Thermal adaptation of mesophilic and thermophilic FtsZ assembly by modulation of the critical concentration

Peptidoglycan synthesis drives a single population of septal cell wall synthases during division in Bacillus subtilis

Bacterial cell division requires septal peptidoglycan (sPG) synthesis by the divisome complex. Treadmilling of the essential tubulin homologue FtsZ has been implicated in septal constriction, though its precise role remains unclear. Here we used live-cell single-molecule imaging of the divisome transpeptidase PBP2B to investigate sPG synthesis dynamics in Bacillus subtilis. In contrast to previous models, we observed a single population of processively moving PBP2B molecules whose motion is driven by peptidoglycan synthesis and is not associated with FtsZ treadmilling. However, despite the asynchronous motions of PBP2B and FtsZ, a partial dependence of PBP2B processivity on FtsZ treadmilling was observed. Additionally, through single-molecule counting experiments we provide evidence that the divisome synthesis complex is multimeric. Our results support a model for B. subtilis division where a multimeric synthesis complex follows a single track dependent on sPG synthesis whose activity and dynamics are asynchronous with FtsZ treadmilling.

Structures of a FtsZ single protofilament and a double-helical tube in complex with a monobody

FtsZ polymerizes into protofilaments to form the Z-ring that acts as a scaffold for accessory proteins during cell division. Structures of FtsZ have been previously solved, but detailed mechanistic insights are lacking. Here, we determine the cryoEM structure of a single protofilament of FtsZ from Klebsiella pneumoniae (KpFtsZ) in a polymerization-preferred conformation. We also develop a monobody (Mb) that binds to KpFtsZ and FtsZ from Escherichia coli without affecting their GTPase activity. Crystal structures of the FtsZ-Mb complexes reveal the Mb binding mode, while addition of Mb in vivo inhibits cell division. A cryoEM structure of a double-helical tube of KpFtsZ-Mb at 2.7 Å resolution shows two parallel protofilaments. Our present study highlights the physiological roles of the conformational changes of FtsZ in treadmilling that regulate cell division.

Glutamate Dehydrogenase (GdhA) of Streptococcus pneumoniae Is Required for High Temperature Adaptation

During its progression from the nasopharynx to other sterile and nonsterile niches of its human host, Streptococcus pneumoniae must cope with changes in temperature. We hypothesized that the temperature adaptation is an important facet of pneumococcal survival in the host. Here, we evaluated the effect of temperature on pneumococcus and studied the role of glutamate dehydrogenase (GdhA) in thermal adaptation associated with virulence and survival. Microarray analysis revealed a significant transcriptional response to changes in temperature, affecting the expression of 252 genes in total at 34°C and 40°C relative to at 37°C. One of the differentially regulated genes was gdhA, which is upregulated at 40°C and downregulated at 34°C relative to 37°C. Deletion of gdhA attenuated the growth, cell size, biofilm formation, pH survival, and biosynthesis of proteins associated with virulence in a temperature-dependent manner. Moreover, deletion of gdhA stimulated formate production irrespective of temperature fluctuation. Finally, ΔgdhA grown at 40°C was less virulent than other temperatures or the wild type at the same temperature in a Galleria mellonella infection model, suggesting that GdhA is required for pneumococcal virulence at elevated temperature.

Gene knockout revealed the role of gene feoA in cell growth and division of Lactobacillus delbrueckii subsp. bulgaricus

Gene feoA plays an important role in cell growth because of its function of transport Fe²⁺ which is a necessary element for cells. In this study, the recombinant plasmid pUC19-feoA-Tet was successfully constructed using the inserted gene inactivation method. Using the homologous recombination technique, the tet gene was used as a resistance screening marker to knock out the feoA gene of Lactobacillus delbrueckii subsp. bulgaricus 34.5 (strain 34.5). Comparative analysis of growth curves revealed the growth changes in the absence of feoA gene in strain 34.5. The results showed that the growth of the bacteria was prolonged by 2 h and could be restored in the stationary phase. To further study whether feoA is related to the cell division of strain 34.5, the qPCR experiment was carried out. The results showed that, compared with the wild-type strain, the expression of genes related to cell division in the mutant strain was up-regulated in the pre-log phase, down-regulated in the late-log phase, and returned to the original level in the stationary phase. These findings provide ideas for Lactobacillus delbrueckii subsp. bulgaricus to control division and cell cycle.

