Activation of the integrative and conjugative element Tn916causes growth arrest and death of host bacteria

Abstract

Integrative and conjugative elements (ICEs) serve as major drivers of bacterial evolution. These elements often confer some benefit to a host cell, including antibiotic resistance, metabolic capabilities, or pathogenic determinants. ICEs can also have negative impacts on their host cells. Here, we investigated the effects of the ICE (conjugative transposon) Tn916 on host cells. Because Tn916 is active in a relatively small subpopulation of host cells, we developed a fluorescent reporter system for monitoring activation of Tn916 in single cells. We found that when active in Bacillus subtilis and its natural host Enterococcus faecalis, Tn916 inhibited cell division and most cells died. We also observed these phenotypes on the population level in B. subtilis utilizing a modified version of Tn916 that can be activated in the majority of cells. We identified two genes (orf17 and orf16) in Tn916 that were sufficient to cause host growth defects and identified a single gene, yqaR, that is found in a defective phage (skin) in the B. subtilis chromosome that is required for this phenotype. However, these three genes are only partially responsible for the growth defect caused by Tn916, indicating that Tn916 possesses multiple mechanisms to affect growth and viability of host cells. These results highlight the complex relationships that conjugative elements have with their host cells and the interplay between mobile genetic elements.

Activation of TnSmu1, an integrative and conjugative element, by an ImmR-like transcriptional regulator in Streptococcus mutans

“…For example, setR cannot be deleted, a CI-like repressor found on a Vibrio cholerae mobile element known as SXT (Beaber et al ., 2002). It was also recently observed that activation of Tn 916 causes severe cell growth defects (Bean et al ., 2022:916). Tn 916 only activates in a small percentage (0.1-3%) of cells and the lethality of Tn 916 was discovered by activating it in a much larger proportion of cells.…”

TnSmu1 is a functional integrative and conjugative element in Streptococcus mutans that when expressed causes growth arrest of host bacteria

“…Tn 916 , an ICE related to Tn Smu1, causes growth arrest and death of host cells following excision and expression of its genes (Bean et al, 2022a). In contrast, ICE Bs1, which encodes conjugation machinery and regulatory proteins similar to those encoded by Tn Smu1, does not cause death of its host cells (Babic et al, 2011; Bean et al, 2022a). Therefore, we wondered whether or not Tn Smu1 manipulated the growth and-or viability of its host cells.…”

“…Tn 916 was discovered through its ability to spread tetracycline resistance through clinical isolates of Enterococcus (Franke and Clewell, 1981a, 1981b), thus providing a clear benefit to its host cells. However, activation of Tn 916 halts cell growth and leads to decreased bacterial viability (Bean et al, 2022a). Similarly, when activated, ICE clc causes slow growth and decreased viability (Reinhard et al, 2013).…”

“…They can benefit their host cells through associated cargo genes that confer specific phenotypes, such as antibiotic resistances, metabolic traits, and virulence factors. However, some ICEs can manipulate host development, growth, and viability (Beaber et al, 2004;Bean et al, 2022a;Jones et al, 2021;Pembroke and Stevens, 1984;Reinhard et al, 2013). This is similar to plasmids, which are known to provide beneficial phenotypes to their hosts but are energetically costly to maintain (San Millan and MacLean, 2017).…”

“…ICEs often benefit their host cells through associated cargo genes that confer specific phenotypes (mentioned above). However, ICEs can also manipulate host development, growth, and viability (Beaber et al, 2004; Bean et al, 2022a; Jones et al, 2021; Pembroke and Stevens, 1984; Reinhard et al, 2013).…”