Bridging the Gap: Model Systems to Pathogens - A Celebration to Honor the Research Career of Dr. Issar Smith

Organizers: Barry Kreiswirth and David Perlin, PHRI/New Jersey Medical School-UMDNJ

Please join us in celebrating the career of Dr. Issar Smith (Smitty) who has spent over 42 years at the Public Health Research Institute studying the control of sporulation and gene regulation in Bacillus subtilis and pathogenesis in Mycobacterium tuberculosis. In an attempt to honor the research focus on Smitty's career, we have assembled eight celebrated speakers and colleagues, including two members of the National Academy of Sciences, who have made significant advances in their fields.

Presentations and Abstracts

I Never Met a Microbe I Didn't Like
Stanley Falkow, Stanford University

Issar Smith's love of the tubercle bacillus has provided him with a marvelous research career and it has engaged him in the pursuit of understanding how this remarkable microorganism can persist in the human host usually without causing symptoms and avoid the admirable defense mechanisms human evolution has designed to eliminate foreign invaders. As a counterpoint, I will attempt to describe how another persistent facultative intracellular microbe, Salmonella enterica, manages to avoid the host immune system and the factors at play involved in its transmission from an infected host to a susceptible naive host. Finally, I will argue that some of the most feared human pathogens including the tubercle bacillus might legitimately be considered to be members of the human indigenous flora which play as much of a protective role as they do as agents of disease.

Noise and Bistability in Bacterial Development
David Dubnau, PHRI

In clonal bacterial populations, all cells are equal, but some are more equal than others. Because many biological processes involve the participation of small numbers of molecules and because the interactions of these molecules occur randomly, there is heterogeneity in the cellular concentration of regulatory molecules. This heterogeneity, or "noise", can have regulatory and developmental consequences. It has been shown, for instance, that the developmental state known as competence is determined by noise in the expression of a transcription factor in the bacterium Bacillus subtilis. There is mounting evidence that such stochastic determination of cell fate is widespread among microorganisms and even in eukaryotic developmental systems. Some examples will be discussed, together with the ecological relevance of these phenomena for bacteria.

Sinful Days: Sigma, Smitty and Sporulation
Richard M. Losick, Harvard College

Bacillus subtilis is traditionally thought of as a solitary creature. But years of manipulation in the laboratory has robbed the spore-forming bacterium of its natural social behavior. In contrast to laboratory strains, wild strains of B. subtilis form architecturally complex communities of cells on surfaces. These biofilms consist of long chains of cells held together by an extracellular matrix. Production of the matrix is governed by an intricate regulatory network, at the heart of which are two key proteins discovered by Issar Smith: SinI and SinR. Pioneering work by Smith showed that these proteins form a pathway of repression and antirepression with SinI being an antirepressor that binds to and inhibits the SinR, which is a repressor. Interestingly, the logic of the SinI/SinR pathway is used a second time in biofilm formation. A second key regulator of genes involved in matrix formation is the repressor AbrB, which we now know is also negatively regulated by an antirepressor. Thus, biofilm formation is governed by two parallel pathways of repression and antirepression. Finally, recent work has revealed that the circuitry governing biofilm formation involves two additional regulatory proteins that are themselves homologs of SinI and SinR. Thus, Issar Smith's seminal work continues to be at the heart of current research on his former favorite bacterium.

Genetics: From Model Organism to Diffficult Pathogens
Brigitte Gicquel, Institut Pasteur

Scientists who started their university education during the seventies were amazed by the powerful discoveries of the structure of the genetic material, the genetic code, the organisation of genes, group of genes and their regulation. They were impressed by the universality of the architecture and functioning of living organisms.

This gave us the dream to use these discoveries to unravel virulence mechanisms of major pathogens like M. tuberculosis and help in the design of more efficient vaccines, drugs and diagnostic tools. We have shared such a dream with Issar Smith and thus, opened the way to the identification of regulatory pathways which control the expression of virulence genes.

We then applied the new technologies allowing global analysis using mutant libraries, microarrays and sequencing to discover the redundancy of many genes and functions as well as the diversity of the pathogen that uses the diversity of the host for a fruitful interaction leading to the disease and resistance to drugs initially designed to kill the pathogen.

The new generation of scientists is now facing new challenges having to deal with a new level of information. We started out at the level of one gene, one function. They will have to deal with hundreds of genomes of pathogens and their hosts. It is this diversity that has resulted in chronic infections like tuberculosis. We now have to crack these complex interactions in order to discover innovative intervention against leading causes of infectious diseases.

Mycobacterium Tuberculosis: Here Today, and Here Tomorrow
David Russell, Cornell University

Mycobacterium tuberculosis remains one of the most serious scourges of mankind, accounting for up to 2 million deaths per year. Our lab is dedicated to the study of pathogenic mycobacteria and the main goals of the work in the lab fall into three discrete areas of research addressing the interaction between the macrophage and the bacterium. Firstly, the intracellular vacuole in which the bacillus resides exhibits arrested maturation and fails to differentiate into acidic, hydrolytically-active lysosomes. We are actively pursuing both the mechanism and consequences of this unusual strategy for intracellular survival. If the macrophage is activated, the host cell can overcome this blockage and deliver the bacterium to a lysosomal compartment, culminating ultimately in the death of the bacterium. Secondly, Mycobacterium tuberculosis varies its transcriptional response according to the changing environments within its host cell. We are exploiting microarray analysis of these changing patterns to pursue three distinct goals. 1. Real-time readouts of bacterial fitness; promoter GFP fusions are being generated to provide real-time reports of the intracellular environments. 2. These plasmid-encoded reporters are being transformed into transposon libraries to facilitate screening for sensor/effector cascades that allow the bacterium to detect and respond to environmental shifts. 3. The reporters are also being exploited to develop a High-Throughput Screen platform for interrogating small molecule libraries for compounds that kill intracellular bacteria as part of a new drug discovery program. Finally, collaborative work on human tuberculosis patients in Blantyre, Malawi and in Cape Town, South Africa are providing fresh insights into how a latent infection progresses to an active infection capable of transmission. We have performed cryostat-sectioning, laser-capture microdissection, and microarray analysis on tissue from human TB patients. The data reveal a profile of dysregulated lipid metabolism that culminates in accumulation of caseum (lipid) in the core of the granuloma. This leads to necrosis and release of viable infectious bacilli into the airways of the individual, thus completing the infection cycle of the disease.

Modern TB Therapy-From Dreams, to Fulfillment, then Nightmares
Michael D. Iseman, University of Colorado

From Hippocrates onward clinicians have pursued the cure for phthisis. Two thousand years of medical history is littered with the names of giants who'd struggled to understand and conjure up remedies for consumption.

Koch identified the pathogen in 1882 but it was not until 1944 that effective drugs were found – Waksman & Schatz and streptomycin, Lehmann and PAS. By 1952, the Holy (Curative) Trinity was complete with INH.

1960 – 1990 might be described as the era of optimism: INH, Streptomycin and ethambutol cured in 18 months; INH and rifampin cured in 9 months; IHN, RIF and PZA reduced the duration to cure to six months; and – intermittent (2 or 3 days/week) treatment made directly-observed therapy feasible.

However, from 1990 forward we have seen our optimistic plans unravel due to the extraordinary accelerant efforts of the AIDS virus on both the spread of TB and the explosion of first MDR-TB and now XDR-TB.

We must now reconsider all of our fundamental paradigms for the future of TB control.