural crops are exposed to various abiotic and biotic stresses that can constrain crop productivity. Focusing on a limited subset of key groups of organisms has the potential to facilitate the monitoring of the functions of human-managed ecosystems. Endophytic bacteria can enhance plant stress resistance and can help plants to cope with the negative impacts of stress factors through the induction of different mechanisms, influencing plant biochemistry and physiology. In this study, we characterise endophytic bacteria isolated from different plants based on their metabolic activity and ability to synthesise 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD), the activity of hydrolytic exoenzymes, the total phenolic compounds (TPC) and iron-complexing compounds (ICC). Test GEN III MicroPlate indicated that the evaluated endophytes are highly metabolically active, and the best used substrates were amino acids, which may be important in selecting potential carrier components for bacteria in biopreparations. The ACCD activity of strain ES2 (Stenotrophomonas maltophilia) was the highest, whereas that of strain ZR5 (Delftia acidovorans) was the lowest. Overall, the obtained results indicated that ∼91.3% of the isolates were capable of producing at least one of the four hydrolytic enzymes. In addition, most of the tested strains produced ICC and TPC, which play a significant role in reducing stress in plants. The results of this study suggest that the tested endophytic bacterial strains can potentially be used to mitigate climate change-associated stresses in plants and to inhibit plant pathogens.

A novel fungal-algal coupling system for slaughterhouse wastewater treatment and lipid production

In this study, a novel fungal-algal coupling system was established for slaughterhouse wastewater treatment with Chlorella sp. DT025 and a new fungus, Penicillium sp. AHP141. With the optimization of cultivation conditions for the fungal-algal coupling system, the harvest efficiency of Chlorella sp. DT025 reached 99.79%. The mechanism of microalgae harvest of the fungal-algal system was revealed to be related to the morphological characteristics, surface charge, and the secretion of humic acid-like compounds and tryptophan on the surface of the fungi cells. For the original slaughterhouse wastewater treatment, the fungal-algal coupling system had a better removal efficiency of COD, TN, and TP than both monoculture systems. In the high-concentration artificial slaughterhouse wastewater, COD removal of the fungal-algal system reached more than 5350 mg/L. The lipid production of the fungal-algal coupling system in the high-concentration artificial slaughterhouse wastewater treatment was improved by 343.33% to 1.33 g/L compared to the microalgae monoculture treatment.

Insights into differences between spore-assisted and pellet-assisted microalgae harvesting using a highly efficient fungus: Efficiency, high-value substances, and mechanisms

To achieve efficient and low-cost microalgae harvesting, investigations were conducted on the harvesting efficiency and potential mechanisms of Chlorella sp. HQ by filamentous fungi using two strategies, fungal spore-assisted harvesting (FSH) and fungal pellet-assisted harvesting (FPH). Five of the 19 fungal species isolated from domestic sewage could form pellets, and Aspergillus niger HW8-1 comprised the highest harvesting efficiencies of 99.17 % and 88.70 % for FPH and FSH, respectively. FSH had 2-3 times more lipids and polysaccharides in fungus-alga pellets and caused richer saturated and monounsaturated fatty acids compared with FPH. Moreover, by optimizing the microalgae preculture time, glucose concentration, and microalgae initial density, the contents of high-value substances, such as lipids, polysaccharides, and proteins of fungus-alga pellets after FPH were improved from 5.96 %, 5.67 %, and 7.27 % to 20.18 %, 24.34 % and 10.48 %, respectively. Furthermore, fungal pellets secreted more extracellular polymeric substances (EPS) during FPH than those by FSH, which could chemisorb algal cells by lowering the surface potential of fungal pellets. FPH caused algal cells to cover the outside, which increased the light exposure area of algae, thereby increasing the photosynthesis rate, whereas FSH mainly captured microalgae physically through mycelium entanglement.

