Victoria J Orphan

PI | Caltech |


My research sits at the interface of microbial ecology, biogeochemistry, and geobiology. We employ molecular ‘omics, fluorescence, electron, and secondary ion imaging methods, stable isotopes, and biogeochemical analyses to understand the activity, ecology, and interspecies interactions between environmental microorganisms involved in anaerobic carbon, nitrogen and sulfur cycling in ocean ecosystems and extreme environments. We are particularly interested in understanding the physiology, adaptation, and structuring of microbial communities in low energy environments and the ecophysiology and interactions of multi-celled syntrophic consortia of archaea and bacteria engaged in anaerobic oxidation of methane in the deep sea.

Selected Publications:

Chadwick, G.L., Otero, F.J., Gralnick, J.A., Bond, D.R. and Orphan, V.J., 2019. NanoSIMS imaging reveals metabolic stratification within current-producing biofilms. Proceedings of the National Academy of Sciences, 116(41), pp.20716-20724.

Members of the Geobacteraceae are important iron reducing bacteria in anoxic marine environments, coupling organic carbon mineralization to iron respiration through a process known as extracellular electron transfer. Cultured members of Geobacter represent model electrogenic bacteria that are capable of forming thick conductive biofilms on electrodes (mimicking iron oxides), but the underlying biological mechanisms controlling the limit of current production and growth with increasing distance from the electrode is not well-understood. This work investigated the spatial limits of extracellular electron transfer by Geobacter using quantitative stable isotope probing and single cell resolved nanoscale secondary ion mass spectrometry, showing that the highest cell activity is restricted to layers closest to the electrode rather than across the entire biofilm. This metabolic observation fundamentally changes our understanding of electron flow and cell growth within current-producing biofilms and provides constraints on the physical structure of natural communities and syntrophic associations reliant on this process for growth.

Metcalfe, K.S., Murali, R., Mullin, S.W. Connon, S.A. Orphan, V.J. 2020. Experimentally-validated correlation analysis reveals new anaerobic methane oxidation partnerships with consortium-level heterogeneity in diazotrophy. ISME J .

Research Interests

Ecology, Geobiology, Physiology, Biogeochemistry, Ocean Science, Imaging, Isotopes, Molecular, Anaerobes, Syntrophy, Methane

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Victoria J Orphan