Synergistic effects of oleaginous yeast Rhodotorula glutinis and microalga Chlorella vulgaris for enhancement of biomass and lipid yields

A fast microbial nitrogen-assimilation technology enhances nitrogen migration and single-cell-protein production in high-ammonia piggery wastewater

Conventional methods, such as freshwater dilution and ammonia stripping, have been widely employed for microalgae-based piggery wastewater (PW) treatment, but they cause high freshwater consumption and intensive ammonia loss, respectively. This present work developed a novel fast microbial nitrogen-assimilation technology by integrating nitrogen starvation, zeolite-based adsorption, pH control, and co-culture of microalgae-yeast for the PW treatment. Among them, the nitrogen starvation accelerated the nitrogen removal and shortened the treatment period, but it could not improve the tolerance level of microalgal cells to ammonia toxicity based on oxidative stress. Therefore, zeolite was added to reduce the initial total ammonia-nitrogen concentration to around 300 mg/L by ammonia adsorption. Slowly releasing ammonia at the later phase maintained the total ammonia-nitrogen concentration in the PW. However, the pH increase could cause lots of ammonia loss air and pollution and inhibit the desorption of ammonia from zeolite and the growth and metabolism of microalgae during the microalgae cultivation. Thus, the highest biomass yield (3.25 g/L) and nitrogen recovery ratio (40.31%) were achieved when the pH of PW was controlled at 6.0. After combining the co-cultivation of microalgae-yeast, the carbon-nitrogen co-assimilation and the alleviation of pH fluctuation further enhanced the nutrient removal and nitrogen migration to high-protein biomass. Consequently, the fast microbial nitrogen-assimilation technology can help update the industrial system for high-ammonia wastewater treatment by improving the treatment and nitrogen recovery rates.

Engineering oleaginous red yeasts as versatile chassis for the production of oleochemicals and valuable compounds: Current advances and perspectives

Enabling the transition towards a future circular bioeconomy based on industrial biomanufacturing necessitates the development of efficient and versatile microbial platforms for sustainable chemical and fuel production. Recently, there has been growing interest in engineering non-model microbes as superior biomanufacturing platforms due to their broad substrate range and high resistance to stress conditions. Among these non-conventional microbes, red yeasts belonging to the genus Rhodotorula have emerged as promising industrial chassis for the production of specialty chemicals such as oleochemicals, organic acids, fatty acid derivatives, terpenoids, and other valuable compounds. Advancements in genetic and metabolic engineering techniques, coupled with systems biology analysis, have significantly enhanced the production capacity of red yeasts. These developments have also expanded the range of substrates and products that can be utilized or synthesized by these yeast species. This review comprehensively examines the current efforts and recent progress made in red yeast research. It encompasses the exploration of available substrates, systems analysis using multi-omics data, establishment of genome-scale models, development of efficient molecular tools, identification of genetic elements, and engineering approaches for the production of various industrially relevant bioproducts. Furthermore, strategies to improve substrate conversion and product formation both with systematic and synthetic biology approaches are discussed, along with future directions and perspectives in improving red yeasts as more versatile biotechnological chassis in contributing to a circular bioeconomy. The review aims to provide insights and directions for further research in this rapidly evolving field. Ultimately, harnessing the capabilities of red yeasts will play a crucial role in paving the way towards next-generation sustainable bioeconomy.

Lipid Production of Schizochytrium sp. HBW10 Isolated from Coastal Waters of Northern China Cultivated in Food Waste Hydrolysate

Marine oleaginous thraustochytrids have attracted increasing attention for their great potential in producing high-value active metabolites using various industrial and agricultural waste. Food waste containing abundant nutrients is considered as an excellent feedstock for microbial fermentation. In this study, a thraustochytrid strain Schizochytrium sp. HBW10 was isolated from a water column in Bohai Bay in Northern China for the first time. Further lipid production characteristics of S. sp. HBW10 were investigated utilizing sulfuric acid hydrolysate of food waste (FWH) from two different restaurants (FWH1 and FWH2) with the initial pH value adjusted by NaOH or NaHCO3. Results showed that the highest concentration of total fatty acids (TFAs) was observed in FWH2 medium with the 50% content level on the fifth day, reaching up to 0.34 g/L. A higher initial pH promoted the growth and saturated fatty acid (SFA) accumulation of S. sp. HBW10, achieving nearly 100% of the sum of saturated and monounsaturated fatty acids (SMUFAs) in TFAs with initial pH7 and pH8 in FWH1 medium. This work demonstrates a possible way for lipid production by thraustochytrids using food waste hydrolysate with a higher initial pH (pH7~pH8) adjusted by NaHCO3.

Combined zeolite-based ammonia slow-release and algae-yeast consortia to treat piggery wastewater: Improved nitrogen and carbon migration

Integration of zeolite-based ammonia adsorption and algae-yeast consortia was developed to remediate piggery wastewater (PW) containing high concentrations of total ammonia nitrogen (TAN) and total organic carbon (TOC). After optimizing the conditions of ammonia adsorption in the PW. Zeolite addition mitigated ammonia toxicity, allowing zeolites to gradually release ammonia while effectively attenuating algal oxidative stress caused by high TAN concentration. Coupling zeolite-based adsorption and yeast co-incubation further increased TOC degradation and available C/N ratio, thus improving biomass (4.51 g/L), oil yield (2.11 g/L), and nutrient removal (84.18%-99.14%). The integrated microalgae-based PW treatment exhibited higher carbon migration into biomass (46.14%) and reduced treatment costs than conventional approaches. Simultaneously, the lowest carbon migration to wastewater also meant the smallest carbon emission into water bodies. These findings demonstrate that this novel strategy can remove nutrients in raw PW effectively and produce high oil-rich biomass in a sustainable and environmentally-friendly manner.

