Novel hopanoid cyclases from the environment.

Area of Science:

• Geobiology
• Biogeochemistry
• Molecular Biology

Background:

• Hopanoids are widespread isoprenoid lipids originating primarily from bacteria.
• They serve as valuable biomarkers for reconstructing past geobiological communities.
• Previous studies relied on culture collections, overlooking uncharacterized prokaryotic communities.

Purpose of the Study:

• To investigate the phylogenetic diversity of hopanoid producers using culture-independent methods.
• To identify the sources of hopanoids in modern environments.
• To understand the distribution and ecological significance of hopanoid biosynthesis.

Main Methods:

• Analysis of squalene-hopene cyclase (sqhC) gene sequences from marine and lacustrine bacterioplankton.
• Inclusion of publicly available sqhC fragments from metagenomic libraries.
• Phylogenetic analysis to determine the evolutionary relationships of hopanoid-producing bacteria.

Main Results:

• Environmental sqhC sequences showed low amino acid identity (<60%) to known relatives, indicating novel lineages.
• Genes associated with known cyanobacterial hopanoid production were not detected in contemporary samples.
• The study suggests that hopanoid biosynthesis is rare, potentially limited to <10% of bacterial species.

Conclusions:

• The primary sources of geological hopanoid biomarkers remain largely unknown.
• The discrepancy between modern and ancient hopanoid records, particularly concerning cyanobacteria, needs further investigation.
• Understanding contemporary hopanoid distribution is crucial for interpreting the sedimentary record and the function of these lipids.