Autotrophic Cultures Research Articles

Comparison of Biohydrogen Production by Tetraselmis subcordiformis During Cultivation Using Soil-Less Agricultural Wastewater and Effluent from Microbial Fuel Cells

The development and implementation of innovative production technologies have a direct influence on the creation of new sources of pollution and types of waste. An example of this is the wastewater from soil-less agriculture and the effluent from microbial fuel cells. An important topic is the development and application of methods for their neutralisation that take into account the assumptions of global environmental policy. The aim of the present study was to determine the possibilities of utilising this type of pollution in the process of autotrophic cultivation of the biohydrogen-producing microalgae Tetraselmis subcordiformis. The highest biomass concentration of 3030 ± 183 mgVS/L and 67.9 ± 3.5 mg chl-a/L was observed when the culture medium was wastewater from soil-less agriculture. The growth rate in the logarithmic growth phase was 270 ± 16 mgVS/L-day and 5.95 ± 0.24 mg chl-a/L-day. In the same scenario, the highest total H2 production of 161 ± 8 mL was also achieved, with an observed H2 production rate of 4.67 ± 0.23 mL/h. Significantly lower effects in terms of biomass production of T. subcordiformis and H2 yield were observed when fermented dairy wastewater from the anode chamber of the microbial fuel cell was added to the culture medium.

Sustainable conversion of carbon dioxide to high-value antioxidant astaxanthin through microbial electrosynthesis-assisted microalgae cultivation

Microbial electrosynthesis (MES) effectively converts carbon dioxide (CO2) to short carboxylic acids but has lower efficiency for higher molecular value-added products. This study used a two-stage process integrating MES with microalgae cultivation to convert CO2 into a value-added chemical—astaxanthin, a xanthophyll carotenoid with strong antioxidant activity. In the first stage, MESs featuring platinum-coated anodes and carbonaceous cathodes were employed to bioelectrochemically convert CO2 to volatile fatty acids (VFAs). In the second stage, microalgal cultivation for sustainable astaxanthin production was conducted using a VFA-containing MES effluent. In the MES operation, a newly designed cathode with alternating layers of carbon felt (CF) and reticulated vitreous carbon (RVC) significantly improved hydrodynamics and bacterial attachment. Consequently, the CF/RVC composite cathode produced 7.68 g/L VFAs from CO2, with the highest production rate of 1225.72 mg/L/day and the highest coulombic efficiency of 94.15 % at 2.8 V. Feeding acetate-containing catholyte effluent demonstrated faster growth of microalgae and astaxanthin accumulation compared to autotrophic culture, indicating synergistic integration of MES and microalgae for capturing value from CO2. Among tested microalgae strains, Haematococcus pluvialis most efficiently accumulated astaxanthin up to 12.95 mg/L as cultured with MES effluent. Successful CO2-to-astaxanthin conversion using MES and microalgae can contribute to resolving unprecedented environmental challenges attributed to the excess emission of CO2.

Mixotrophic culture enhances fucoxanthin production in the haptophyte Pavlova gyrans

Fucoxanthin is a versatile substance in the food and pharmaceutical industries owing to its excellent antioxidant and anti-obesity properties. Several microalgae, including the haptophyte Pavlova spp., can produce fucoxanthin and are potential industrial fucoxanthin producers, as they lack rigid cell walls, which facilitates fucoxanthin extraction. However, the commercial application of Pavlova spp. is limited owing to insufficient biomass production. In this study, we aimed to develop a mixotrophic cultivation method to increase biomass and fucoxanthin production in Pavlova gyrans OPMS 30543X. The effects of culturing OPMS 30543X with different organic carbon sources, glycerol concentrations, mixed-nutrient conditions, and light intensities on the consumption of organic carbon sources, biomass production, and fucoxanthin accumulation were analyzed. Several organic carbon sources, such as glycerol, glucose, sucrose, and acetate, were examined, revealing that glycerol was well-consumed by the microalgae. Biomass and fucoxanthin production by OPMS 30543X increased in the presence of 10 mM glycerol compared to that observed without glycerol. Metabolomic analysis revealed higher levels of the metabolites related to the glycolytic, Calvin–Benson–Bassham, and tricarboxylic acid cycles under mixotrophic conditions than under autotrophic conditions. Cultures grown under mixotrophic conditions with a light intensity of 100 µmol photons m−2 s−1 produced more fucoxanthin than autotrophic cultures. Notably, the amount of fucoxanthin produced (18.9 mg/L) was the highest reported thus far for Pavlova species. In conclusion, the use of mixotrophic culture is a promising strategy for increasing fucoxanthin production in Pavlova species.Key points• Glycerol enhances biomass and fucoxanthin production in Pavlova gyrans• Metabolite levels increase under mixotrophic conditions• Mixotrophic conditions and medium-light intensity are appropriate for P. gyrans