Microalgal co-cultivation -recent methods, trends in omic-studies, applications, and future challenges

The burgeoning human population has resulted in an augmented demand for raw materials and energy sources, which in turn has led to a deleterious environmental impact marked by elevated greenhouse gas (GHG) emissions, acidification of water bodies, and escalating global temperatures. Therefore, it is imperative that modern society develop sustainable technologies to avert future environmental degradation and generate alternative bioproduct-producing technologies. A promising approach to tackling this challenge involves utilizing natural microbial consortia or designing synthetic communities of microorganisms as a foundation to develop diverse and sustainable applications for bioproduct production, wastewater treatment, GHG emission reduction, energy crisis alleviation, and soil fertility enhancement. Microalgae, which are photosynthetic microorganisms that inhabit aquatic environments and exhibit a high capacity for CO2 fixation, are particularly appealing in this context. They can convert light energy and atmospheric CO2 or industrial flue gases into valuable biomass and organic chemicals, thereby contributing to GHG emission reduction. To date, most microalgae cultivation studies have focused on monoculture systems. However, maintaining a microalgae monoculture system can be challenging due to contamination by other microorganisms (e.g., yeasts, fungi, bacteria, and other microalgae species), which can lead to low productivity, culture collapse, and low-quality biomass. Co-culture systems, which produce robust microorganism consortia or communities, present a compelling strategy for addressing contamination problems. In recent years, research and development of innovative co-cultivation techniques have substantially increased. Nevertheless, many microalgae co-culturing technologies remain in the developmental phase and have yet to be scaled and commercialized. Accordingly, this review presents a thorough literature review of research conducted in the last few decades, exploring the advantages and disadvantages of microalgae co-cultivation systems that involve microalgae-bacteria, microalgae-fungi, and microalgae-microalgae/algae systems. The manuscript also addresses diverse uses of co-culture systems, and growing methods, and includes one of the most exciting research areas in co-culturing systems, which are omic studies that elucidate different interaction mechanisms among microbial communities. Finally, the manuscript discusses the economic viability, future challenges, and prospects of microalgal co-cultivation methods.

Industrially Important Fungal Carotenoids: Advancements in Biotechnological Production and Extraction

Carotenoids are lipid-soluble compounds that are present in nature, including plants and microorganisms such as fungi, certain bacteria, and algae. In fungi, they are widely present in almost all taxonomic classifications. Fungal carotenoids have gained special attention due to their biochemistry and the genetics of their synthetic pathway. The antioxidant potential of carotenoids may help fungi survive longer in their natural environment. Carotenoids may be produced in greater quantities using biotechnological methods than by chemical synthesis or plant extraction. The initial focus of this review is on industrially important carotenoids in the most advanced fungal and yeast strains, with a brief description of their taxonomic classification. Biotechnology has long been regarded as the most suitable alternative way of producing natural pigment from microbes due to their immense capacity to accumulate these pigments. So, this review mainly presents the recent progress in the genetic modification of native and non-native producers to modify the carotenoid biosynthetic pathway for enhanced carotenoid production, as well as factors affecting carotenoid biosynthesis in fungal strains and yeast, and proposes various extraction methods to obtain high yields of carotenoids in an attempt to find suitable greener extraction methods. Finally, a brief description of the challenges regarding the commercialization of these fungal carotenoids and the solution is also given.

Artificial microbial consortia for bioproduction processes

The application of artificial microbial consortia for biotechnological production processes is an emerging field in research as it offers great potential for the improvement of established as well as the development of novel processes. In this review, we summarize recent highlights in the usage of various microbial consortia for the production of, for example, platform chemicals, biofuels, or pharmaceutical compounds. It aims to demonstrate the great potential of co-cultures by employing different organisms and interaction mechanisms and exploiting their respective advantages. Bacteria and yeasts often offer a broad spectrum of possible products, fungi enable the utilization of complex lignocellulosic substrates via enzyme secretion and hydrolysis, and microalgae can feature their abilities to fixate CO2 through photosynthesis for other organisms as well as to form lipids as potential fuelstocks. However, the complexity of interactions between microbes require methods for observing population dynamics within the process and modern approaches such as modeling or automation for process development. After shortly discussing these interaction mechanisms, we aim to present a broad variety of successfully established co-culture processes to display the potential of artificial microbial consortia for the production of biotechnological products.

