Growth of Chlamydomonas reinhardtii in acetate-free medium when co-cultured with alginate-encapsulated, acetate-producing strains of Synechococcus sp. PCC 7002

Synthetic, marine, light-driven, autotroph-heterotroph co-culture system for sustainable β-caryophyllene production

Applying low-cost substrate is critical for sustainable bioproduction. Co-culture of phototrophic and heterotrophic microorganisms can be a promising solution as they can use CO2 and light as feedstock. This study aimed to create a light-driven consortium using a marine cyanobacterium Synechococcus sp. PCC 7002 and an industrial yeast Yarrowia lipolytica. First, the cyanobacterium was engineered to accumulate and secrete sucrose by regulating the expression of genes involved in sucrose biosynthesis and transport, resulting in 4.0 g/L of sucrose secretion. Then, Yarrowia lipolytica was engineered to efficiently use sucrose and produce β-caryophyllene that has various industrial applications. Then, co- and sequential-culture were optimized with different induction conditions and media compositions. A maximum β-caryophyllene yield of 14.1 mg/L was obtained from the co-culture. This study successfully established an artificial light-driven consortium based on a marine cyanobacterium and Y. lipolytica, and provides a foundation for sustainable bioproduction from CO2 and light through co-culture systems.

Bottom-up construction and screening of algae-bacteria consortia for pollutant biodegradation

Microbial communities have been used as important biological tools for a variety of purposes associated with agriculture, the food industry and human health. Artificial engineering of microbial communities is an emerging field of research motivated by finding stable and efficient microbial systems. However, the successful design of microbial communities with desirable functions not only requires profound understanding of microbial activities, but also needs efficient approaches to piece together the known microbial traits to give rise to more complex systems. This study demonstrates the bottom-up integration of environmentally isolated phototrophic microalgae and chemotrophic bacteria as artificial consortia to bio-degrade selected volatile organic compounds (VOCs). A high throughput screening method based on 96-well plate format was developed for discovering consortia with bioremediation potential. Screened exemplar consortia were verified for VOCs degradation performance, among these, certain robust consortia were estimated to have achieved efficiencies of 95.72% and 92.70% and near 100% removal (7 days) of benzene, toluene, and phenol, respectively, with initial concentrations of 100 mg/L. VOCs degradation by consortia was mainly attributed to certain bacteria including Rhodococcus erythropolis, and Cupriavidus metallidurans, and directly contributed to the growth of microalgae Coelastrella terrestris (R = 0.82, p < 0.001). This work revealed the potential of converting VOCs waste into algal biomass by algae-bacteria consortia constructed through a bottom-up approach. The screening method enables rapid shortlisting of consortia combinatorial scenarios without prior knowledge about the individual strains or the need for interpreting complex microbial interactions.

Photobiohydrogen Production and Strategies for H2 Yield Improvements in Cyanobacteria

Hydrogen gas (H2) is one of the potential future sustainable and clean energy carriers that may substitute the use of fossil resources including fuels since it has a high energy content (heating value of 141.65 MJ/kg) when compared to traditional hydrocarbon fuels [1]. Water is a primary product of combustion being a most significant advantage of H2 being environmentally friendly with the capacity to reduce global greenhouse gas emissions. H2 is used in various applications. It generates electricity in fuel cells, including applications in transportation, and can be applied as fuel in rocket engines [2]. Moreover, H2 is an important gas and raw material in many industrial applications. However, the high cost of the H2 production processes requiring the use of other energy sources is a significant disadvantage. At present, H2 can be prepared in many conventional ways, such as steam reforming, electrolysis, and biohydrogen production processes. Steam reforming uses high-temperature steam to produce hydrogen gas from fossil resources including natural gas. Electrolysis is an electrolytic process to decompose water molecules into O2 and H2. However, both these two methods are energy-intensive and producing hydrogen from natural gas, which is mostly methane (CH4) and in steam reforming generates CO2 and pollutants as by-products. On the other hand, biological hydrogen production is more environmentally sustainable and less energy intensive than thermochemical and electrochemical processes [3], but most concepts are not yet developed to production scale.

Biohydrogen production from Euglena acus microalgae available in Bangladesh

Hydrogen is generally considered as an ideal non-polluting future energy carrier because it releases energy and water as a byproduct on combustion. Besides, hydrogen possesses the highest energy density on mass basis compared to any other fuel. However, hydrogen production in a sustainable and environmentally friendly way still remains a challenge. Recently, biohydrogen production from green microalgae has gained significant attention due to availability of the feedstock, which are environmentally friendly and renewable. Biohydrogen production from photosynthetic microalgae is attractive, however in the current context, it has a low yield, and an optimization of the affecting parameters including algae concentration, light intensity, culture medium, etc. is critical. In this study, biohydrogen was produced in laboratory from Euglena acus microalgae as it was locally available in Bangladesh.•The effect of two different culture mediums (i.e. sulfur-rich and sulfur-deprived TAP mediums) for microalgae cultivation and biohydrogen yield were studied.•Depending on the concentration of microalgae (50% and 75% by weight) in the medium solution ∼3 ml to 5 ml biohydrogen was obtained.

