Functions of the Essential Gene mraY in Cellular Morphogenesis and Development of the Filamentous Cyanobacterium Anabaena PCC 7120

Bacterial cell shape is determined by the peptidoglycan (PG) layer. The cyanobacterium Anabaena sp. PCC 7120 (Anabaena) is a filamentous strain with ovoid-shaped cells connected together with incomplete cell constriction. When deprived of combined nitrogen in the growth medium, about 5–10% of the cells differentiate into heterocysts, cells devoted to nitrogen fixation. It has been shown that PG synthesis is modulated during heterocyst development and some penicillin-binding proteins (PBPs) participating in PG synthesis are required for heterocyst morphogenesis or functioning. Anabaena has multiple PBPs with functional redundancy. In this study, in order to examine the function of PG synthesis and its relationship with heterocyst development, we created a conditional mutant of mraY, a gene necessary for the synthesis of the PG precursor, lipid I. We show that mraY is required for cell and filament integrity. Furthermore, when mraY expression was being limited, persistent septal PG synthetic activity was observed, resulting in increase in cell width. Under non-permissive conditions, filaments and cells were rapidly lysed, and no sign of heterocyst development within the time window allowed was detected after nitrogen starvation. When mraY expression was being limited, a high percentage of heterocyst doublets were found. These doublets are formed likely as a consequence of delayed cell division and persistent septal PG synthesis. MraY interacts with components of both the elongasome and the divisome, in particular those directly involved in PG synthesis, including HetF, which is required for both cell division and heterocyst formation.

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An increase in the level of 2-oxoglutarate promotes heterocyst development in the cyanobacterium Anabaena sp. strain PCC 7120

Microbiology ◽

10.1099/mic.0.26462-0 ◽

2003 ◽

Vol 149 (11) ◽

pp. 3257-3263 ◽

Cited By ~ 43

Author(s):

Jian-Hong Li ◽

Sophie Laurent ◽

Viren Konde ◽

Sylvie Bédu ◽

Cheng-Cai Zhang

Keyword(s):

Inorganic Nitrogen ◽

Cell Types ◽

Filamentous Cyanobacterium ◽

Nitrogen Status ◽

Gene Encoding ◽

Combined Nitrogen ◽

Cyanobacterium Anabaena ◽

Anabaena Sp ◽

Pcc 7120 ◽

Heterocyst Development

In the filamentous cyanobacterium Anabaena sp. strain PCC 7120, a starvation of combined nitrogen induces differentiation of heterocysts, cells specialized in nitrogen fixation. How do filaments perceive the limitation of the source of combined nitrogen, and what determines the proportion of heterocysts? In cyanobacteria, 2-oxoglutarate provides a carbon skeleton for the incorporation of inorganic nitrogen. Recently, it has been proposed that the concentration of 2-oxoglutarate reflects the nitrogen status in cyanobacteria. To investigate the effect of 2-oxoglutarate on heterocyst development, a heterologous gene encoding a 2-oxoglutarate permease under the control of a regulated promoter was expressed in Anabaena sp. PCC 7120. The increase of 2-oxoglutarate within cells can trigger heterocyst differentiation in a subpopulation of filaments even in the presence of nitrate. In the absence of a source of combined nitrogen, it can increase heterocyst frequency, advance the timing of commitment to heterocyst development and further increase the proportion of heterocysts in a patS mutant. Here, it is proposed that the intracellular concentration of 2-oxoglutarate is involved in the determination of the proportion of the two cell types according to the carbon/nitrogen status of the filament.

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Relationship among Several Key Cell Cycle Events in the Developmental Cyanobacterium Anabaena sp. Strain PCC 7120

Journal of Bacteriology ◽

10.1128/jb.00524-06 ◽

2006 ◽

Vol 188 (16) ◽

pp. 5958-5965 ◽

Cited By ~ 23

Author(s):

Samer Sakr ◽

Melilotus Thyssen ◽

Michel Denis ◽

Cheng-Cai Zhang

Keyword(s):

