P53: Phylogenetic Analysis of Ethanologenic Acetogens Belonging to Clostridial rRNA Homology Group 1

Synthesis gas, a mixture of primarily CO, H₂, and CO₂, is a major building block in the production of biofuels and chemicals.  Several phylogenetically diverse groups of anaerobic bacteria have the ability to convert components of synthesis gas to a variety of commercially-important products including acetate, ethanol, butyrate, butanol, and hydrogen.  A select subgroup, the ethanologenic acetogens exhibit the ability to simultaneously utilize hydrogen and carbon monoxide to form ethanol, and small amounts of acetate while using carbon dioxide as a carbon source and electron acceptor.  There has been recent interest in the commercial exploitation of this group of bacteria for the manufacture of fuel-grade ethanol from synthesis gas; however, the phylogeny and physiology of this group has remained obscure.

In this study, we used 16s rRNA sequences, DNA-DNA reassociation, and PCR-based DNA fingerprinting to characterize phylogenetic linkages between five known representatives of this group, which included Clostridium ragsdalei, C. autoethanogenum, C. ljungdahlii PETC, C. ljungdahlii C-01, and C. ljungdahlii ERI-2.  Pairwise analyses of 16S rRNA sequences for all comparisons exceeded 99.27% similarity.  Three methods used for DNA fingerprinting, repetitive extragenic palindromic elements (REP), conserved repetitive DNA elements (BOX) and entrobacterial repetitive PCR intergenic consensus sequences (ERIC), showed that C. ragsdalei, C. ljungdahlii ERI-2, and C. ljungdahlii C-01 were most distantly related.  DNA-DNA reassociation data indicated that ERI-2 and C-01 should be re-classified as separate species when compared to the type strain, C. ljungdahlii PETC.  Finally, other gene sequences useful in predicting relatedness of ethanologenic acetogens will be discussed.