February 2014 – Kelly Rice Lab – Examination of the Staphylococcus aureus nitric oxide reductase (saNOR) reveals its contribution to modulating intracellular NO levels and cellular respiration
Staphylococcus aureus nitrosative stress resistance is due in part to flavohemoprotein (Hmp). Although hmp is present in all sequenced S. aureus genomes, 37% of analyzed strains also contain nor, encoding a predicted quinol-type nitric oxide (NO) reductase (saNOR). DAF-FM staining of NO-challenged wild-type, nor, hmp and nor hmp mutant biofilms suggested that Hmp may have a greater contribution to intracellular NO detoxification relative to saNOR. However, saNOR still had a significant impact on intracellular NO levels and complemented NO detoxification in a nor hmp mutant. When grown as NO-challenged static (low-oxygen) cultures, hmp and nor hmp mutants both experienced a delay in growth initiation, whereas the nor mutant’s ability to initiate growth was comparable with the wild-type strain. However, saNOR contributed to cell respiration in this assay once growth had resumed, as determined by membrane potential and respiratory activity assays. Expression of nor was upregulated during low-oxygen growth and dependent on SrrAB, a two-component system that regulates expression of respiration and nitrosative stress resistance genes. High-level nor promoter activity was also detectable in a cell subpopulation near the biofilm substratum. These results suggest that saNOR contributes to NO-dependent respiration during nitrosative stress, possibly conferring an advantage to nor+ strains in vivo.
Learn more about Dr. Rice!
Department of Microbiology and Cell Science University of Florida
Ph.D. (2001) University of Toronto, Toronto, ON, Canada
Post-doctoral training (2001-2005) University of Idaho, Moscow, ID
Instructor (2005-2008) University of Nebraska Medical Center, Omaha, NE
Bacterial and Viral Pathogens (MCB4203), Advanced Microbiology Lab (MCB4034L), Undergraduate Research
Description of Research
My research program focuses on aspects of bacterial physiology and cell communication that contribute to biofilm development of pathogenic Gram-positive bacteria. Specific research projects currently under investigation include:
1. Determining the contributions of endogenous nitric oxide (NO) to biofilm, physiology and cell-signaling in Staphylococcus aureus. NO is a free-radical gas that has been well-characterized as a signaling molecule in eukaryotes, and more recently, a role for this versatile molecule in regulating bacterial physiology and biofilm development has also been recognized. Our research is focused on dissecting the pathways of endogenous NO production and consumption in Staphylococcus aureus (MSSA and MRSA), a notorious pathogen that causes a wide variety of serious infections in mammals. This work also seeks to identify the upstream regulators and downstream cellular targets of endogenously-produced NO, and to determine how these processes relate to biofilm development.
2. Characterizing the role and regulation of cell death in Streptococcus mutans biofilms. The cid and lrg operons encode membrane proteins that have been shown to be involved in cell death and lysis regulation in several bacteria. Our research focuses on the Cid/Lrg system of Streptococcus mutans, the primary causative agent of dental caries. There appear to be distinct differences in the organization and regulation of S. mutans cid and lrg compared to what is known in other organisms, and some of these genes affect S. mutans virulence traits such as oxidative stress resistance, competence, and biofilm formation. A better understanding of how cid and lrg specificallycontribute to these virulence phenotypes may allow the development of new anti-caries strategies. This research is conducted in collaboration with Dr. Sang-Joon Ahn, Research Assistant Professor, Dept. Oral Biology, UF.
3. Investigating microgravity effects on S. mutans physiology, gene expression, and biofilm development. The health of astronauts during space flight is of paramount concern, as various detrimental health effects resulting from exposure to microgravity conditions have been documented. In fact, simulated microgravity exposure has been shown by others to cause increased mandibular and alveolar bone loss and decreased saliva flow, two host factors that could predispose astronauts to caries and/or periodontal disease. Although the host response to microgravity has been well-studied, the response of cariogenic bacteria such as S. mutans has not been rigorously assessed. Therefore we are studying the response of S. mutans physiology, biofilm formation and global gene expression to simulated microgravity conditions.