Composite Bacterial Hopanoids and Their Microbial Producers across Oxygen Gradients in the Water Column of the California Current

Abstract

bHopanoids are pentacyclic triterpenoid lipids produced by many prokaryotes as cell membrane components. The structural variations of composite hopanoids, or bacteriohopanepolyols (BHPs), produced by various bacterial genera make them potentially useful molecular biomarkers of bacterial communities and metabolic processes in both modern and ancient environments. Building on previous work suggesting that organisms in low-oxygen environments are important contributors to BHP production in the marine water column and that there may be physiological roles for BHPs specific to these environments, this study investigated the relationship between trends in BHP structural diversity and abundance and the genetic diversity of BHP producers for the first time in a low-oxygen environment of the Eastern Tropical North Pacific. Amplification of the hopanoid biosynthesis gene for squalene hopene cyclase (sqhC) indicated far greater genetic diversity than would be predicted by examining BHP structural diversity alone and that greater sqhC genetic diversity exists in the marine environment than is represented by cultured representatives and most marine metagenomes. In addition, the genetic relationships in this data set suggest microaerophilic environments as potential "hot spots" of BHP production. Finally, structural analysis of BHPs showed that an isomer of the commonly observed BHP bacteriohopanetetrol may be linked to a producer that is more abundant in low-oxygen environments. Results of this study increase the known diversity of BHP producers and provide a detailed phylogeny with implications for the role of hopanoids in modern bacteria, as well as the evolutionary history of hopanoid biosynthesis, both of which are important considerations for future interpretations of the marine sedimentary record.

Interdecadal changes in intensity of the oxygen minimum zone off Concepción, Chile (~ 36° S), over the last century

“…3a, b and c). Observed changes in abundance and distribution of C 31 and C 32 hopanols, in concomitance with past variations of O 2 in the water column at the study site, are consistent with previous findings by Saenz et al (2011) and Kharbush et al (2013). These authors found that the composition and abundance of BHPs, the biological sources of hopanoids, change with decreasing O 2 in the water column of the Peruvian margin, Arabian Sea, Cariaco Basin, and in the eastern tropical North Pacific.…”

The Bacteriohopanepolyol Inventory of Novel Aerobic Methane Oxidising Bacteria Reveals New Biomarker Signatures of Aerobic Methanotrophy in Marine Systems

“…The limited BHP distributions are also comparable to other reported marine sediment BHP signatures, all dominated by BHT and BHT isomer, from a number of locations including the Black Sea [88], the Benguela upwelling system [89], and the Arabian Sea [90]. More recently a similar pattern was also seen in water column samples from the California Current system, where the wide diversity observed in the gene responsible for hopane cyclisation (squalene-hopene cyclase) was not reflected by distinct BHP fingerprints related to this potential range of source-organisms [91]. However, genetic information is quickly lost, and we must strive to find lipid biomarkers to trace particular metabolisms in the geological record.…”

Intact polar diacylglycerol biomarker lipids isolated from suspended particulate organic matter accumulating in an ultraoligotrophic water column

“…DNA was extracted from a portion of each GF/F filter based on an existing phenol-CHCl3 extraction protocol described by Kharbush et al (2013) and Rusch et al (2007). 16S…”