A state of the art review on the co-cultivation of microalgae-fungi in wastewater for biofuel production

The microalgae have a great potential as the fourth generation biofuel feedstock to deal with energy crisis, but the cost of production and biomass harvest are the major hurdles in terms of large scale production and applications. Using filamentous fungi to culture targeted alga for biomass accumulation and eventually harvesting is a sustainable way to mitigate environmental impacts. Microalgal co-culture method could be an alternative to overcome limitations and increase biomass yield and lipid accumulation. It was found to be the high feasibility for the production of biofuels from fungi and microalgae using wastewater. This article aimed to state the synergistic approaches, their culture protocols, harvesting procedure and their potential biotechnological applications. Additionally, algal-fungal consortia could digest cellulosic biomass, potentially reducing operating costs as part of industrial need. As a result of co-cultivation, biofuel production could be economically feasible owing to its excellent ability to treat wastewater and be eco-friendly. The implications of the innovative co-cultivation technology have demonstrated the potential for further development based on the policies that have been supported and implemented.

Enhanced production of amylase, pyruvate and phenolic compounds from glucose by light-driven Aspergillus niger-CuS nanobiohybrids

BACKGROUND

The demand for value-added compounds such as amylase, pyruvate and phenolic compounds produced by biological methods has prompted the rapid development of advanced technologies for their enhanced production. Nanobiohybrids (NBs) make use of both the microbial properties of whole-cell microorganisms and the light-harvesting efficiency of semiconductors. Photosynthetic NBs were constructed that link the biosynthetic pathways of Aspergillus niger with CuS nanoparticles.

RESULTS

In this work, NB formation was confirmed by negative values of the interaction energy, i.e., 2.31 × 10⁸ to -5.52 × 10⁸ kJ mol^-1 for CuS-Che NBs, whereas for CuS-Bio NBs the values were -2.31 × 10⁸ to -4.62 × 10⁸ kJ mol^-1 for CuS-Bio NBs with spherical nanoparticle interaction. For CuS-Bio NBs with nanorod interaction, it ranged from -2.3 × 10⁷ to -3.47 × 10⁷ kJ mol^-1 . Further, the morphological changes observed by scanning electron microscopy showed the presence of the elements Cu and S in the energy-dispersive X-ray spectra and the presence of CuS bonds in Fourier transform infrared spectroscopy indicate NB formation. In addition, the quenching effect in photoluminescence studies confirmed NB formation. Production yields of amylase, phenolic compounds and pyruvate amounted to 11.2 μmol L^-1, 52.5 μmol L^-1 and 28 nmol μL^-1, respectively, in A. niger-CuS Bio NBs on the third day of incubation in the bioreactor. Moreover, A niger cells-CuS Bio NBs had amino acids and lipid yields of 6.2 mg mL^-1 and 26.5 mg L^-1, respectively. Furthermore, probable mechanisms for the enhanced production of amylase, pyruvate and phenolic compounds are proposed.

CONCLUSION

Aspergillus niger-CuS NBs were used for the production of the amylase enzyme and value-added compounds such as pyruvate and phenolic compounds. Aspergillus niger-CuS Bio NBs showed a greater efficiency compared to A. niger-CuS Che NBs as the biologically produced CuS nanoparticles had a higher compatibility with A. niger cells. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Immobilization of Diatom Phaeodactylum tricornutum with Filamentous Fungi and Its Kinetics

Immobilizing microalgae cells in a hyphal matrix can simplify harvest while producing novel mycoalgae products with potential food, feed, biomaterial, and renewable energy applications; however, limited quantitative information to describe the process and its applicability under various conditions leads to difficulties in comparing across studies and scaling-up. Here, we demonstrate the immobilization of both active and heat-deactivated marine diatom Phaeodactylum tricornutum (UTEX 466) using different loadings of fungal pellets (Aspergillus sp.) and model the process through kinetics and equilibrium models. Active P. tricornutum cells were not required for the fungal-assisted immobilization process and the fungal isolate was able to immobilize more than its original mass of microalgae. The Freundlich isotherm model adequately described the equilibrium immobilization characteristics and indicated increased normalized algae immobilization (g algae removed/g fungi loaded) under low fungal pellet loadings. The kinetics of algae immobilization by the fungal pellets were found to be adequately modeled using both a pseudo-second order model and a model previously developed for fungal-assisted algae immobilization. These results provide new insights into the behavior and potential applications of fungal-assisted algae immobilization.

