B. subtilis as a probiotic and its role in intestinal colonization by pathogenic fungi C. albicans - implications for inflammatory bowel disease - Abstract
Inflammatory bowel disease (IBD) is caused by an inappropriate immune response, typically against intestinal
microbes, resulting in inflammation of the intestines. In the last five years alone, 70,000 new IBD cases have
been diagnosed in the US, representing a serious public health challenge of increasing medical and socio–
economic importance. IBD is triggered by environmental factors, which within the intestine, is rich in microbes -
beneficial, commensal as well as pathogenic. Here we will study the interactions between a beneficial bacteria
Bacillus subtilis and an opportunistic fungal pathogen Candida albicans. Overgrowth of C. albicans in the gut
has been linked to inflammation of the digestive tract. Some associated genetic and environmental factors
have been characterized but the underlying molecular and immunological mechanisms remain unknown.
This proposal will test the role of microbial interactions and associated immune responses. Microbes residing
in the host niche of the gut must cope with alterations during long-term persistence in the host. They must also
adapt rapidly to changes to ensure growth and survival during infection. Our goal is to determine the molecular
mechanisms of cross-kingdom microbial interaction and host-microbe interactions with in a live host to gain a
better understanding of healthy interactions versus disease. Our working hypothesis is that B. subtilis has
probiotic properties because pre-exposure to B. subtilis protects the host from future C. albicans
infections. We are just beginning to understand the genes involved in the interaction between C. albicans and
B. subtilis as well as C. albicans and the host. Here, we will identify the molecular mechanisms that govern
disease progression, and determine how specific mutations directly affect microbial interactions, host
recognition, host response, and virulence. One of the major virulence factors in C. albicans is its morphogenic
plasticity. We will use multiple morphogenic forms of C. albicans – pathogenic forms as well as GUT-adapted
commensals forms that are able to evade the host innate immune system thereby affecting disease outcomes.
We will also use B. subtilis mutants that are unable to form protective biofilms and strains where key proteins
are fluorescently tagged for microscopy. These investigations will be conducted in the intestine of a live animal
host – C. elegans. We will address the following questions: (1) what bacterial genes dictate the outcome of a
fungal infection? (2) how fit are these mutants under physiologically relevant infection conditions within a live
host? (3) what host innate immunity genes are involved in maintaining a healthy microbiota? (4) how does the
host recognize and respond to the repertoire of morphologies it encounters? These studies will advance our
understanding of microbial interactions from the pathogen perspective and will help reveal the role of the host
in maintaining balanced relationship in healthy individuals as well as how disruption of this interaction causes
devastating inflammation in the host.