Managing the interactions of illumination, nitrogen, and sodium bicarbonate for autotrophic biomass production and macromolecules accumulation in the microalga Chlorella sorokiniana

Understanding how cultivation variables holistically impact microalgal biomass production and macromolecule accumulation is essential toward sustainable scaling-up in open ponds. Efficient, non-wasteful resource utilization is imperative. This study examines the effects of three factors —illumination intensity, nitrogen loading, and inorganic carbon loading (as NaHCO3)—on Chlorella sorokiniana autotrophic cultures. By employing a Taguchi L9 design, these factors were evaluated, while let varying across three levels each. Illumination has the most significant effect on biomass production, while nitrogen loading inversely affected protein and carbohydrate content. No factor appeared significant for lipid accumulation, hinting that carbohydrate biosynthesis might overshadow lipid production. Using the derived statistical model, optimal conditions for maximizing biomass were determined: 7500 lx illumination, 250 mg NaNO3 L−1, and 750 mg NaHCO3 L−1, resulting in a biomass yield of 1105 mg L−1 in 16 days, with a robust R-squared (pred) value of 95.85 %. The obtained insight supports sustainable microalgal biomass production.

Unraveling non-linear dynamics of biomass, photosynthesis efficiency, and lipid accumulation in Chlorella vulgaris under mixotrophic cultivation

In recent years, the potential of microalgae-based biofuels as a renewable energy source has garnered significant attention due to their inherent ability to sequester carbon dioxide (CO2) efficiently. This study investigates Chlorella vulgaris FACHB-8's growth, photosynthesis, and lipid accumulation under different carbon source and CO2 concentration conditions with Central composite design. Results reveal that a 10% CO2 concentration enhances biomass and cell count, yielding 0.94 g L−1 and 106.8 × 106 cells·ml−1, respectively, after 14 days of autotrophic cultivation. However, excessive CO2 inhibits growth, notably observed with 20% CO2 yielding 0.86 g L−1 biomass. Pigment content positively correlates with biomass under autotrophic conditions, reaching 42.55 mg g−1 in the 10% CO2 group. Under photosynthetic mixotrophy, carbonic anhydrase activity decreases with higher CO2 concentrations, suggesting reduced enzyme demand. Glucose exhibits the highest lipid content (31.87%), surpassing autotrophic conditions (24.80%). Glycerol presents favorable lipid content (31.78%) and settling efficiency (85.07%), indicating potential for self-flocculation harvesting. Chlorophyll fluorescence data highlight active photosynthesis in mixotrophic conditions, with glucose and sucrose affecting energy conversion. This highlights the critical role of microalgae biofuels in the pursuit of cleaner and more sustainable energy solutions.

Effects of the supernatant of Chlorella vulgaris cultivated under different culture modes on lettuce (Lactuca sativa L.) growth.

