An international team of researchers from the United Kingdom and China has created droplet-based algal micro-reactors capable of aerobic or hypoxic photosynthesis at room temperature in air.
Electron microscopy image of a densely packed droplet of hydrogen-producing algal cells. Scale bar – 10 micrometers. Image credit: Xin Huang, Harbin Institute of Technology.
“Our methodology is facile and should be capable of scale-up without impairing the viability of the living cells,” said Professor Xin Huang, a researcher at Harbin Institute of Technology.
“It also seems flexible; for example, we recently captured large numbers of yeast cells in the droplets and used the microbial reactors for ethanol production.”
Normally, algal cells fix carbon dioxide and produce oxygen by photosynthesis.
Professor Huang and colleagues used sugary droplets packed with living algal cells to generate hydrogen, rather than oxygen, by photosynthesis.
They trapped 10,000 or so algal cells in each droplet, which were then crammed together by osmotic compression.
By burying the cells deep inside the droplets, oxygen levels fell to a level that switched on special enzymes called hydrogenases that hijacked the normal photosynthetic pathway to produce hydrogen.
In this way, around a quarter of a million microbial factories, typically only one-tenth of a millimeter in size, could be prepared in one milliliter of water.
To increase the level of hydrogen evolution, the researchers coated the living micro-reactors with a thin shell of bacteria, which were able to scavenge for oxygen and therefore increase the number of algal cells geared up for hydrogenase activity.
Although still at an early stage, the study provides a step towards photobiological green energy development under natural aerobic conditions.
“Using simple droplets as vectors for controlling algal cell organization and photosynthesis in synthetic micro-spaces offers a potentially environmentally benign approach to hydrogen production that we hope to develop in future work,” said Professor Stephen Mann, co-director of the Max Planck Bristol Centre for Minimal Biology.
The team’s work was published in the journal Nature Communications.
Z. Xu et al. 2020. Photosynthetic hydrogen production by droplet-based microbial micro-reactors under aerobic conditions. Nat Commun 11, 5985; doi: 10.1038/s41467-020-19823-5