Cell Cycle ◽

Flow Cytometry ◽

Cell Division ◽

Cell Growth ◽

Cell Size ◽

Dna Content ◽

Small Cells ◽

Filamentous Cyanobacterium ◽

Pcc 7120 ◽

Heterocyst Development

ABSTRACT When grown in the absence of a source of combined nitrogen, the filamentous cyanobacterium Anabaena sp. strain PCC 7120 develops, within 24 h, a differentiated cell type called a heterocyst that is specifically involved in the fixation of N2. Cell division is required for heterocyst development, suggesting that the cell cycle could control this developmental process. In this study, we investigated several key events of the cell cycle, such as cell growth, DNA synthesis, and cell division, and explored their relationships to heterocyst development. The results of analyses by flow cytometry indicated that the DNA content increased as the cell size expanded during cell growth. The DNA content of heterocysts corresponded to the subpopulation of vegetative cells that had a big cell size, presumably those at the late stages of cell growth. Consistent with these results, most proheterocysts exhibited two nucleoids, which were resolved into a single nucleoid in most mature heterocysts. The ring structure of FtsZ, a protein required for the initiation of bacterial cell division, was present predominantly in big cells and rarely in small cells. When cell division was inhibited and consequently cells became elongated, little change in DNA content was found by measurement using flow cytometry, suggesting that inhibition of cell division may block further synthesis of DNA. The overexpression of minC, which encodes an inhibitor of FtsZ polymerization, led to the inhibition of cell division, but cells expanded in spherical form to become giant cells; structures with several cells attached together in the form of a cloverleaf could be seen frequently. These results may indicate that the relative amounts of FtsZ and MinC affect not only cell division but also the placement of the cell division planes and the cell morphology. MinC overexpression blocked heterocyst differentiation, consistent with the requirement of cell division in the control of heterocyst development.

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Identification of the oriC region and its influence on heterocyst development in the filamentous cyanobacterium Anabaena sp. strain PCC 7120

Microbiology ◽

10.1099/mic.0.047241-0 ◽

2011 ◽

Vol 157 (7) ◽

pp. 1910-1919 ◽

Cited By ~ 7

Author(s):

Yin Zhou ◽

Wen-Li Chen ◽

Li Wang ◽

Cheng-Cai Zhang

Keyword(s):

Regulatory Function ◽

Filamentous Cyanobacterium ◽

Chromosomal Dna ◽

Unicellular Cyanobacterium ◽

Prolonged Incubation ◽

Combined Nitrogen ◽

Oric Region ◽

Cyanobacterium Anabaena ◽

Pcc 7120 ◽

Heterocyst Development

Anabaena sp. strain PCC 7120 (Anabaena PCC 7120) is a filamentous, nitrogen-fixing cyanobacterium. Upon deprivation of combined nitrogen, about 5–10 % of the cells become heterocysts, i.e. cells devoted to N2 fixation. Heterocysts are intercalated among vegetative cells and distributed in a semi-regular pattern, and adjacent heterocysts are rarely observed. Previously, we showed that the cell cycle could play a regulatory function during heterocyst development, although the mechanism involved remains unknown. As a further step to understand this phenomenon, we identified the oriC region for chromosomal DNA replication, located between dnaA and dnaN. The oriC region of Anabaena PCC 7120 was able to support the self-replication of a plasmid in the unicellular cyanobacterium Synechocystis sp. PCC 6803. Surprisingly, integration of the oriC region into the chromosome of Anabaena PCC 7120 through homologous recombination led to much slower cell growth in the absence of a combined-nitrogen source and to multiple contiguous proheterocysts after prolonged incubation. Real-time RT-PCR showed that expression of two heterocyst-related genes, hetR and hetN, was altered in these strains: hetR expression remained high 48 h after induction, and hetN increased to high levels after induction for 12 h. These results suggest that the balance between oriC and DnaA could be important for heterocyst development.

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Inhibition of Cell Division Suppresses Heterocyst Development in Anabaena sp. Strain PCC 7120

Journal of Bacteriology ◽

10.1128/jb.188.4.1396-1404.2006 ◽

2006 ◽

Vol 188 (4) ◽

pp. 1396-1404 ◽

Cited By ~ 44

Author(s):

Samer Sakr ◽

Robert Jeanjean ◽

Cheng-Cai Zhang ◽

Tania Arcondeguy

Keyword(s):

