Summary
Many bacterial genomes carry multiple prophages that compete with each other, potentially affecting the physiology, fitness, and pathogenicity of their hosts. However, molecular mechanisms of ...such prophage–prophage conflicts remain poorly understood. The genome of Shewanella oneidensis MR‐1, a Gammaproteobacterium residing in aquatic environments and notable for its ability to reduce metal ions, harbours four prophages, two of which (LambdaSo and MuSo2) form infectious virions during biofilm formation. Here, we constructed indicator strains of LambdaSo and MuSo2 by deleting the corresponding prophages from the MR‐1 chromosome and investigated their reproduction. Interestingly, the fitness of MuSo2 increased in the absence of LambdaSo, suggesting that prophage LambdaSo repressed MuSo2 reproduction. Partial deletion of LambdaSo from the MR‐1 chromosome revealed that gene cluster R of LambdaSo, which was responsible for the switch to the lytic cycle and LambdaSo genome replication initiation, was necessary and sufficient to repress MuSo2. Furthermore, activation of cluster R genes facilitated replication of cluster R‐encoding DNA and inhibited host and MuSo2 DNA replication. These findings suggest that LambdaSo represses MuSo2 propagation by inhibiting DNA replication during simultaneous induction. We predict that such a mechanism of inter‐prophage interference is more widespread in bacteria than currently appreciated.
Members of the family
have non-enveloped tailless icosahedral virions with a protein-rich internal lipid membrane. The genome is a linear double-stranded DNA of about 30 kbp with inverted terminal ...repeats and terminal proteins. The capsid has a pseudo triangulation
28
symmetry and is built of two major capsid protein types. Spike complexes decorate fivefold vertices. Sphaerolipoviruses have a narrow host range and a lytic life cycle, infecting haloarchaea in the class Halobacteria (phylum Euryarchaeota). This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family
which is available at ictv.global/report/sphaerolipoviridae.
Abstract
Many prokaryotic viruses are temperate and their reactivation is tightly regulated. However, except for a few bacterial model systems, the regulatory circuits underlying the exit from ...lysogeny are poorly understood, especially in archaea. Here, we report a three-gene module which regulates the switch between lysogeny and replicative cycle in a haloarchaeal virus SNJ2 (family Pleolipoviridae). The SNJ2 orf4 encodes a winged helix-turn-helix DNA binding protein which maintains lysogeny through repressing the expression of the viral integrase gene intSNJ2. To switch to the induced state, two other SNJ2-encoded proteins, Orf7 and Orf8, are required. Orf8 is a homolog of cellular AAA+ ATPase Orc1/Cdc6, which is activated upon mitomycin C-induced DNA damage, possibly through posttranslational modification. Activated Orf8 initiates the expression of Orf7 which, in turn, antagonizes the function of Orf4, leading to the transcription of intSNJ2, thereby switching SNJ2 to the induced state. Comparative genomics analysis revealed that the SNJ2-like Orc1/Cdc6-centered three-gene module is common in haloarchaeal genomes, always present in the context of integrated proviruses. Collectively, our results uncover the first DNA damage signaling pathway encoded by a temperate archaeal virus and reveal an unexpected role of the widely distributed virus-encoded Orc1/Cdc6 homologs.
