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Open research questions in Algal biology and biofuel production

27 unresolved questions extracted from the limitations and future-work sections of 367 Algal biology and biofuel production papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • The transport pathways, target mol- ecules, and detoxification mechanisms in different organ- isms are not yet fully understood, and research gaps in these areas remain. These bio- compounds have a vast range of chemical structures and modes of action, but no standardized mechanisms have been defined to date. Furthermore, the interactions between allelochemicals and the soil microenvironment are poorly understood, which underscores the need for further research into how microbial communities modify or degrade these bio- active substances.

    Microalgal biopesticides in the circular economy: harnessing algae for sustainable pest management · 2026 · DOI

  • The two-step cultivation strategy has an initial phase in which cells are grown under ideal or nutrient-rich conditions, followed by a second phase in which specific stress conditions are imposed to drive the metabolic flux towards the synthesis of the desired molecule. This approach focused on achieving high biomass production in induced stress-mediated metabolic stage I, while stage II reprogramming to enhance the synthesis of desired metabolites, such as lipids, carbohydrates, and proteins (Nagappan et al., 2019). Several studies using the two-step cultivation system have highlighted its potential and limitations. For example, Perečinec et al (2022) demonstrated that precise selenite dosing and timing are important to prevent excessive ROS accumulation and cell death, unlike the tolerant lag-phase adaptation observed in a one-stage system (Perečinec et al., 2022). With the same approach, a two-step regulatory strategy was employed to enhance both lipid and biomass productivity, where supplementation with additional phosphorus and nitrogen by the end of the second day significantly improved lipid yield (Li et al., 2023). Despite these promising outcomes, the effectiveness of the two-step system depends primarily on prior knowledge of the strain’s physiology, growth conditions, and appropriate stress inducers. Although extensive research has been conducted using the twostage approach, obtaining consistent results is challenging and may fall short of the precision and efficiency achievable with genetically modified strains. Therefore, a deeper understanding of stress responses and metabolite induction is necessary to address these limitations. Further, several operational and physiological constraints also complicate the two-step cultivation system. A fundamental challenge lies in the trade-off between biomass accumulation and lipid production, where excessive or poorly treatments can suppress growth and reduce timed stress productivity (Shokravi et al., 2020). For example, high inoculum density in stage II can affects light penetration, thereby limiting photosynthetic efficiency and reducing metabolic flux towards the production of desired metabolites. While interventions such as artificial lighting or reduced culture depth can partially mitigate these effects, they will reflect an increase in production costs (Shokravi et al., 2020). For example, in a study performed by Singh and Sharma (2012), cultures started at 0.5 OD (680 nm) showed reduced light penetration and shading effects, whereas those started at 0.1 OD (680 nm) showed limited productivity due to insufficient initial biomass (Singh and Sharma, 2012).

    Inducible two-step cultivation of microalgae: engineering the growth and lipid biosynthesis for biofuel production · 2026 · DOI

  • Our results suggest that photoheterotro- phy allows airborne bacteria to access an additional energy source—light—when organic substrates are scarce, thereby promoting ATP synthesis and poten- tially enhancing stress response capabilities.

    Phototrophy improves the aerial fitness in a photoheterotrophic Methylobacterium isolated from clouds · 2026 · DOI

  • However, this interpretation remains speculative, and further investigation is required. Food Chem Toxicol 47:2189–2195 Richmond A, Lichtenberg E, Stahl B, Vonshak A (1990) Quantitative assessment of the major limitations on productivity of Spirulina platensis in open raceways.

    Selective culture of Arthrospira platensis by continuous NH3 exposure to control microalgal contaminants and grazers, exemplified by Synechococcus leopoliensis · 2026 · DOI

