Horizontal gene transfer (HGT) is a driving force in bacterial evolution, permitting bacteria to acquire new genes and phenotypes. Horizontal gene transfer is largely mediated by mobile genetic elements, including viruses, conjugative plasmids, and integrative and conjugative elements (ICEs), also known as conjugative transposons. Conjugative elements are well known agents contributing to the spread of genes for antibiotic resistances, pathogenesis, symbiosis, metabolism, and more, and are largely responsible for the surge in drug- resistant and multi-drug-resistant bacterial pathogens. ICEs are widespread in bacteria and appear to be the most prevalent type of conjugative element. They reside integrated in a host genome. Under certain conditions, they can excise to form a circle and then a single strand of DNA can be transferred to appropriate recipient cells. In addition to mediating their own transfer, ICEs can mobilize (transfer) other DNA elements, including plasmids, that are not able to self-transfer. Despite the prevalence and importance of ICEs, there are fundamental deficiencies in our understanding of these mobile genetic elements. Many basic mechanisms of ICE function are not well understood, especially in Gram-positive bacteria. Components of the bacterial host components play key roles in ICE biology, but the identities and functions of these host components in the ICE life-cycle are largely unknown. ICEs commonly co-exist with other mobile genetic elements, including phages. Despite this co-occurrence, little is known about effects these elements have on one another. The mobile genetic element ICEBs1 is an integrative and conjugative element in Bacillus subtilis. ICEBs1 gene expression, excision, and mating are induced following DNA damage (the SOS response) and under conditions of crowding, provided that the neighboring cells do not contain a copy of the element. The ability to experimentally induce ICEBs1 in virtually all cells in a population and achieve relatively high frequencies of conjugation allow us to answer previously intractable or unstudied problems fundamental to conjugation and HGT. This project will focus on: 1) newly discovered properties of ICEBs1 that appear to be broadly conserved, 2) identifying and elucidating host functions that are important for ICEBs1 life cycle, and 3) characterizing interactions between ICEBs1 and a lysogenic phage found in the genome of many strains of B. subtilis. Based on homologies and the conserved life cycle of ICEs, insights gained from studying ICEBs1 and its host, B. subtilis, are likely to be generally relevant to many other mobile genetic elements and their hosts. Our findings should be relevant to the transfer of genes, including those encoding antibiotic resistances, between bacteria growing in many different environments, including humans.

Public Health Relevance

Mobile genetic elements and horizontal gene transfer in microbes contribute significantly to pathogenesis and the spread of antibiotic resistances. Despite their importance, mechanisms controlling a common type of mobile element and the identities and roles of host genes involved in their spread are poorly understood, especially in Gram positive bacterial pathogens. This project is directly related to mechanisms controlling the spread of antibiotic resistances and pathogenic determinants.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Prokaryotic Cell and Molecular Biology Study Section (PCMB)
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Reddy, Michael K
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Massachusetts Institute of Technology
Schools of Arts and Sciences
United States
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Johnson, Christopher M; Grossman, Alan D (2016) The Composition of the Cell Envelope Affects Conjugation in Bacillus subtilis. J Bacteriol 198:1241-9
Wright, Laurel D; Grossman, Alan D (2016) Autonomous Replication of the Conjugative Transposon Tn916. J Bacteriol 198:3355-3366
Wright, Laurel D; Johnson, Christopher M; Grossman, Alan D (2015) Identification of a Single Strand Origin of Replication in the Integrative and Conjugative Element ICEBs1 of Bacillus subtilis. PLoS Genet 11:e1005556
Leonetti, Cori T; Hamada, Matt A; Laurer, Stephanie J et al. (2015) Critical Components of the Conjugation Machinery of the Integrative and Conjugative Element ICEBs1 of Bacillus subtilis. J Bacteriol 197:2558-67
Johnson, Christopher M; Grossman, Alan D (2015) Integrative and Conjugative Elements (ICEs): What They Do and How They Work. Annu Rev Genet 49:577-601
DeWitt, Tyler; Grossman, Alan D (2014) The bifunctional cell wall hydrolase CwlT is needed for conjugation of the integrative and conjugative element ICEBs1 in Bacillus subtilis and B. anthracis. J Bacteriol 196:1588-96
Johnson, Christopher M; Grossman, Alan D (2014) Identification of host genes that affect acquisition of an integrative and conjugative element in Bacillus subtilis. Mol Microbiol 93:1284-301
Thomas, Jacob; Lee, Catherine A; Grossman, Alan D (2013) A conserved helicase processivity factor is needed for conjugation and replication of an integrative and conjugative element. PLoS Genet 9:e1003198
Menard, Kayla L; Grossman, Alan D (2013) Selective pressures to maintain attachment site specificity of integrative and conjugative elements. PLoS Genet 9:e1003623
Kommineni, Sushma; Lama, Amrita; Popescu, Benjamin et al. (2012) Global transcriptional control by NsrR in Bacillus subtilis. J Bacteriol 194:1679-88

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