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Green microalga Botryococcus braunii is a eukaryotic photosynthetic microorganism considered as a rich source of biofuel compounds, such as hydrocarbons and lipids, despite its rather slow growth. To improve the biomass, hydrocarbon, and lipid productivity, an ethyl methanesulfonate-induced mutagenesis was carried out on the indigenous microalga, Botryococcus braunii AARL G036. Among those mutants, EMS-mutant E1.0H15 gave the highest biomass and hydrocarbon productivity, which was higher than 1.17, 1.45, and 1.16-fold, respectively, when compared with the wild type (WT). Subsequently, two-stage cultivation with crucial stress factors was successfully exploited to boost the biofuel productivity of EMS-mutant E1.0H15 by increasing the lipid content by 1.22-fold (up to 48.6%) and by 1.20-fold for the hydrocarbon content (up to 71.6%) compared to one-stage cultivation. More importantly, after 24-month maintenance, the high biofuel productivity in EMS-mutant E1.0H15 remains unchanged. In addition, the fatty acid composition (>96% C16–C18) and fuel properties of the mutated microalgal lipid-derived biodiesel indicated good oxidation stability (17.5 h) and high heating values (38.6 MJ kg−1), which were in accordance with those of the international standards, i.e., EN-14214 and ASTM D675140. This strategy could contribute greatly to the further development of the microalgal strain, allowing improvement and cultivation for the desired biofuel properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Microalgae growth-promoting bacteria (MGPB), both actinobacteria and non-actinobacteria, have received considerable attention recently because of their potential to develop microalgae-bacteria co-culture strategies for improved efficiency and sustainability of the water-energy-environment nexus. Owing to their diverse metabolic pathways and ability to adapt to diverse conditions, microalgal-MGPB co-cultures could be promising biological systems under uncertain environmental and nutrient conditions. This review proposes the recent updates and progress on MGPB for microalgae cultivation through co-culture strategies. Firstly, potential MGPB strains for microalgae cultivation are introduced. Following, microalgal-MGPB interaction mechanisms and applications of their co-cultures for biomass production and wastewater treatment are reviewed. Moreover, state-of-the-art studies on synthetic biology and metabolic network analysis, along with the challenges and prospects of opting these approaches for microalgal-MGPB co-cultures are presented. It is anticipated that these strategies may significantly improve the sustainability of microalgal-MGPB co-cultures for wastewater treatment, biomass valorization, and bioproducts synthesis in a circular bioeconomy paradigm. [Display omitted] • Microalgae growth promoting bacteria (MGPB) have potential in co-cultures. • Microalgal-MGPB co-culture interaction mechanisms are described. • Biomass production and wastewater treatment via co-cultures are reviewed. • Synthetic biology and metabolic networks in co-cultures are discussed. • Prospects for future research on microalgal-MGPB co-cultures are proposed. [ABSTRACT FROM AUTHOR]

The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) derived from cyanobacteria is an environmentally friendly biodegradable polymer. The low yield of PHBV's production is the main hindrance to its sustainable production, and the manipulation of PHBV production processes could potentially overcome this obstacle. The present research investigated evolutionarily divergent cyanobacteria obtained from local environments of Thailand. Among the strains tested, Cyanosarcina sp. AARL T020, a hot spring cyanobacterium, showed a high rate of PHBV accumulation with a fascinating 3-hydroxyvalerate mole fraction. A two-stage cultivation strategy with sole organic carbon supplementation was successful in maximizing cyanobacterial PHBV production. The use of an optimized medium in the first stage of cultivation provided a 4.9-fold increase in biomass production. Subsequently, the addition of levulinic acid in the second stage of cultivation can induce significant biomass and PHBV production. With this strategy, the final biomass production and PHBV productivity were increased by 6.5 and 73.2 