ANOXYGENIC MICROBIAL MATS OF HOT-SPRINGS - THERMOPHILIC CHLOROBIUM SP

Non-laminated, green to yellow-green microbial mats, with Chlorobium sp. as the only phototroph, occurred from 55 to about 40-degrees-C in hot springs in and near Rotorua, New Zealand. The pH ranged from 4.3 to 6.2 and sulfide from 0.2 to 1.8 mM. This Chlorobium sp. is unique in its ability to form populations at temperatures as high as 55-degrees-C. Spectroradiometric measurements with a fiber-optic microprobe in the intact chlorobium mass showed great opacity with less than 0.1% of the incident radiation (at photosynthetically usable wavelengths) available at 0.7 mm depth within the mat, although the concentrated Chlorobium population sometimes extended to 3 mm depth. Sulfide-dependent, anoxygenic photosynthesis was demonstrated by [C-14]bicarbonate assimilation in mat suspensions and in intact mats by a sulfide-specific microelectrode. No oxygen evolution occurred and no O2 was present within the mat. A light-enhanced uptake of [C-14]acetate also occurred in cell suspensions. This rate was not enhanced by sulfide.