Rhizobium meliloti contains a novel second homolog of the cell division gene ftsZ

Abstract

We have identified a second homolog of the cell division gene,ftsZ, in the endosymbiont Rhizobium meliloti. The ftsZ2 gene was cloned by screening a genomic A library with a probe derived from PCR amplification of a highly conserved domain. It encodes a 36-kDa protein which shares a high level of sequence similarity with the FtsZ proteins of Escherichia coli and BaciUus subtilis and FtsZl (Zl) of R. meliloti but lacks the carboxy-terminal region conserved in other FtsZ proteins. The identity of theftsZ2 gene product was confirmed both by in vitro transcription-translation in an R. meliloti S-30 extract and by overproduction in R. meliloti cells. As with Zl, the overproduction of FtsZ2 in E. coli inhibited cell division and induced filamentation, although to a lesser extent than with Zl. However, the expression offtsZ2 in E. coli under certain conditions caused some cells to coil dramatically, a phenotype not observed during Zl overproduction. Although several Tn3-GUS (glucuronidase) insertions in a plasmid-borneftsZ2 gene failed to cross into the chromosome, one interruption in the chromosomal ftsZ2 gene was isolated, suggesting that ftsZ2 is nonessential for viability. The two ftsZ genes were genetically mapped to the R. meliloti main chromosome, approximately 100 kb apart.The earliest known step in Escherichia coli cell division is the formation of a ring consisting of the FtsZ protein at the division site (5). FtsZ is also necessary for the formation of both vegetative and asymmetric sporulation septa in Bacillus subtilis (2). Cells containing very high levels of FtsZ or a temperature-sensitive FtsZ under nonpermissive conditions will form long, nonseptate filaments, presumably because the division ring cannot be formed (3, 39). It is not known how FtsZ, which is uniformly distributed during most of the cell cycle, assembles at the correct time in the center of the predivisional cell. However, the recent demonstrations that E. coli FtsZ binds GTP and has GTPase activity (10,26,29) suggest that GTP binding and hydrolysis by FtsZ could catalyze the assembly of the ring structure, in a manner analogous to filament formation by tubulins (34). The three previously sequenced FtsZ proteins, from E. coli, B. subtilis, and Rhizobium meliloti (1,21,40), all share a completely conserved 13-amino-acid domain that is very similar to the proposed GTP binding domain of tubulins (10) MATERIALS AND METHODSBacterial strains and plasmids. All strains and plasmids used in this study are listed in Table 1.Bacterial growth and induction conditions. All E. coli strains were grown in Luria broth (LB) (30) plus 10 ,ug of tetracycline and 50 ,ug of ampicillin per ml for plasmids in host strain XL1-Blue. Isopropyl-,B-D-thiogalactopyranoside (IPTG) inductions of E. coli cells were done by streaking colonies on agar plates containing LB, antibiotics, and 1 mM IPTG. R. meliloti cells were induced for protein overproduction by the addition of 1 mM IPTG to cells growing in LB plus 10 ,ug of tetracycline per ml in late exponential phase.Pre...

The FtsZ-Like Protein FtsZm of Magnetospirillum gryphiswaldense Likely Interacts with Its Generic Homolog and Is Required for Biomineralization under Nitrate Deprivation

“…The only other species for which two ftsZ paralogs have been investigated to some extent is S. meliloti (11,46). The first homolog (FtsZ1) contains an extended C-terminal part (see Fig.…”

“…Whereas most bacteria that rely on FtsZ for division have merely one ftsZ gene, a few alphaproteobacteria such as members of the Rhizobiales (11) and Magnetospirillum species were found to possess multiple ftsZ homologs (12). In Sinorhizobium, for example, one isoform (ftsZ1) is essential and expressed in free-living, nonsymbiotic cells, whereas the second, truncated gene (ftsZ2) is not essential but is likely involved when cells differentiate into bacteroids (13,14).…”

“…In Sinorhizobium, for example, one isoform (ftsZ1) is essential and expressed in free-living, nonsymbiotic cells, whereas the second, truncated gene (ftsZ2) is not essential but is likely involved when cells differentiate into bacteroids (13,14). Heterologous expression of the two FtsZ proteins from Sinorhizobium meliloti blocked cell division in Escherichia coli, and replacement of the FtsZ1 C terminus by green fluorescent protein (GFP) led to polymerization into axial protein filaments (11,15,16). A function for the truncated ftsZ has not been demonstrated.…”

Molecular Determinants of a Symbiotic Chronic Infection

“…Several S. meliloti genes involved in cell division have been characterized, for instance ftsZ1 and ftsZ2 (108,110,111), as well as minCDE (28). Blocking the process of cell division via overexpression of ftsZ1 or minCD causes altered cell morphology during free-living growth that is reminiscent of the branched and filamentous bacteroid (28,95).…”

The dnaA gene of Rhizobium meliloti lies within an unusual gene arrangement

“…One of the more striking changes that occur is the cessation of DNA replication and cell division. To initiate our studies of genes involved in cell cycle regulation, we previously isolated two unique ftsZ genes, and we are now studying their roles in R. meliloti cell division (29). Since proper DNA replication is normally a prerequisite for cell septation, we are interested in identifying key DNA replication genes that may serve as control points.…”