Acetic acid is key for synergetic hydrogen production in Chlamydomonas-bacteria co-cultures.

This study is a proof of concept for the synergetic biohydrogen production in alga-bacteria co-cultures. Algal hydrogen photoproduction was obtained in sugar-containing media only when the green alga Chlamydomonas reinhardtii was co-cultured with Pseudomonas putida (40.8 ml H2·L-1), Escherichia coli (35.1 ml H2·L-1) and Rhizobium etli (16.1 ml H2·L-1). Hydrogen photo-production in these co-cultures was not only linked to the induction of hypoxia, but to the ability of the bacteria to produce acetic acid from sugars. Synergetic hydrogen production was achieved by integrating the photobiological and fermentative production in Chlamydomonas and Escherichia coli co-cultures supplemented with glucose, which resulted in 60% more H2 production than the sum of the respective monocultures. This cooperation relied on the ability of the alga to consume the excreted bacterial acetic acid, which benefited both bacterial and algal hydrogen production. This knowledge may open new possibilities for the biohydrogen production from industrial wastes.