Seminars in Cell & Developmental Biology
completion of a prior event before initiation of a subsequent event . 
However , in the cell cycle of bacteria dividing under high nutrient or high growth conditions , the events of cell growth , chromosome replication , chromosome segregation and the assembly of the division machinery at the division site occur simultaneously . 
The chromosome begins a subsequent round of replication prior to the completion of the first , a mechanism termed multifork replication . 
As the round of replication nears completion , the division machinery accumulates and assembles at the division site in preparation for septation , although the subsequent splitting of the daughter cells is held off until midcell has been cleared of DNA . 
The simultaneous nature of these cell cycle events in bacteria makes advance 
1. Introduction
dination of chromosome replication with cell division to produce viable daughter cells . 
The ordering of distinct events of cell growth , chromosome replication , chromosome segregation and cytokinesis ( cell division ) is fundamental to the cell cycle in actively dividing eukaryotic cells and occurs through checkpoints that ensure Survival of any cellular organism relies on the efficient coor ¬ 
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All rights reserved . 
in this area challenging due to the difficulty in separating these processes and , despite intense investigation over several decades , the exact mechanism as to how bacteria spatially and temporally couple septum formation with the replication and segregation of the genetic material is not yet clearly understood . 
This review focuses on the current evidence of a coordinating link between these processes in Bacillus subtilis ( Gram-positive model system ) and Escherichia coli ( Gram-negative model system ) , and the latest advances in chromosome conformation capture techniques to bring us one step closer to answering this fundamental question . 
2. DNA replication
divided into three main stages : initiation , synthesis ( or elongation ) and termination . 
A key regulatory molecule for ensuring that replication occurs only once per cycle and in synchrony with cell growth and division is initiator DnaA , an AAA + ATPase ( ATPases Associated with various cellular Activities ) found in virtually all bacteria [ 1,2 ] : levels of DnaA are stringently controlled . 
Means of its control vary amongst bacteria and have been recently reviewed [ 1,3,4 ] . 
In its ATP-bound form DnaA exists as a helical oligomer that binds to specific AT-rich sequences ( DnaA-boxes ) within oriC . 
It is the binding of DnaA to the single chromosome origin of replication , oriC , positioned ◦ ◦ replication . 
At these sites DnaA forms a highly ordered nucleoprotein complex , the DNA-unwinding element ( DUE ) [ 1,5 ] , effectively melting and unwinding the local double stranded DNA to allow the recruitment of the replication machinery [ 5,6 ] . 
case loader ( DnaI ) and co-loader proteins ( DnaD and DnaB ) that are also recruited to this site actively load the helicase ( DnaC ) to establish the replication fork [ 7 -- 9 ] . 
DNA primase ( DnaG ) , DNA polymerase III holoenzyme ( PolC ) and the accessory polymerase ( DnaE ) then bind to the oriC region and , together with the other replication proteins , form the replisome thus completing the initiation stage [ 8 ] . 
A similar process , although with differing proteins , occurs in E. coli , as reviewed by [ 10 ] . 
[ Note , particularly that the DNA helicase in E. coli is named DnaB , not DnaC as it is in B. subtilis and that there is no homolog of the B. subtilis DnaB in E. coli . ] 
the circular chromosome [ 11 -- 13 ] . 
The two replication forks continue bi-directionally until they encounter the terminus region ( Ter ) , at which point the replisome disassembles allowing the decatenation and subsequent complete separation of the newly replicated sister chromosomes [ 14,15 ] . 
Resolution of the chromosomes , when required , is then completed by the combined action of site-specific recombinases located at the terminus ( XerCD in E. coli , and RipX and CodV in B. subtilis ) and DNA translocases ( FtsK in E. coli , and SpoIIIE in B. subtilis ) [ 16 -- 21 ] . 
DNA replication is a tightly regulated and ordered process at the 0 / 360 chromosome position that initiates Working together with oriC-bound DnaA , in B. subtilis , the heli-Starting at oriC , DNA synthesis occurs bi-directionally around 
3. Chromosome segregation
regation occur concomitantly . 
Soon after the origin regions are replicated , they migrate in opposite directions towards the future division sites , located at the cell quarter positions [ 22 ] . 
Most research on chromosome segregation in bacteria has focussed on how these newly-replicated origin regions separate . 