Enhanced biomass and lipid production by light exposure with mixed culture of Rhodotorula glutinis and Chlorella vulgaris using acetate as sole carbon source

Microbial biomass and lipid production with mixed-culture of Rhodotorula glutinis and Chlorella vulgaris using acetate as sole carbon source was investigated. Synergistic effect of mixed-culture using 20 g/L acetate significantly promoted cell growth and acetate utilization efficiency. Increasing the proportion of algae in co-culture was beneficial for biomass and lipid accumulation and the optimal ratio of yeast/algae was 1:2. Light exposure further enhanced biomass and lipid titer with 6.9 g/L biomass and 2.6 g/L lipid (38.3 % lipid content) obtained in a 5L bioreactor. The results of lipid classes and fatty acid profiles moreover indicated that more neutral lipids and linolenic acid were synthesized in mixed-culture under light exposure condition, suggesting the great potential in applications of biofuels production. This study provided new insight and strategy for economical microbial biomass and lipid production by light-exposed mixed-culture using inexpensive acetate as carbon source.

Screening of symbiotic Streptomyces spp. and optimization of microalgal growth in a microalgae-actinomycetes co-culture system

Microalgal biodiesel as a substitute for fossil energy has attracted extensive attention. However, the high cost of microalgae cultivation limits the industrial production of microalgal biodiesel. The co-culture system may offer a means to increase microalgae's biomass production. In this study, Streptomyces strains were selected to construct and optimize co-culture systems with Monoraphidium sp. HDMA-11 and the algal cell biomass, lipid content, phycocyanin content, starch content, and fatty acid composition were determined. The results showed that Streptomyces nojiriensis significantly promoted Monoraphidium sp. HDMA-11 growth and a co-culture system were established. Orthogonal experiments showed that the Monoraphidium sp. HDMA-11 biomass was further increased when the initial culture pH was 7.5, the inoculation time of Streptomyces strain supernatants was 36 h, the volume ratio of microalgal actinomycetes was 1:1, and no additional acetic acid was added. Under these conditions, compared with monocultured Monoraphidium sp. HDMA-11, the cell biomass and lipid productivity of the co-culture system increased by 525.8 and 155.1%, respectively. These results suggest that S. nojiriensis supernatant potentially enhances microalgae biomass and may represent a new method to improve microalgae growth.

Multiscale engineering of microbial cell factories: A step forward towards sustainable natural products industry

Microbial cell factories (bacteria and fungi) are the leading producers of beneficial natural products such as lycopene, carotene, herbal medicine, and biodiesel etc. These microorganisms are considered efficient due to their effective bioprocessing strategy (monoculture- and consortial-based approach) under distinct processing conditions. Meanwhile, the advancement in genetic and process optimization techniques leads to enhanced biosynthesis of natural products that are known functional ingredients with numerous applications in the food, cosmetic and medical industries. Natural consortia and monoculture thrive in nature in a small proportion, such as wastewater, food products, and soils. In similitude to natural consortia, it is possible to engineer artificial microbial consortia and program their behaviours via synthetic biology tools. Therefore, this review summarizes the optimization of genetic and physicochemical parameters of the microbial system for improved production of natural products. Also, this review presents a brief history of natural consortium and describes the functional properties of monocultures. This review focuses on synthetic biology tools that enable new approaches to design synthetic consortia; and highlights the syntropic interactions that determine the performance and stability of synthetic consortia. In particular, the effect of processing conditions and advanced genetic techniques to improve the productibility of both monoculture and consortial based systems have been greatly emphasized. In this context, possible strategies are also discussed to give an insight into microbial engineering for improved production of natural products in the future. In summary, it is concluded that the coupling of genomic modifications with optimum physicochemical factors would be promising for producing a robust microbial cell factory that shall contribute to the increased production of natural products.

Use of Fungal Mycelium as Biosupport in the Formation of Lichen-Like Structure: Recovery of Algal Grown in Sugarcane Molasses for Lipid Accumulation and Balanced Fatty Acid Profile

In this study, a lichen-like structure was obtained through the production of a unique biomass, formed by algae cells of Scenedesmus obliquus adhering to the mycelium of filamentous fungal Mucor circinelloides. This structure was composed in two steps; in the first one, microalgal cells and spores were incubated separately, and in the second one, after 72 h of growth, isolated, mature mycelium was harvested and added to cell culture. For spores’ incubation, a culture medium containing only 2 g·L⁻¹ of glucose and minerals was used. This culture medium, with low sugar content, provided a fungal biomass to the anchorage of microalgae cells. WC medium was used without and with sugarcane molasses supplementation for microalgae cells’ incubation. The lichen-type structure that was formed resulted in 99.7% efficiency in the recovery of microalgae cells and in up to 80% efficiency in the recovery of algae biomass in the lichen biomass composition. In addition, the resulting consortium attained a satisfactory lipid accumulation value (38.2 wt%) with a balanced fatty acid composition of 52.7% saturated plus monounsaturated fatty acids and 47.4% polyunsaturated fatty acids. Since fungal species are easy to recover, unlike microalgae, the lichen-like structure produced indicates an efficient low-cost bioremediation and harvesting alternative; in addition, it provides an oleaginous biomass for various industrial applications.

