4. Discussion
4.1. Method improvement
In this study, we systematically evaluated T-RFLP protocols targeting
the alkB gene as a functional marker to monitor changes in
alkane degrading soil bacterial communities. Although the applied
inosine-containing degenerate primers might not cover all alkB
paralogs equally, they promise to be most suitable for a broad range
of alkB genotypes from phylogenetically diverse community
members [18]. Since different template and restriction enzyme
concentrations resulted in identical community profiles, PCRinherent
biases such as preferential amplification by highly
degenerate primers [8] or the occurrence of pseudo-T-RFs [40]
could be regarded as negligible here, but should be kept in mind
in future application.
An in silico evaluation revealed strong differences among restriction
enzymes applied in existing protocols [9e12]. Enzymes
producing low T-RF richness might lack the sensitivity to detect
subtle changes in the alkB gene pool, thus obscuring influences of
environmental parameters on the alkane degradation potential.
Accordingly, Engebretson and Moyer [28] advised a careful choice
of restriction enzymes for 16S rRNA gene profiling. They observed
ranges of 210e322 T-RFs produced by different enzymes on the
same sequence subset in an in silico restriction.
4.2. Detection of spatiotemporal community changes in a complex
soil environment
T-RFLP analysis of bacterial communities in soils revealed that
alkB gene pools were more sensitive to alkane input than 16S rRNA
gene pools. In our test system, we refrained from examining soil
communities pre-exposed to high amounts of hydrocarbons or
subjected to strong selection pressure for alkane degraders as
would have been the case in contaminated soils [10]. Whereas it
appears straightforward that the functional guild of alkane degraders
responded stronger to alkanes than the entire community,
the overall diversity of alkB genes in soil environments without preexposure
to substantial amounts of alkanes is somewhat surprising.
Depth-related differences in alkB gene T-RF dynamics probably
reflected lower alkane provision in deeper bulk soil, which was
independent of the soil type. The identical mean T-RF richness of