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The community structure and physiological characteristics of three microbial mat communities in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica) were compared. One of the mats was located at the edge of a stream and was dominated by diatoms (with a thin basal layer of oscillatorian cyanobacteria), whereas the other two mats, located over moist soil and the bottom of a pond, respectively, were dominated by cyanobacteria throughout their vertical profiles. The predominant xanthophyll was fucoxanthin in the stream mat and myxoxanthophyll in the cyanobacteria-dominated mats. The sheath pigment scytonemin was absent in the stream mat but present in the soil and pond mats. The stream mat showed significantly lower delta13C and higher delta15N values than the other two mats. Consistent with the delta15N values, N2 fixation was negligible in the stream mat. The soil mat was the physiologically most active community. It showed rates of photosynthesis three times higher than in the other mats, and had the highest rates of ammonium uptake, nitrate uptake and N2 fixation. These observations underscore the taxonomic and physiological diversity of microbial mat communities in the maritime Antarctic region.

The three-dimensional structures of two types of cyanobacterium-dominated microbial mats from meltwater ponds on the McMurdo Ice Shelf were as determined by using a broad suite of complementary techniques, including optical and fluorescence microscopy, confocal scanning laser microscopy, scanning electron microscopy with back-scattered electron-imaging mode, low-temperature scanning electron microscopy, and microanalyitical X-ray energy dispersive spectroscopy. By using a combination of the different in situ microscopic techniques, the Antarctic microbial mats were found to be structures with vertical stratification of groups of cyanobacteria and mineral sediments, high contents of extracellular polymeric substances, and large void spaces occupied by water. In cyanobacterium-rich layers, heterocystous nostocalean and nonheterocystous oscillatorialean taxa were the most abundant taxa and appeared to be intermixed with fine-size deposits of epicellular silica and calcium carbonate. Most of the cyanobacterial filaments had similar orientations in zones without sediment particles, but thin filaments were tangled among thicker filaments. The combination of the microscopic techniques used showed the relative positions of biological and mineral entities within the microbial mats and enabled some speculation about their interactions.

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