Rhodosporidium toruloides and Tetradesmus obliquus Populations Dynamics in Symbiotic Cultures, Developed in Brewery Wastewater, for Lipid Production

In this work, primary brewery wastewater (PBWW) and secondary brewery wastewater (SBWW) separately, or mixed at the ratios of 1:1 (PBWW:SBWW) and 1:7 (PBWW:SBWW), with or without supplementation with sugarcane molasses (SCM), were used as culture media for lipid production by a mixed culture of the oleaginous yeast Rhodosporidium toruloides NCYC 921 and the microalgae Tetradesmus obliquus (ACOI 204/07). Flow cytometry was used to understand the dynamics of the two micro-organisms during the mixed cultures evolution, as well as to evaluate the physiological states of each micro-organism, in order to assess the impact of the different brewery effluent media composition on the microbial consortium performance. Both brewery wastewaters (primary and secondary) without supplementation did not allow R. toruloides heterotrophic growth. Nevertheless, all brewery wastewater media, with and without SCM supplementation, allowed the microalgae growth, although the yeast was the dominant population. The maximum total biomass concentration of 2.17 g L^-1 was achieved in the PBWW mixed cultivation with 10 g L^-1 of SCM. The maximum lipid content (14.86% (w/w DCW)) was obtained for the mixed culture developed on SBWW supplemented with 10 g L^-1 of SCM. This work demonstrated the potential of using brewery wastewater supplemented with SCM as a low-cost culture medium to grow R. toruloides and T. obliquus in a mixed culture for brewery wastewater treatment with concomitant lipid production.

A review on co-culturing of microalgae: A greener strategy towards sustainable biofuels production

There is a growing global recognition that microalgae-based biofuel are environment-friendly and economically feasible options because they incur several advantages over traditional fossil fuels. Also, the microalgae can be manipulated for extraction of value-added compounds such as lipids (triacylglycerols), carbohydrates, polyunsaturated fatty acids, proteins, pigments, antioxidants, various antimicrobial compounds, etc. Recently, there is an increasing focus on the co-cultivation practices of microalgae with other microorganisms to enhance biomass and lipid productivity. In a co-cultivation strategy, microalgae grow symbiotically with other heterotrophic microbes such as bacteria, yeast, fungi, and other algae/microalgae. They exchange nutrients and metabolites; this helps to increase the productivity, therefore facilitating the commercialization of microalgal-based fuel. Co-cultivation also facilitates biomass harvesting and waste valorization, thereby help to build an algal biorefinery platform for bioenergy production along with multivariate high value bioproducts and simultaneous waste bioremediation. This article comprehensively reviews various microalgae cultivation practices utilizing co-culture approaches with other algae, fungi, bacteria, and yeast. The review mainly focuses on the impact of several binary culture strategies on biomass and lipid yield. The advantages and challenges associated with the procedure along with their respective cultivation modes have also been presented and discussed in detail.

Carotenoids from fungi and microalgae: A review on their recent production, extraction, and developments

The demand for carotenoids from natural sources obtained by biological extraction methods is increasing with the development of biotechnology and the continued awareness of food safety. Natural plant-derived carotenoids have a relatively high production cost and are affected by the season, while microbial-derived carotenoids are favored due to their natural, high-efficiency, low production cost, and ease of industrialization. This article reviewed the following aspects of natural carotenoids derived from microorganisms: (1) the structures and properties of main carotenoids; (2) fungal and microalgal sources of the main carotenoids; (3) influencing factors and modes of improvement for carotenoids production; (4) efficient extraction methods for carotenoids; and (5) the commercial value of carotenoids. This review provided a reference and guidance for the development of natural carotenoids derived from microorganisms.

Optogenetic strategies for the control of gene expression in yeasts

Optogenetics involves the use of light to control cellular functions and has become increasingly popular in various areas of research, especially in the precise control of gene expression. While this technology is already well established in neurobiology and basic research, its use in bioprocess development is still emerging. Some optogenetic switches have been implemented in yeasts for different purposes, taking advantage of a wide repertoire of biological parts and relatively easy genetic manipulation. In this review, we cover the current strategies used for the construction of yeast strains to be used in optogenetically controlled protein or metabolite production, as well as the operational aspects to be considered for the scale-up of this type of process. Finally, we discuss the main applications of optogenetic switches in yeast systems and highlight the main advantages and challenges of bioprocess development considering future directions for this field.

Co-culturing microbial consortia: approaches for applications in biomanufacturing and bioprocessing

The application of microbial co-cultures is now recognized in the fields of biotechnology, ecology, and medicine. Understanding the biological interactions that govern the association of microorganisms would shape the way in which artificial/synthetic co-cultures or consortia are developed. The ability to accurately predict and control cell-to-cell interactions fully would be a significant enabler in synthetic biology. Co-culturing method development holds the key to strategically engineer environments in which the co-cultured microorganism can be monitored. Various approaches have been employed which aim to emulate the natural environment and gain access to the untapped natural resources emerging from cross-talk between partners. Amongst these methods are the use of a communal liquid medium for growth, use of a solid-liquid interface, membrane separation, spatial separation, and use of microfluidics systems. Maximizing the information content of interactions monitored is one of the major challenges that needs to be addressed by these designs. This review critically evaluates the significance and drawbacks of the co-culturing approaches used to this day in biotechnological applications, relevant to biomanufacturing. It is recommended that experimental results for a co-cultured species should be validated with different co-culture approaches due to variations in interactions that could exist as a result of the culturing method selected.

Study on the isoprene-producing co-culture system of Synechococcus elongates-Escherichia coli through omics analysis

BACKGROUND

The majority of microbial fermentations are currently performed in the batch or fed-batch manner with the high process complexity and huge water consumption. The continuous microbial production can contribute to the green sustainable development of the fermentation industry. The co-culture systems of photo-autotrophic and heterotrophic species can play important roles in establishing the continuous fermentation mode for the bio-based chemicals production.

