Structural and geomicrobiological characteristics of a microbial communityfrom a cold sulfide spring

The Ancaster sulfur spring is a cold (9 degreesC) sulfur spring located nea r Ancaster, Ontario, Canada, which hosts an abundant and diverse microbial mat community. We conducted an extensive microscopical study of the microbi al community of this spring using a number of techniques: phase light, conf ocal scanning laser microscopy, conventional scanning electron microscopy u sing both chemical/critical point drying and cryofixation preparative techn iques, environmental scanning electron microscopy, and transmission electro n microscopy. The latter two techniques were coupled with energy dispersive X-ray spectrometry for elemental analysis to complement wet geochemical da ta collected on bulk spring water and mat pore water. In the anoxic source of the spring, green and purple sulfur bacteria were found together with a sulfide-utilizing type of cyanobacteria that had the unusual characteristic of storing colloidal sulfur intracellularly. Deeper within the source, the mats were dominated by green sulfur bacteria and thick biofilms of cells t hat precipitated Fe and Zn sulfide minerals on their surfaces. Downstream f rom the source, thick, filamentous white mats lined the stream channel, for med by a diverse mass of nonphotosynthetic sulfur oxidizers, which were res ponsible for forming thick masses of spherical colloidal sulfur. These were distinguished by ESEM-EDS from cells by their simple elemental composition (only S was detected). Aqueous geochemistry analysis by ICP-MS showed that some elements (Fe, C, P, Zn, Mg, Ba) were present at higher levels in mat pore water than in bulk spring water. Our approach allowed us to gain an ap preciation of the characteristics of this microbial community and allowed u s to develop a good understanding of the types of microorganisms present an d infer some of the relationships among the members of the community. In ad dition, we wish to convey the utility of a thorough microscopical approach in geomicrobiological and microbial ecology studies.