Photosynthesis and pigment production: elucidation of the interactive effects of nutrients and light on Chlamydomonas reinhardtii

Chlamydomonas reinhardtii produces a variety of compounds that can be beneficial to human and animal health. Among these compounds, application of photosynthetic pigments, such as chlorophylls and carotenoids, has gained considerable interest in numerous industries. A better understanding on the interactive effects of essential nutrients and light on microalgal physiology and pigment production would be beneficial in improving cultivation strategies. Therefore, this study evaluated biomass, carotenoid and chlorophyll yield and the following fluorescence parameters: quantum yield in PS II [Y(II)] and electron transport rate (ETR) using response surface methodology (RSM). The F_v/F_m, Y(NO) and Y(NPQ) were also monitored; however, no significant relationship was observed. From the investigation it was apparent that nitrogen and carbon; as well as the interactive effects of (nitrogen and carbon) and (carbon and light irradiance) were significant factors. The model predicted the optimum conditions for maximum carotenoids (8.15 ± 0.389 mg g^-1) were 08.7 mol l^-1 of nitrogen, 0.2 mol l^-1 and 50 μmol photon m^-2 s^-1 of light irradiance. While maximum chlorophyll (33.6 ± 0.854 mg g^-1) required a higher nitrogen (11.21 mol l^-1). The photosynthetic parameters [Y(II), ETR] was correlated with the primary pigments and biomass production. Increased photosynthetic activity was associated with high carbon and light. The Y(II)and ETR of PSII under these conditions were 0.2 and ~ 14, respectively. This approach was accurate in developing the model, optimizing factors and analysing interaction effects. This study served to provide a better understanding on the interactions between factors influencing pigment biosynthesis and photosynthetic performance of Chlamydomonas reinhardtii.

Biotransformation of 2,4-dinitrotoluene in a phototrophic co-culture of engineered Synechococcus elongatus and Pseudomonas putida

In contrast to the current paradigm of using microbial mono-cultures in most biotechnological applications, increasing efforts are being directed towards engineering mixed-species consortia to perform functions that are difficult to programme into individual strains. In this work, we developed a synthetic microbial consortium composed of two genetically engineered microbes, a cyanobacterium (Synechococcus elongatus PCC 7942) and a heterotrophic bacterium (Pseudomonas putida EM173). These microbial species specialize in the co-culture: cyanobacteria fix CO2 through photosynthetic metabolism and secrete sufficient carbohydrates to support the growth and active metabolism of P. putida, which has been engineered to consume sucrose and to degrade the environmental pollutant 2,4-dinitrotoluene (2,4-DNT). By encapsulating S. elongatus within a barium-alginate hydrogel, cyanobacterial cells were protected from the toxic effects of 2,4-DNT, enhancing the performance of the co-culture. The synthetic consortium was able to convert 2,4-DNT with light and CO2 as key inputs, and its catalytic performance was stable over time. Furthermore, cycling this synthetic consortium through low nitrogen medium promoted the sucrose-dependent accumulation of polyhydroxyalkanoate, an added-value biopolymer, in the engineered P. putida strain. Altogether, the synthetic consortium displayed the capacity to remediate the industrial pollutant 2,4-DNT while simultaneously synthesizing biopolymers using light and CO2 as the primary inputs.

Growth and secretome analysis of possible synergistic interaction between green algae and cyanobacteria

Synergistic coexistence of nitrogen fixing cyanobacteria such as Anabaena variabilis, Nostoc muscorum and Westiellopsis prolifica with green algae namely Scenedesmus obliquus, Chlorella vulgaris and Botryococcus braunii was studied under nitrogen deficient conditions. The effect of these interactions was investigated on growth, fixed nitrogen content, lipid content and their secretomes in individual cultures and cocultures. Based on the cocultivation studies, it was found that out of the nine interactions studied, B. braunii-N. muscorum synergism was best established. This interaction resulted in a maximum of 50% enhancement in nitrogen fixation in B. braunii-N. muscorum co-culture leading to 27% enhancement in lipid content (membrane and neutral lipid). In general, B. braunii co-cultures showed an enhancement in biomass content of up to 38%. Secretome analysis showed presence of new and modified secondary metabolites having roles in quorum sensing/quenching, interspecies signaling, N-fixation, carbon metabolism, lipid metabolism, antimicrobial activity. Compounds such as trichloroacetic acid and hexadecane were identified that are known to have roles in nitrogen assimilation and carbon metabolism, respectively, were present in some of the co-culture secretomes. The combination of B. braunii-N. muscorum led to the formation of new compounds such as triacontanol which have role in improvement of glucose-lipid metabolism and 9-octadecenamide that is known to be a phytohormone.

