Microbial colonization of aquifer sediment exposed in a groundwater well in northern Germany

Microbial growth within the water-saturated subsurface environment was investigated by exposing sandy sediments to groundwater for 12 weeks at a depth of 10 or 20 m in a stainless-steel groundwater well. Washing and heating the sediment to 600 degrees C (removal of organic carbon) prior to the exposure did not prevent the natural microbial community from colonizing the sterilized sediment samples. Total cell counts of more than 10(7) or 10(8) per g of dried sediment were obtained. Viable cell counts of 10(5) cells per g on oligotrophic media indicated the presence, within the exposed sediment, of a highly active and multiplying biota. Microscopic analysis of enrichments inoculated with exposed sediment samples revealed a total of 45 different morphotypes, approximately 42% of the microbial community observed in previous studies of this site. The interstitial water running off of the retrieved sediment contained only 17 morphotypes and had up to 6 x 10(5) viable cells per ml.