Photoexcretion and Fate of Glycolate in a Hot Spring Cyanobacterial Mat
Applied and Environmental Microbiology, 1988
Photosynthesis by Synechococcus lividus, the sole oxygenic phototroph inhabiting the surface of the 55°C
cyanobacterial mat in Mushroom Spring, Yellowstone National Park, causes superoxic and alkaline conditions
which promote glycolate photoexcretion. At 02 concentrations characteristic of the top 2 mm of mat during the
day, up to 11.8% of NaH14CO3 fixed in the light was excreted, and glycolate accounted for up to 58% of the
excreted photosynthate. Glycolate was neither incorporated nor metabolized by S. lividus, but it was
incorporated by filamentous microorganisms in the mat. Incubation of mat samples with NaH14CO3 resulted
in labeling of both S. lividus and filaments, but the addition of nonradioactive glycolate increased the level of
14C in the aqueous phase and decreased the extent of labeling of filaments. This suggests that cross-feeding of
glycolate from S. lividus to filamentous heterotrophs occurs and that underestimation of the extent of
photoexcretion is probable.
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