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1. Movement dynamics of divisome proteins and PBP2x:FtsW in cells of Streptococcus pneumoniae

   https://doi.org/10.1073/pnas.1816018116  

   Perez, Amilcar J. ; Cesbron, Yann ; Shaw, Sidney L. ; Bazan Villicana, Jesus ; Tsui, Ho-Ching T. ; Boersma, Michael J. ; Ye, Ziyun A. ; Tovpeko, Yanina ; Dekker, Cees ; Holden, Seamus ; et al ( February 2019 , Proceedings of the National Academy of Sciences)

   Bacterial cell division and peptidoglycan (PG) synthesis are orchestrated by the coordinated dynamic movement of essential protein complexes. Recent studies show that bidirectional treadmilling of FtsZ filaments/bundles is tightly coupled to and limiting for both septal PG synthesis and septum closure in some bacteria, but not in others. Here we report the dynamics of FtsZ movement leading to septal and equatorial ring formation in the ovoid-shaped pathogen,Streptococcus pneumoniae. Conventional and single-molecule total internal reflection fluorescence microscopy (TIRFm) showed that nascent rings of FtsZ and its anchoring and stabilizing proteins FtsA and EzrA move out from mature septal rings coincident with MapZ rings early in cell division. This mode of continuous nascent ring movement contrasts with a failsafe streaming mechanism of FtsZ/FtsA/EzrA observed in a ΔmapZmutant and anotherStreptococcusspecies. This analysis also provides several parameters of FtsZ treadmilling in nascent and mature rings, including treadmilling velocity in wild-type cells andftsZ(GTPase) mutants, lifetimes of FtsZ subunits in filaments and of entire FtsZ filaments/bundles, and the processivity length of treadmilling of FtsZ filament/bundles. In addition, we delineated the motion of the septal PBP2x transpeptidase and its FtsW glycosyl transferase-binding partner relative to FtsZ treadmilling inS. pneumoniaecells. Five lines of evidence support the conclusion that movement of the bPBP2x:FtsW complex in septa depends on PG synthesis and not on FtsZ treadmilling. Together, these results support a model in which FtsZ dynamics and associations organize and distribute septal PG synthesis, but do not control its rate inS. pneumoniae.

    

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2. Cell division is antagonized by the activity of peptidoglycan endopeptidases that promote cell elongation

   https://doi.org/10.1111/mmi.14587  

   Truong, Thao T. ; Vettiger, Andrea ; Bernhardt, Thomas G. ( August 2020 , Molecular Microbiology)

   A peptidoglycan (PG) cell wall composed of glycans crosslinked by short peptides surrounds most bacteria and protects them against osmotic rupture. InEscherichia coli, cell elongation requires crosslink cleavage by PG endopeptidases to make space for the incorporation of new PG material throughout the cell cylinder. Cell division, on the contrary, requires the localized synthesis and remodeling of new PG at midcell by the divisome. Little is known about the factors that modulate transitions between these two modes of PG biogenesis. In a transposon‐insertion sequencing screen to identify mutants synthetically lethal with a defect in the division protein FtsP, we discovered that mutants impaired for cell division are sensitive to elevated activity of the endopeptidases. Increased endopeptidase activity in these cells was shown to interfere with the assembly of mature divisomes, and conversely, inactivation of MepS was found to suppress the lethality of mutations in essential division genes. Overall, our results are consistent with a model in which the cell elongation and division systems are in competition with one another and that control of PG endopeptidase activity represents an important point of regulation influencing the transition from elongation to the division mode of PG biogenesis.

    

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3. Vibrio cholerae adapts to sessile and motile lifestyles by cyclic di-GMP regulation of cell shape

   https://doi.org/10.1073/pnas.2010199117  

   Fernandez, Nicolas L. ; Hsueh, Brian Y. ; Nhu, Nguyen T. Q. ; Franklin, Joshua L. ; Dufour, Yann S. ; Waters, Christopher M. ( November 2020 , Proceedings of the National Academy of Sciences)

