Distribution of hopanoids along a land to sea transect: Implications for microbial ecology and the use of hopanoids in environmental studies

Abstract

Bacteriohopanepolyols (BHPs) are lipid constituents of diverse bacteria and have great potential as taxonomically and environmentally diagnostic biomarkers. In order to examine their environmental behavior and potential for tracing biogeochemical processes, we analyzed BHPs and geohopanoids (the diagenetic products of BHPs) in soils and surface sediments from the middle Yangtze River catchment to the East China Sea (ECS) shelf. These data are compared to an up-to-date survey of BHP distributions in soils, including regions collectively covering the Arctic, temperate, subtropics, and tropics. Regional climatic differences, particularly temperature, likely exert an important control on BHP distributions in soils. In the aquatic (river-estuaryshelf) setting, BHP concentrations and structural diversity are substantially lower than in soils, suggesting that in aquatic environments either bacterial biodiversity is lower or there is not the same requirement for hopanoid synthesis. However, different aquatic regimes vary substantially: high BHP diversity and enhanced BHP production occur in the biogeochemically dynamic Yangtze estuary, whereas BHP distribution is uniform with much less structural diversity in the oligotrophic ECS open shelf. The R soil index, based on the relative abundances of soil-marker BHPs against bacteriohopanetetrol, is suggested as a new approach to trace soil organic matter input into marine sediments. The R soil indices decrease from the river to the ECS, correlating strongly with branched and isoprenoid tetraether indices and moderately correlating with δ 13 C of organic carbon values and the concentrations of higher plant biomarkers, demonstrating their ability to trace soil organic matter inputs at least to the ECS.

Bacteriohopanepolyols in tropical soils and sediments from the Congo River catchment area

“…Greater diversity was found within soils vs. the wetland and estuarine samples, consistent with other studies (e.g. Pearson et al, 2009;Zhu et al, 2011). BHT cyclitol ether (1h) was one of the most dominant BHPs in the soils, wetlands and estuarine sediments.…”

“…The R soil index (as defined by Zhu et al, 2011) was calculated according to the relative concentrations of BHT (1b) and all soil marker BHPs. The R 0 soil index was later proposed as an alternative index excluding methylated homologues for settings where the C-2 methylated soil marker BHPs were infrequently/intermittently present (Dogrul Selver et al, 2012) and is calculated according to the relative concentrations of BHT (1b) and adenosylhopane (1a), adenosylhopane type 2 (1c) and adenosylhopane type 3 (1d).…”

“…Soils generally contain higher BHP concentration and greater structural diversity than lacustrine and marine sediments Coolen et al, 2008;Cooke et al, 2008b;Blumenberg et al, 2010;Zhu et al, 2011), with the exception of deep sea-fan sediments with very high terrigenous input (Handley et al, 2010;Wagner et al, 2014). For example, Cooke et al (2008a) reported high structural diversity and concentration of hopanoids in soils (up to 20 BHPs in two of four surface soils from the northern UK), and Zhu et al (2011) up to 20 BHPs in a soil from the Yangtze River catchment. However, a recent study of two surface soils and three surface wetland sediments from the Amazon found the highest BHP concentration and greatest structural diversity within wetland sediments (18 in sediments vs. 13 in the soils; Wagner et al, 2014), suggesting wetlands as possibly a significant source of BHPs in shelf and fan systems.…”

“…In comparison, few studies have detailed the distribution of BHPs in modern tropical soils (Pearson et al, 2009;Wagner et al, 2014). Soils generally contain higher BHP concentration and greater structural diversity than lacustrine and marine sediments Coolen et al, 2008;Cooke et al, 2008b;Blumenberg et al, 2010;Zhu et al, 2011), with the exception of deep sea-fan sediments with very high terrigenous input (Handley et al, 2010;Wagner et al, 2014). For example, Cooke et al (2008a) reported high structural diversity and concentration of hopanoids in soils (up to 20 BHPs in two of four surface soils from the northern UK), and Zhu et al (2011) up to 20 BHPs in a soil from the Yangtze River catchment.…”

“…transport (Cooke et al, 2008bZhu et al, 2011;Dogrul Selver et al, 2012, 2015. Another group of diagnostic markers comprises those produced by aerobic methane oxidising bacteria (methanotrophs), including 35-aminobacteriohopane-31,32,33,34-tetrol (aminotetrol; 1e); 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol; 1f), unsaturated aminopentol (4/5f) and aminopentol isomer (1f 0 ; e.g.…”