Diversity of hopanoids and squalene-hopene cyclases across a tropical land-sea gradient

Pearson, A.; Leavitt, W. D.; Sáenz, J. P.; Summons, R. E.; Tam, M. C. M.; Close, H. G. (2009) Environmental Microbiology, 11(5), 1208–1223. DOI: 10.1111/j.1462-2920.2008.01817.x

Summary

This study surveyed the diversity of hopanoid cyclases (sqhC) and Bacteriohopanepolyols across a land-sea gradient on San Salvador Island, Bahamas. For the first time, quantification of BHP lipids was overlaid with sqhC phylogeny from the same sites, revealing that environmental cyclase sequences average less than 65% amino acid identity to known relatives. The greatest lipid diversity occurred in soil, while marine samples contained fewer identifiable Hopanoids but at higher fractional abundance. The work identified a new, apparently ubiquitous group of marine hopanoid producers with no close cultured relatives.

Key Findings

• Soil-dominated BHPs were aminobacteriohopanetriol and adenosylhopane; marine-dominated BHPs were bacteriohopanetetrol and bacteriohopaneribonolactone
• A novel, ubiquitous clade of marine sqhC sequences was identified with no cultured close relatives
• 2-MethylDiplopterol increased in relative abundance from land to ocean, while aminotriol and aminotetrol decreased or disappeared
• Cyclitol ethers were trace in soil, absent in the estuary, and moderate in open marine settings, suggesting a dominant marine source
• Small quantities of 2-methylbacteriohopanepolyols were detectable in all environments
• Overall hopanoid distributions correlated with major phylogenetic families and/or environmental setting

Our Contribution

Saenz contributed to sample collection and lipid analysis as part of the MIT-WHOI team during his graduate studies, providing expertise in BHP extraction and characterization across the environmental gradient.

Significance

This work established that hopanoid biomarker distributions shift systematically across terrestrial-to-marine environments and that much of the biosynthetic diversity in nature comes from uncultured organisms. These findings are foundational for interpreting hopanoid signatures in the geological record and for understanding the ecological niches of hopanoid-producing bacteria.