Trace Metal Biosignatures

Author:

Cameron, Vyllinniskii

Graduate Program:

Geosciences

Degree:

Doctor of Philosophy

Document Type:

Dissertation

Date of Defense:

August 10, 2008

Committee Members:

Christopher Howard House, Committee Chair/Co-Chair
Susan Louise Brantley, Committee Member
Lee Kump, Committee Member
Caryl Ann Gronwall, Committee Member

Keywords:

Trace metals
Biosignatures
Nickel Stable Isotopes
Hyperthermophiles
Methanogen
Tungsten

Abstract:

Trace metals are vital components of biological systems. Microbial trace metal utilization, as observed in extant microorganisms, can provide information regarding metabolic processes, environmental conditions and potential biosignatures. Additionally, inferences may be possible regarding the nature and evolution of early life on Earth. This thesis investigates microbial trace metal utilization via a series of laboratory growth experiments involving pure cultures of primarily archaeal hyperthermophiles, with the aim of discovering potential biosignatures. Trace metal contents of investigated microorganisms revealed a distinct metallome pattern and possible biosignature for the methanogen M. jannaschii in which high cellular concentrations of Ni, Co and W were observed. Microorganisms can alter mineral substrates through scavenging of bioessential trace metals, which may produce biomarkers. To investigate whether hyperthermophiles produce ligands under metal-limited conditions, supernatant growth experiments were conducted with hyperthermophiles in the presence of powdered basalt. Tungsten (W) was targeted as the metal of interest as it has been shown to be an important bioessential nutrient required for the growth of many hyperthermophiles. Bulk results from all experiments suggest hyperthermophiles do not produce W ligands however, due to reproducibility issues, the role of W as a possible hyperthermophile biosignature remains unresolved. Finally, novel Ni stable isotopic investigations were performed for geological and biological materials. Mass spectrometry, column chemistry and microbiological protocols specific to Ni and hyperthermophiles, were developed and established. Terrestrial and extraterrestrial geological materials vary within a small range of Ni isotopic compositions: -0.04 to +0.36 per mil. Relative to the starting composition of the growth media, diverse metabolic groups of methanogens impart distinct and significant mass-dependent fractionations on Ni isotopes, preferentially sequestering the lighter isotopes which results in an isotopic fractionation on the order of ~ 0.8 - 1.0 per mil. Non-methanogenic cells also produced a small fractionation. Organisms in general may fractionate Ni isotopes but not as significantly as methanogens. Ni isotopes may be useful, not only as a general methanogenic biomarker but also as a marker for distinguishing between diverse metabolic groups. Ni stable isotopes may have important implications in the fields of transition metal isotopes, geomicrobiology and astrobiology.