Hopanoids, a group of isoprenoid lipids produced by certain bacteria, are common biomarkers that are informative about past life. However, several mysteries remain regarding their purpose and production in vivo. One of these mysteries is why certain strains of bacteria possess two copies of a gene, sqhC, whose product, the enzyme squalene-hopene cyclase, is instrumental in the production of hopanoids. It is unusual for bacteria to have two copies of a gene due to the added energy cost of replicating the second copy. Therefore, it is posited that there is some evolutionary advantage to this second copy of sqhC. Additionally, every sqhC2-containing strain examined also has a gene for a TetR-family transcriptional repressor immediately upstream of sqhC2, which may regulate sqhC2 expression. Starting from Pearson et al.’s (2007) list of genera whose strains may have two copies of sqhC, phylogenetic trees were constructed to examine the evolutionary relatedness of sqhC1, sqhC2, and the tetR gene associated with sqhC2. These indicate that sqhC2 and tetR may have co-evolved, supporting the idea that this TetR protein regulates sqhC2, and that different genera evolved sqhC2 independently several times, forming several orthologous clades, supporting the idea that sqhC2 and its associated tetR carry an evolutionary advantage. The tetR gene associated with sqhC2 was unable to be knocked out in Methylobacterium extorquens CM4, which may indicate that regulation is necessary to the evolutionary advantage conferred by sqhC2, but this is pure speculation.
Behnke, Rowan, "THE FUNCTION AND PHYLOGENY OF A DUPLICATE SQUALENE-HOPENE CYCLASE GENE IN METHYLOBACTERIUM EXTORQUENS CM4" (2022). Earth & Planetary Sciences Undergraduate Student Research. 1.