Bacillus species have been involved in metal association
as biosorbents, but there is not a clear understanding of
this chelating property. In order to evaluate this metal
chelating capacity, cultures and spores from Grampositive
bacteria of species either able or unable to
produce surface layer proteins (S-layers) were analyzed
for their capacity of copper biosorption. Only those
endowed of S-layers, like Bacillus sphaericus and B.
thuringiensis, showed a significant biosorption capacity.
This capacity (nearly 50%) was retained after heating of
cultures, thus supporting that structural elements of the
envelopes are responsible for such activity. Purified Slayers
from two Bacillus sphaericus strains had the ability
to biosorb copper. Copper biosorption parameters were
determined for strain B. sphaericus 2362, and after
analyses by means of the Langmuir model, the affinity
and capacity were shown to be comparable to other
bacterial biosorbents. A competitive effect of Ca2+ and
Zn2+, but not of Cd2+, was also observed, thus indicating
that other cations may be biosorbed by this protein.
Spores that have been shown to be proficient for copper
biosorption were further analyzed for the presence of Slayer
content. The retention of S-layers by these spores
was clearly observed, and after extensive treatment to
eliminate the S-layers, the biosorption capacity of these
spores was significantly reduced. For the first time, a
direct correlation between S-layer protein content and
metal biosorption capacity is shown. This capacity is
linked to the retention of S-layer proteins attached to
Bacillus spores and cells.
Metal, S-layer, spores, biosorption, Bacillus