Silica Precipitation Induced by the Anaerobic Sulfate Reducing Bacterium Desulfovibrio Desulfuricans: Effects Upon Cell Morphology and Implications for Preservation

Abstract

Growth experiments utilizing the sulfate reducing bacterium, Desulfovibrio desul-furicans, suggest a microbial influence in. Experiments conducted with 400 ppm silica produced a dense precipitate of silica within 72 hours in which cells were entombed and caught in cellular division. Experiments conducted in the absence of cells required one month or longer for a loose flocculant of silica to develop; in some samples a precipitate did not form over a 3 month duration. The silicification phenomenon greatly altered the morphology of the bacteria causing deformation of rod-shaped vibrios into partially collapsed cocci and intermediate morphological varieties. This alteration was probably caused by osmotic shock influenced by crystallite accumulation at the cell wall and concomitant retardation of solute transport during silica polymerization. It is suggested that these experiments more closely reproduce natural conditions of silicification of microorganisms than have previous studies and that the morphological change may have implications for interpreting the Precambrian microbial fossil record.