RESULTS

In the present paper, the co-culture system of Synechococcus elongates-Escherichia coli was established and put into operation stably for isoprene production. Compared with the axenic culture, the fermentation period of time was extended from 100 to 400 h in the co-culture and the isoprene production was increased to eightfold. For in depth understanding this novel system, the differential omics profiles were analyzed. The responses of BL21(DE3) to S. elongatus PCC 7942 were triggered by the oxidative pressure through the Fenton reaction and all these changes were linked with one another at different spatial and temporal scales. The oxidative stress mitigation pathways might contribute to the long-lasting fermentation process. The performance of this co-culture system can be further improved according to the fundamental rules discovered by the omics analysis.

CONCLUSIONS

The isoprene-producing co-culture system of S. elongates-E. coli was established and then analyzed by the omics methods. This study on the co-culture system of the model S. elongates-E. coli is of significance to reveal the common interactions between photo-autotrophic and heterotrophic species without natural symbiotic relation, which could provide the scientific basis for rational design of microbial community.

Predicting Nash equilibria for microbial metabolic interactions

MOTIVATION

Microbial metabolic interactions impact ecosystems, human health and biotechnology profoundly. However, their determination remains elusive, invoking an urgent need for predictive models seamlessly integrating metabolism with evolutionary principles that shape community interactions.

RESULTS

Inspired by the evolutionary game theory, we formulated a bi-level optimization framework termed NECom for which any feasible solutions are Nash equilibria of microbial community metabolic models with/without an outer-level (community) objective function. Distinct from discrete matrix games, NECom models the continuous interdependent strategy space of metabolic fluxes. We showed that NECom successfully predicted several classical games in the context of metabolic interactions that were falsely or incompletely predicted by existing methods, including prisoner's dilemma, snowdrift and cooperation. The improved capability originates from the novel formulation to prevent 'forced altruism' hidden in previous static algorithms while allowing for sensing all potential metabolite exchanges to determine evolutionarily favorable interactions between members, a feature missing in dynamic methods. The results provided insights into why mutualism is favorable despite seemingly costly cross-feeding metabolites and demonstrated similarities and differences between games in the continuous metabolic flux space and matrix games. NECom was then applied to a reported algae-yeast co-culture system that shares typical cross-feeding features of lichen, a model system of mutualism. 488 growth conditions corresponding to 3,221 experimental data points were simulated. Without training any parameters using the data, NECom is more predictive of species' growth rates given uptake rates compared with flux balance analysis with an overall 63.5% and 81.7% reduction in root-mean-square error for the two species.

AVAILABILITY

Simulation code and data are available at https://github.com/Jingyi-Cai/NECom.git.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Optimal integration of microalgae production with photovoltaic panels: environmental impacts and energy balance

BACKGROUND

Microalgae are 10 to 20 times more productive than the current agricultural biodiesel producing oleaginous crops. However, they require larger energy supplies, so that their environmental impacts remain uncertain, as illustrated by the contradictory results in the literature. Besides, solar radiation is often too high relative to the photosynthetic capacity of microalgae. This leads to photosaturation, photoinhibition, overheating and eventually induces mortality. Shadowing microalgae with solar panels would, therefore, be a promising solution for both increasing productivity during hotter periods and producing local electricity for the process. The main objective of this study is to measure, via LCA framework, the energy performance and environmental impact of microalgae biodiesel produced in a solar greenhouse, alternating optimal microalgae species and photovoltaic panel (PV) coverage. A mathematical model is simulated to investigate the microalgae productivity in raceways under meteorological conditions in Sophia Antipolis (south of France) at variable coverture percentages (0% to 90%) of CIGS solar panels on greenhouses constructed with low-emissivity (low-E) glass.

RESULTS

A trade-off must be met between electricity and biomass production, as a larger photovoltaic coverture would limit microalgae production. From an energetic point of view, the optimal configuration lies between 10 and 20% of PV coverage. Nevertheless, from an environmental point of view, the best option is 50% PV coverage. However, the difference between impact assessments obtained for 20% and 50% PV is negligible, while the NER is 48% higher for 20% PV than for 50% PV coverage. Hence, a 20% coverture of photovoltaic panels is the best scenario from an energetic and environmental point of view.

CONCLUSIONS

In comparison with the cultivation of microalgae without PV, the use of photovoltaic panels triggers a synergetic effect, sourcing local electricity and reducing climate change impacts. Considering an economic approach, low photovoltaic panel coverage would probably be more attractive. However, even with a 10% area of photovoltaic panels, the environmental footprint would already significantly decrease. It is expected that significant improvements in microalgae productivity or more advanced production processes should rapidly enhance these performances.

