Lipid Biomarkers and Carbon Isotope Signatures of a Microbial ( Beggiatoa ) Mat Associated with Gas Hydrates in the Gulf of Mexico

Abstract

White and orange mats are ubiquitous on surface sediments associated with gas hydrates and cold seeps in the Gulf of Mexico. The goal of this study was to determine the predominant pathways for carbon cycling within an orange mat in Green Canyon (GC) block GC 234 in the Gulf of Mexico. Our approach incorporated laser-scanning confocal microscopy, lipid biomarkers, stable carbon isotopes, and 16S rRNA gene sequencing. Confocal microscopy showed the predominance of filamentous microorganisms (4 to 5 m in diameter) in the mat sample, which are characteristic of Beggiatoa. The phospholipid fatty acids extracted from the mat sample were dominated by 16:17c/t (67%), 18:17c (17%), and 16:0 (8%), which are consistent with lipid profiles of known sulfur-oxidizing bacteria, including Beggiatoa. These results are supported by the 16S rRNA gene analysis of the mat material, which yielded sequences that are all related to the vacuolated sulfur-oxidizing bacteria, including Beggiatoa, Thioploca, and Thiomargarita. The ␦ 13 C value of total biomass was ؊28.6‰; those of individual fatty acids were ؊29.4 to ؊33.7‰. These values suggested heterotrophic growth of Beggiatoa on organic substrates that may have ␦ 13 C values characteristic of crude oil or on their by-products from microbial degradation. This study demonstrated that integrating lipid biomarkers, stable isotopes, and molecular DNA could enhance our understanding of the metabolic functions of Beggiatoa mats in sulfide-rich marine sediments associated with gas hydrates in the Gulf of Mexico and other locations.Microbial mats dominated by sulfur-oxidizing Beggiatoa and Thioploca spp. are widespread in estuarine, continental shelf, deep-sea hydrothermal vent, and cold-seep environments, where reduced sulfur species are abundant.

Lipids of sulfate-reducing bacteria and sulfur-oxidizing bacteria found in the Dongsheng uranium deposit

“…However, in the meth-anogenesis zone, abundant 16:1ω6, 16:1ω8, 18:1ω6, 16:1ω8 also are expected (Zhang et al, 2005 and references therein) [27]. Lacking of monounsaturated fatty acids in this study rules out the possibility of methanogens were a main source.…”

“…Third, it has been shown that i15:0, a15:0, i17:0 and a17:0 fatty acids can be synthesized by microbes [30]. Finally, bacteria have been shown to have fatty acids with carbon numbers mainly between C 12 to C 20 , containing abundant branched saturated and monounsaturated fatty acids [20,[22][23][24][25][26][27]31,32]. The fatty acids detected in this study contained branched saturated fatty acids (e.g.…”

“…i15:0, a15:0, i17:0, and a17:0) [23][24][25][26][27][33][34][35][36]. Fatty acid 10me16:0 was previously found only in actinomycetes [37] and Agrobacterium tumefaciens [38].…”

“…All analyses were carried out both in selected ion and full scan double modes. Fatty acids were identified by mass spectra, relative retention times and comparison with published data [20,[23][24][25][26][27]. Fatty acid nomenclature is in the form of "A:BωC", where "A" designates the total number of carbons, "B" designates the number of double bonds, and "C" designates the distance of the closest unsaturation from the aliphatic end of the molecule.…”

Abundance and distribution of fatty acids within the walls of an active deep-sea sulfide chimney

“…However, as reported by Ben-Mlih et al (1992), an absence of the usual phytoplankton markers (e.g., 20:5ω3 or 22:6ω3) and the high levels of bacterial populations lead to the conclusion that all the ω7 series are of bacterial origin. Furthermore, many previous studies of the gas hydrate and cold seep settings widely considered C16:1ω7 and C18:1ω7 as the signature biomarker for SOB (McCaffrey et al, 1989;Guezennec and Fiala-Medioni, 1996;Zhang et al, 2005;Li et al, 2007). Therefore, the possible sources of 16:1ω7 and 18:1ω7 acids are considered SOB in the present study, which is a major primary producer in the seafloor hydrothermal environment (Jannasch, 1983;Hedrick et al, 1992;López-García et al, 2003).…”