Work

Positive control of the integrative and conjugative element Tn 916 and its limited gene expression in transconjugants

Year: 2026

Type: preprint

Abstract: Integrative and conjugative elements (ICEs) are widespread in bacteria and typically confer important phenotypes to their hosts. Following excision from the host chromosome, an ICE can transfer to a new cell through the element-encoded conjugation machinery (a type IV secretion system) to create a transconjugant. Tn 916 , a well-studied ICE that confers tetracycline resistance, is found in several Gram-positive pathogens and has been widely studied in Bacillus subtilis . Unlike most ICEs, Tn 916 causes host-cell death following its activation (excision and gene expression). We found that orf7 and orf8 (renamed sig7 and sig8 ), two regulatory genes in Tn 916 , encode a two-subunit (split) sigma factor of RNA polymerase, Sig7-8, that activates transcription from P orf7 (now P sig7 ) and is required for excision of the element. Importantly, production of Sig7-8, either from P sig7 or another strong promoter, caused cell death. Using a Cre recombinase reporter to detect gene expression, we detected little or no transcription from P sig7 in transconjugants. This lack of transcription from P sig7 in transconjugants was essential for fitness of both the element and its host: forcing transcription from P sig7 in transconjugants caused either loss of Tn 916 or death of nascent transconjugants. Our findings indicate that, unlike other well-studied ICEs (e.g., ICE Bs1 ) that use repressors to control gene expression and are expressed in nascent transconjugants, most Tn 916 genes remain off following transfer to a new host. This regulation prevents Tn 916 from killing transconjugants and allows successful horizontal transfer and maintains the potential for future activation in the new host.

Source: bioRxiv (Cold Spring Harbor Laboratory)

DOI: 10.64898/2026.10.01.756105

Authors: Alexa F. S. Gomberg, Alan D. Grossman

Institution: Massachusetts Institute of Technology

Language: English

Topic: Bacterial Genetics and Biotechnology

Subfield: Genetics

Field: Biochemistry, Genetics and Molecular Biology

Domain: Life Sciences

Open Access status: green

Funders: National Institutes of Health, National Institute of General Medical Sciences

Award: Mechanisms and regulation of replication, the cell cycle, gene expression, and horizontal gene transfer in prokaryotes, focusing on Bacillus subtilis.