Low doses of toxicants can enhance algae potential as biodiesel and biomass feedstocks

The ambitious target of worldwide governments for achieving carbon neutrality by the middle of the current century confers a key role to negative emission technologies. To meet this target, algae-based renewable bioenergy is expected to find larger-scale application. However, the photosynthetic efficiency and potential of algae to produce biomass and biofuel should be improved, and further bioengineering developments are needed. Considerable evidence has recently accumulated to show that a plethora of toxicants stimulate algae at low doses (hormesis), an effect that is controversial to the long-held belief that toxicants only suppress algae at high doses. Low doses of toxicants induce mild oxidative stress, which increases the synthesis of photosynthetic pigments and thus sunlight capturing potential. Photosynthesis is enhanced, and algal growth and biomass also increase. Protein content, total lipids, and biochemical quality are also increased in a dose-dependent manner, indicating the potential of low-dose stress to enhance algal biomass and biofuel. Underlying molecular mechanisms driving these uncovered low-dose-stress responses started to be unraveled, providing an opportunity for novel bioengineering developments to maximize algal potential as feedstock for the production of carbon-neutral fuel. Further scientific developments are needed to improve the performance of algae as a feedstock, reduce the cost of their cultivation, and enhance their resilience in toxicant-containing wastewater. These also call for reduction of toxicants to low levels adequate for improved performance of algae cultured for bioenergy feedstock.