A review on mycelial pellets as biological carriers: Wastewater treatment and recovery for resource and energy

Mycelial pellets, a new environment friendly biological carrier, have received wide attention from researchers due to porosity, stability and unique biocompatibility. In this article, the theoretical basis and mechanism of mycelial pellets as a biological carrier were analyzed from the properties of mycelial pellets and the interaction between mycelial pellets and other microorganisms. This article aims to collate and present the current application and development trend of mycelial pellets as biological carriers in wastewater treatment, resource and energy recovery, especially the symbiotic particle system formed by mycelial pellets and microalgae is an important way to break through the technical bottleneck of biodiesel recovery from wastewater. This review also analyzes the research hotspots and trends of mycelial pellets as carriers in recent years, discusses the challenges faced by this technology, and puts forward corresponding solutions.

Microalgae cultivation in wastewater from agricultural industries to benefit next generation of bioremediation: a bibliometric analysis

The aim of this study was to provide a bibliometric analysis and mapping of existing scientific papers, focusing on microalgae cultivation coupled with biomass production and bioremediation of wastewater from agricultural industries, including cassava, dairy, and coffee. Using the Web of Science (WoS) database for the period 1996-2021, a search was performed using a keyword strategy, aiming at segregating the papers in groups. For the first search step, the keywords "wastewater treatment", AND "microalgae", AND "cassava" OR "dairy" OR "coffee" were used, resulting in 59 papers. For the second step, the keywords "wastewater treatment" AND "biomass productivity" AND "microalgae" AND "economic viability" OR "environmental impacts" were used, which resulted in 34 articles. In these papers, keywords such as "carbon dioxide biofixation" and "removal of nutrients by the production of biomass by microalgae" followed by "environmental and economic impacts" were highlighted. Some of these papers presented an analysis of the economic feasibility of the process, which reveal the state-of-the-art setup required to make the cultivation of microalgae economically viable. Researches focusing on the efficiency of microalgae biomass harvesting are needed to improve the integration of microalgae production in industrial eco-parks using wastewater to achieve the global goal of bioremediation and clean alternatives for renewable energy generation.

A fungal immobilization technique for efficient harvesting of oleaginous microalgae: Key parameter optimization, mechanism exploration and spent medium recycling

To confront with energy crisis, microalgae as the promising feedstock have a great potential in exploring renewable energy field, whereas the high costs related to medium preparation and biomass harvesting are the main bottleneck to hinder the development on a large scale. Though cultivation of filamentous fungi for microalgae harvesting is an efficient, sustainable and emerging method, and the studies on specific mechanisms and spent medium recycling for efficiency improvement as well as resource saving through a co-pelletization mode are urgently needed. Hence, in this study, the harvesting process of autotrophic microalgae Chlorella vulgaris by pre-cultured Aspergillus oryzae pellets was investigated systematically. The highest efficiency (99.23%) was obtained within 5 h under the optimized conditions of 30 °C, 130 rpm and fungi:algae ratio of 1:1 on a dry weight basis without demand for pH adjustment (initial value on 9.68). Charge neutralization was not the main mechanisms involved in fungi-algae aggregations, and the functional group changes on cell surfaces as well as secreted metabolites in medium could be mainly responsible for inducing the bioflocculation process. After harvesting, separated water could also effectively support microalgae re-growth. The biomass concentration in medium with 50% recycling was higher than that in fresh medium, while lipid content was increased from 24.37% to 33.97% in fully recycled medium. These results indicated that the pellet-assisted mode for algal harvesting is a promising way to promote biofuel production and resource recycling.

Co-culture of fungi-microalgae consortium for wastewater treatment: A review

The treatment of wastewater by microalgae has been studied and proved to be effective through previous studies. Due to the small size of microalgae, how to efficiently harvest microalgae from wastewater is a crucial factor restricting the development of algal technologies. Fungi-assisted microalgae bio-flocculation for microalgae harvesting and wastewater treatment simultaneously, which was overlooked previously, has attracted increasing attention in the recent decade due to its low cost and high efficiency. This review found that fungal hyphae and microalgae can stick together due to electrostatic neutralization, surface protein interaction, and exopolysaccharide adhesion in the co-culture process, realizing co-pelletization of microalgae and fungi, which is conducive to microalgae harvesting. Besides, the combination of fungi and microalgae has a complementary effect on pollutant removal from wastewaters. The co-culture of fungi-microalgae has excellent development prospects with both environmental and economic benefits, and it is expected to be applied on an industrial scale.

