Bioremediation into conservation practice. Bioremediation is less harsh
than the use of environmentally-toxic chemicals or aggressive mechanical
procedures, which should be considered to be destructive methods. Research
into the practical application of bioremedial technologies has recently pro-
gressed through the work of two European Community-funded projects.
BIOREINFORCE successfully demonstrated that dead cells from active bio-
calcifying strains showed a much higher and/or faster production of CaCO 3
crystals than less active strains. By identifying the genes responsible for crys-
tal formation in bacteria, the project aimed to biologically produce chemicals
that induce calcification on stones without using living bacterial cells. BIO-
BRUSH (www.biobrush.org) linked the mineralisation processes that remove
stone crusts to consolidation by biomineralisation. Bacteria were applied
directly to stone surfaces using techniques with a low degree of risk to both
environment and conservators. Multiple short-term applications of aerotoler-
ant sulfate-reducing bacteria within an appropriate delivery system was very
successful in removing black crusts from marble both in the laboratory and
in situon buildings. A new mortar system incorporating nitrate-reducing bac-
teria capable of removing nitrates was also developed. Biocalcifying bacteria
were shown to deposita calcite layer without significant reduction in poros-
ity or subsequent growth of contaminating microorganisms.
4.7 Replacement
When consolidation methods fail or are inappropriate due to costs or con-
servation policy, then, usually as a last resort, replacement of material is required.
Replacement is problematic in some buildings because it is not possible to
Stone 237
Figure 11Encrustation of bacteria cells applied to stone during biocalcification activity