Improvement of Euglena gracilis Paramylon Production through a Cocultivation Strategy with the Indole-3-Acetic Acid-Producing Bacterium Vibrio natriegens

We investigated the putative effects on the growth and paramylon production of Euglena gracilis of cocultivation with Vibrio natriegensE. gracilis heterotrophically cocultivated with V. natriegens displayed significant increases in biomass productivity and paramylon content. In addition, the effects of the bacterial inoculum density and the timing of inoculation on the growth of E. gracilis were examined, to determine the optimal conditions for cocultivation. With the optimal deployment of V. natriegens, biomass productivity and paramylon content were increased by more than 20% and 35%, respectively, compared to those in axenic E. gracilis cultures. Interestingly, indole-3-acetic acid biosynthesized by V. natriegens was responsible for these enhancements of E. gracilis The morphology of cocultured E. gracilis cells was assessed. Paramylon granules extracted from the cocultivation were significantly larger than those from axenic culture. Our study showed that screening for appropriate bacteria and subsequent cocultivation with E. gracilis represented an effective way to enhance biomass and metabolite production.IMPORTANCEEuglena gracilis has attracted special interest due to its ability to excessively accumulate paramylon. Paramylon is a linear β-1,3-glucan polysaccharide that is the principal polymer for energy storage in E. gracilis The polysaccharide features high bioactive functionality in the immune system. This study explored a new method to enhance the production of paramylon by E. gracilis, through cocultivation with the indole-3-acetic acid-producing bacterium Vibrio natriegens The enhanced production was achieved indirectly with the phytohormone-producing bacteria, instead of direct application of the hormone. The knowledge obtained in this study furthers the understanding of the effects of V. natriegens on the growth and physiology of E. gracilis.

Comparative evaluation of different carbon sources supply on simultaneous production of lipid and carotene of Rhodotorula glutinis with irradiation and the assessment of key gene transcription

To investigate the feasibility of simultaneously enhancing lipid and carotene production by irradiation with different carbon sources, a strategy by controlling the carbon sources supply were selected to culture Rhodotorula glutinis under the irradiation condition. The results demonstrated that the irradiation indeed enhanced cell growth, lipid and carotene production with different carbon sources supply. Besides, the fatty acids profiling as revealed by more unsaturated fatty acids (mainly C16:1, C18:2 and C18:3) and less saturated fatty acids (C18:0, C22:0 and C24:0) were found during the process of irradiation. Compared with the control, the increase of the transcription levels in genes connected with substrates assimilation, lipid production and carotene accumulation were observed under the irradiation condition. The results suggest the possibility of using irradiation as an effective strategy to increase the production of both lipid and carotene with the controlled carbon sources supply.

Co-culturing of oleaginous microalgae and yeast: paradigm shift towards enhanced lipid productivity

Oleaginous microalgae and yeast are the two major propitious factories which are sustainable sources for biodiesel production, as they can accumulate high quantities of lipids inside their bodies. To date, various microalgal and yeast species have been exploited singly for biodiesel production. However, despite the ongoing efforts, their low lipid productivity and the high cost of cultivation are still the major bottlenecks hindering their large-scale deployment. Co-culturing of microalgae and yeast has the potential to increase the overall lipid productivity by minimizing its production cost as both these organisms can utilize each other's by-products. Microalgae act as an O₂ generator for yeast while consuming the CO₂ and organic acids released by the yeast cells. Further, yeast can break complex sugars in the medium, which can then be utilized by microalgae thereby opening new options for copious and low-cost feedstocks such as agricultural residues. The current review provides a historical and technical overview of the existing studies on co-culturing of yeast and microalgae and elucidates the crucial factors that affect the symbiotic relationship between these two organisms. Furthermore, the review also highlighted the advantages and the future perspectives for paving a path towards a sustainable biodiesel product.

The algal trophic mode affects the interaction and oil production of a synergistic microalga-yeast consortium

The use of non-food feedstocks to produce renewable microbial resources can limit our dependence on fossil fuels and lower CO₂ emissions. Since microalgae display a virtuous CO₂ and O₂ exchange with heterotrophs, the microalga Chlamydomonas reinhardtii was combined with the oleaginous yeast Lipomyces starkeyi, known for their production of oil, base material for biodiesel. The coupled growth was shown to be synergistic for biomass and lipid production. The species were truly symbiotic since synergistic growth occurred even when the alga cannot use the organic carbon in the feedstock and in absence of air, thus depending entirely on CO₂-O₂ exchange. Since addition of acetate as the algal carbon source lowered the performance of the consortium, the microbial system design should take into account algal mixotrophy. The mixed biomass was found be suitable for biodiesel production, and whereas lipid production increased in the consortium, yields should be improved in future studies.

Co-cultivation of Rhodotorula glutinis and Chlorella pyrenoidosa to improve nutrient removal and protein content by their synergistic relationship

With the continuous development of the livestock breeding industry, the amount of piggery wastewater discharged increases year by year, and the pressure of controlling environmental pollution continuously increases. A novel method using a co-culture of Chlorella pyrenoidosa and Rhodotorula glutinis in piggery wastewater was proposed in this study, which was aimed at treating piggery wastewater and producing useful products. The results showed that the optimal inoculum ratio of algae to yeast was 3 : 1 in the wastewater, which achieved the removal efficiencies of 58.53%, 36.07%, 33.20% and 56.25% for ammoniacal nitrogen (NH₃-N), total nitrogen (TN), total protein (TP) and chemical oxygen demand (COD), respectively, after 6 d. The synergistic relationship of C. pyrenoidosa and R. glutinis was preliminarily validated using the oxygen/carbon dioxide exchange balance and scanning electron microscopy images. The co-cultivation system gained 59.8% (w/w) protein within 5 d which can be used as a feed additive, and produces aquatic animals with better growth and quality. Thus, the 1000 litre pilot scale bioreactor was used indoors and removed 82.65% of TN, 53.51% of TP, 93.48% of NH₃-N and 85.44% of COD in 21 d which gave a better performance for TN (p < 0.05) than the bench scale results. This system improves the nutrition removal and protein production efficiencies, and is a promising method for piggery wastewater treatment and the pig breeding industry.