CO2 capture by microalgae is a feasible strategy to reduce CO2 emissions. However, large amounts of cell-free supernatant will be produced after microalgal harvesting, which may be harmful to the environment if it is disorderly discharged. In this study, Chlorella vulgaris (C. vulgaris) was cultivated under three common cultivation modes (autotrophic culture (AC), heterotrophic culture (HC) and mixotrophic culture (MC)), and the obtained supernatant was used as fertilizer to investigate its effect on the growth of lettuce. The biomass concentration of C. vulgaris cultivated under MC and HC was 3.25 and 2.59 times that of under AC, respectively. The contents of macronutrients in supernatant obtained from AC were higher than those of MC and HC. However, the contents of amino acids and hormones in supernatant obtained from MC and HC were higher than those of AC. The fresh shoot weight, fresh root weight and root length of lettuce treated with supernatant were significantly higher than that of control treatment. In addition, the contents of chlorophyll, soluble sugar and soluble protein in lettuce treated with supernatant were also higher than that of control treatment. However, the contents of nitrate in lettuce treated with supernatant was lower than that of control treatment. These results showed that the supernatant could promote the growth of lettuce and was a potential of fertilizer for crop planting.

Gas fermentation combined with water electrolysis for production of polyhydroxyalkanoate copolymer from carbon dioxide by engineered Ralstonia eutropha

A recycled-gas closed-circuit culture system was developed for safe autotrophic cultivation of a hydrogen-oxidizing, polyhydroxyalkanoate (PHA)-producing Ralstonia eutropha, using a non-combustible gas mixture with low-concentration of H2 supplied by water electrolysis. Automated feedback regulation of gas flow enabled input of H2, CO2, and O2 well balanced with the cellular demands, leading to constant gas composition throughout the cultivation. The engineered strain of R. eutropha produced 1.71 g/L of poly(3-hydroxybutyrate-co-12.5 mol% 3-hydroxyhexanoate) on a gas mixture of H2/CO2/O2/N2 = 4:12:7:77 vol% with a 69.2 wt% cellular content. Overexpression of can encoding cytosolic carbonic anhydrase increased the 3HHx fraction up to 19.6 mol%. The yields of biomass and PHA on input H2 were determined to be 72.9 % and 63.1 %, corresponding to 51.0 % and 44.2 % yield on electricity, respectively. The equivalent solar-to-biomass/PHA efficiencies were estimated to be 2.1–3.8 %, highlighting the high energy conversion capability of R. eutropha.

Production of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from CO2 via pH-Stat Jar Cultivation of an Engineered Hydrogen-Oxidizing Bacterium Cupriavidus necator.

The copolyester of 3-hydroxybutyrate (3HB) and 3-hydoxyhexanoate (3HHx), PHBHHx, is a biodegradable plastic characterized by high flexibility, softness, a wide process window, and marine biodegradability. PHBHHx is usually produced from structurally related carbon sources, such as vegetable oils or fatty acids, but not from inexpensive carbon sources such as sugars. In previous studies, we demonstrated that engineered strains of a hydrogen-oxidizing bacterium, Cupriavidus necator, synthesized PHBHHx with a high cellular content not only from sugars but also from CO2 as the sole carbon source in the flask culture. In this study, the highly efficient production of PHBHHx from CO2 was investigated via pH-stat jar cultivation of recombinant C. necator strains while feeding the substrate gas mixture (H2/O2/CO2 = 80:10:10 v/v%) to a complete mineral medium in a recycled-gas, closed-circuit culture system. As a result, the dry cell mass and PHBHHx concentration with the strain MF01/pBPP-ccrMeJAc-emd reached up to 59.62 ± 3.18 g·L-1 and 49.31 ± 3.14 g·L-1, respectively, after 216 h of jar cultivation with limited addition of ammonia and phosphate solutions. The 3HHx composition was close to 10 mol%, which is suitable for practical applications. It is expected that the autotrophic cultivation of the recombinant C. necator can be feasible for the mass production of PHBHHx from CO2.