The Min system negatively regulates the position of the Z ring, which serves as a scaffold for the divisome that mediates bacterial cytokinesis. In Escherichia coli, this system consists of MinC, ...which antagonizes assembly of the tubulin homologue FtsZ. MinC is recruited to the membrane by MinD and induced by MinE to oscillate between the cell poles. MinC is a dimer with each monomer consisting of functionally distinct MinCN and MinCC domains, both of which contact FtsZ. According to one model, MinCC/MinD binding to the FtsZ tail positions MinCN at the junction of two GDP-containing subunits in the filament, leading to filament breakage. Others posit that MinC sequesters FtsZ–GDP monomers or that MinCN caps the minus end of FtsZ polymers and that MinCC interferes with lateral interactions between FtsZ filaments. Here, we isolated minC mutations that impair MinCN function and analyzed FtsZ mutants resistant to MinC/MinD. Surprisingly, we found mutations in both minC and ftsZ that differentiate inhibition by MinC from inhibition by MinC/MinD. Analysis of these mutations suggests that inhibition of the Z ring by MinC alone is due to sequestration, whereas inhibition by MinC/MinD is not. In conclusion, our genetic and biochemical data support the model that MinC/MinD fragments FtsZ filaments
Summary
A short conserved motif located at the carboxy terminus of FtsZ, referred to here as the CCTP (conserved carboxy‐terminal peptide), is required for the interaction of FtsZ with many of its ...partners. In Escherichia coli interaction of FtsZ with its membrane anchors, ZipA and FtsA, as well as the spatial regulators of Z‐ring formation, MinC and SlmA, requires the CCTP. ZipA interacts with FtsZ with high affinity and interacts with the CCTP with low affinity, but the reason for this difference is not clear. In this study, we show that this difference is due to the oligomerization of FtsZ converting the CCTP to a multivalent ligand that binds multiple ZipAs bound to a surface with high avidity. Artificial dimerization of the CCTP is sufficient to increase the affinity for ZipA in vitro. Similar principles apply to the interaction of FtsZ with SlmA. Although done in vitro, these results have implications for the recruitment of FtsZ to the membrane in vivo, the interaction of FtsZ with spatial regulators and the reconstitution of FtsZ systems in vitro.
Summary
In
E
scherichia coli
, precise placement of the cytokinetic
Z
ring at midcell requires the concerted action of the three
M
in proteins.
MinD
activates
MinC
, an inhibitor of
FtsZ
, at least ...in part, by recruiting it to the membrane and targeting it to the
Z
ring, while
MinE
stimulates the
MinD ATP
ase inducing an oscillation that directs
MinC
/
MinD
activity away from midcell. Recently,
MinC
and
MinD
were shown to form copolymers of alternating dimers of
MinC
and
MinD
, and it was suggested that these copolymers are the active form of
MinC
/
MinD
. Here, we use
MinD
mutants defective in binding
MinC
to generate heterodimers with wild‐type
MinD
that are unable to form
MinC
/
MinD
copolymers. Similarly,
MinC
mutants defective in binding to
MinD
were used to generate heterodimers with wild‐type
MinC
that are unable to form copolymers. Such heterodimers are active and in the case of
MinC
were shown to mediate spatial regulation of the Z ring demonstrating that
MinC
/
MinD
copolymer formation is not required. Our results are consistent with a model in which a membrane anchored
MinC
/
MinD
complex is targeted to the
Z
ring through the conserved carboxy tail of
FtsZ
leading to breakage of
FtsZ
filaments.
subsp.
is a major pathogen affecting fisheries worldwide and is a well-known pigmented member of the
genus. This subspecies produces melanin at ≤22°C. However, melanogenesis decreases as the culture ...temperature increases and is completely suppressed at 30°C to 35°C, while bacterial growth is unaffected. The mechanism and biological significance of this temperature-dependent melanogenesis remain unclear. Heterologous expression of an
subsp.
4-hydroxyphenylpyruvate dioxygenase (HppD), the most critical enzyme in the homogentisic acid (HGA)-melanin synthesis pathway, results in thermosensitive pigmentation in
, suggesting that HppD plays a key role in this process. In this study, we demonstrated that the thermolability of HppD is responsible for the temperature-dependent melanization of
subsp.
Substitutions of three residues, S18T, P103Q, and L119P, in
subsp.
HppD increased the thermostability of this enzyme and resulted in temperature-independent melanogenesis. Moreover, the replacement of the corresponding residues in HppD from
strain WS, which forms pigment independent of temperature, with those of
subsp.
HppD resulted in thermosensitive melanogenesis. A structural analysis suggested that mutations at these sites, especially at position P103, strengthen the secondary structure of HppD and greatly improve its thermal stability. Additionally, we found that the HppD sequences of all
subsp.
isolates were identical and that two of the three residues were clearly distinct from those of other
strains.
subsp. s
is the causative agent of furunculosis, a bacterial septicemia of cold-water fish of the
family. Although other
species can produce melanin,
subsp.
is the only member of this genus that has been reported to exhibit temperature-dependent melanization. Here, we demonstrated that thermosensitive melanogenesis in
subsp.
strains is due to the thermolability of 4-hydroxyphenylpyruvate dioxygenase (HppD). Additionally, we confirmed that this thermolabile HppD exhibited higher activity at low temperatures than its mesophilic homologues, suggesting this as an adaptive strategy of this enzyme to the psychrophilic lifestyle of
subsp.