Microalgal bio-flocculation: present scenario and prospects for commercialization

The need for sustainable production of renewable biofuel has been a global concern in the recent times. Overcoming the tailbacks of the first- and second-generation biofuels, third-generation biofuel using microalgae as feedstock has emerged as a plausible alternative. It has an added advantage of preventing any greenhouse gas (GHG) emissions with simultaneous carbon dioxide sequestration. Dewatering of microalgal culture is one of the many concerns regarding industrial-scale biofuel production. The small size of microalgae and dilute nature of its growth cultures creates huge operational cost during biomass separation, limiting economic feasibility of algae-based fuels. Considering the recovery efficiency, operation economics, technological feasibility and cost-effectiveness, bio-flocculation is a promising method of harvesting. Moreover, advantage of bio-flocculation over other conventional methods is that it does not incur the addition of any external chemical flocculants. This article reviews the current status of bio-flocculation technique for harvesting microalgae at industrial scale. The various microbial strains that can be prospective bioflocculants have been reviewed along with its application and advantages over chemical flocculants. Also, this article proposes that the primary focus of an appropriate harvesting technique should depend on the final utilization of the harvested biomass. This review article attempts to bring forth the beneficial aspects of microbial aided microalgal harvesting with a special attention on genetically modified self-flocculation microalgae.

Symbiotic Associations: Key Factors That Determine Physiology and Lipid Accumulation in Oleaginous Microorganisms

Symbiosis naturally provides an opportunity for microorganisms to live together by mutual or one-way benefit. In symbiotic relationships, the microorganisms usually overcome the limitations of being free-living. Understanding the symbiotic relationships of oleaginous microorganisms provides potential route for the sustainable production of microbial-based alternative fuels. So far, several studies have been conducted in oleaginous microorganisms for the production of alternative fuels. However, some oleaginous microorganisms require high quantity of nutrients for their growth, and high level of energy and chemicals for harvest and separation of lipid bodies. Symbiotic associations can successfully be applied to address these issues. Of symbiotic associations, lichens and selective species of oleaginous endosymbiotic mucoromycotina have received substantial interest as better models to study the evolutionary relationships as well as single-cell oil production. Construction of artificial lichen system composed of cyanobacteria and oleaginous yeast has been achieved for sustainable production of lipids with minimum energy demand. Recently, endosymbiotic mucoromycotina species have been recognized as potential sources for biofuels. Studies found that endohyphal bacterium influences lipid profiling in endosymbiotic mucoromycotina species. Studies on the genetic factors related to oleaginous characteristics of endosymbiotic mucoromycotina species are scarce. In this regard, this review summarizes the different forms of symbiotic associations of oleaginous microorganisms and how symbiotic relationships are impacting the lipid formation in microorganisms. Further, the review also highlights the importance of evolutionary relationships and benefits of co-culturing (artificial symbiosis) approaches for sustainable production of biofuels.

Omics approaches for microalgal applications: Prospects and challenges

In recent impetus of phycological research, microalgae have emerged as a potential candidate for various arena of application-driven research. Omics-based tactics are used for disentangling the regulation and network integration for biosynthesis/degradation of metabolic precursors, intermediates, end products, and identifying the networks that regulate the metabolic flux. Multi-omics coupled with data analytics have facilitated understanding of biological processes and allow ample access to diverse metabolic pathways utilized for genetic manipulations making microalgal factories more efficient. The present review discusses state-of-art "Algomics" and the prospect of microalgae and their role in symbiotic association by using omics approaches including genomics, transcriptomics, proteomics and metabolomics. Microalgal based uni- and multi-omics approaches are critically analyzed in wastewater treatment, metal toxicity and remediation, biofuel production, and therapeutics to provide an imminent outlook for an array of environmentally sustainable and economically viable microalgal applications.

Potential role of N-acetyl glucosamine in Aspergillus fumigatus-assisted Chlorella pyrenoidosa harvesting

BACKGROUND

Algal harvesting is a major cost which increases biofuel production cost. Algal biofuels are widely studied as third-generation biofuel. However, they are yet not viable because of its high production cost which is majorly contributed by energy-intensive biomass harvesting techniques. Biological harvesting method like fungal-assisted harvesting of microalgae is highly efficient but poses a challenge due to its slow kinetics and poorly understood mechanism.

