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Project Progress

This year we refined MBGC to reflect more details of the carbon cycles. Under conditions where mat porewaters supersaturated in molecular oxygen, MBGC simulates photorespiration and the cyanobacteria excrete sugars. When mat porewaters become anoxic after sundown, the cyanobacteria begin to take up and ferment these sugars. We added a cyanobacterial fermentation function to MBGC, using the photorespiration exudates as a substrate. We used the following published stoichiometric relationship (Moezellar et al. 1996) to determine how much reduced carbon and energy are produced for use by other organisms.

20 umol glucose-glycogen → 17.6 umol ethanol + 22.9 umol acetate + 25.9 umol formate + 1.4umol H₂ + 9.3 umol CO₂

The fermentation rate function itself is basically a simple algorithm that turns on and off based on presence or absence of oxygen, and is based on the rates found by Moezellar et al., 1996.

The new source of carbon and energy for the simulated sulfate reducing bacteria changes the maximum rate of sulfate reduction from the old modeled rate. In the original SRB model, where exudates were supplied directly from photosynthesis, thus the maximum rate of sulfate reduction occurred at midday. Now the maximum occurs at night.

Reference: Moezelaar R. S.M. Buvank, and LJ. Stahl (1996). Fermentation and sulfur reduction in the mat-building cyanobacterium Microcoleus chthonoplastes. Applied and Environmental Microbiology 62(5) 1752-1758.

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