The polar localization of AidB-YFP is preserved in HeLa cells and RAW264.7 macrophages at different times post-infection. We therefore propose that AidB is a marker of new poles and constriction sites. To the best of our knowledge, it is the first time that a particular subcellular localization is described for one of the actors involved in the

alkylation damage repair. Interestingly, the constriction site corresponds to the location of the future new poles just after completion of cell division. We therefore propose a model (Figure 6) in which AidB-YFP is not only localized at the new pole, but also at the constriction site in dividing cells, a mechanism by which AidB-YFP would be ideally localized for a localization at the new pole in newly formed sibling cells. This model implies that when new poles mature to old poles, after cell division, they are no longer labelled with AP24534 AidB-YFP (Figure 6). Figure

6 Model for the localization of AidB-YFP along B. abortus cell cycle. The PdhS-mCherry is labelling the old pole of B. abortus. AidB-YFP is therefore localized at the new pole, as suggested by Figure 2. In dividing cells, we hypothesize that AidB-YFP is first present at the young pole (the new pole that becomes old) and at the constriction site. This localization at the young pole would be lost afterwards, allowing the generation of two sibling cells with a AZD5363 unique pole of AidB-YFP. The new (n), young (y) and old (o) poles are labelled. In this model, the constriction region would be the preparation site for the new poles of the sibling cells. In the conditions tested, overexpression of aidB leads to bacteria with aberrant morphology (Figure 5). This

could be due to defects in cell division, cell growth or coordination between both. One hypothesis would be that AidB could indirectly contribute to the generation of new poles, and overexpression of aidB would result in the generation of additional new poles, forming bacteria with abnormal morphology, Terminal deoxynucleotidyl transferase e.g. multipolar shapes (Figure 5). The selective advantage of the polar localization of AidB is unknown, but it could be related to its role in the adaptative response to alkylating agents, suggested here to block cell cycle before cell division (Figure 3B). This would be consistent with a role of AidB in limiting alkylating damage to DNA, which would logically block replication initiation and/or progression. The B. abortus AidB protein has a high level of identity (42%) to E. coli AidB, suggesting functional conservation between the two proteins. This prediction is supported by the increased sensitivity of the B. abortus aidB mutant strain to the alkylating agent EMS compared to the wild-type control (Figure 1). Brucella genomes contain the ada, alkA and alkB genes necessary for an adaptative response to alkylation damage similar to the one reported for E. coli [11]. We propose that one possible function of AidB would be to help in the detoxification of some alkylating agents, like in E. coli.