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

Algae-Bacteria Consortia as a Strategy to Enhance H2 Production

“…However, different consortia can attain noticeable H 2 production in TAP medium at higher light intensities ( Table 1 ), which open the possibility to further explore H 2 production under non-stressful conditions to avoid S removal and two-phase bioreactors. Finally, the use of H 2 -producing bacterial strains such as wild-type strains of E. coli in media supplemented with glucose brings up the possibility to combine H 2 production from both alga and bacterium [ 56 ]. This consortium can produce up to 32.7 mL/L, which is higher than the production reported for other consortia in TAP-S medium ( Table 1 ).…”

“…As mentioned before, the donation of fermentative metabolites from Chlamydomonas to different bacteria can promote bacterial H 2 production. However, the opposite flux (from bacteria to alga) can also benefit both algal and bacterial H 2 production, especially when acetic acid is produced and secreted by the bacteria [ 56 ]. In Figure 2 , some of the metabolites that can be potentially exchanged between algae and other microorganisms during both growth and H 2 production conditions are depicted.…”

“…When co-culturing Chlamydomonas with different non-H 2 producing bacteria in acetate-free media supplemented with sugars (glucose or mannitol), algal H 2 production can be observed if acetic acid is excreted by the bacteria. The amount of acetic acid excreted by the bacteria directly correlates with the capacity of Chlamydomonas to produce H 2 [ 56 ]. Moreover, as demonstrated by Fakhimi et al [ 56 ] using E. coli and Chlamydomonas co-cultures incubated with glucose as the sole carbon source, it is possible to produce H 2 in a synergetic way (60% more H 2 than the sum of the respective control monocultures), with acetic acid probably being the metabolite linking dark H 2 production with H 2 photoproduction ( Figure 2 ).…”

“…The amount of acetic acid excreted by the bacteria directly correlates with the capacity of Chlamydomonas to produce H 2 [ 56 ]. Moreover, as demonstrated by Fakhimi et al [ 56 ] using E. coli and Chlamydomonas co-cultures incubated with glucose as the sole carbon source, it is possible to produce H 2 in a synergetic way (60% more H 2 than the sum of the respective control monocultures), with acetic acid probably being the metabolite linking dark H 2 production with H 2 photoproduction ( Figure 2 ). This study entails a proof-of-concept linking dark bacteria and algae H 2 production.…”

“…The presence of acetate in the medium promotes O 2 consumption, represses CO 2 fixation, and decreases the photosynthetic rates [ 92 , 93 , 94 , 95 ]; all of these factors favor H 2 production. In addition, the presence of acetic acid in the culture media has been reported as a key parameter for photo-H 2 production in Chlamydomonas monocultures [ 14 ] and co-cultures [ 56 ], whose role is partially independent of its capacity to promote hypoxia [ 14 ]. It has been suggested that, under light, nutrient-repleted conditions and hypoxia, the assimilation (or photoassimilation) of acetic acid, and not starch mobilization, can provide, directly or indirectly, electrons for the PSII-independent H 2 production pathway [ 13 , 14 ].…”