RESULTS

In this study, we investigate Aspergillus fumigatus-Chlorella pyrenoidosa attachment resulting in a harvesting efficiency of 90% within 4 h. To pinpoint the role of extracellular metabolite, several experiments were performed by eliminating the C. pyrenoidosa or A. fumigatus spent medium from the C. pyrenoidosa-A. fumigatus mixture. In the absence of A. fumigatus spent medium, the harvesting efficiency dropped to 20% compared to > 90% in the control, which was regained after addition of A. fumigatus spent medium. Different treatments of A. fumigatus spent medium showed drop in harvesting efficiency after periodate treatment (≤ 20%) and methanol-chloroform extraction (≤ 20%), indicating the role of sugar-like moiety. HR-LC-MS (high-resolution liquid chromatography-mass spectrometry) results confirmed the presence of N-acetyl-d-glucosamine (GlcNAc) and glucose in the spent medium. When GlcNAc was used as a replacement of A. fumigatus spent medium for harvesting studies, the harvesting process was significantly faster (p < 0.05) till 4 h compared to that with glucose. Further experiments indicated that metabolically active A. fumigatus produced GlcNAc from glucose. Concanavalin A staining and FTIR (Fourier transform infrared spectroscopy) analysis of A. fumigatus spent medium- as well as GlcNAc-incubated C. pyrenoidosa cells suggested the presence of GlcNAc on its cell surface indicated by dark red dots and GlcNAc-specific peaks, while no such characteristic dots or peaks were observed in normal C. pyrenoidosa cells. HR-TEM (High-resolution Transmission electron microscopy) showed the formation of serrated edges on the C. pyrenoidosa cell surface after treatment with A. fumigatus spent medium or GlcNAc, while Atomic force microscopy (AFM) showed an increase in roughness of the C. pyrenoidosa cells surface upon incubation with A. fumigatus spent medium.

CONCLUSIONS

Results strongly suggest that GlcNAc present in A. fumigatus spent medium induces surface changes in C. pyrenoidosa cells that mediate the attachment to A. fumigatus hyphae. Thus, this study provides a better understanding of the A. fumigatus-assisted C. pyrenoidosa harvesting process.

A rapid method for harvesting and immobilization of oleaginous microalgae using pellet-forming filamentous fungi and the application in phytoremediation of secondary effluent

A rapid method for harvesting and immobilization of oleaginous microalgae using pellet-forming filamentous fungi was developed. The suitable conditions for pellet formation by filamentous fungi were determined. Among the strains tested, Trichoderma reesei QM 9414 showed superior pellet forming ability. Its pellets were used to harvest oleaginous microalga Scenedesmus sp. With increasing volume ratio of fungal pellets to microalgae culture up to 1:2, >94% of microalgal cells were rapidly harvested within 10 min. The ratio of fungal pellets could manipulate both harvesting time and initial concentration of microalgal cells in the pellets. The microalgae-fungal pellets were successfully used as immobilized cells for effective phytoremediation of secondary effluent from seafood processing plants under nonsterile condition. The chemical oxygen demand, total nitrogen, and total phosphorus removal were >74%, >44%, and >93%, respectively. The scanning electron microscopy showed that the microalgal cells were not only entrapped in the pellets but also got attached to the fungal hyphae with sticky exopolysaccharides, possibly secreted by the fungi. The extracted lipids from the pellets were mainly composed of C16-C18 (>83%) with their suitability as biodiesel feedstocks. This study has shown the promising strategy to rapidly harvest and immobilize microalgal cells and the possible application in phytoremediation of industrial effluent.

Pretreated animal and human waste as a substantial nutrient source for cultivation of microalgae for biodiesel production

The use of human and animal wastes for fertilization of aquaculture ponds has been practiced for thousands of years. In the present work, we have used the excreta (human urine, poultry waste, cow dung, and urine) as a nutrient source for the cultivation of Chlorella singularis, Micractinium pusillum, and Chlorella sorokiniana strains of microalgae. Different solid wastes were treated with 60 mM H₂SO₄ for the extraction of nutrients. After treatment, the supernatant of different solid wastes and liquid waste were diluted 5, 10, 15, and 20% to be used as a media for the cultivation of microalgae. Chlorella sorokiniana was able to grow in all concentration of excreta media. The maximum growth rate 140 ± 3.1 mg/L/day and lipid production (45.5 ± 2.3 mg/L/day) was obtained in 20% poultry. Among the different excreta media used for cultivation of microalgae, poultry media displayed the best results and thus, should be used for large scale cultivation of microalgae.