Nitrate-Reducing Fe(II)-Oxidizing microorganisms: linking Fe, C and N Cycles in subsurface environments

The discovery of the Nitrate-Reducing Fe(II)-Oxidizing (NRFeOx) microbial metabolism, which couples the oxidation of Fe(II) to the reduction of nitrate (NO3-) using organic matter or carbon dioxide (CO2) as carbon source, was a major milestone in microbial ecology (Straub et al. 1996). NRFeOx microorganisms play an essential role on a global scale in three of the most important biogeochemical cycles: iron (Fe), carbon (C) and nitrogen (N) (Kappler et al. 2021, Huang et al. 2021). In addition, these organisms participate in the mobilization or stabilization of organic carbon, as well as in CO2 fixation, thus contributing to the reduction of atmospheric CO2 (Kappler et al. 2021). Finally, the activity of these microorganisms is key to remove the pollutant NO3- from aquifers, which is one of the major worldwide environmental issues since many environments exceed the maximum regulatory concentration (50 mg L-1) (Kazakis et al. 2020 ). A plethora of NRFeOx microorganisms have been described in the last decades. However, most of these microorganisms have been reclassified as chemodenitrifiers. That is to say, Fe(II) is not enzymatically oxidized but indirectly by the reactive nitrogen species produced during denitrification (Fig. 1 ). In fact, only in three cultures so far, named KS, BP and AG, has the presence of true NRFeOx metabolism been unequivocally demonstrated (Straub et al. 1996, Huang et al. 2021b, Jakus et al. 2021b). Cultures KS, BP and AG have been studied thoroughly in the past years, analyzing the rate and mechanism by which these communities carry out autotrophic NRFeOx. Different omics studies have revealed that cultures KS, BP and AG consist of a mixture of bacterial species, which collaborate in order to grow under autotrophic NRFeOx conditions. Each culture is dominated by a novel candidate species of the genus Ferrigenium (Huang et al. 2022) capable of fixing CO2 and oxidizing Fe(II), but which requires flanking species to complete denitrification (Huang et al. 2021b, He et al. 2016, Huang et al. 2021a). Interestingly, these communities not only carry out NRFeOx using dissolved Fe(II) as energy source (Straub et al. 1996, Huang et al. 2021b, Jakus et al. 2021b), but they can also oxidize Fe(II) minerals, the main form in which Fe(II) can be found in the Earth's crust (Huang et al. 2021). In fact, Fe(II)-bearing minerals are thought to be the main drivers of NO3- reduction in subterranean environments (Huang et al. 2021), which has additional ecological consequences. NRFeOx microorganisms can trigger the turnover of the Fe(II)-bearing minerals, resulting in the mobilization of mineral structural elements such as S, P, C or contaminant heavy metals and the precipitation of Fe(III) minerals at circumneutral pH (Weber et al. 2001, Jakus et al. 2021a). Here, we will present a review of the insights learned from the three NRFeOx autotrophic cultures and discuss their ecological role, their importance in biogeochemical cycles, and their potential biotechnological applications.

Characterization of the Pyrroloquinoline Quinone Producing Rhodopseudomonas palustris as a Plant Growth-Promoting Bacterium under Photoautotrophic and Photoheterotrophic Culture Conditions.

Rhodopseudomonas palustris is a purple non-sulfide bacterium (PNSB), and some strains have been proven to promote plant growth. However, the mechanism underlying the effect of these PNSBs remains limited. Based on genetic information, R. palustris possesses the ability to produce pyrroloquinoline quinone (PQQ). PQQ is known to play a crucial role in stimulating plant growth, facilitating phosphorous solubilization, and acting as a reactive oxygen species scavenger. However, it is still uncertain whether growth conditions influence R. palustris's production of PQQ and other characteristics. In the present study, it was found that R. palustris exhibited a higher expression of genes related to PQQ synthesis under autotrophic culture conditions as compared to acetate culture conditions. Moreover, similar patterns were observed for phosphorous solubilization and siderophore activity, both of which are recognized to contribute to plant-growth benefits. However, these PNSB culture conditions did not show differences in Arabidopsis growth experiments, indicating that there may be other factors influencing plant growth in addition to PQQ content. Furthermore, the endophytic bacterial strains isolated from Arabidopsis exhibited differences according to the PNSB culture conditions. These findings imply that, depending on the PNSB's growing conditions, it may interact with various soil bacteria and facilitate their infiltration into plants.

