Chlamydomonas reinhardtii and Microbacterium fakhimi sp. nov., amutualistic association that favor sustainable hydrogen production

Abstract A multispecies bacterial community including Microbacterium fakhimi sp. nov., Stenotrophomonas goyi sp. nov., and Bacillus cereus greatly promoted sustained hydrogen production by the microalga Chlamydomonas reinhardtii when cocultivated in mannitol- and yeast extract-containing medium (up to 313 mL·L -1 ). Alga viability was also largely prolonged in the cocultures (>45 days) without any nutrient supplementation. Among the bacterial community, Microbacterium fakhimi sp. nov. was the main responsible for the hydrogen production improvement. Nonetheless, the use of the entire bacterial community allowed a better growth of the alga during hydrogen production. Chlamydomonas reinhardtii and Microbacterium fakhimi sp. nov. established a mutualistic association, based on the release of ammonium and acetic acid from the bacterium, while the alga provided sulfur-containing metabolites and complemented the bacterial auxotrophy for biotin and thiamine. This study uncovers the potential of the Chlamydomonas-bacteria consortia for durable and stable H 2 production while allowing the simultaneous production of biomass.