Holden Lab: Research Projects

CO2 Fixation in Hyperthermophilic Crenarchaeota

This project examines the role of the reductive citric acid cycle in CO2 fixation in hyperthermophilic crenarchaeota, namely Pyrobaculum islandicum, Pyrolobus fumarii, and Acidianus brierleyi, and its association with other CO2 uptake and anabolic pathways such as the 3-hydroxypropionate cycle and the citramalate cycle. Our studies have shown that P. islandicum uses acylated citrate lyase as a counterpart to citrate synthase to control the direction of carbon flow in the cycle, and that a mechanism other than pyruvate synthase is responsible for converting acetyl-CoA into other organic compounds during anabolism. The organism also uses acetate as a carbon source but only when H2 and a trace amount of organic material are available.

Hu, Y., and J.F. Holden (2006) Citric acid cycle in the hyperthermophilic archaeon Pyrobaculum islandicum grown autotrophically, heterotrophically, and mixotrophically with acetate. J. Bacteriol. 188:4350-4355.

Dissimilatory Iron Reduction in Hyperthermophilic Crenarchaeota

This project examines terminal electron acceptor processes in hyperthermophilic crenarchaeota, namely Pyrobaculum aerophilum, Pyrobaculum islandicum, and Pyrodictium abyssi, with emphasis on understanding their physiological mechanisms of dissimilatory iron reduction. Our studies have shown that iron reduction in P. aerophilum is regulated and that insoluble iron can be reduced without direct contact suggesting that it produces an extracellular mediator for reduction. The organism does not produce polyheme c-type cytochromes, which sets it apart from some mesophilic bacteria such as Shewanella and Geobacter species, but does produce at least one monoheme c-type cytochrome when cultures are grown on iron.

Feinberg, L.F., and J.F. Holden (2006) Characterization of dissimilatory Fe(III) versus NO3- reduction in the hyperthermophilic archaeon Pyrobaculum aerophilum. J. Bacteriol. 188:525-531.

Ecology of Hyperthermophilic Archaea in Deep-Sea Hydrothermal Vents

This project examines the spatial distribution, metabolic processes, and growth constraints of hyperthermophilic archaea in deep-sea hydrothermal vent environments, primarily within hydrothermal sulfide deposits. Our study site is at the Endeavour segment of the Juan de Fuca Ridge in the northeastern Pacific Ocean, which is one of three Integrated Study Sites designated by the RIDGE2000 Program for intensive interdisciplinary study and will soon be a part of the NEPTUNE regional cabled ocean observatory. Field samples for our studies were collected in spring 2004 and again in summer of 2006 using the deep-sea research submarine Alvin.