Separation involves the ParABS system and SMC ( Structural Maintenance of Chromosome ) condensin complex in B. subtilis , and the MukBEF complex in E. coli . 
aration in a number of bacteria , including B. subtilis , the ParABS system was first identified by the discovery of two proteins , ParA In B. subtilis and E. coli , DNA replication and chromosome seg-Although it is now known to be required for chromosome sep-and ParB , required for effective plasmid partitioning on the P1 plasmid hosted in E. coli [ 23 ] . 
ParB was found to bind co-operatively to the parS cis-acting site along with ParA , a Walker-type ATPase , to form a large nucleoprotein complex resulting in replicated plasmids segregating bidirectionally to the cell poles [ 24 ] . 
Since its discovery , par loci have been subsequently found on the chromosome of over 65 % of all sequenced bacterial genomes [ 25 ] , including B. subtilis . 
In B. subtilis however , the components of the ParABS system are known as Soj ( ParA ) and Spo0J ( ParB ) because they had been previously observed in B. subtilis having an effect on sporulation [ 26 ] . 
Cells lacking Spo0J mislocalise sister origin positions [ 27 ] , suggesting a role for this protein in separating the newly duplicated chromosome origins in B. subtilis . 
Subsequently it was shown that Spo0J binds to several parS sites located within the oriC region [ 28,29 ] , and in cells labelled with Spo0J-GFP , Spo0J co-localises with oriC and appears as distinct compact foci positioned at the cell quarters [ 30,31 ] . 
Several elegant studies in recent years have revealed significant insight into the roles of the ParABS system and the SMC condensin complex in chromosome segregation in B. subtilis . 
Following binding to parS , Spo0J spreads onto non-specific neighbouring DNA , drawing them together to form a nucleoprotein complex ( see Fig. 1B ) [ 30,32 ] . 
The method by which Spo0J spreads has been recently proposed by Graham et al. , such that Spo0J forms clusters on neighbouring DNA bridging them together , forming DNA loops [ 33 ] . 
The formation of these long-distance DNA loops is suggested to facilitate the condensation and compaction of the origin-proximal region of the chromosome as well as the recruitment and loading of the SMC constituents ( Fig. 1B ) [ 33 ] . 
The SMC condensin complex ( from now on referred to as simply SMC ) , made up of proteins Smc , ScpA and ScpB , and supplemented by the ParABS system , is then suggested to draw the sister origins away from each other [ 34 ] . 
Essentially , SMC resolves the origins enabling ParABS to actively segregate origins towards opposite poles . 
The extent to which Soj actually plays a role in the active segregation of chromosomes is unknown . 
Interestingly it was shown that the primary role of Soj is likely to be in regulating the initiation of DNA replication ( Fig. 1A ) . 
It does this by directly interacting with the initiation protein , DnaA [ 35 ] , inhibiting or promoting DnaA activity . 
As a monomer , Soj inhibits DnaA activity by preventing formation of its helical oligomer , whereas the Soj dimer relieves this inhibition by allowing DnaA to form oligomers . 
This ability to switch however is mediated by its interaction with DNA-bound Spo0J ( Fig. 1A ) [ 36 ] . 
So it is now clear that Spo0J has two separate roles , one in the regulation of DnaA via its effect on Soj self-association , and another in chromosome segregation . 
These functions have been shown to reside in different domains [ 37 ] . 
The mechanism of chromosome segregation in E. coli is more elusive . 
While the ParABS system is absent in this organism it does possess a distant relative of the SMC complex , MukBEF , a protein complex existing in enterobacteria and some - proteobacteria [ 38,39 ] . 
This complex plays a key role in separating newly replicated oriC regions [ 40 ] and , together with topoisomerase IV ( TopoIV ) , in promoting DNA decatenation [ 41 ] . 
Although it does n't share any homology with Spo0J , MukB is thought to have a similar bridging function , in that it binds DNA forming a cluster , creating bridges with randomly colliding protein-free DNA . 
Rybenkov et al. postulates that the formation of these bridges stabilises DNA compaction , potentially assisting in pulling apart the sister chromosomes [ 42 ] . 
It is unlikely these proteins are the sole players in chromosome segregation and there are several hypotheses as to how E. coli and other bacteria segregate their chromosomes [ 12,43,44 ] . 
In fact , biophysical models in E. coli suggest that chromosome segregation is generated via entropic forces [ 45 ] . 
Application of polymer physics concepts to the bacterial chromosome by Jun and Mulder , resulted in a passive segregation model where th replicated sister chromosomes themselves possess internal forces leading to entropic repulsion or exclusion [ 45 ] . 
