detail. Four histidine-rich regions (histidine boxes IeIV) are highly
conserved within known AlkB sequences and regarded as essential
for activity [17]. Multiple gene copies per cell (gene paralogy) have
been reported. They potentially originated from gene duplication or
horizontal gene transfer [18,19]. The different sets of alkB genes are
thought to code for enzymes with distinct substrate ranges [20,21].
Some of the before mentioned studies [9e12] used identical
gene-specific PCR primers targeting alkB genes for T-RFLP profiling,
but all used different restriction enzymes and no systematic
method evaluation was conducted. Moreover, the alkB gene paralogy
might bias the assignment of T-RFs to community members.
For the same reason, alkane degrader richness could be overestimated,
and thus interpretation of diversity indices would be
hampered. Similarly, 16S rRNA gene T-RFLP profiles of soil samples
might overestimate alkane degrader richness as they include also
non-alkane degrading bacteria questioning the reliability of diversity
indices when monitoring the responses of alkane degrading
bacterial communities by T-RFLP.
The main objective of this study was to identify advantages and
pitfalls of the various fingerprinting methods when monitoring
alkane degrading communities in soil. Therefore, we evaluated
different alkB T-RFLP protocols in order to achieve a most robust
and sensitive description of alkane degrading bacterial communities.
An extensive in silico restriction of published alkB sequences
was conducted for an a priori identification of the most suitable
restriction enzyme. Subsequently, the method was challenged by
applying it to a soil environment characterized by high microbial
diversity and relatively low hydrocarbon input (agricultural soil
microcosms covered with a plant litter layer). The results were
compared to overall bacterial community T-RFLP profiles targeting
a phylogenetic marker gene (16S rRNA gene). Finally, diversity
indices deduced from profiles of either marker gene were
compared to each other and to an alkane degrading enrichment
culture derived from the soil samples. With this, we intended to
reveal the suitability of the different methods to estimate diversity
changes of bacterial communities responding to alkane input.