16S rRNA gene diversity of attached and unattached bacteria in boreholes along the access tunnel to the Äspö hard rock laboratory, Sweden

A total of 155 16S rRNA genes that were cloned from unattached and attached bacteria in nine boreholes down to 626 m below ground were partially sequenced. Attached bacteria were examined with scanning electron microscopy (SEM). The distribution of the 16S rRNA genes found was related to the different types of groundwaters studied. Several of the sequences obtained could be identified on genus level as one of the genera Acinetobacter, Bacillus, Desulfovibrio or Thiomicrospira. The 16S rRNA genes from 20 selected isolates were closely related to the sulphate reducers Desulfomicrobium baculatum or Desulfovibrio sp., the iron reducer Shewanella putrefaciens, or distantly related to the Gram-positive genus Eubacterium. Viable counts confirmed the presence of sulphate-reducing bacteria.