Cell Division ◽

Fluorescent Protein ◽

Ring Structure ◽

Molecular Evidence ◽

Filamentous Cyanobacterium ◽

Heterocyst Differentiation ◽

Ftsz Ring ◽

Pcc 7120 ◽

Heterocyst Development

ABSTRACT When the filamentous cyanobacterium Anabaena PCC 7120 is exposed to combined nitrogen starvation, 5 to 10% of the cells along each filament at semiregular intervals differentiate into heterocysts specialized in nitrogen fixation. Heterocysts are terminally differentiated cells in which the major cell division protein FtsZ is undetectable. In this report, we provide molecular evidence indicating that cell division is necessary for heterocyst development. FtsZ, which is translationally fused to the green fluorescent protein (GFP) as a reporter, is found to form a ring structure at the mid-cell position. SulA from Escherichia coli inhibits the GTPase activity of FtsZ in vitro and prevents the formation of FtsZ rings when expressed in Anabaena PCC 7120. The expression of sulA arrests cell division and suppresses heterocyst differentiation completely. The antibiotic aztreonam, which is targeted to the FtsI protein necessary for septum formation, has similar effects on both cell division and heterocyst differentiation, although in this case, the FtsZ ring is still formed. Therefore, heterocyst differentiation is coupled to cell division but independent of the formation of the FtsZ ring. Consistently, once the inhibitory pressure of cell division is removed, cell division should take place first before heterocyst differentiation resumes at a normal frequency. The arrest of cell division does not affect the accumulation of 2-oxoglutarate, which triggers heterocyst differentiation. Consistently, a nonmetabolizable analogue of 2-oxoglutarate does not rescue the failure of heterocyst differentiation when cell division is blocked. These results suggest that the control of heterocyst differentiation by cell division is independent of the 2-oxoglutarate signal.

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The developmental regulator PatD modulates assembly of the cell‐division protein FtsZ in the cyanobacterium Anabaena sp. PCC 7120

Environmental Microbiology ◽

10.1111/1462-2920.15682 ◽

2021 ◽

Author(s):

Li Wang ◽

Tian‐Cai Niu ◽

Ana Valladares ◽

Gui‐Ming Lin ◽

Ju‐Yuan Zhang ◽

...

Keyword(s):

Cell Division ◽

Cyanobacterium Anabaena ◽

Anabaena Sp ◽

Cell Division Protein ◽

Pcc 7120

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Manipulation of Pattern of Cell Differentiation in a hetR Mutant of Anabaena sp. PCC 7120 by Overexpressing hetZ Alone or with hetP

Life ◽

10.3390/life8040060 ◽

2018 ◽

Vol 8 (4) ◽

pp. 60 ◽

Cited By ~ 5

Author(s):

He Zhang ◽

Xudong Xu

Keyword(s):

Cell Differentiation ◽

Peptide Inhibitor ◽

Filamentous Cyanobacterium ◽

Heterocyst Differentiation ◽

Cyanobacterium Anabaena ◽

Anabaena Sp ◽

Pcc 7120

In the filamentous cyanobacterium, Anabaena sp. PCC 7120, single heterocysts differentiate at semi-regular intervals in response to nitrogen stepdown. HetR is a principal regulator of heterocyst differentiation, and hetP and hetZ are two genes that are regulated directly by HetR. In a hetR mutant generated from the IHB (Institute of Hydrobiology) substrain of PCC 7120, heterocyst formation can be restored by moderate expression of hetZ and hetP. The resulting heterocysts are located at terminal positions. We used a tandem promoter, PrbcLPpetE, to express hetZ and hetP strongly in the hetR mutant. Co-expression of hetZ and hetP enabled the hetR mutant to form multiple contiguous heterocysts at both terminal and intercalary positions. Expression of hetZ, alone resulted in terminally located heterocysts, whereas expression of hetP, alone produced enlarged cells in strings. In the absence of HetR, formation of heterocysts was insensitive to the peptide inhibitor, RGSGR.

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Anabaena sp. Strain PCC 7120 hetY Gene Influences Heterocyst Development

Journal of Bacteriology ◽

10.1128/jb.185.23.6995-7000.2003 ◽

2003 ◽

Vol 185 (23) ◽

pp. 6995-7000 ◽

Cited By ~ 7

Author(s):

Ho-Sung Yoon ◽

Martin H. Lee ◽

Jin Xiong ◽

James W. Golden

Keyword(s):

Atp Binding ◽

Binding Motif ◽

Filamentous Cyanobacterium ◽

Hypothetical Proteins ◽

Nitrogen Fixing ◽

Fixed Nitrogen ◽

Anabaena Sp ◽

Time Required ◽

Pcc 7120 ◽

Heterocyst Development

ABSTRACT The filamentous cyanobacterium Anabaena (Nostoc) sp. strain PCC 7120 responds to starvation for fixed nitrogen by producing a semiregular pattern of nitrogen-fixing cells called heterocysts. Overexpression of the hetY gene partially suppressed heterocyst formation, resulting in an abnormal heterocyst pattern. Inactivation of hetY increased the time required for heterocyst maturation and caused defects in heterocyst morphology. The 489-bp hetY gene (alr2300), which is adjacent to patS (asl2301), encodes a protein that belongs to a conserved family of bacterial hypothetical proteins that contain an ATP-binding motif.

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