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The bacterial world is the largest unexplored biological
reservoir on Earth, yet we know very little about its structure and
function in natural ecosystems. It is now evident that many bacteria
exist in complex social networks dependent on a level of cooperation
and communication. A major interaction involves cell-to-cell
communication, called quorum sensing (QS), and is used by bacteria
to ‘sense’ surrounding bacterial cell densities and regulate gene
expression accordingly. While this process was discovered over 3
decades ago, its ecological relevance has remained largely
uncharacterized. As a result, we still know very little about the
diversity of QS genes in natural systems or how environmental
conditions affect their level of expression. Herein lies a
significant gap in the knowledge of broader natural bacterial
interactions that must be examined to understand the structure and
functions of microbial communities.
In collaboration with the laboratory of Dr. Sean Norman, we are utilizing state-of-the-art methods involving functional metagenomics and GeneChip Expression arrays to explore the diversity
and expression of QS genes occurring within two distinct types of
microbial mat ecosystems, marine stromatolites (at Highborne Cay,
Bahamas) and hypersaline mats (at San Salvador Island, Bahamas).
Our goals are to: 1) generate and screen BAC metagenomic
libraries from both stromatolites and hypersaline mats to identify
genes involved in quorum sensing; (2) Use confocal scanning laser
microscopy combined with fluorescence in-situ hybridization to
identify microspatial distributions of QS genes in regards to the
major microbial functional groups and the diel cycle; (3) Use
quantitative RT-PCR and Microarray analysis to measure diel patterns
of QS gene expression and compare the level of expression to
chemical signal patterns.
Microbial mats are one of the oldest and most-diverse biological
systems on Earth, and some (stromatolites) have contributed to
biogeomineral formation and the geochemical evolution of the Earth.
Thus, the mat system provides both an exciting and ideal platform for
developing and employing metagenomic tools to understand
environmental genomic interactions.
Fig. 1. Clusters of microbial cells within a microbial
mat. Each cluster may contain different groups of bacteria, and may
communicate within/between groups- regulating gene expression in a
coordinated manner. These ‘microscale process’ may facilitate a
more efficient cycling of nutrients, and greater adaptability of
microbial communities to changing environmental conditions.
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