However , recent evidence suggests that these entropic forces are insufficient to complete whole chromosome segregation [ 46,47 ] , highlighting the high complexity of chromosome segregation which requires several different components or modes of action for successful execution . 
4. Cell division and regulation of division-site placement
cific division proteins to the right place ( midcell ) at the right time within the cell cycle . 
The first and foremost of these proteins to localise to midcell is the tubulin-like protein , FtsZ which assembles at the inner face of the cytoplasmic membrane into a ring structure known as the Z ring [ 48 ] . 
The Z ring then facilitates the recruitment of all the other division proteins , together called the divisome [ 49 -- 51 ] , and provides a contractile force required for the invagination of the envelope layers , or at least the inner cell membrane . 
Thus , precise recruitment of FtsZ to midcell is central to the regulation of cell division and FtsZ has , over the last 20 years , become one of the most studied bacterial proteins . 
Much has been elucidated about FtsZ and most , if not all , of the divisome proteins [ 51 ] , but what yet escapes us is how the assembly of this crucial machinery , not only precisely finds the midcell , but how it does so in concert with the replication and segregation of the chromosome ? 
This question is of utmost importance as the correct timing and positioning of the Z ring between the DNA at midcell is quintessential to the competitive long-term survival of bacteria . 
Cell division is dependent on the localisation of numerous spe ¬ 
4.1. Negative regulators of Z ring placement
has been described as regulated by the combined action of the Min system and nucleoid occlusion . 
The Min system prevents the Z ring from forming at the cell poles and nucleoid occlusion prevents the Z ring from forming within the vicinity of the chromosome [ 52 -- 54 ] . 
The overall result is that the two systems prevent the Z ring from forming anywhere other than the cell centre ( Fig. 2A ) . 
For the past two decades , the positioning of Z ring formation extensive research has revealed several components of this system that function in a co-operative manner to inhibit polar Z ring assembly and division at the poles . 
In E. coli and B. subtilis the Min system consists of two main proteins , MinC and MinD , that function to prevent FtsZ assembly and cell division at the cell poles , and additional Min proteins unique to each organism , that assist in different modes of action . 
For a complete review of the Min system and its mode of action , the reader is encouraged to read recent reviews [ 58 -- 60 ] . 
tion over the DNA , and is mediated by proteins SlmA ( in E. coli ) and Noc ( in B. subtilis ) [ 52,53 ] . 
Although no sequence homology exists between the two , both SlmA and Noc possess similar characteristics : both proteins bind to specific regions scattered around the chromosome , except for the terminus region , which is largely devoid of these binding sites [ 61 ] . 
This pattern of binding supports the proposal that as chromosome replication nears completion and the terminus region occupies the central position in the cell , SlmA and Noc are no longer present in this region , relieving this area of nucleoid occlusion , thus allowing a Z ring to form there [ 52 ] . 
SlmA and Noc however , have differing modes of action . 
Recent studies into the activity of SlmA have elucidated two potential mechanisms as to how it inhibits Z ring formation . 
In the first , SlmA promotes FtsZ depolymerisation [ 62 -- 64 ] . 
When bound to its specific DNA binding sites ( SBS ) , SlmA attaches to the highly conserved C-terminal tail of FtsZ where it competes for binding with other interacting or regulatory partners of FtsZ , including ZipA , FtsZ , ZapD , MinC and ClpX [ 64 ] . 
This promotes further interactions between SlmA and FtsZ , leading to FtsZ protofilament breakage independent of the GTPase activity of FtsZ [ 64,65 ] . 
In a second , alternative hypothesis , Tonthat et al. have suggested that SlmA binds to DNA as a dimer of dimers and spreads along nascent DNA where it forms higher-order nucleoprotein complexes that capture and inhibit FtsZ from coalescing into functional Z rings [ 66 ] . 
Continuing studies into the activity of SlmA are required to elucidate which hypothesis is correct , and , further , to understand how SlmA is able to carry out these membrane-localised functions when tethered to the DNA . 
effect by recruiting DNA to the membrane periphery via its newly discovered ability to bind the membrane [ 67 ] . 
Adams et al. propose a model in which Noc mediates its Z ring inhibitory function by physically crowding the available space between the DNA and the membrane periphery such that Z rings are unable to form there [ 67 ] . 
The model raises several questions . 
Is Noc abundant enough within the cell to mediate this crowding effect on its own or are there other protein players involved ? 
Is this Noc activity coupled with the transertion effect , a theory postulated over 20 years ago , which couples transcription , translation and insertion of membrane proteins ? 