  • J. Energy Res. 2023 (1), 5412660–5412668. doi:10.1155/2023/5412660 future bioenergy production. Int. for Panahi, Y., Khosroshahi, A. Y., Sahebkar, A., and Heidari, H. R. (2019). Impact of cultivation condition and media content on Chlorella vulgaris composition. Adv. Pharm. Bull. 9 (2), 182–194. doi:10.15171/apb.2019.022 Porninta, K., Khemacheewakul, J., Techapun, C., Phimolsiripol, Y., Jantanasakulwong, K., Sommanee, S., et al. (2023). Pretreatment and enzymatic hydrolysis optimization of lignocellulosic biomass for ethanol, xylitol, and phenylacetylcarbinol co-production using Candida magnoliae. Front. Bioeng. Biotechnol. 11, 1332185. doi:10.3389/fbioe. 2023.1332185 Qi, F., Shen, P., Hu, R., Xue, T., Jiang, X., Qin, L., et al. (2020). Carotenoids and lipid production from Rhodosporidium toruloides cultured in tea waste hydrolysate. Biotechnol. Biofuels 13 (1), 74. doi:10.1186/s13068-020-01712-0 Ren, S., Shao, C., Zhu, F., Schagerl, M., Hu, X., Sobhi, M., et al. (2025). Optimization and synergistic enhancement of microalgae productivity in laboratory raceway ponds via coregulation of automated light-supplemented mixers and electric field system. Biotechnol. Biofuels Bioprod. 18 (1), 63. doi:10.1186/s13068-025-02658-x Rohit, M. V., and Venkata Mohan, S. (2018). Quantum yield and fatty acid profile variations with nutritional mode during microalgae cultivation. Front. Bioeng. Biotechnol. 6 (SEP), 111. doi:10.3389/fbioe.2018.00111 Schnurr, P. J., Molenda, O., Edwards, E., Espie, G. S., and Allen, D. G. (2016). Improved biomass productivity in algal biofilms through synergistic interactions between photon flux density and carbon dioxide concentration. Bioresour. Technol. 219, 72–79. doi:10. 1016/j.biortech.2016.06.129 Shi, K., Gao, Z., Shi, T. Q., Song, P., Ren, L. J., Huang, H., et al. (2017). Reactive oxygen species-mediated cellular stress response and lipid accumulation in oleaginous microorganisms: the state of the art and future perspectives. Front. Microbiol. 8 (Number MAY), 793. doi:10.3389/fmicb.2017.00793 Shi, T.-Q., Wang, L.-R., Zhang, Z.-X., Sun, X.-M., and Huang, H. (2020). Stresses as firstline tools for enhancing lipid and carotenoid production in microalgae. Front. Bioeng. Biotechnol. 8, 610. doi:10.3389/fbioe.2020.00610 Su, H., Zhang, X., He, Y., Li, L., Wang, Y., Hong, G., et al. (2020). Transcriptomic analysis reveals the molecular adaptation of three major secondary metabolic pathways to multiple macronutrient starvation in tea (Camellia sinensis). Genes. 11 (3), 241. doi:10.3390/genes11030241 Tomar, S., Agarwal, S., Singh, H., Kumar, R., Qureshi, K. A., Jaremko, M., et al. (2023). Microalgae: a promising source for biofuel production. Biocatal. Agric. Biotechnol. 53, 102877. doi:10.1016/J.BCAB.2023.102877 Tsarpali, M., Arora, N., Kuhn, J.

    Valorization of acid-hydrolyzed tea stem waste for sustainable biodiesel production using Chlorella vulgaris: a biorefinery approach · 2026 · DOI

  • for attenuation From a mechanistic perspective, elevated irradiance can compensate in dark, colored matrices by increasing photon availability in deeper regions of the reactor and improving the probability that cells experience periods above the local light compensation point. However, excessive surface irradiance can also increase the risk of photoinhibition and photo-oxidative stress, particularly under suboptimal mixing where cells remain exposed to high light for prolonged intervals (García-Robledo et al., 2012; Panahi et al., 2019). In the present system, the absence of growth suppression at the highest evaluated PPFD is consistent with the concept that the hydrolysate matrix itself acts as a partial “optical buffer,” reducing the effective internal irradiance through absorption and scattering and thereby lowering the photoinhibition risk at the cell level. However, mitigating this optical introduces a complex trade-off that must be critically evaluated through a Life Cycle Assessment (LCA) perspective. On one hand, utilizing highly concentrated waste streams is beneficial for the water consumption aspect of the LCA, as it drastically reduces the freshwater footprint of the bioprocess. On the other hand, a more concentrated hydrolysate fundamentally increases medium turbidity and color intensity. At larger scales, this inherent turbidity is further compounded by mutual cell shading and complex light–dark cycling, which inherently cap volumetric productivity (Akca et al., 2024; Kumar et al., 2015). To maintain baseline photosynthetic performance in such dense media, significantly higher levels of incident irradiance are required. As highlighted in recent scale-up studies, photon delivery often becomes the primary energetic bottleneck when utilizing dark, hydrolysate-rich cultivation matrices (Hoeniges et al., 2022; Ren et al., 2025). This forced increase in irradiance has a direct, negative impact on the energy consumption aspect of the LCA. Consequently, any industrial scale-up of this process cannot simply maximize waste concentration; it must critically evaluate the optical parameters to find the optimal balance between minimizing the freshwater footprint and minimizing the electrical energy required for photon delivery. Furthermore, while 240 µmol photons m-2 s-1 yielded the highest productivity in this study, the absolute upper threshold of irradiance was not established; future research should investigate whether even higher light intensities could further enhance biomass yields without inducing photoinhibition.

