Carotenoid biomarkers as an imperfect reflection of theanoxygenic phototrophic community in meromicticFayetteville Green Lake

摘要

Organic biomarkers in marine sedimentary rocks hold important clues about the early history of Earth’s surfaceenvironment. The chemical relicts of carotenoids fromanoxygenic sulfur bacteria are of particular interest to geoscientistsbecause of their potential to signal episodes of marine photic-zone euxinia such as those proposed forextended periods in the Proterozoic as well as brief intervals during the Phanerozoic. It is therefore critical toconstrain the environmental and physiological factors that influence carotenoid production and preservation inmodern environments. Here, we present the results of coupled pigment and nucleic acid clone library analysesfrom planktonic and benthic samples collected from a microbially dominated meromictic lake, Fayetteville GreenLake (New York). Purple sulfur bacteria (PSB) are abundant and diverse both in the water column at the chemoclineand in benthic mats below oxygenated shallow waters, with different PSB species inhabiting the two environments.Okenone (from PSB) is an abundant carotenoid in both the chemocline waters and in benthic mats.Green sulfur bacteria and their primary pigment Bchl e are also represented in and below the chemocline. However,the water column and sediments are devoid of the green sulfur bacteria carotenoid isorenieratene. Theunexpected absence of isorenieratene and apparent benthic production of okenone provide strong rationale forcontinued exploration of the microbial ecology of biomarker production in modern euxinic environments.