����������� The
effect of earthworm (Lumbricus terrestris) activity
on microbial community composition was investigated in a Gilpin silt loam soil
(fine-loamy, mixed, semiactive, mesic
Typic Hapludults). Fingerprints
of bacterial community structure were constructed using PCR amplicons
of bacterial 16S rDNA separated by denaturing
gradient gel electrophoresis (DGGE).� Culture-dependent
(CD-DGGE) and culture-independent (CI-DGGE) approaches were taken to compare untreated
soil; soil that contained worms feeding on manure and/or soil; and worm casts.
Analysis of similarity (ANOSIM) established that significant differences
existed between community fingerprints within individual gels. ANOSIM R values
were as follows: R= 0.93 (P<0.001) for CD-DGGE fingerprint; R= 0.89 (P<0.001)
for CI-DGGE fingerprint; and R= 0.95 (P<0.001) for a combined CI and CD DGGE
fingerprint. Differences in the similarity data were explored using non-metric
Multidimensional Scaling (MDS) and UPGMA.��
Ordination plots and cluster analysis separated earthworm casts from
soil treatments for both CD-DGGE and CI -DGGE profiles. CD analysis resulted in
73 total bands; 20 were unique to soil treatments while 24 were unique to
earthworm casts.� CI analysis resulted in
64 total bands; 17 were unique to soil and 31 unique to earthworm casts.� Community fingerprints obtained from cast
materials separated according to the worm's food source. Soils containing both
earthworms and manure separated from all other soil treatments.� Differences in community fingerprints between
untreated control soil and soil that received only earthworms were not
apparent. �The large separation between
CD and CI data indicated different bacterial communities were detected by these
methods.� Major trends observed above also
were evident in separate analyses employing PCR amplification of nirK �for DGGE, and BIOLOG Eco Plates for
community level physiological profiles (CLPP). �Data suggest that bacterial communities are
modified after ingestion, however resultant changes in
the soil bacterial community only occurred when earthworms consumed a soil
manure mixture.