Tetraselmis suecica and Porphyridium cruentum exopolysaccharides show anti-VHSV activity on RTG-2 cells

The use of functional feed additives is an important approach to both, prevent and fight, viral diseases in aquaculture. In this regard, microalgae-derived products, and, more specifically, microalgal exopolysaccharides (EPSs), have attracted attention, since multiple biotechnological applications are being described for these molecules. Furthermore, depending on culture conditions, the composition and, therefore, properties of EPSs can vary. In the present study, the antiviral activity of EPSs from Tetraselmis suecica and Porphyridium cruentum cultured under autotrophic and heterotrophic conditions has been evaluated in vitro against Viral Haemorrhagic Septicaemia Virus (VHSV), an important pathogen in fish farming. Results showed that EPSs from both species have anti-VHSV activity. T. suecica EPSs from autotrophic cultures showed the strongest effect, since both, adsorption and post-adsorption phases of the VHSV multiplication cycle were affected. In contrast, both, autotrophic and heterotrophic P. cruentum EPSs showed anti-VHSV activity only after the adsorption phase. These results pave the way to use these EPSs to fight VHSV infections, and animate to evaluate the EPS antiviral activity against other viral pathogens relevant to the aquaculture industry.

Autotrophic production of bio-functional proteins from freshwater microalgae using natural water medium for an economical and ecofriendly approach

As natural repositories of a broad spectrum of bioactive compounds ranging from pigments and enzymes to unique fatty acids and proteins, microalgae have attracted growing interest for their potential to produce bio-functional proteins. This comprehensive study examines the autotrophic cultivation of freshwater microalgae, focusing on protein production using a photobioreactor and natural water as the growth medium. The cultivation strategy eliminated the need for supplemented nutrients, enhancing environmental sustainability and cost- effectiveness. The study achieved a biomass production rate of 0.262 mg/L/day and a notable protein yield of 27.69 mg/L/day. Our findings support the feasibility and efficacy of employing natural water as a cultivation medium for freshwater microalgae for protein production. This approach alleviates the environmental burden associated with synthetic growth media and contributes to reducing operational costs. The study thus demonstrates the potential for this methodology to pave the way for a new, eco-friendly, and economically sustainable paradigm in the production of algal bio-functional proteins. Moreover, the widespread availability of natural resources makes this approach highly adaptable and scalable for larger production systems.

Transcriptomic and metabolomic analyses revealed regulation mechanism of mixotrophic Cylindrotheca sp. glycerol utilization and biomass promotion

BackgroundDiatoms have been viewed as ideal cell factories for production of some high-value bioactive metabolites, such as fucoxanthin, but their applications are restrained by limited biomass yield. Mixotrophy, by using both CO2 and organic carbon source, is believed effective to crack the bottleneck of biomass accumulation and achieve a sustainable bioproduct supply.ResultsGlycerol, among tested carbon sources, was proved as the sole that could significantly promote growth of Cylindrotheca sp. with illumination, a so-called growth pattern, mixotrophy. Biomass and fucoxanthin yields of Cylindrotheca sp., grown in medium with glycerol (2 g L−1), was increased by 52% and 29%, respectively, as compared to the autotrophic culture (control) without compromise in photosynthetic performance. As Cylindrotheca sp. was unable to use glycerol without light, a time-series transcriptomic analysis was carried out to elucidate the light regulation on glycerol utilization. Among the genes participating in glycerol utilization, GPDH1, TIM1 and GAPDH1, showed the highest dependence on light. Their expressions decreased dramatically when the alga was transferred from light into darkness. Despite the reduced glycerol uptake in the dark, expressions of genes associating with pyrimidine metabolism and DNA replication were upregulated when Cylindrotheca sp. was cultured mixotrophically. Comparative transcriptomic and metabolomic analyses revealed amino acids and aminoacyl-tRNA metabolisms were enhanced at different timepoints of diurnal cycles in mixotrophic Cylindrotheca sp., as compared to the control.ConclusionsConclusively, this study not only provides an alternative for large-scale cultivation of Cylindrotheca, but also pinpoints the limiting enzymes subject to further metabolic manipulation. Most importantly, the novel insights in this study should aid to understand the mechanism of biomass promotion in mixotrophic Cylindrotheca sp.

