Project Summary/Abstract
A healthy human microbiome is intrinsically linked to vital physiological aspects such as development, immune
function, and nutrition. The composition and function of the human microbiota is significantly influenced by
access to key metal micronutrients including iron, copper, zinc, and cobalt. Although mechanisms of competition
for metals have been studied in metal-limited environmental systems, how the human microbiota acquires metals
and responds to changes in host metal homeostasis remains under investigated, even as microorganisms must
compete with one another for limited resources at metal-limited body sites. Production of metallophores, small-
molecule natural products that bind metals with high affinity and selectivity, can enable colonization of metal-
limited environments; for example, we recently showed that Escherichia coli Nissle 1917 persists in the zinc-
limited inflamed gut by producing zinc-binding yersiniabactin. Metallophore-production can also benefit other,
non-producer organisms in microbial systems, as metallophores can be shared goods in complex microbial
communities. Recent examples have revealed that Bacteroides thetaiotaomicron, a human commensal
bacterium, uses siderophores produced by other bacteria for iron acquisition during iron-limitation. However,
despite significant numbers of metallophore biosynthetic gene clusters (BGCs) present in metagenomics
sequencing data from human-derived microbiota samples, elucidation of the chemical structures and properties
of these microbial molecules remain limited by various analytical, chemical, and biological challenges. This lack
of reliable methods precludes our understanding of functional roles of these molecules. Therefore, the goal of
this proposal is to elucidate the structure and functions of microbially-derived metallophores as modulating
microbe-microbe and community interactions within human microbiomes. To accomplish this, our laboratory will
investigate several critical questions, broadly these are: 1) what metallophores are produced by the human
microbiota and how are they biosynthesized? 2) what are their metal preferences and specificities? 3) how do
these molecules modulate microbial interactions? 4) what are the effects of altered microbial interactions? With
these questions in mind, we develop discovery-based approaches to find uncharacterized microbial
metallophores, pursue chemical structure elucidation and characterization of biosynthesis, and investigate
growth and metal acquisition of wild-type and genetic deletion mutants (lacking metallophore-production ability)
to understand functional roles of these molecules in monoculture, co-culture, and in complex microbial model
systems. Elucidating the metal-uptake molecules and mechanisms used by the microbiota to withstand altered
metal homeostasis may allow for the development of microbiome-based therapeutics, identification of
microbiome-derived biomarkers, and an improved understanding of metal imbalances. This research will provide
fundamental insight how members of the microbiota interact through metal competition, a key mechanism by
which both opportunistic infections and probiotic organisms are established and persist within the microbiome.