UC Santa Cruz

Arsenic is a naturally occurring ubiquitous metalloid that is usually associated with Iron, sulfur and other compounds in the earth’s crust. In some places around the world the bio-geochemical conditions can cause the mineral bound form of arsenic (arsenate) to be reduced to a more water-soluble form (arsenite). In its reduced state, arsenic can seep from the soil down into ground water aquifers and contaminate drinking water supplies. The effects of drinking arsenic tainted water are devastating, however the current methods of detecting arsenic contamination are difficult to implement in most communities that rely on individual tube wells for drinking water.

Dissimilatory arsenic reducing microbes can release terminal electrons, from their electron transport chain, onto arsenic in the nearby environment. These electrons then cause arsenate to be reduced to arsenite leading to eventual arsenic pollution of drinking water. However, arsenic reduction only occurs when more favorable terminal electron acceptors, like oxygen or nitrate, are depleted. An understanding of the genetic and biochemical triggers that activate dissimilatory arsenic reduction will help future detection and bioremediation efforts. This dissertation is a compilation of several systems level studies I performed in order to investigate the molecular mechanisms regulating arsenic reduction in Shewanella sp. ANA-3. The techniques include transcriptomics, molecular biology and comparative genomics. Using systems biology techniques I identified important regulatory parameters in activating respiratory arsenic reduction in three forms:

• Transcriptomics of ANA-3 during arsenic reduction vs. growth on oxygen or fumarate

• Characterization of the role of cAMP as a global regulator of cellular respiration in ANA-3

• Isolation of a novel arsenic respiring microbe from an arsenic rich hot spring

Systems biological approaches in Shewanella represent a new frontier that considers the sum of biological processes that allow this genre of microbes to thrive in some of the most hostile environments on earth. My findings contribute to both a broad understanding of cellular respiration in Shewanella and the mechanistic criteria for arsenic reduction.