Additionally , what effect does this recruitment of the DNA to the cell periphery have on chromosome organisation and what happens to this organisation in the absence of Noc ? 
Noc could potentially impact chromosome orga-nisation or segregation in a way not previously considered . 
Noc belongs to the ParB family and shares ∼ 40 % sequence homology with the known chromosome segregation protein , Spo0J [ 68 ] . 
Furthermore , unlike in B. subtilis , Staphylococcus aureus cells with a noc deletion form a significant number of anucleate cells , even during normal , unperturbed growth [ 69 ] , thus suggesting a role for Noc in chromosome segregation in this organism . 
This raises the possibility that Noc could also be impacting chromosome organisation or segregation in B. subtilis to influence cell division . 
ulatory systems has shown that they can not be the sole regulators Since the discovery of the Min system over 30 years ago [ 55 -- 57 ] , Nucleoid occlusion on the other hand , inhibits Z ring forma-In contrast , Noc in B. subtilis mediates its nucleoid occlusion Continued study of the Min system and nucleoid occlusion reg-of correct placement of the Z ring at midcell . 
Under normal growth conditions , when either the Min system or Noc/SlmA in B. subtilis or E. coli are deleted , cells continue to grow and divide without major changes to cell viability [ 52,53,70 ] . 
However , although division is significantly perturbed in B. subtilis and E. coli cells devoid of both the Min system and their respective nucleoid occlusion proteins , Z rings nonetheless preferentially form at midcell in internucleoid positions with high precision [ 53,71,72 ] . 
Thus , it appears that the role of the Min system and Noc/SlmA is to ensure there is sufficient FtsZ for Z ring assembly at the desired division site in B. subtilis and E. coli by limiting the regions in which FtsZ can accumulate . 
Additionally , a number of bacteria possess only one system , or do not possess either the nucleoid occlusion or the Min protein homologues . 
Instead , positive mechanisms regulating Z ring positioning have recently been revealed by studies on several of these bacteria , including Streptococcus pneumoniae , Myxococcus xanthus and Streptomyces coelicolor . 
These are illustrated in Fig. 2B and described below . 
4.2. Positive regulators of Z ring placement
A novel protein in S. pneumonia , recently described by two independent studies , is named MapZ ( Mid-cell Anchored Protein Z ) or LocZ ( Localising at midcell of FtsZ ) [ 73,74 ] . 
MapZ localises to the midcell division site prior to any division proteins , including FtsZ and FtsA . 
This localisation of MapZ drives the recruitment of FtsZ to its midcell position . 
Following Z ring assembly , MapZ splits into two rings , which migrate bidirectionally , in tandem with the equatorial rings , to the future division sites [ 73,74 ] . 
Similarly , the ParA-like protein , PomZ ( Positioning at Midcell of FtsZ ) , discovered by Treuner-Lange et al. in M. xanthus , localises at the cell centre prior to , and independently of , FtsZ [ 75 ] . 
However , PomZ appears to have a positive spatial and temporal regulatory role . 
In newborn cells , PomZ is seen to co-localise with the nucleoid . 
Only once the nucleoid replicates does PomZ migrate to midcell to promote FtsZ recruitment . 
How it does so is not yet understood . 
The lack of in vitro interaction between purified FtsZ and PomZ , led Treuner-Lange et al. to postulate the existence of interacting partners to mediate PomZ regulatory activity on FtsZ [ 75 ] . 
Interacting proteins positively regulating Z ring placement have also been observed in S. coelicolor . 
S. coelicolor possesses a novel set of proteins unique to Actinobacteria which promote FtsZ recruitment and polymerisation at the correct site . 
In sporulating S. coelicolor cells , the membrane-associated SsgB is localised at midcell by its interaction with SsgA ; SsgB then recruits and tethers FtsZ to the division site [ 76,77 ] . 
An outstanding question in these organisms is how do these proteins recognise the future division site ? 
Is there a signal or unidentified marker ? 
And do such positive systems exist in bacteria that possess the Min system and/or nucleoid occlusion proteins ? 
Given that neither the Min system nor nucleoid occlusion are essential in positioning the Z ring correctly in either E. coli or B. subtilis , it would suggest some other regulatory system exists in these bacteria . 
A recent positive regulation link has been found between cell division and glycolysis in B. subtilis . 
