Biomass generation and heterologous isoprenoid milking from engineered microalgae grown in anaerobic membrane bioreactor effluent

Abstract

Wastewater (WW) treatment in anaerobic membrane bioreactors (AnMBR) is considered more sustainable than in their aerobic counterparts. However, outputs from AnMBR are mixed methane and carbon dioxide gas streams as well as ammonium- (N) and phosphate- (P) containing waters. Using AnMBR outputs as inputs for photoautotrophic algal cultivation can strip the CO2 and remove N and P from effluent which feed algal biomass generation. Recent advances in algal engineering have generated strains for concomitant high-value side product generation in addition to biomass, although only shown in heavily domesticated, lab-adapted strains. Here, investigated whether such a strain of Chlamydomonas reinhardtii could be grown directly in AnMBR effluent with CO2 at concentrations found in its off-gas. The domesticated strain was found to proliferate over bacteria in the non-sterile effluent, consume N and P to levels that meet general discharge or reuse limits, and tolerate cultivation in modelled (extreme) outdoor environmental conditions prevalent along the central Red Sea coast. High-value co-product milking was then demonstrated, up to 837 micro g / L culture in 96 h, in addition to algal biomass production, ~2.4 g CDW / L in 96 h, directly in effluents. This is the first demonstration of a combined bio-process that employs a heavily engineered algal strain to enhance the product generation potentials from AnMBR effluent treatment. This study shows it is possible to convert waste into value through use of engineered algae while also improve wastewater treatment economics through co-product generation.

Engineered production of isoprene from the model green microalgaChlamydomonas reinhardtii

“…As alternatives to fermentative hosts, algal chassis can produce heterologous products of interest directly from CO 2 as a carbon source, while consuming nitrogen and phosphorous sources in water (de Freitas et al, 2023). These properties make microalgae interesting for sustainable bio-production concepts that convert waste to value.…”

“…It was recently shown that heterologous patchoulol production was lower when cells were exposed to modeled higher temperature and light environmental conditions (de Freitas et al, 2023), suggesting that both temperature and light regimes impact isoprenoid biosynthesis in the alga. Isoprene synthases have optimal catalytic activities at ∼42 °C (Li et al, 2019).…”

“…It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted January 13, 2023. ; https://doi.org/10.1101/2023.01.12.523746 doi: bioRxiv preprint For the green alga, catalytic activity of the IbIspS mediated by temperature appears to be the most significant factor in isoprene production, and that optimal enzyme activity is likely outside its range of growth temperatures. However, daily high temperature peaks are tolerated for C. reinhardtii, as recently shown in environmental modelling in the extreme environment of the Red Sea coast (de Freitas et al, 2022). It could, therefore, be possible to create cultivation parameters that balance cell growth densities and temperature in lower and consistent light conditions to maximize isoprene yields.…”

“…For the green alga, catalytic activity of the IbIspS mediated by temperature appears to be the most significant factor in isoprene production, and that optimal enzyme activity is likely outside its range of growth temperatures. However, daily high temperature peaks are tolerated for C. reinhardtii, as recently shown in environmental modelling in the extreme environment of the Red Sea coast (de Freitas et al, 2022). It could, therefore, be possible to create cultivation parameters that balance cell growth densities and temperature in lower and consistent light conditions to maximize isoprene yields.…”

Cultivation of the polyextremophile Cyanidioschyzon merolae 10D during summer conditions on the coast of the Red Sea and its adaptation to hypersaline sea water

“…Most desert countries have coastal regions, including the Arabian Peninsula, Northern Australia, Chile, and North Africa (Lefers et al, 2020;Greene et al, 2022). At these locales, saline microalgal processes are logical (Ishika et al, 2017), and inland, where human settlements occur, freshwater algal cultivation can participate in waste-water treatment and reuse (de Freitas et al, 2023). It was recently reported that the geographical areas with the highest potential for onshore marine microalgae biomass production were between 30°N and 30°S in the so-called "hot belt countries" (Greene et al, 2022).…”