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Two strains ofBacillus sp. and a strain ofBrevibacterium sp., originally isolated from a natural quartzite surface, were characterized and employed as test strains with several methods: acridine orange fluorochromation and epifluorescence microscopy were used for detection of individual cells; scanning and transmission microscopy for studying attachment behavior; replica techniques in combination with electron microscopy for following surface interaction effects; and chemical analysis of SiO2 for detecting possible silica leaching activities. The experimental results clearly showed that the three test strains were able to attach to and grow on the precleaned quartz surfaces. Attachment modes were either by direct sorption mechanisms (Brevibacterium sp. S) or the production of adhesive polymers (Bacillus sp. U andBacillus sp. W). In short-term contact incubation experiments with rich media, neither quartz crystal surface structures nor bacterial cell surfaces appeared to be changed. Likewise, significant biochemical dissolution and mechanical dislocation of SiO2 (which would have indicated rapid bacterial weathering activities) could not be detected. The importance of quartz purity and crystalline structure for the initiation of weathering processes is discussed. |
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