The strictly conserved
sequences among
subsp.
isolates and the specific possession of P103 and L119 residues could be used as a reference for the identification of
subsp.
isolates.
Recent environmental and metagenomic studies have considerably increased the repertoire of archaeal viruses and suggested that they play important roles in nutrient cycling in the biosphere. However, ...very little is known about how they regulate their life cycles and interact with their hosts. Here, we report that the life cycle of the temperate haloarchaeal virus SNJ1 is controlled by the product ORF4, a small protein belonging to the antitoxin MazE superfamily. We show that ORF4 controls the lysis-lysogeny switch of SNJ1 and mediates superinfection immunity by repression of genomic DNA replication of the superinfecting viruses. Bioinformatic analysis shows that ORF4 is highly conserved in two SNJ1-like proviruses, suggesting that the mechanisms for lysis-lysogeny switch and superinfection immunity are conserved in this group of viruses. As the lysis-lysogeny switch and superinfection immunity of archaeal viruses have been poorly studied, we suggest that SNJ1 could serve as a model system to study these processes.
Archaeal viruses are important parts of the virosphere. Understanding how they regulate their life cycles and interact with host cells provide crucial insights into their biological functions and the evolutionary histories of viruses. However, mechanistic studies of the life cycle of archaeal viruses are scarce due to a lack of genetic tools and demanding cultivation conditions. Here, we discover that the temperate haloarchaeal virus SNJ1, which infects
sp. strain J7, employs a lysis-lysogeny switch and establishes superinfection immunity like bacteriophages. We show that its ORF4 is critical for both processes and acts as a repressor of the replication of SNJ1. These results establish ORF4 as a master regulator of SNJ1 life cycle and provides novel insights on the regulation of life cycles by temperate archaeal viruses and on their interactions with host cells.
Summary
In Escherichia coli, precise placement of the cytokinetic Z ring at midcell requires the concerted action of the three Min proteins. MinD activates MinC, an inhibitor of FtsZ, at least in ...part, by recruiting it to the membrane and targeting it to the Z ring, while MinE stimulates the MinD ATPase inducing an oscillation that directs MinC/MinD activity away from midcell. Recently, MinC and MinD were shown to form copolymers of alternating dimers of MinC and MinD, and it was suggested that these copolymers are the active form of MinC/MinD. Here, we use MinD mutants defective in binding MinC to generate heterodimers with wild‐type MinD that are unable to form MinC/MinD copolymers. Similarly, MinC mutants defective in binding to MinD were used to generate heterodimers with wild‐type MinC that are unable to form copolymers. Such heterodimers are active and in the case of MinC were shown to mediate spatial regulation of the Z ring demonstrating that MinC/MinD copolymer formation is not required. Our results are consistent with a model in which a membrane anchored MinC/MinD complex is targeted to the Z ring through the conserved carboxy tail of FtsZ leading to breakage of FtsZ filaments.
MinC and MinD are involved in spatial regulation of the Z ring. Here we test the proposal that copolymers consisting of alternating dimers of MinC and MinD are involved in this regulation by generating heterodimers of MinC or MinD that are unable to form copolymers. Such nonpolymerizing mutants function normally excluding a physiological role for MinC/MinD copolymers.
The family
includes tailless icosahedral viruses with an internal lipid membrane. The capsid is constructed from two major capsid proteins, both with a single jelly-roll fold. The genome is a ...circular dsDNA molecule of 16-19 kb. All members infect halophilic archaea in the class Halobacteria (phylum Euryarchaeota) and are temperate viruses, their proviruses residing in host cells as extrachromosomal episomes. Once the lytic life cycle is triggered, production of virions causes cell lysis. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family
which is available at ictv.global/report/simuloviridae.
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