Rock colonized with Thiothrix and associated Bacteria.
FISH micrographs of Deltaproteobacteria associated with Gammaproteobacteria in incubations with a) 13C-acetate, 15NH4+ and ~10 at.% 34SO42- or b) 13C-acetate, 15NH4+ and ~15 at.% 33SO42-. The bottom row shows the corresponding nanoSIMS ratio image for c) 34S/32S or d) 33S/32S.
|
I am currently working on developing techniques for the application of 33S and 34S labeled sulfate and elemental sulfur in probing biological sulfur cycling. Using environmental microbial communities from White Point Beach, CA, I examined the intracellular transfer of biologically derived sulfide with triple stable isotope labeling experiments: 13C, 15N and 33S or 34S. Silicon wafers colonized by microbial mats in situ, were incubated with isotopically labeled substrates and subsequently analyzed by fluorescent in situ hybridization (FISH) coupled to nanometer-scale secondary ion mass spectrometry (NanoSIMS) allowing the simultaneous measurement of 13C/12C, 15N/14N, 33S/32S and 34S/32S of individual cells.
|
Co-culture of Methanosarcina acetivorans (red) and Desulfococcus multivorans (green).
Aggregate of ANME-2C (red) and Deltaproteobacteria (green) from Hydrate Ridge sediment.
|
The microbially mediated anaerobic oxidation of methane (AOM) is carried out by anaerobic methane-oxidizing archaea (ANME) in syntrophic association with sulfate-reducing bacteria (SRB). Understanding the metabolic interplay between the ANME and SRB in consortia is made difficult by the lack of cultured representatives. However, methanogenic archaea, that are closely related to their ANME counterparts, and SRB also form syntrophic consortia in both the environment and in laboratory grown co-cultures. Zhang et al. (2009, PNAS) demonstrated that the central metabolic pathway is reflected in the hydrogen isotopic fractionation between bacterial fatty acids and growth water. I am comparing the hydrogen isotopic fractionation of fatty acids from SRB cultures, aggregate forming archaeal and bacterial co-cultures and sediment cores associated with a variety of active methane seep settings. Syntrophic associations in these systems shift the δD of fatty acids from the values typically for selected growth conditions. This indicates that hydrogen is likely an important intermediate in these syntrophic systems and that mixed microbial communities in the environmental present an additional challenge to the application of this proxy for metabolic pathways requiring more study of mixed cultures
|
Nitrateitrate reducing enrichments with pristane (A–D) and phytane (E–H), showing loss of (A and E) nitrate, production of (B and F) nitrite and (C and G) dissolved inorganic carbon (DIC), and stoichiometrically predicted substrate degradation (D and H). δ13C values of DIC (I) respired from 13C-labeled Ph (δ13C +292‰).
|
|