A New Look at Factors Affecting Microbial Silicification: Effects of Microbe to Solution Ratio, Al and Fe on Silica Accumulation on B. subtilis Surfaces

Details A New Look at Factors Affecting Microbial Silicification: Effects of Microbe to Solution Ratio, Al and Fe on Silica Accumulation on B. subtilis Surfaces A New Look at Factors Affecting Microbial Silicification: Effects of Microbe to Solution Ratio, Al and Fe on Silica Accumulation on B. subtilis Surfaces

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.b13b1072t&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #B13B-1072

Biology

0406 Astrobiology And Extraterrestrial Materials

Scientific paper

In this investigation, we aim to constrain the geochemical conditions that favor siliceous microfossil formation. This work will provide a framework for assessing the biogenic origin of putative microfossils in siliceous hydrothermal deposits on early Earth, and potentially, on Mars. Previous work on silicification of microbial cells has been done under unnatural conditions or when cells were physiological stressed. Here, we attempt to reduce the amount reduce the amount of physiological stress on the organisms and to better emulate the natural environment. Silicification experiments involving the gram-positive bacterium, Bacillus subtilis, have been conducted under different experimental conditions to provide insight into the processes that affect silicification of microorganisms. Experiments were conducted with silica stock solution at an initial pH of 8, and with and without added Al and Fe, in two different experimental designs. The first experimental design represented a silica-limited environment in which the ratio of exponentially growing culture (O.D.600 = 0.2) to silica-rich stock solution was very high (1:1 v/v). Silica concentrations declined likely due to nucleation and precipitation mediated by microbial surfaces, and the pH dropped from 8.0 to 6.5. The presence of Fe and Al resulted in lower dissolved silica concentrations, suggesting additional effects of these ions on nucleation and precipitation. The second experimental design used a lower ratio of exponentially growing culture (O.D.600 = .2) to silica-rich stock solution (0.004:1 v/v) resulting in a stable concentration of silica, which was also accompanied by a slight decline in pH. This latter design is more similar to the cell:silica ratios found in natural environments. B. subtilis cells were examined using scanning electron microscopy (SEM) accompanied by energy dispersive spectrometry (EDS). Cells exhibited silica crystallites under SEM and yet continued to undergo cell division in an environment of limited resources. Silicification in the low-ratio experiments appeared to be more efficient as cells were more encrusted with Si than cells in the high-ratio experiments. Further, sporulation was more efficient in the low-ratio experiments.

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