    Valorization of acid-hydrolyzed tea stem waste for sustainable biodiesel production using Chlorella vulgaris: a biorefinery approach · 2026 · DOI

  • The ability of MBC culture to reflocculate after EPS extraction suggests potential for non-destructive, cyclic EPS harvesting, but this requires further development into a scalable production module.

    Biofilm-driven flocculation in microalgae-bacteria consortia: Mechanisms and biotechnological implications · 2026 · DOI

  • The utility of EPS as a functional bioflocculant depends strongly on the consistency and safety of the extracted material, requiring future applications to establish standardization protocols.

    Biofilm-driven flocculation in microalgae-bacteria consortia: Mechanisms and biotechnological implications · 2026 · DOI

  • If EPS is used in food, feed or pharma-related contexts, rigorous toxicological assessment is required, as residual cell content or unknown metabolites in the extract could limit its commercial viability.

    Biofilm-driven flocculation in microalgae-bacteria consortia: Mechanisms and biotechnological implications · 2026 · DOI

  • Batch-to-batch variability must be expected since MBC composition and EPS profiles can shift over time due to internal species dynamics or environmental influences, requiring regular compositional monitoring.

    Biofilm-driven flocculation in microalgae-bacteria consortia: Mechanisms and biotechnological implications · 2026 · DOI

  • In the cold climates of countries like Canada, algae cultivation in open raceway pond (ORP) systems is limited to a short period of the year when pond surface water temperatures and ambient light conditions enable optimal culture growth.

    Development of cost models of algae production in a cold climate using different production systems · 2019 · DOI

  • Photon-to-biomass conversion efficiency in oxygenic phototrophs can vary widely under controlled cultivation, yet its mechanistic origin remains difficult to resolve at the system level.

    A mechanistic framework for photon-to-carbon efficiency: coupling photosynthetic energy supply and light respiration in microalgae · 2026 · DOI

  • To support industrial translation, future research should focus on continuous cultivation strategies, scale-appropriate photobioreactor design for dark effluents under non-sterile outdoor conditions, and rigorous validation through techno-economic…

    Valorization of acid-hydrolyzed tea stem waste for sustainable biodiesel production using Chlorella vulgaris: a biorefinery approach · 2026 · DOI

  • Future research should focus on refining extraction and functionalization methods, optimizing delivery mechanisms, and conducting in-depth clini- cal studies to validate the long-term safety and efficacy of microalgal-derived proteins.

    Harnessing microalgal proteins as sustainable bioactive ingredients for cosmetics: green extraction, functionalization, and advanced delivery systems · 2026 · DOI

  • The observed growth of Pseudomonas spp. under enzymatic treatment could result from differences in concentration, mixture composition, or the presence of other Pseudomonas species, which requires further clarification.

    Biofilm-driven flocculation in microalgae-bacteria consortia: Mechanisms and biotechnological implications · 2026 · DOI

  • Future efforts should explore how engineered flocs behave under scaled conditions and continuous cultivation, including stability, performance under environmental stress, and reproducibility.

    Biofilm-driven flocculation in microalgae-bacteria consortia: Mechanisms and biotechnological implications · 2026 · DOI

  • In contrast, understanding of the evolutionary responses of photosymbioses to persistent warming remains limited and direct observations of evolution in response to warming are scarce, as many associations are slow-evolving and do not enable observations on a tractable timescale.

    One year of warming leads to the total loss of productivity in a widespread photosymbiosis · 2024 · DOI

  • This study therefore presents trends in bioenergy production from orange industrial by‐products with the aim of supporting further research on energy recovery from orange industry solid waste and to assist future decision making in this field of science.

    Bioenergy production from orange industrial waste: a case study · 2020 · DOI

  • The effect of β ‐glucosidase on the hydrolysis of algal cellulose, and the comparison between the effect of the addition of α ‐amylase and amyloglucosidase separately or together on the hydrolysis of algal starch, have not been described previously.

    Synergism of cellulases and amylolytic enzymes in the hydrolysis of microalgal carbohydrates · 2018 · DOI

  • Phytoplankton constitute an important component of surface water ecosystems; however little is known about their contribution to biotransformation of organic micropollutants.

    Exploring micropollutant biotransformation in three freshwater phytoplankton species · 2017 · DOI

  • In the present study, the productivity of lipid, starch, and protein fractions were shown through growth experiments to vary widely with species, feeding regime, and harvesting period.

    Time‐dependent life cycle assessment of microalgal biorefinery co‐products · 2016 · DOI

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27 open questions have been extracted from the limitations and future-work passages of 367 Algal biology and biofuel production papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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