Alignment of microbial fitness with engineered product formation: obligatory coupling between acetate production and photoautotrophic growth

BACKGROUND

Microbial bioengineering has the potential to become a key contributor to the future development of human society by providing sustainable, novel, and cost-effective production pipelines. However, the sustained productivity of genetically engineered strains is often a challenge, as spontaneous non-producing mutants tend to grow faster and take over the population. Novel strategies to prevent this issue of strain instability are urgently needed.

RESULTS

In this study, we propose a novel strategy applicable to all microbial production systems for which a genome-scale metabolic model is available that aligns the production of native metabolites to the formation of biomass. Based on well-established constraint-based analysis techniques such as OptKnock and FVA, we developed an in silico pipeline-FRUITS-that specifically 'Finds Reactions Usable in Tapping Side-products'. It analyses a metabolic network to identify compounds produced in anabolism that are suitable to be coupled to growth by deletion of their re-utilization pathway(s), and computes their respective biomass and product formation rates. When applied to Synechocystis sp. PCC6803, a model cyanobacterium explored for sustainable bioproduction, a total of nine target metabolites were identified. We tested our approach for one of these compounds, acetate, which is used in a wide range of industrial applications. The model-guided engineered strain shows an obligatory coupling between acetate production and photoautotrophic growth as predicted. Furthermore, the stability of acetate productivity in this strain was confirmed by performing prolonged turbidostat cultivations.

CONCLUSIONS

This work demonstrates a novel approach to stabilize the production of target compounds in cyanobacteria that culminated in the first report of a photoautotrophic growth-coupled cell factory. The method developed is generic and can easily be extended to any other modeled microbial production system.

Robust Microplate-Based Methods for Culturing and in Vivo Phenotypic Screening of Chlamydomonas reinhardtii

Chlamydomonas reinhardtii (Cr), a unicellular alga, is routinely utilized to study photosynthetic biochemistry, ciliary motility, and cellular reproduction. Its minimal culture requirements, unicellular morphology, and ease of transformation have made it a popular model system. Despite its relatively slow doubling time, compared with many bacteria, it is an ideal eukaryotic system for microplate-based studies utilizing either, or both, absorbance as well as fluorescence assays. Such microplate assays are powerful tools for researchers in the areas of toxicology, pharmacology, chemical genetics, biotechnology, and more. However, while microplate-based assays are valuable tools for screening biological systems, these methodologies can significantly alter the conditions in which the organisms are cultured and their subsequent physiology or morphology. Herein we describe a novel method for the microplate culture and in vivo phenotypic analysis of growth, viability, and photosynthetic pigments of C. reinhardtii. We evaluated the utility of our assay by screening silver nanoparticles for their effects on growth and viability. These methods are amenable to a wide assortment of studies and present a significant advancement in the methodologies available for research involving this model organism.

Mimicking lichens: incorporation of yeast strains together with sucrose-secreting cyanobacteria improves survival, growth, ROS removal, and lipid production in a stable mutualistic co-culture production platform

BACKGROUND

The feasibility of heterotrophic-phototrophic symbioses was tested via pairing of yeast strains Cryptococcus curvatus, Rhodotorula glutinis, or Saccharomyces cerevisiae with a sucrose-secreting cyanobacterium Synechococcus elongatus.

RESULTS

The phototroph S. elongatus showed no growth in standard BG-11 medium with yeast extract, but grew well in BG-11 medium alone or supplemented with yeast nitrogen base without amino acids (YNB w/o aa). Among three yeast species, C. curvatus and R. glutinis adapted well to the BG-11 medium supplemented with YNB w/o aa, sucrose, and various concentrations of NaCl needed to maintain sucrose secretion from S. elongatus, while growth of S. cerevisiae was highly dependent on sucrose levels. R. glutinis and C. curvatus grew efficiently and utilized sucrose produced by the partner in co-culture. Co-cultures of S. elongatus and R. glutinis were sustained over 1 month in both batch and in semi-continuous culture, with the final biomass and overall lipid yields in the batch co-culture 40 to 60% higher compared to batch mono-cultures of S. elongatus. The co-cultures showed enhanced levels of palmitoleic and linoleic acids. Furthermore, cyanobacterial growth in co-culture with R. glutinis was significantly superior to axenic growth, as S. elongatus was unable to grow in the absence of the yeast partner when cultivated at lower densities in liquid medium. Accumulated reactive oxygen species was observed to severely inhibit axenic growth of cyanobacteria, which was efficiently alleviated through catalase supply and even more effectively with co-cultures of R. glutinis.

