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An experimental investigation into the influence of bacteria on the dissolution and precipitation of silica and the fossilization of micro-organisms in deep-sea siliceous sediments under low temperature/high pressure conditions


The experimental work was made on samples of deep sea diatomaceous sediments obtained from the South Atlantic Ocean and on cultures of diatoms.

Bacteria involvement in the degradation of diatoms and diatom oozes involved both the metabolization of the organic products of lysed diatoms as well as dissolution of the mineral frustules by their exoenzymes.

The artificial fossilization of bacteria using silica (tetraethoxysilane, TEOS) provided an indication of how bacteria are silicified under different conditions. Extracelluar polymeric material (EPM) and Gram positive bacteria with a thick glycocalyx were most easily fossilized suggesting that the water content, chemical composition and consequent chemophysical behaviour of the organic matter is an important factor controlling the nucleation of minerals. Silica nucleated within days on the organic substrate as tiny nanometre sized crystals which gradually grew in size by further nucleation and coalescence to form spheres up to 50 um in diameter, and included other particles, organic as well as inorganic. They have a mammillated morphology and a relatively electron dense texture. An other type of silica deposit consists of a fine, less electron dense granular material which also included both organic and mineral particles.

An investigation was carried out into biofilm and microbial mat development on the deep sea floor and showed the almost ubiquitous presence of biofilms at sediment surfaces. The most extensive mat development was found in sediments below the sea ice, demonstrating that this is an in situ phenomenon and microbial mats are not simply the result of sediment marine snow or mucus flocs. Where extensively developed the mats undoubtedly influence biogeochemical processes and early diagenesis at the surface of sediments. A further effect of microbial mats is the stabilization of sediment surfaces and, thus, the retardation of sediment erosion.

A scanning electron microscopy (SEM) investigation of biofilm development in different types of water pipes demonstrated that smooth surfaced or fine grained material was more conducive to biofilm development and that, depending on water type, bacterially mediated precipitation of minerals within the biofilm could take place. Furthermore, bacterial erosion of the substrate (eg a steel pipe) also occurred.

Funding Scheme

CSC - Cost-sharing contracts


Università degli Studi di Bologna
Via Del Guasto 5/A
40126 Bologna