Microelectrode Studies of Interstitial Water Chemistry and Photosynthetic Activity in a Hot Spring Microbial Mat

Abstract

Microelectrodes were used to measure oxygen, pH, and oxygenic photosynthetic activity in a hot spring microbial mat (Octopus Spring, Yellowstone National Park), where the cyanobacterium Synechococcus lividus and the filamentous bacterium Chloroflexus aurantiacus are the only known phototrophs. The data showed very high biological activities in the topmost layers of the microbial mat, resulting in extreme values for oxygen and pH. At a 1-mm depth at a 55°C site, oxygen and pH reached 900 ,uM and 9.4, respectively, just after solar noon, whereas anox;c conditions with a pH of 7.2 were measured before sunrise. Although diurnal changes between these extremes occurred over hours during a diurnal cycle, microbial activity was great enough to give the same response in I to 2 min after artificial shading. Oxygenic photosynthesis was confined to a 0.5to 1.1mm layer at sites with temperatures at or above about 50°C, with maximum activities in the 55 to 60°C region. The data suggest that S. lividus is the dominant primary producer of the mat.

Isolation and characterization of thermophilic methanogenic bacteria from mushroom compost

“…thermal volcanic environments, sewage sludge digesters, sediments and rumen [6,19]. Nevertheless methanogenesis is also reported for environments where oxygen production occurs under light [20,21]. Here we report the isolation of a methanogen from mushroom Phase I compost, an environment, where oxygen is believed to be readily available.…”

The long-term effects of UV exclusion on the microbial composition and photosynthetic competence of bacteria in hot-spring microbial mats

“…The only other phototrophs present would be bacteriochlorophyll-containing Chloro£exus or relatives of this genus which are primarily photo-and chemo-heterotrophs which show little incorporation of inorganic carbon in these waters. Chloro£exus as a photoautotroph requires sul¢de (or H 2 ) as electron donor [39,40,41], and the soluble sul¢de levels downstream in the low-temperature Octopus Spring are very low and then only below 3 mm depth in the mat [42]. Thus, photoautotrophic green sulfur bacteria and purple sulfur bacteria would not be expected, except as minor components.…”

Accumulation and utilization of polysaccharide by hot-spring phototrophs during a light-dark transition

“…This is 80-fold higher than the protein content of the Mushroom Spring cell suspension we used, and provides an approximation of the extent to which the Mushroom Spring cells were diluted; (2) oxygen availability differed in the cell suspension. In the mat, the oxygen concentration is rapidly reduced to zero in the dark [3], because of the high oxygen demand by the dense microbial population. In contrast, we attempted to keep the suspension oxic in the dark by injecting air at each sampling interval, because we were specifically interested in the physiological response of the cells under these conditions.…”

“…The mat present at this site is typical of many hot-spring mats in western North America, in that the thin (1 ram) top layer consists primarily of the cyanobacterium Synechococcus. This organism is responsible for a large part of the primary production in these mat systems, and influences the diurnal changes in oxygen and pH which occur [3]. The photoheterotrophic bacterium Chloroflexus aurantiacus is also present in this layer [4].…”