Nakatsu, C.H., Carmosini, N., Baldwin, B.,
Beasley, F., Kourtev, P. and
Konopka, A. (2005). Soil microbial community responses to
additions of organic carbon substrates and heavy metals (Pb and
Cr). Appl. Environ. Microbiol., 71: 7679-7689.
Microcosm experiments were conducted with soils contaminated with
heavy metals (Pb and Cr) and aromatic hydrocarbons to determine
the effects of each upon microbial community structure and
function. Organic substrates were added as a driving force for
change in the microbial community. Glucose represented an energy
source used by a broad variety of bacteria, whereas fewer soil
species were expected to use xylene. The metal amendments were
chosen to inhibit the acute rate of organic mineralization by
either 50% or 90%, and lower mineralization rates persisted over
the entire 31-day incubation period. Significant biomass increases
were abolished when metals were added in addition to organic
carbon. The addition of organic carbon alone had the most
significant impact on community composition and led to the
proliferation of a few dominant phylotypes, as detected by
PCR-denaturing gradient gel electrophoresis of bacterial 16S rRNA
genes. However, the community-wide effects of heavy metal addition
differed between the two carbon sources. For glucose, either Pb or
Cr produced large changes and replacement with new phylotypes. In
contrast, many phylotypes selected by xylene treatment were
retained when either metal was added. Members of the
Actinomycetales were very prevalent in microcosms with xylene and
Cr(VI); gene copy numbers of biphenyl dioxygenase and phenol
hydroxylase (but not other oxygenases) were elevated in these
microcosms, as determined by real-time PCR. Much lower metal
concentrations were needed to inhibit the catabolism of xylene
than of glucose. Cr(VI) appeared to be reduced during the 31-day
incubations, but in the case of glucose there was substantial
microbial activity when much of the Cr(VI) remained. In the case
of xylene, this was less clear.