Enhancing oil production and harvest by combining the marine alga Nannochloropsis oceanica and the oleaginous fungus Mortierella elongata

BACKGROUND

Although microalgal biofuels have potential advantages over conventional fossil fuels, high production costs limit their application in the market. We developed bio-flocculation and incubation methods for the marine alga, Nannochloropsis oceanica CCMP1779, and the oleaginous fungus, Mortierella elongata AG77, resulting in increased oil productivity.

RESULTS

By growing separately and then combining the cells, the M. elongata mycelium could efficiently capture N. oceanica due to an intricate cellular interaction between the two species leading to bio-flocculation. Use of a high-salt culture medium induced accumulation of triacylglycerol (TAG) and enhanced the contents of polyunsaturated fatty acids (PUFAs) including arachidonic acid and docosahexaenoic acid in M. elongata. To increase TAG productivity in the alga, we developed an effective, reduced nitrogen-supply regime based on ammonium in environmental photobioreactors. Under optimized conditions, N. oceanica produced high levels of TAG that could be indirectly monitored by following chlorophyll content. Combining N. oceanica and M. elongata to initiate bio-flocculation yielded high levels of TAG and total fatty acids, with ~ 15 and 22% of total dry weight (DW), respectively, as well as high levels of PUFAs. Genetic engineering of N. oceanica for higher TAG content in nutrient-replete medium was accomplished by overexpressing DGTT5, a gene encoding the type II acyl-CoA:diacylglycerol acyltransferase 5. Combined with bio-flocculation, this approach led to increased production of TAG under nutrient-replete conditions (~ 10% of DW) compared to the wild type (~ 6% of DW).

CONCLUSIONS

The combined use of M. elongata and N. oceanica with available genomes and genetic engineering tools for both species opens up new avenues to improve biofuel productivity and allows for the engineering of polyunsaturated fatty acids.

Applications of microalgal biofilms for wastewater treatment and bioenergy production

BACKGROUND

Microalgae have shown clear advantages for the production of biofuels compared with energy crops. Apart from their high growth rates and substantial lipid/triacylglycerol yields, microalgae can grow in wastewaters (animal, municipal and mining wastewaters) efficiently removing their primary nutrients (C, N, and P), heavy metals and micropollutants, and they do not compete with crops for arable lands. However, fundamental barriers to the industrial application of microalgae for biofuel production still include high costs of removing the algae from the water and the water from the algae which can account for up to 30-40% of the total cost of biodiesel production. Algal biofilms are becoming increasingly popular as a strategy for the concentration of microalgae, making harvesting/dewatering easier and cheaper.

RESULTS

We have isolated and characterized a number of natural microalgal biofilms from freshwater, saline lakes and marine habitats. Structurally, these biofilms represent complex consortia of unicellular and multicellular, photosynthetic and heterotrophic inhabitants, such as cyanobacteria, microalgae, diatoms, bacteria, and fungi. Biofilm #52 was used as feedstock for bioenergy production. Dark fermentation of its biomass by Enterobacter cloacae DT-1 led to the production of 2.4 mol of H₂/mol of reduced sugar. The levels and compositions of saturated, monosaturated and polyunsaturated fatty acids in Biofilm #52 were target-wise modified through the promotion of the growth of selected individual photosynthetic inhabitants. Photosynthetic components isolated from different biofilms were used for tailoring of novel biofilms designed for (i) treatment of specific types of wastewaters, such as reverse osmosis concentrate, (ii) compositions of total fatty acids with a new degree of unsaturation and (iii) bio-flocculation and concentration of commercial microalgal cells. Treatment of different types of wastewaters with biofilms showed a reduction in the concentrations of key nutrients, such as phosphates, ammonia, nitrates, selenium and heavy metals.

CONCLUSIONS

This multidisciplinary study showed the new potential of natural biofilms, their individual photosynthetic inhabitants and assembled new algal/cyanobacterial biofilms as the next generation of bioenergy feedstocks which can grow using wastewaters as a cheap source of key nutrients.