Aiming at treating piggery wastewater and producing useful products, a novel method using a co-culture of Chlorella pyrenoidosa and Rhodotorula glutinis in piggery wastewater was proposed in this study to improve nutrient removal and the protein content in the feed produced.

Efficient resource recycling from liquid digestate by microalgae-yeast mixed culture and the assessment of key gene transcription related to nitrogen assimilation in microalgae

To determine the feasibility of microalgae-yeast mixed culture using the liquid digestate of dairy wastewater (LDDW) for biofuels and single cell protein (SCP) production, the cell growth, nutrient removal and outputs evaluation of the mono and mixed culture of Chlorella vulgaris and Yarrowia lipolytica in LDDW were investigated by adding glycerol as carbon source. The results showed that the mixed culture could enhance the biological utilization efficiency of nitrogen and phosphorus, and obtain higher yield of biomass (1.62 g/L), lipid (0.31 g/L), protein (0.51 g/L), and higher heating value (34.06 KJ/L). Compared with the mono culture of C. vulgaris, a decline of the transcription level in nitrate reductase and glutamine synthetase II genes in C. vulgaris was observed in the mixed culture when ammonia was sufficient. The results suggest the possibility of using the mixed culture for the efficient treatment of LDDW and resources recycling.

Enhanced single cell oil production by mixed culture of Chlorella pyrenoidosa and Rhodotorula glutinis using cassava bagasse hydrolysate as carbon source

The single cell oil (SCO) production by the mono and mixed culture of microalgae Chlorella pyrenoidosa and red yeast Rhodotorula glutinis was investigated using non-detoxified cassava bagasse hydrolysate (CBH) as carbon source. The results suggested that the two strains were able to tolerate and even degrade some byproducts presented in the CBH, and the mixed culture approach enhanced the degradation of certain byproducts. Biomass (20.37 ± 0.38 g/L) and lipid yield (10.42 ± 1.21 g/L) of the mixed culture achieved in the batch culture were significantly higher than that of the mono-cultures (p < 0.05). The fed-batch culture further raised the biomass and lipid yield to 31.45 ± 4.93 g/L and 18.47 ± 3.25 g/L, respectively. The lipids mainly composed of oleic acid and palmitic acid, suggesting the potential applications such as biofuel feedstock, cosmetics, food additives and lubricant. This study provided new insights for the integration of the economical SCO production with agro-industrial waste disposal.

Combined yeast and microalgal cultivation in a pilot-scale raceway pond for urban wastewater treatment and potential biodiesel production

A mixed culture of oleaginous yeast Lipomyces starkeyi and wastewater native microalgae (mostly Scenedesmus sp. and Chlorella sp.) was performed to enhance lipid and biomass production from urban wastewaters. A 400 L raceway pond, operating outdoors, was designed and used for biomass cultivation. Microalgae and yeast were inoculated into the cultivation pond with a 2:1 inoculum ratio. Their concentrations were monitored for 14 continuous days of batch cultivation. Microalgal growth presented a 3-day initial lag-phase, while yeast growth occurred in the first few days. Yeast activity during the microalgal lag-phase enhanced microalgal biomass productivity, corresponding to 31.4 mgTSS m^-2 d^-1. Yeast growth was limited by low concentrations in wastewater of easily assimilated organic substrates. Organic carbon was absorbed in the first 3 days with a 3.7 mgC L^-1 d^-1 removal rate. Complete nutrient removal occurred during microalgal linear growth with 2.9 mgN L^-1 d^-1 and 0.96 mgP L^-1 d^-1 removal rates. Microalgal photosynthetic activity induced high pH and dissolved oxygen values resulted in natural bactericidal and antifungal activity. A 15% lipid/dry weight was measured at the end of the cultivation time. Fatty acid methyl ester (FAME) analysis indicated that the lipids were mainly composed of arachidic acid.

Heterotrophic culture of Chlorella pyrenoidosa using sucrose as the sole carbon source by co-culture with immobilized yeast

Glucose is normally used as the carbon source for heterotrophic cultivation of algal cells, whereas sucrose is difficult to be heterotrophicly utilized by them. In this study, a new co-culture system was developed through mixed culture of Chlorella pyrenoidosa with immobilized Saccharomyces cerevisiae in the dark to effectively obtain pure algal suspension using sucrose as only carbon source. In this system, a pure algal suspension with a concentration of 2.08g/L was obtained. The lipid content reached 29%, which was higher than that obtained in glucose contained system. In addition, the immobilized yeast beads were repeatedly used for at least three times. Through immobilization, the choice for the yeast strains that are able to hydrolyze sucrose was not limited by its product and pure algal suspension was efficiently obtained. This strategy may effectively decrease the cost of carbon source in the heterotrophic cultivation of microalgae.