Peculiarities of determining the morphogenesis of plants Corylus avellana L. and Prunus dulcis (Mill.) D.A.Webb in vitro culture

ABSTRACT The purpose of the research was to identify the physiological–biochemical and anatomical–morphological peculiarities found during in vitro cultivation of Corylus avellana L. and Prunus dulcis (Mill.) D.A.Webb, which occur as a result of the action of trophic and phytohormonal determinants. The research was conducted on three hazelnut varieties (Trapezund, Jefferson, Tonda Gentile Romana) and four almond varieties (E5 Borozan, M41 Alex, Georgia, Louise). A theoretical and experimental rationale for their use in the microclonal propagation of these cultures has been developed. The effectiveness of the preparatory stage before introduction into aseptic conditions for growing mother plants in closed soil conditions with scattered artificial lighting and microbiological protection has been proven. This reduced self-intoxication by oxidation products with phenol-like substances and microflora contamination of primary explants. Among the nutrient media compared, the best was Nas and Read (NRM) for hazelnuts and Nas Almond Medium (NAM) for almonds. Passaging on the same media leads to a decrease in regeneration indicators. In regenerants of almonds, the rosette of the shoots was noted, and in hazelnuts, the death of apical buds was also found. To prevent this, alternating NRM and driver and kuniyuki walnut (DKW) media for hazelnuts and NAM and Quirin and Lepoivre (QL) for almonds was effective. Long-term cultivation on media with a high content of synthetic analogues of phytohormones leads to the accumulation of phytotoxic effects with each subsequent passage. The phytotoxic effect of cytokinins was manifested in hyperhydration of shoots and of auxins in callus fertilisation. On comparing the ontogenesis of regenerants from explants isolated from mother plants aged 30–180 days, it was found that the optimal age for hazelnut and almond was 90 days. To reset the trophic and hormonal determinants, the introduction of explant donors into a state of dormancy has been successfully used. At the final fourth stage of microclonal propagation, in order to adapt plants simultaneously with an increase in the number of regenerants, it is effective to use the photoautotrophic method of microclonal propagation with intensive lighting and air enriched with carbon dioxide. For the transition of plants from conventional heterotrophic propagation to autotrophic cultivation, an intermediate stage of pre-adaptation of regenerants in wet chamber conditions is effective.

Application of Chlorella vulgaris for nutrient removal from synthetic wastewater and MBR-treated bio-park secondary effluent: growth kinetics, effects of carbon and phosphate concentrations

Application of Chlorella vulgaris for polishing secondary effluent of a wastewater treatment (containing C, N and P) was investigated. As a first step, batch experiments were conducted in Bold's Basal Media (BBM) to quantify the effects of orthophosphates (0.1-107mg/L), organic carbon (0-500mg/L as acetate) and N/P ratio on the growth of Chlorella vulgaris. The results revealed that the orthophosphate concentration was found to control the removal rates of nitrates and phosphates; however, both were effectively removed (> 90%) when the initial orthophosphate concentration was 4-12mg/L. The maximum nitrate and orthophosphate removals were observed at an N:P ratio of ~ 11. However, the specific growth rate (µ) was significantly increased (from 0.226 to 0.336g/g/day) when the initial orthophosphate concentration was 0.1-4.3mg/L. On the other hand, the presence of acetate had significantly improved the specific growth and specific nitrate removal rates of Chlorella vulgaris. The specific growth rate increased from 0.34g/g/day in a purely autotrophic culture to 0.70g/g/day in the presence of acetate. Subsequently, the Chlorella vulgaris (grown in BBM) was acclimated and grown in the membrane bioreactor (MBR)-treated real-time secondary effluent. Under the optimised conditions, 92% nitrate and 98% phosphate removals (with a growth rate of 0.192g/g/day) were observed in the bio-park MBR effluent. Overall, the results indicate that coupling Chlorella vulgaris as a polishing treatment in existing wastewater treatment units could be beneficial for highest level of water reuse and energy recovery goals.