Monahan et al. describe a model in which PDH E1 ( the E1 subunit of pyruvate dehydrogenase , required for the metabolism of pyruvate at the final stage of glycolysis ) positively regulates Z ring assembly by co-localizing with the chromosome in a pyruvate-dependent manner [ 78 ] . 
This system may help to coordinate bacterial division with nutritional conditions to ensure the survival of newborn cells . 
Indeed , increasing evidence is pointing towards aspects of DNA replication and chromosome organisation/segregation influencing cell division in B. subtilis and E. coli cation and cell division in bacteria came from studies in B. subtilis . 
B. subtilis cells are able to begin septation when only 70 % of the chromosome has been replicated [ 79 ] . 
Given that Z ring formation precedes septation , this means mechanisms must be at play to trigger this first stage of cell division earlier on in DNA replication . 
Moreover , blocking the initiation of DNA replication in B. subtilis significantly affects Z ring positioning , suggesting a link between these two processes [ 80,81 ] . 
Examining this more closely Moriya et al. examined the effect of different blocks at the initiation stage of DNA replication and found that , the earlier the block in initiation , the less likely a Z ring would form at midcell , with completion of the initiation stage allowing midcell Z rings to form at wild-type levels . 
Moriya et al. proposed a model , called the Ready-Set-Go model , linking the progression of initiation of DNA replication to midcell Z ring assembly , such that as the initiation phase progresses , midcell becomes increasingly available or `` potentiated '' for Z ring assembly ( Fig. 3 ) . 
This coincides nicely with the finding that the initiation phase of DNA replication in B. subtilis involves several proteins that assemble at oriC in a step-wise manner [ 8 ] . 
Most significantly , the `` Ready Set Go '' phenomenon is independent of Noc [ 82 ] , and has a positive influence on Z ring placement . 
What this Z ring potential at midcell actually is , is currently unclear . 
It is possible that the build-up of the replisome proteins at the medially located oriC acts as a beacon for progressive FtsZ accumulation there . 
Importantly , this study highlighted that Noc activity is insufficient in inhibiting cell division during initiation of DNA replication , suggesting other Noc-independent inhibition strategies must be in place within cells for proper cell division , an idea also supported by studies of Bernard et al. [ 83 ] . 
in B. subtilis is further demonstrated in studies by Arjes et al. . 
The authors show that extended inhibition of DNA initiation replication results in an irreversible block to cell division and vice versa . 
This phenomenon was adequately termed the point of no return ( PONR ) [ 84 ] . 
What the trigger for the PONR is and why bacteria are unable to resume growth remain outstanding questions . 
The phenomenon is however independent of the SOS-response and cellular levels of DnaA and FtsZ ; and microarray data suggest that the trigger for the PONR may be post-transcriptional [ 84 ] . 
to DNA replication in E. coli . 
Cambridge et al. found midcell Z ring assembly was inhibited when DNA replication elongation was blocked [ 85 ] . 
Importantly , this occurred in a SlmA - , MinC - and SOS-independent manner . 
Overall , this finding suggests that DNA replication playing a positive role in Z ring positioning is not exclusive to B. subtilis , but is likely to occur in a number of organisms . 
The first suggestion of a coordinated link between DNA repli-Linkage between initiation of DNA replication and cell division More recently , midcell Z ring assembly has also been linked 
6. Coordinating cell division with chromosome organisation and segregation
cally associated with coordinating cell division and chromosome segregation , a variety of mutations in chromosome segregation proteins have long been known to lead to incorrect Z ring positioning in both E. coli and B. subtilis [ 26,39 ] , providing clear evidence that the two processes are connected . 
The absence of any of the constituents of the E. coli MukBEF complex results in temperature sensitivity , loss of chromosome organisation and condensation , and generation of ∼ 5 % anucleate cells at the permissive temperature due to Z ring misplacement [ 39 ] . 
Similarly , B. subtilis cells lacking smc ( under slow growth conditions ) or spo0J exhibit aberrant positioning , or level of condensation of the nucleoid , and While the nucleoid occlusion proteins Noc and SlmA are typialso result in formation of anucleate cells [ 26,27,86,87 ] . 
In minimal media , deletion of both smc and spo0J enhances this effect whereby the frequency of anucleate cells increases to 19 % , with 12 % of cells containing nucleoids guillotined by the septum [ 27 ] . 
While these cell division phenotypes of chromosome segregation mutants have been known for a long time , it remains unclear if chromosome segregation and division site positioning are coupled by the chromosome segregation proteins themselves . 
