Understanding phycosomal dynamics to improve industrial microalgae cultivation

Algal-bacterial interactions are ubiquitous in both natural and industrial systems, and the characterization of these interactions has been reinvigorated by potential applications in biosystem productivity. Different growth conditions can be used for operational functions, such as the use of low-quality water or high pH/alkalinity, and the altered operating conditions likely constrain microbial community structure and function in unique ways. However, research is necessary to better understand whether consortia can be designed to improve the productivity, processing, and sustainability of industrial-scale cultivations through different controls that can constrain microbial interactions for maximal light-driven outputs. The review highlights current knowledge and gaps for relevant operating conditions, as well as suggestions for near-term and longer-term improvements for large-scale cultivation and polyculture engineering.

Innovative strategies in algal biomass pretreatment for biohydrogen production

Biohydrogen is one of the cleanest renewable energies with a high calorific value. Algal biomass can be utilized as a sustainable feedstock for biohydrogen production via dark fermentation. However, the recovery of fermentable sugar from algal biomass is challenging because of the diversity and complex cell wall composition and therefore, requires an additional pretreatment step. However, most of the conventional pretreatment strategies suffer from limited technological feasibility and poor economic viability. In this context, this review aims to present the structural complexities of the cell wall of algae and highlight the innovative approaches such as the use of hybrid technologies, biosurfactants, nanoparticles, and genetic engineering approaches for the hydrolysis of algal biomass and improved biohydrogen production. Additionally, a comprehensive discussion of the comparative evaluation of various pretreatment methods, and the techno-economic and life cycle assessment of algal biohydrogen production is also presented in this review.

Sustainable production of EPA-rich oil from microalgae: Towards an algal biorefinery

Utilization of sustainable natural resources such as microalgae has been considered for the production of biofuels, aquaculture feed, high-value bioactives such as omega-3 fatty acids, carotenoids, etc. Eicosapentaenoic acid (EPA) is an omega-3 fatty acid present in fish oil, which is of physiological importance to both humans and fishes. Marine microalgae are sustainable sources of lipid rich in EPA and different species have been explored for the production of EPA as a single product. There has been a rising interest in the concept of a multi-product biorefinery, focusing on maximum valorization of the algal biomass. Targeting one or more value-added compounds in a biorefinery scenario can improve the commercial viability of low-value products like triglycerides for biofuel. This approach has been viewed by technologists and experts as a sustainable and economically feasible possibility for the large-scale production of microalgae for its potential applications in biodiesel and jet fuel production, nutraceuticals, animal and aquaculture feeds, etc. In this review paper, we describe the recent developments in the production of high-value EPA-rich oil from microalgae, emphasizing on the upstream and downstream bioprocess techniques, and the advantages of considering an EPA-rich oil based biorefinery.

Algal Lysis by Sagittula stellata for the Production of Intracellular Valuables

The purpose of this study was to examine the efficacy of the algicidal bacterium Sagittula stellata on the cell lysis of Nannochloropsis oceanica, a microalga found in the marine environment, in order to extract intracellular valuables. Algicidal bacteria are capable of lysing algal cell walls while keeping lipids and proteins intact yet separated. We obtained these microbes from locations with consistent algae blooms and found that the bacterium Sagittula stellata displayed significant algicidal properties toward Nannochloropsis oceanica, achieving an algicidal rate of 80.1%. We detected a decrease of 66.2% in in vivo fluorescence intensity in algae cultures, obtained a recoverable crude lipid content of 23.3% and a polyunsaturated fatty acid (PUFA) ratio of 29.0% of bacteria-treated algae, and observed the lysis of the cell membrane and the structure of the nucleus of algae. We also identified the inhibited transcription of the ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit (rbcS) gene and proliferating cell nuclear antigen (PCNA)-related genes and the upregulated heat shock protein (hsp) gene in algal cells during bacterial exposure. Our results indicate that Sagittula stellata effectively lysed microalgae cells, allowing the recovery of intracellular valuables. The algicidal method of Sagittula stellata on Nannochloropsis oceanica cells was confirmed to be a direct attack (or predation), followed by an indirect attack through the secretion of extracellular algicidal compounds. This study provides an important framework for the broad application of algicidal microorganisms in algal cell disruption and the production of intracellular valuables.

Algicidal microorganisms and secreted algicides: New tools to induce microalgal cell disruption

Cell disruption is one of the most critical steps affecting the economy and yields of biotechnological processes for producing biofuels from microalgae. Enzymatic cell disruption has shown competitive results compared to mechanical or chemical methods. However, the addition of enzymes implies an associated cost in the overall production process. Recent studies have employed algicidal microorganisms to perform enzymatic cell disruption and degradation of microalgae biomass in order to reduce this associated cost. Algicidal microorganisms induce microalgae growth inhibition, death and subsequent lysis. Secreted algicidal molecules and enzymes produced by bacteria, cyanobacteria, viruses and the microalga themselves that are capable of inducing algal death are classified, and the known modes of action are described along with insights into cell-to-cell interaction and communication. This review aims to provide information regarding microalgae degradation by microorganisms and secreted algicidal substances that would be useful for microalgae cell breakdown in biofuels production processes. A better understanding of algae-to-algae communication and the specific mechanisms of algal cell lysis is expected to be an important breakthrough for the broader application of algicidal microorganisms in biological cell disruption and the production of biofuels from microalgae biomass.