Thermal cultivation of halophilic Cyanobacterium aponinum for C-phycocyanin production and simultaneously reducing carbon emission using wastewater

A newly halophilic Cyanobacteria aponinum PCC10605 is first explored as a robust blue alga compared to Chlorella sorokiniana (CS), Chlorella vulgaris (CV) and Chlamydomonas reinhardtii (CC400) that can be cultured at high salinity and mesophilic condition. The Logistic and Gompertz models were applied to evaluate cell growth of four algal strains under mixotrophic and autotrophic cultivation, thus the optimal condition for PCC10605 was indicated in autotrophic and 20 g/L seawater at 39°C. When nitrogen and phosphorus concentration was at the ratio of 3:1, PCC10605 grew fast and had the better C-phycocyanin (C-PC) productivity, achieving to 1.53 g/L of biomass and 0.492 g/L of C-PC under 25% light intensity and 12:12 light period. Finally, a feasible and negative carbon emission via PCC10605 which cultured in the mixed medium and wastewater at 1:2 vol ratio (i.e., M1W2), reaching to 1.227 g/L of biomass concentration, 0.503 g/L C-PC production, reducing 40.5% of chemical oxygen demand (COD), and capturing 1.71 g-CO2 simultaneously in a Photo System Instruments (PSI).

Modeling of microalgal biodiesel production integrated to a sugarcane ethanol plant: Energy and exergy efficiencies and environmental impacts due to trade-offs in the usage of bagasse in the Brazilian context

The Brazilian sugarcane mills already provide significant amounts of renewable products (ethanol and bioelectricity) through self-sufficient bagasse cogeneration. Gaseous outputs of the sector can provide streams rich in biogenic carbon dioxide (CO2), suitable for the autotrophic cultivation of microalgae and aim, hereinafter, their conversion into biodiesel. This work modeled the integration of an ethanol plant with a cogeneration system, covering the enzymatic hydrolysis of bagasse and the production of microalgae biodiesel. A standard ethanol plant yielding 96 L ethanol/t cane may produce an additional 7.5–30 L microalgae biodiesel/t cane but at the expense of its energy self-sufficiency; the biorefinery must recur to fossil resources unless other biomass (besides bagasse) and coproducts by the plant's neighborhood can be exploited. The process simulation is conducted in nine cases derived from a central composite design with two factors – the fraction of bagasse destined for the hydrolysis system (x1) and the fraction of ethanol sent to produce anhydrous ethanol (x2) – and three levels for each factor (0, 50, 100%). Energy ratios between representative outputs and inputs – Net energy ratio (NER) and Fossil energy ratio (FER) –, direct CO2 emission, and exergy efficiencies were calculated as representative responses to evaluate the plant's technical and environmental efficiencies. Statistical tools (t-Student test, ANOVA, and R2) showed that the constructed models were robust and that the responses varied significantly with x1, while x2 produced mild or negligible effects. The highest achievable NER and FER were 0.83 and 2.09, respectively. The whole system resulted in a FER equal to 1 when bagasse usage is split in half between the hydrolysis and cogeneration systems. This result guarantees that the energy related to the useful products is higher than the requirements of fossil energy inputs, within an acceptable range. The optimum CO2 emission and exergy efficiency were found when 6–8% of the bagasse is hydrolyzed, which is also a range covering attractive energy ratios. The proposed integration benefits the sector, but resorting to renewable sources to supply energy deficits, developing the technological exploitation over wasted coproducts, and studying heat and mass integration of processes are highly recommended to enhance the global-system performance.