fold, respectively. The GC-MS, FTIR, and NMR analyses confirmed that the obtained PHBV consisted of two subunits of 3-hydroxyvaryrate and 3-hydroxybutyrate. Interestingly, the cyanobacterial PHBV contained a very high 3-hydroxyvalerate mole fraction (94%) exhibiting a low degree of crystallinity and expanding in processability window, which could be applied to polymers for desirable advanced applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chlorella integrated into zero-waste biorefining for biodiesel and biofertilizer. • Optimal DES pretreatment: 1.6:1 CH 3 COOH-ChCl ratio, 0.36 g biomass, 2.5 mins. • Optimal lipid recovery: 10-min extraction, 1:3 MeOH-BuOH ratio. • Microalgal biodiesel meets favorable fuel characteristics. • De-oiled microalgal waste boosts lettuce pigments and alters microbial communities. Microalgal biomass is gaining increasing attention to produce high-value co-products. This study proposes integrating Chlorella microalgal biomass into a zero-waste biorefining system, aiming to produce biodiesel and biofertilizer. It investigates optimal conditions for ultrasound-assisted deep eutectic solvent (DES) pretreatment and lipid recovery to enhance the extraction of lipids. Optimal DES pretreatment was identified as a 1.6:1 acetic acid-to-choline chloride molar ratio, 0.36 g biomass loading, and 2.50 min of pretreatment. Lipid recovery succeeded with a 10-minute extraction time and a 1:3 methanol-to-butanol volume ratio. These conditions yielded biodiesel-quality lipids at 139.52 mg/g microalgal biomass with superior fuel characteristics. The de-oiled microalgal biomass residue exhibited promise as a lettuce biofertilizer, enhancing photosynthetic pigments but potentially reducing yields by 40 %. The study also notes changes in rhizosphere microbial communities, indicating both stimulatory and inhibitory effects on beneficial microbes. This study has the potential to enhance sustainability in energy, agriculture, and the environment. [ABSTRACT FROM AUTHOR]

Two promising oleaginous microalgae, Scenedesmus sp. SPP and marine Chlorella sp. were cultivated under various trophic modes. Both microalgae grew best under mixotrophic/nitrogen-rich mode, indicating good metabolisms of both inorganic (CO 2) and organic (glucose) carbon sources. While mixotrophic/nitrogen-starvation conditions promoted the accumulation of lipids with superior biodiesel properties. The key energy sources, including light intensity, CO 2 and glucose concentrations, for mixotrophic cultivation of the selected Scenedesmus sp. SPP was simultaneously optimized by Response Surface Methodology. High light intensity combined with high CO 2 retarded growth but stimulated lipid/pigment synthesis. Two-stage mixotrophic cultivation using optimal conditions for biomass (light intensity 4.8 klux, CO 2 13%, glucose 1% under nitrogen-rich mode) followed by those for lipid accumulation (light intensity 6.0 klux, CO 2 15%, glucose 1% under nitrogen-starvation mode) successfully enhanced biomass by 1.46 folds and lipids by 1.39 folds and also improved the biodiesel properties. These strategies may significantly contribute to the development of microalgae-based biofuel and biochemical industries. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Actinomycete co-culture successfully enhanced both microalgal biomass and lipid. • Piscicocus intestinalis WA3 produced high algal growth-promoting agents. • Microbial lipids are composed of C16-C20 fatty acids with good fuel properties. • Biogas effluent can be used as cost-effective media for actinomycete co-culture. In this study, an innovative approach to enhance the production of microalgal biomass and lipid as a promising sustainable feedstock for biodiesel was proposed using an actinomycetes co-culture with microalgae in the biogas digestate effluent (BDE) that can be employed as an environmentally friendly and cost-effective strategy. Among tested actinomycete isolates, Piscicocus intestinalis WA3 produced indole-3-acetic acid and siderophores as algal growth promoting agents and showed effective lipid accumulation with satisfying fatty acids composition. During co-cultivation of P. intestinalis WA3 with microalga Tetradesmus obliquus AARL G022 in the BDE, biomass production, chlorophyll a content, and lipid productivity were significantly increased by 1.30 folds, 1.39 folds, and 1.55 folds, respectively, compared to microalgae monoculture. The accumulated lipids contained long-chain fatty acids with better fuel properties that could potentially be used as biodiesel feedstock. The overall results evidenced that actinomycete co-culture would contribute greatly to the cost-effective production of environmental-friendly microbial-based biofuel. [ABSTRACT FROM AUTHOR]

