Cutting down on fossil fuel consumption means gaining independence from a limited resource. Besides smarter use and higher energy efficiency there is a clear need for alternative, no-compromise solutions to cover energy demand. Plants offer a renewable energy source, but supply and price of raw materials for biodiesel applications are limited and hard to predict. Cultivation, harvest, extraction are energy-intensive processing steps. Ideally, bio-based photosynthesizing materials should have a high energy content, require minimal space and grow rapidly.

Algae - to some extent - fulfill this requirement. Several companies (also in the Danube Region) have therefore set up facilities for vertical culturing of algae and subsequent harvest of biomass incl. lipids. A recent research article (Front. Plant Sci., 28 June 2018 | https://doi.org/10.3389/fpls.2018.00741 ) is of high relevance for them, and for any start-ups wishing to jump on the “algae business”.

So far, improving lipid (=energy) production in algae by manipulating cultivation conditions poses a dilemma: Lipid contents do increase e.g. under high-light conditions (using up energy!).

Alternatively, lipid production can be enhances if algae are cultivated in nitrogen-deprived nutrient solution. However, lack of nitrogen automatically stops cell growth (biomass production). Thus, depending on conditions you end up either with little, energy-rich biomass, or with lots of energy-poor biomass.

The authors (a team from Shanghai University) found that supplementing algae cultures with a special bacterium solves the dilemma. What´s so special about the bacterium? Azotobacter chroococcum is capable of nitrogen fixation from air. When co-cultured with the algae (here: Chlamydomonas reinhardtii), the bacterium ensures continuous nitrogen supply for its green partner. The algae thus experience no “hunger”, allowing them to keep growing even in nitrogen-deprived culture broth. Yet, they get the signal for activating their lipid production machinery. Thus, lipid content more than doubles within 9 days, reaching 65%. Incredibly fat! The maximum lipid productivity (per liter of culture, per day) increases almost 20-fold compared to bacterium-free algae cultures. This means: lots of biomass with high energy content. Lipids from algae are comparatively easy to extract, and the authors also know the precise composition of that fatty cocktail (e.g. stearic acid 50%).

Photo provided by PP Economica