Detection and response of organisms to oxidative stress, biological iron-sulfur cluster assembly and repair
We are currently working on two interrelated projects in our lab. The first project examines the physiological response of a pathogenic bacterium to oxidative stress. The second project uses a model organism to dissect how organisms metabolize small oxidant sensitive inorganic cofactors.
1) Staphylococcus aureus is a human commensal bacterium that is naturally carried by 20-50% of the population. This bacterium can cause infections that range from relatively harmless furuncles and carbuncles to life threatening endocarditus and necrotizing pneumonia. Staphylococcus aureus infections have historically been associated with open-wounds, hospital visits, and immuno-compromised persons, but recently, infections are being seen in relatively healthy individuals that have not been associated with hospital settings (community acquired infections). Many of these infections are caused by strains of S. aureus that are resistant to nearly all commonly used antibiotics, including methicillin, greatly complicating the treatment of infections caused by this aggressive pathogen.
One research focus of our laboratory is to determine how community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) detects and responds to host defense systems. Neutrophil granulocytes are white blood cells that provide humans with a "first line" of defense against CA-MRSA infections. Neutrophils engulf and kill bacteria, in part, by bombarding them with poisonous oxidants such as bleach, superoxide, and hydrogen peroxide. Remarkably, strains of CA-MRSA can survive this attach and successfully invade host tissues. Our lab uses a variety of biochemical and genetic techniques to understand what is unique about the physiology of CA-MRSA that allows it withstand high degrees of oxidative stress. We also study how CA-MRSA detects and responds to the presence of neutrophils and oxidative stress.
2) The second focus of our work examines the metabolism of simple inorganic cofactors called iron-sulfur (Fe-S) clusters. Proteins with [Fe-S] clusters have an ever-expanding repertoire of biological functions. These metalloproteins are involved in some of the most fundamental life-sustaining processes on Earth such as biological nitrogen fixation, photosynthesis, and cellular respiration. To this end, the evolution of all life can be considered dependent on the successful and controlled synthesis and maintenance of [Fe-S] clusters. Free iron and free sulfur are toxic to cells and Iron-sulfur clusters are easily damaged by oxidants. Therefore, complex cellular machinery has evolved to tightly control the synthesis and repair of [Fe-S] clusters. Despite the recognized and central role of [Fe-S] clusters in biology, our understanding of how these inorganic cofactors are metabolized is limited by our lack of basic knowledge in which gene products control the synthesis, trafficking, and repair of these clusters and how these gene products are integrated into cellular metabolic networks.
The work on our second project aims to address remaining questions in [Fe-S] cluster metabolism and take advantage of integrative studies to uncover the biochemical function of genes of unknown function involved in [Fe-S] metabolism. Because all cells face similar challenges in integrating their metabolism and many metabolic paradigms are conserved, these studies are conducted using the model bacterium Salmonella enterica for simplicity and technical feasibility.