Oleaginous microalgae are gaining increasing attention for simultaneous wastewater bioremediation and biofuel feedstock production. In this study, four oleaginous species of microalgae including Chlamydomonas sp. WWP, Scenedesmus sp. HP56, Haematococcus sp., and Nannochloropsis sp., were screened for their growth and lipid production at 30, 35, and 40 °C, under light intensity at 3, 4, and 5 klux. Among the strains screened, Haematococcus sp. grew best and gave comparable high growth at 30 °C and 35 °C (0.7–0.8 g/L) indicating its thermotolerant characteristic, and the optimal light intensity was found at 4 klux. Haematococcus sp. also grew well using unsterile secondary effluent from the seafood processing plant and produced high biomass (0.53–0.57 g/L) and lipids (0.17–0.19 g/L), especially in the column photobioreactor (CP). The repeated-batch outdoor cultivation mode showed that CP equipped with four-blade baffles was most efficient for the production of biomass (0.40–0.63 g/L) and lipids (0.15–0.30 g/L) during 4 cycles. The microalga also removed total nitrogen and total phosphorus from secondary effluent by 70.59% and 94.97%, respectively. The fatty acid compositions in microalgal lipids were C16-C18, especially palmitic acid, oleic acid, and linolenic acid, which show superior fuel properties, suggesting their promising use as biodiesel feedstocks. These strategies may have a significant impact not only on bioremediation of industrial effluent but also low-cost production of microalgae-based biodiesel feedstocks. [Display omitted] • Haematococcus sp. was suitable oleaginous microalga for outdoor cultivation. • Column photobioreactor with 4-blade baffles most enhanced microalgal growth. • Repeated-batch cultivation effectively produced biomass of 0.40–0.63 g/L. • Total nitrogen and total phosphorus in effluent were removed by 70.59% and 94.97%. • The microalgal lipids have high potential as biodiesel feedstocks. [ABSTRACT FROM AUTHOR]

This research focused on utilizing photoautotrophically-cultivated microalgae as efficient converters of CO 2 into high-quality renewable biodiesel. This study investigated the feasibility of capturing CO 2 from the atmosphere (0.04 % CO 2) and simulating industrial sources (20–40 % CO 2) for utilization as a simulated waste carbon source for the growth and biodiesel feedstock accumulation of three photoautotrophically-cultivated microalgae species, including Chlorella sp. AARL G049, Tetradesmus obliquus AARL G090, and Desmodesmus opoliensis AARL G085. The results demonstrated that all the tested microalgae are promising CO 2 -to-fuel converters due to their ability to efficiently convert CO 2 into lipid-rich biomass, which can subsequently be processed into biodiesel. All three strains of microalgae displayed remarkable CO 2 capture capabilities as well as significant biomass production and lipid accumulation, with the highest performance observed under a 20 % CO 2 concentration. The microalgae demonstrated CO 2 fixation rates ranging from 0.020 to 0.072 g-CO 2 /L/day, leading to significant improvements in both biomass productivity, which ranged from 0.011 to 0.040 g/L/day, and lipid accumulation, which ranged from 0.22 to 3.39 mg/L/day. Additionally, the lipid content varied between 5.04 % and 14.75 %. Interestingly, changes in CO 2 concentration, ranging from 0.04 % to 40 %, significantly influenced the composition of fatty acids, leading to elevated levels of C16–C18 fatty acids. Nevertheless, these alterations had a minimal impact on the overall quality of biodiesel. The estimated fuel characteristics of the produced biodiesel complied with global specifications for biodiesel, providing better oxidative stability (≥6 h), high heating value (≥39 MJ/kg), and cetane number (≥47). Therefore, this study emphasizes sustainable CO 2 capture and the potential of microalgae as a renewable source of economically viable biodiesel. [ABSTRACT FROM AUTHOR]