   The cell morphology of rod-shaped bacteria is determined by the rigid net of peptidoglycan forming the cell wall. Alterations to the rod shape, such as the curved rod, occur through manipulating the process of cell wall synthesis. The human pathogenVibrio choleraetypically exists as a curved rod, but straight rods have been observed under certain conditions. While this appears to be a regulated process, the regulatory pathways controlling cell shape transitions inV. choleraeand the benefits of switching between rod and curved shape have not been determined. We demonstrate that cell shape inV. choleraeis regulated by the bacterial second messenger cyclic dimeric guanosine monophosphate (c-di-GMP) by posttranscriptionally repressing expression ofcrvA, a gene encoding an intermediate filament-like protein necessary for curvature formation inV. cholerae.This regulation is mediated by the transcriptional cascade that also induces production of biofilm matrix components, indicating that cell shape is coregulated withV. cholerae’s induction of sessility. During microcolony formation, wild-typeV. choleraecells tended to exist as straight rods, while genetically engineering cells to maintain high curvature reduced microcolony formation and biofilm density. Conversely, straightV. choleraemutants have reduced swimming speed when using flagellar motility in liquid. Our results demonstrate regulation of cell shape in bacteria is a mechanism to increase fitness in planktonic and biofilm lifestyles.

    

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4. Phage-Encoded Sigma Factors Alter Bacterial Dormancy

   https://doi.org/10.1128/msphere.00297-22  

   Schwartz, D. A. ; Lehmkuhl, B. K. ; Lennon, J. T. ( August 2022 , mSphere)

   Imperiale, Michael J. (Ed.)

   ABSTRACT By entering a reversible state of reduced metabolic activity, dormant microorganisms are able to tolerate suboptimal conditions that would otherwise reduce their fitness. Dormancy may also benefit bacteria by serving as a refuge from parasitic infections. Here, we focus on dormancy in the Bacillota , where endospore development is transcriptionally regulated by the expression of sigma factors. A disruption of this process could influence the survivorship or reproduction of phages that infect spore-forming hosts with implications for coevolutionary dynamics. We characterized the distribution of sigma factors in over 4,000 genomes of diverse phages capable of infecting hosts that span the bacterial domain. From this, we identified homologs of sporulation-specific sigma factors in phages that infect spore-forming hosts. Unlike sigma factors required for phage reproduction, we provide evidence that sporulation-like sigma factors are nonessential for lytic infection. However, when expressed in the spore-forming Bacillus subtilis , some of these phage-derived sigma factors can activate the bacterial sporulation gene network and lead to a reduction in spore yield. Our findings suggest that the acquisition of host-like transcriptional regulators may allow phages to manipulate a complex and ancient trait in one of the most abundant cell types on Earth. IMPORTANCE As obligate parasites, phages exert strong top-down pressure on host populations with eco-evolutionary implications for community dynamics and ecosystem functioning. The process of phage infection, however, is constrained by bottom-up processes that influence the energetic and nutritional status of susceptible hosts. Many phages have acquired auxiliary genes from bacteria, which can be used to exploit host metabolism with consequences for phage fitness. In this study, we demonstrate that phages infecting spore-forming bacteria carry homologs of sigma factors, which their hosts use to orchestrate gene expression during spore development. By tapping into regulatory gene networks, phages may manipulate the physiology and survival strategies of nongrowing bacteria in ways that influence host-parasite coevolution. 

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5. Phage-encoded sigma factors alter bacterial dormancy

   https://doi.org/10.1101/2021.11.12.468384  

   Schwartz DA, Lekmkuhl BK ( January 2021 , bioRxiv)

   By entering a reversible state of reduced metabolic activity, dormant microorganisms are able to tolerate suboptimal conditions that would otherwise reduce their fitness. Dormancy may also benefit bacteria by serving as a refuge from parasitic infections. Here we focus on dormancy in the Firmicutes, where endospore development is transcriptionally regulated by the expression of sigma factors. A disruption of this process could influence the survivorship and reproduction of phages that infect spore-forming hosts with implications for coevolutionary dynamics. Here, we characterized the distribution and diversity of sigma factors in nearly 3,500 phage genomes. Homologs of sporulation-specific sigma factors were identified in phages that infect spore-forming hosts. Unlike sigma factors required for phage reproduction, the sporulation-like sigma factors were non-essential for lytic infection. However, when expressed in the spore-forming Bacillus subtilis, sigma factors from phages activated the bacterial sporulation gene network and reduced spore yield. Our findings suggest that the acquisition of host-like transcriptional regulators may allow phages to manipulate a complex and ancient trait in one of the most abundant cell types on Earth. 

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