Research Interests - Dr. Tony Lobo

My students and I have research interests in two areas of microbiology- in bacterial pathogenesis (the mechanisms by which bacteria cause disease in a host), and the molecular basis of microbial physiology (the metabolic processes carried out by microbes for survival and growth).  In both areas, which I describe below in greater detail, I make use of classical microbiological techniques as well as genetic and molecular approaches in my investigations.

              Escherichia coli is a normal inhabitant of the intestinal tracts of mammals and birds.  Certain strains of E. coli are capable of causing disease in humans at sites outside the intestine, such as the urinary tract or the kidney.  These strains differ from other E. coli in a few characteristics that give these strains disease-causing (pathogenic) ability.  One of these traits is the ability to produce a toxin called a hemolysin.  The E. coli hemolysin destroys a variety of host cell types by creating pores in the outer membrane of the target cells, causing them to burst.  My interests lie in understanding how the structure of the hemolysin molecule relates to its function in binding to and creating a pore within the target cell's membrane.  For example, the hemolysin requires calcium to be active and calcium has been shown to bind to the molecule.  How does calcium change the structure of the hemolysin to convert it from an inactive to an active form?  We try to answer this question through a combination of genetic (engineering mutations into the genes responsible, screening for altered phenotypes) and biochemical (looking for physical changes in the toxin by column chromatography, measuring calcium-binding ability of mutant hemolysins) approaches.

              Another bacterial toxin that interests me is another hemolysin, that produced by Moraxella bovis.  M. bovis causes a form of conjunctivitis (pink eye) in cattle.  Not much is known about the factors that contribute to the pathogenic ability of M. bovis.  I have evidence that the M. bovis hemolysin is related to that of E. coli.  Work awaits to characterize this toxin further and to determine its role in disease caused by M. bovis.

              My other major research area is study of the molecular biology of a group of unique microbes called the Archaea (formerly the Archaeobacteria).  These are considered to be an ancient line of organisms, unrelated to any others on Earth, which today inhabit extreme environments (sulfur-rich anaerobic sites, hydrothermal vents, hypersaline ponds) that may be remnants of conditions on the surface of the planet early in its history.  Although the existence of these organisms has been known for quite some time, relatively little is known about their physiology, biochemistry, and genetics.

              I am investigating two areas of archaeal physiology currently: nitrogen fixation (the utilization of atmospheric nitrogen gas as a source of cellular nitrogen) by methane-producing archaea, and transport of substances across cellular membranes in extremely halophilic archaea.  Regarding the former, as a doctoral student I purified the enzyme responsible for converting nitrogen gas to ammonia (a form of nitrogen usable by the organism); I would like to learn more about other proteins involved in nitrogen fixation by methanogenic archaea, as well as the genes that encode them.  For the latter, we have identified a gene in the extreme halophile Halobacterium cutirubrum that is homologous to genes encoding membrane-bound transporter proteins found in organisms ranging from bacteria to humans.  I would like to isolate, or clone, this gene in order to study it further and find out what role it plays in the physiology of this extreme halophile.  Because homologues of this gene may exist in the three major cell types, eukaryotic, bacterial, and now possibly archaeal, I am interested in this gene as an example of one that might have existed in the earliest cellular life forms on earth.  We have also acquired a phage (a virus of prokaryotic cells) that infects the extreme halophile Halorubrum coriense.  Experiments are underway aimed at identifying the molecules associated with phage binding.