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In bacterial genomes composed of more than one chromosome, one replicon is typically larger, harbors more essential genes than the others, and is considered primary. The greater variability of secondary chromosomes among related taxa has led to the theory that they serve as an accessory genome for specific niches or conditions. By this rationale, purifying(More)
It has become clear that different genome regions need not evolve uniformly. This variation is particularly evident in bacterial genomes with multiple chromosomes, in which smaller, secondary chromosomes evolve more rapidly. We previously demonstrated that substitution rates and gene dispensability were greater on secondary chromosomes in many bacterial(More)
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In bacterial chromosomes, the position of a gene relative to the single origin of replication generally reflects its replication timing, how often it is expressed, and consequently, its rate of evolution. However, because some archaeal genomes contain multiple origins of replication, bias in gene dosage caused by delayed replication should be minimized and(More)
BACKGROUND Twelve populations of the bacterium, Escherichia coli, adapted to a simple, glucose-limited, laboratory environment over 10,000 generations. As a consequence, these populations tended to lose functionality on alternative resources. I examined whether these populations in turn became inferior competitors in four alternative environments. These(More)
The fitness effect of mutations can be influenced by their interactions with the environment, other mutations, or both. Previously, we constructed 32 ( = 2⁵) genotypes that comprise all possible combinations of the first five beneficial mutations to fix in a laboratory-evolved population of Escherichia coli. We found that (i) all five mutations were(More)
The nematode Caenorhabditis elegans may be killed by certain pathogenic bacteria and thus is a model organism for studying interactions between bacteria and animal hosts. However, growing nematodes on prey bacteria may influence their susceptibility to potential pathogens. A method of axenic nematode culture was developed to isolate and quantify(More)
Gastric infections caused by the environmentally transmitted pathogen, Vibrio parahaemolyticus, have increased over the last two decades, including in many parts of the United States (US). However, until recently, infections linked to shellfish from the cool northeastern US waters were rare. Cases have risen in the Northeast, consistent with changes in(More)
Entomopathogenic associations between nematodes in the genera Steinernema and Heterorhabdus with their cognate bacteria from the bacterial genera Xenorhabdus and Photorhabdus, respectively, are extensively studied for their potential as biological control agents against invasive insect species. These two highly coevolved associations were results of(More)
Experimental evolution paired with modern sequencing can be a powerful approach to identify the mechanisms by which bacteria adapt to discrete environmental conditions found in nature or during infections. We used this approach to identify mechanisms enabling biofilm specialists of the opportunistic respiratory pathogen Burkholderia cenocepacia to regain(More)