The pmoA analyses showed
different patterns in SIP-resolved fingerprints between ammoniumand nitrate (Fig. 6B). For the ammonium treatment, the relative
abundance of T-RFs diverged along the DNA density gradient: the
437-bp T-RF increased markedly with DNA density, the 505-bp and
79-bp T-RFs also increased at the first time point, but the 244-bp TRF
decreased relatively. This indicated the significant incorporation
of 13C into type I methanotrophs, but not in type II methanotrophs
(244 bp). Interestingly, such a resolution was not achieved in the
nitrate treatment. The weak resolution suggested that nitrate
caused more or less homogenous incorporation of 13CH4 in both
type I and type II methanotrophs, making it impossible to resolve
them by DNA density fractionation.