At the heart of this question is the fact that misplacement of Z rings in chromosome segregation mutants can occur indirectly through nucleoid occlusion : chromosome segregation mutants alter chromosome architecture , thus resulting in improper Noc/SlmA-DNA localisation within the cell and misplaced Z rings . 
However , it still remains possible that chromosome segregation proteins may actually directly contribute to Z ring placement , independently of their indirect consequences on nucleoid occlusion . 
One hypothesis is that they may participate directly in establishing the Z ring site ; however no direct interaction between chromosome segregation proteins and FtsZ has ever been reported in the literature . 
A second hypothesis is that through their chromosome-organizing activities , they contribute to an unknown aspect of chromosome organisation that is directly linked to cell division . 
In favour of this hypothesis is the recent observation that the organisation of a specific region of the E. coli chromosome contributes to establishing the Z ring position at midcell . 
Bailey et al. found that the Ter macrodomain of the chromosome in E. coli becomes important for midcell Z ring positioning in the absence of SlmA and the Min system [ 72 ] . 
Specifically , combining the slmA min double mutant with a mutant in MatP ( the protein that organises the Ter macrodomain ) affected midcell Z ring precision . 
The authors also demonstrated that this effect is mediated through interactions between MatP and the divisome proteins ZapB and ZapA . 
These interactions were established by Espéli et al. [ 88 ] . 
Thus , these results suggest that the organisation of the Ter macrodomain plays a positive role in Z ring positioning . 
Intriguingly , in the absence of this link to the Ter macrodomain , SlmA and the Min system , there is still a slight midcell bias for Z ring placement . 
Thus , these modest effects to Z ring positioning suggest that many levels of control are required for bacteria to accurately coordinate division with chromosome organisation . 
In analogy to MatP , and as mentioned above , Spo0J , SMC and MukBEF are suggested to be involved in the overall organisation of the origin region following its replication [ 33,42,89 ] . 
Marbouty et al. and Wang et al. have very recently utilised Hi-C techniques in B. subtilis to elucidate the structure of the chromosome in this organism [ 90,91 ] . 
As well as identifying both short - and long-range chromosomal DNA interactions within the B. subtilis chromosome , both these studies directly demonstrate the requirement of the ParABS system and SMC complex in origin-region resolution , reformation and segregation following its duplication . 
Both studies also elegantly shine a light on the intrinsic link between DNA replication and chromosome organisation . 
Blocking initiation of DNA replication elucidated an effect on these DNA interactions and demonstrated a loss to normal chromosome organisation and segregation . 
These studies make it intriguing to see which chromosome interaction domains are lost in chromosome organisation mutants resulting in abnormal Z ring formation such as those in the absence of spo0J , smc or mukB . 
It is possible that changes to chromosome architecture as a result of the action of chromosome segregation proteins is vital for large scale compaction of the origin region to bring together sequence-distal operons to allow for important interactions , for example to form a signal or to localise protein-protein interactions required for proper Z ring formation . 
Continued studies in this area will surely further lead to the emergence of how these three key processes of DNA replication , chromosome organisation and cell division come together in perfect synchrony ral dynamics of cell division and chromosome segregation proteins and chromosomal loci is a greater appreciation of the architecture of the chromosome under various conditions , and the important role this plays in cell cycle regulation . 
For example , it is not yet clear exactly how or in what way cellular processes such as DNA replication , chromosome segregation or transcription affect chromosome architecture . 
Isolating the influence of each of these processes on chromosome architecture , and pinpointing cause and effect , will be challenging . 
Recent advances in technologies to look closer at how the chromosome is compacted and organised will be of great value in this endeavour . 
Genome-wide conformation capture techniques such as Hi-C and super-resolution microscopy allow us to detect chromosome interaction domains and infer information on the spatial organisation of the chromosome [ 90 -- 93 ] . 
Examining chromosome architecture on a more global scale using these technologies and in different environmental or growth conditions will give us insight into how bacteria coordinate chromosome replication , segregation and Z ring formation under various situations to allow proper daughter cell propagation . 
Critical to a greater understanding of the spatial and tempo ¬ 
Acknowledgements
for providing data prior to publication . 
We are also grateful to Fiona MacIver for critical and proofreading of the manuscript . 
This work was supported by Australian Research Council Discovery Project Grants to E.J.H ( DP120102010 ; DP150102062 ) . 
I.V.H was supported by an Australian Postgraduate Award . 
We thank David Rudner , Marcelo Nollmann and Romain Koszul