A taxonomic distribution of bacterial gene families revealed a subset of gene families found in all 106 genomes (51 families; 11,749 proteins), which can be considered as representing house keeping genes. In addition, there are numerous gene families that are nearly ubiquitous, mainly because of erroneous gene annotations in some organisms, and to a lesser degree caused by non-orthologous gene displacement (unrecognizable homology on the sequence level). Including those gene families with members in more than 95% of the genomes results in an additional 64 families (7686 proteins) that might be considered as part of the core.

• bacterial core families (sensu strictu)
• additional core families