Microbial consortia: a critical look at microalgae co-cultures for enhanced biomanufacturing

Monocultures have been the preferred production route in the bio-industry, where contamination has been a major bottleneck. In nature, microorganisms usually exist as part of organized communities and consortia, gaining benefits from co-habitation, keeping invaders at bay. There is increasing interest in the use of co-cultures to tackle contamination issues, and simultaneously increase productivity and product diversity. The feasibility of extending the natural phenomenon of co-habitation to the biomanufacturing industry in the form of co-cultures requires careful and systematic consideration of several aspects. This article will critically examine and review current work on microbial co-cultures, with the intent of examining the concept and proposing a design pipeline that can be developed in a biomanufacturing context.

From low-cost substrates to Single Cell Oils synthesized by oleaginous yeasts

As new feedstock for biofuels, microbial oils have received worldwide attentions due to their environmentally-friendly characters. Microbial oil production based on low-cost raw materials is significantly attractive to the current biodiesel refinery industry. In terms of SCOs production, oleaginous yeast has numerous advantages over bacteria, molds and microalgae based on their high growth rate and lipid yield. Numerous efforts have been made on the competitive lipid production combining the use of cheap raw materials as substrates by yeasts. In this paper, we provided an overview of lipid metabolism in yeast cells. New advances using oleaginous yeast as a cell factory for high-value lipid production from various low-cost substrates are also reviewed, and the enhanced strategies based on synergistic effects of oleaginous yeast and microalgae in co-culture are discussed in details.

Heterotrophic cultivation of Chlorella pyrenoidosa using sucrose as the sole carbon source by co-culture with Rhodotorula glutinis

Heterotrophic cultivation of microalgae is a feasible alternative strategy to avoid the light limitation of photoautotrophic culture, but the heterotrophic utilization of disaccharides is difficult for microalgae. Aimed at this problem, a co-culture system was developed by mix culture of C. pyrenoidosa and R. glutinis using sucrose as the sole carbon source. In this system, C. pyrenoidosa could utilize glucose and fructose which were hydrolyzed from sucrose by R. glutinis. The highest specific growth rate and final cell number proportion of algae was 1.02day(-1) and 45%, respectively, when cultured at the initial algal cell number proportion of 95.24% and the final algal cell density was 111.48×10(6)cells/mL. In addition, the lipid content was also promoted due to the synergistic effects in mix culture. This study provides a novel approach using sucrose-riched wastes for the heterotrophic culture of microalgae and may effectively decrease the cost of carbon source.

Evaluating feeding strategies for microbial oil production from glycerol by Rhodotorula glutinis

Oil production, from biodiesel by-product glycerol, through microbial fermentation provides a promising option as part of an integrated biorefinery process. However, bioprocessing improvements are required to make the process more efficient. In the present work, different glycerol feeding strategies were evaluated under fed-batch cultivation of the oleaginous yeast Rhodotorula glutinis. Results showed that the concept of targeting first a cell proliferation stage and then a lipid accumulation stage had beneficial effects on both biomass and oil yields. Continual feeding and pulsed feedings, delivering the same total amount of nutrients, resulted in similar values of cellular biomass (∼25 g/L) and oil content (∼40%). In contrast, continual supply of nutrients at higher rates ( >0.8 g/L/h) led to an increase in both cell densities (30 g/L) and oil content (53%), attaining a high oil yield of 16.28 g/L. This suggests that a continual cultivation with two different rates for each stage constitutes an efficient approach to enhance microbial oil production.

The synergistic effects for the co-cultivation of oleaginous yeast-Rhodotorula glutinis and microalgae-Scenedesmus obliquus on the biomass and total lipids accumulation

In this co-culture of oleaginous yeast-Rhodotorula glutinis and microalgae-Scenedesmus obliquus, microalgae potentially acts as an oxygen generator for the growth of aerobic yeast while the yeast mutually provides CO2 to the microalgae as both carry out the production of lipids. To explore the synergistic effects of co-cultivation on the cells growth and total lipids accumulation, several co-culture process parameters including the carbon source concentration, temperature and dissolved oxygen level would be firstly investigated in the flask trials. The results of co-culture in a 5L photobioreactor revealed that about 40-50% of biomass increased and 60-70% of total lipid increased was observed as compared to the single culture batches. Besides the synergistic effects of gas utilization, the providing of trace elements to each other after the natural cells lysis was believed to be another benefit to the growth of the overall co-culture system.

Lipid production by a mixed culture of oleaginous yeast and microalga from distillery and domestic mixed wastewater

Lipid productivity by mixed culture of Rhodosporidium toruloides and Chlorella pyrenoidosa was studied using 1:1 mixed real wastewater from distillery and local municipal wastewater treatment plant with initial soluble chemical oxygen demand (SCOD) around 25,000 mg/L, initial cell density of 2×10(7) cells/mL (yeast) and 5×10(6) cells/mL (microalga), at 30 °C and 2.93 W/m2 (2000 lux, 12:12 h light and dark cycles). Lipid content and lipid yield achieved were 63.45±2.58% and 4.60±0.36 g/L with the associated removal efficiencies for SCOD, total nitrogen (TN), and total phosphorus (TP) at 95.34±0.07%, 51.18±2.17%, and 89.29±4.91%, respectively, after 5 days of cultivation without the pH adjustment. Inoculation of microalgae at 40 h of the initial yeast cultivation and harvesting part of inactive biomass at 72 h by sedimentation could improve both lipid production and wastewater treatment efficiency under non-sterile conditions.