Marine bacteria, in general, tend to be understudied organisms. Yet del Georgio and Williams estimate that they play a greater role in the carbon cycle than global terrestrial respiration. See page 267, here:
www.uv.es/hegigui/Kasper/delGiorgio%202005.pdf#page=278

Teira et al. exposed two bacteria isolates to 1000 ppm CO2. They found the lower pH from the elevated carbon dioxide did not inhibit growth; rather, one of the two showed an increase, with a lower respiration rate. Both showed increased CO2 fixation.

These changes would also "increase the buffering capacity of seawater" and "tend to increase the pH of seawater, acting as a negative feedback between elevated atmospheric CO2 concentrations and ocean acidification."

Response of two marine bacterial isolates to high CO2 concentration
http://digital.csic.es/handle/10261/51029
http://digital.csic.es/bitstream/10261/51029/1/Teira%20et%20...

DB2