Question

From phylogenetic analysis of present day bacteria why do we believe that the bacteria have a thermophilic ancestry?

Answer 1

There are several evidences that suggest that the ancestors of bacteria are thermophiles. Several studies also propose that hyperthrmophiles represent the universal last common ancestors (ULCA) of the present day organisms. The evidences are presented below:-

1. Phylogenetic trees were constructed for bacteria and archaea and based on their 16s rRNA sequence comparisons, it was hypothesized that bacteria and archarea had thermophiles as their ancestors.

2. The hyperthermophilic ancestry was supported by protein phylogeny.

3. A thermophily index was introduced, which was created based on the propensity of amino acids to form proteins of thermophiles/hyperthermophiles and this showed a strong correlation with the optimal growth temperature of several organisms.

4. Based on the above thermophily index, it could also be predicted that the genetic code was formulated at high temperatures.

5. Further, by observing the correlation between the thermophily index and optimal growth temeratures of various organisms, LUCA's origin has been predicted to be in a hyperthermophilic or thermophilic environment. This was possible by reconstructing the ancestral sequence of the LUCA using maximum likelihood and and maximum parsimony methods for two pairs of paralogous genes.