Deletion of SMC renders FtsK essential inCorynebacterium glutamicum

Abstract

AbstractStructural maintenance of chromosomes (SMC) are ubiquitously distributed proteins involved in chromosome organization. Deletion ofsmccauses severe growth phenotypes in many organisms. Surprisingly,smccan be deleted inCorynebacterium glutamicum, a member of the Actinomycetota phylum, without any apparent growth phenotype. Earlier work has shown that SMC inC. glutamicumis loaded in a ParB-dependent fashion to the chromosome and functions in replichore cohesion. The unexpected absence of a growth phenotype in thesmcmutant prompted us to screen for unknown synthetic interactions withinC. glutamicum. Therefore, we generated a high-density Tn-5 library based on wild-type andsmc-deletedC. glutamicumstrains. The transposon sequencing (Tn-seq) data revealed that the DNA-translocase FtsK is essential in asmcdeletion strain. FtsK localized to the septa and cell poles in wild type cells, however deletion ofsmcresulted in a decreased polar FtsK localization. Single-particle tracking analysis further suggests that prolonged FtsK complex activity is both required and sufficient to make up for the absence of SMC, thus achieving efficient chromosome segregation inC. glutamicum. Further, single molecule dynamics of FtsK is influenced, albeit indirectly, by DNA-loaded SMC. Deletion of ParB results in an increased of both SMC and FtsK mobility. While the first change agrees with previous data that show how ParB is essential for SMC loading on DNA, the latter suggests that FtsK mobility is affected in cells with defects in chromosome organization. Based on our data we propose a simple, yet efficient mechanism for efficient DNA segregation inC. glutamicum, even in absence of SMC proteins.ImportanceFaithful DNA segregation is of fundamental importance for life. Bacteria have efficient systems to coordinate chromosome compaction, DNA segregation and cell division. A key factor in DNA compaction is the SMC-complex that is found to be essential in many bacteria. In members of the Actinomycetotasmcis dispensable, but the reason for this was unclear. We show here that the divisome associated DNA-pump FtsK can compensate SMC loss and the subsequent loss in correct chromosome organization. In cells with distorted chromosomes, FtsK functions for an extended period of time at the septum, until chromosomes are segregated.