CONCLUSIONS

The pairing of a cyanobacterium and eukaryotic heterotroph in the artificial lichen of this study demonstrates the importance of mutual interactions between phototrophs and heterotrophs, e.g., phototrophs provide a carbon source to heterotrophs, and heterotrophs assist phototrophic growth and survival by removing/eliminating oxidative stress. Our results establish a potential stable production platform that combines the metabolic capability of photoautotrophs to capture inorganic carbon with the channeling of the resulting organic carbon directly to a robust heterotroph partner for producing biofuel and other chemical precursors.

Dual gradients of light intensity and nutrient concentration for full-factorial mapping of photosynthetic productivity

Optimizing bioproduct generation from microalgae is complicated by the myriad of coupled parameters affecting photosynthetic productivity. Quantifying the effect of multiple coupled parameters in full-factorial fashion requires a prohibitively high number of experiments. We present a simple hydrogel-based platform for the rapid, full-factorial mapping of light and nutrient availability on the growth and lipid accumulation of microalgae. We accomplish this without microfabrication using thin sheets of cell-laden hydrogels. By immobilizing the algae in a hydrogel matrix we are able to take full advantage of the continuous spatial chemical gradient produced by a diffusion-based gradient generator while eliminating the need for chambers. We map the effect of light intensities between 0 μmol m(-2) s(-1) and 130 μmol m(-2) s(-1) (∼28 W m(-2)) coupled with ammonium concentrations between 0 mM and 7 mM on Chlamydomonas reinhardtii. Our data set, verified with bulk experiments, clarifies the role of ammonium availability on the photosynthetic productivity Chlamydomonas reinhardtii, demonstrating the dependence of ammonium inhibition on light intensity. Specifically, a sharp optimal growth peak emerges at approximately 2 mM only for light intensities between 80 and 100 μmol m(-2) s(-1)- suggesting that ammonium inhibition is insignificant at lower light intensities. We speculate that this phenomenon is due to the regulation of the high affinity ammonium transport system in Chlamydomonas reinhardtii as well as free ammonia toxicity. The complexity of this photosynthetic biological response highlights the importance of full-factorial data sets as enabled here.

Encapsulation of Living Cells within Giant Phospholipid Liposomes Formed by the Inverse-Emulsion Technique

Liposomes form spontaneously by the assimilation of phospholipids, the primary component of cell membranes. Due to their unique ability to form selectively permeable bilayers in situ, they are widely used as nanocarriers for drug and small-molecule delivery. However, there is a lack of straightforward methodologies to encapsulate living microorganisms. Here we demonstrate the successful encapsulation of whole cells in phospholipid vesicles by using the inverse-emulsion technique of generating unilamellar vesicles. This method of liposome preparation allows for a facile encapsulation of large biomaterials that previously was not easily attainable. Using Escherichia coli as a model organism, we found that liposomes can protect the bacterium against external protease degradation and from harsh biological environments. Liposomes prepared by the inverse-emulsion method were also capable of encapsulating yeast and were found to be naturally susceptible to hydrolysis by enzymes such as phospholipases, thus highlighting their potential role as cell delivery carriers.

Lauric Acid Production in a Glycogen-Less Strain of Synechococcus sp. PCC 7002

The cyanobacterium Synechococcus sp. Pasteur culture collection 7002 was genetically engineered to synthesize biofuel-compatible medium-chain fatty acids (FAs) during photoautotrophic growth. Expression of a heterologous lauroyl-acyl carrier protein (C12:0-ACP) thioesterase with concurrent deletion of the endogenous putative acyl-ACP synthetase led to secretion of transesterifiable C12:0 FA in CO2-supplemented batch cultures. When grown at steady state over a range of light intensities in a light-emitting diode turbidostat photobioreactor, the C12-secreting mutant exhibited a modest reduction in growth rate and increased O2 evolution relative to the wild-type (WT). Inhibition of (i) glycogen synthesis by deletion of the glgC-encoded ADP-glucose pyrophosphorylase (AGPase) and (ii) protein synthesis by nitrogen deprivation were investigated as potential mechanisms for metabolite redistribution to increase FA synthesis. Deletion of AGPase led to a 10-fold decrease in reducing carbohydrates and secretion of organic acids during nitrogen deprivation consistent with an energy spilling phenotype. When the carbohydrate-deficient background (ΔglgC) was modified for C12 secretion, no increase in C12 was achieved during nutrient replete growth, and no C12 was recovered from any strain upon nitrogen deprivation under the conditions used. At steady state, the growth rate of the ΔglgC strain saturated at a lower light intensity than the WT, but O2 evolution was not compromised and became increasingly decoupled from growth rate with rising irradiance. Photophysiological properties of the ΔglgC strain suggest energy dissipation from photosystem II and reconfiguration of electron flow at the level of the plastoquinone pool.