Characterization of Neochloris oleoabundans under Different Cultivation Modes and First Results on Bioactivity of Its Extracts against HCoV-229E Virus

Microalgae are proposed in several biotechnological fields because of their ability to produce biomass enriched in high-value compounds according to cultivation conditions. Regarding the health sector, an emerging area focuses on natural products exploitable against viruses. This work deals with the characterization of the green microalga Neochloris oleoabundans cultivated under autotrophic and mixotrophic conditions as a source of whole aqueous extracts, tested as antivirals against HCoV-229E (Coronaviridae family). Glucose was employed for mixotrophic cultures. Growth and maximum quantum yield of photosystem II were monitored for both cultivations. Algae extracts for antiviral tests were prepared using cultures harvested at the early stationary phase of growth. Biochemical and morphological analyses of algae indicated a different content of the most important classes of bioactive compounds with antiviral properties (lipids, exo-polysaccharides, and total phenolics, proteins and pigments). To clarify which phase of HCoV-229E infection on MRC-5 fibroblast cells was affected by N. oleoabundans extracts, four conditions were tested. Extracts gave excellent results, mainly against the first steps of virus infection. Notwithstanding the biochemical profile of algae/extracts deserves further investigation, the antiviral effect may have been mainly promoted by the combination of proteins/pigments/phenolics for the extract derived from autotrophic cultures and of proteins/acidic exo-polysaccharides/lipids in the case of mixotrophic ones.

Development of Chlorella pyrenoidosa EMS mutants with enhanced biomass and lipid content for biofuel production

Biodiesel production from microalgae depends on algal biomass production through autotrophic cultivation, and it has a lot of potential as a feasible alternative source of energy. The lethal and mutagenic effects of ethyl methanesulphonate (EMS) are investigated in the present study on the organism Chlorella pyrenoidosa for the generation of paler mutants. The C. pyrenoidosa wild-type strain was treated with 0.1, 0.2, and 0.5 M EMS doses and the colonies that appeared after 20 days of growth on a solid TAP medium were analyzed, and a total of two mutant colonies with less pigmentation were identified. The CPM1 (10.02 ± 0.03 and 3.12 ± 0.04 µg/ml) and CPM2 (9.55 ± 0.0 and 32.84 ± 0.03 µg/ml) mutants had lower chlorophyll a and b and carotenoids content than wild type. Mutants produced significant biomass (1.34- and 1.31-fold enhanced biomass in CPM1 and CPM2) and lipid content than the wild type. These findings suggest that genetic modification of C. pyrenoidosa has the potential to produce strains with increased biomass productivity and lipid content for biofuel production.

Continuous Supply of Non-Combustible Gas Mixture for Safe Autotrophic Culture to Produce Polyhydroxyalkanoate by Hydrogen-Oxidizing Bacteria.

Polyhydroxyalkanoates (PHAs) are eco-friendly plastics that are thermoplastic and biodegradable in nature. The hydrogen-oxidizing bacterium Ralstonia eutropha can biosynthesize poly[(R)-3-hydroxybutyrate] [P(3HB)], the most common PHA, from carbon dioxide using hydrogen and oxygen as energy sources. In conventional autotrophic cultivation using R. eutropha, a gas mixture containing 75–80 vol% hydrogen is supplied; however, a gas mixture with such a high hydrogen content has a risk of explosion due to gas leakage. In this study, we aimed to develop an efficient cell culture system with a continuous supply of a non-combustible gas mixture (H2: O2: CO2: N2 = 3.8: 7.3: 13.0: 75.9) for safe autotrophic culture to produce P(3HB) by hydrogen-oxidizing bacteria, with a controlled hydrogen concentration under a lower explosive limit concentration. When the gas mixture was continuously supplied to the jar fermentor, the cell growth of R. eutropha H16 significantly improved compared to that in previous studies using flask cultures. Furthermore, an increased gas flow rate and agitation speed enhanced both cell growth and P(3HB) production. Nitrogen source deficiency promoted P(3HB) production, achieving up to 2.94 g/L P(3HB) and 89 wt% P(3HB) content in the cells after 144 h cultivation. R. eutropha NCIMB 11599, recombinant R. eutropha PHB-4, and Azohydromonas lata grew in a low-hydrogen-content gas mixture. R. eutropha H16 and recombinant R. eutropha PHB-4 expressing PHA synthase from Bacillus cereus YB-4 synthesized P(3HB) with a high weight-average molecular weight of 13.5–16.9 × 105. Thus, this autotrophic culture system is highly beneficial for PHA production from carbon dioxide using hydrogen-oxidizing bacteria as the risk of explosion is eliminated.