M. jannaschii FtsZ, a key protein in bacterial cell division, is inactivated by peroxyl radical-mediated methionine oxidation

Oxidation and inactivation of FtsZ is of interest due to the key role of this protein in bacterial cell division. In the present work, we studied peroxyl radical (from AAPH, 2,2'-azobis(2-methylpropionamidine)dihydrochloride) mediated oxidation of the highly stable FtsZ protein (MjFtsZ) from M. jannaschii, a thermophilic microorganism. MjFtsZ contains eleven Met, and single Tyr and Trp residues which would be expected to be susceptible to oxidation. We hypothesized that exposure of MjFtsZ to AAPH-derived radicals would induce Met oxidation, and cross-linking (via di-Tyr and di-Trp formation), with concomitant loss of its functional polymerization and depolymerization (GTPase) activities. Solutions containing MjFtsZ and AAPH (10 or 100 mM) were incubated at 37 °C for 3 h. Polymerization/depolymerization were assessed by light scattering, while changes in mass were analyzed by SDS-PAGE. Amino acid consumption was quantified by HPLC with fluorescence detection, or direct fluorescence (Trp). Oxidation products and modifications at individual Met residues were quantified by UPLC with mass detection. Oxidation inhibited polymerization-depolymerization activity, and yielded low levels of irreversible protein dimers. With 10 mM AAPH only Trp and Met were consumed giving di-alcohols, kynurenine and di-Trp (from Trp) and the sulfoxide (from Met). With 100 mM AAPH low levels of Tyr oxidation (but not di-Tyr formation) were also observed. Correlation with the functional analyses indicates that Met oxidation, and particularly Met164 is the key driver of MjFtsZ inactivation, probably as a result of the position of this residue at the protein-protein interface of longitudinal interactions and in close proximity to the GTP binding site.

Behaviors of individual microtubules and microtubule populations relative to critical concentrations: dynamic instability occurs when critical concentrations are driven apart by nucleotide hydrolysis

The concept of critical concentration (CC) is central to understanding the behavior of microtubules (MTs) and other cytoskeletal polymers. Traditionally, these polymers are understood to have one CC, measured in multiple ways and assumed to be the subunit concentration necessary for polymer assembly. However, this framework does not incorporate dynamic instability (DI), and there is work indicating that MTs have two CCs. We use our previously established simulations to confirm that MTs have (at least) two experimentally relevant CCs and to clarify the behavior of individuals and populations relative to the CCs. At free subunit concentrations above the lower CC (CC_Elongation), growth phases of individual filaments can occur transiently; above the higher CC (CC_NetAssembly), the population’s polymer mass will increase persistently. Our results demonstrate that most experimental CC measurements correspond to CC_NetAssembly, meaning that “typical” DI occurs below the concentration traditionally considered necessary for polymer assembly. We report that [free tubulin] at steady state does not equal CC_NetAssembly, but instead approaches CC_NetAssembly asymptotically as [total tubulin] increases, and depends on the number of stable MT nucleation sites. We show that the degree of separation between CC_Elongation and CC_NetAssembly depends on the rate of nucleotide hydrolysis. This clarified framework helps explain and unify many experimental observations.

Survival of E. coli O157:H7, Salmonella Typhimurium, HAdV2 and MNV-1 in river water under dark conditions and varying storage temperatures

The ability of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, Human adenovirus serotype 2 (HAdV2) and Murine Norovirus 1 (MNV-1) to survive in river water at -20, 4, room temperature (~24 °C) and 37 °C, were evaluated under dark conditions. The tested surface water was obtained from the main Nile River in the Dokki area, Giza and sterilized by autoclaving. The pathogens were inoculated separately in the autoclaved river water. Each microcosm was sampled and the test microorganisms counted after zero (immediately following inoculation), 1, 7, 15, 30, 60, 90 and 120 days. Physicochemical parameters including pH, turbidity, electrical conductivity, dissolved oxygen, total dissolved solids, total alkalinity, biological oxygen demand, chemical oxygen demand, nitrates and nitrites, and sulphate, were also measured. For HAdV2, the highest decay rates were observed at 37 °C and room temperature compared to 4 and -20 °C. A similar trend was found for the MNV-1, although unlike the HAdV2, the decay rate was higher at -20 than at 4 °C. Also, 4 °C was the best temperature for the survival of MNV-1 (T₉₀ = 76.9 days), E. coli O157:H7 (T₉₀ = 103 days) and Salmonella Typhimurium (T₉₀ = 105 days). The least survival of the pathogens, except MNV-1, was recorded at 37 °C. These results indicate that under dark conditions and low temperatures, enteric pathogens could be stable for extended periods. No significant statistical correlation was observed between the experimental temperatures and the infectivity of the viral particles. This study provided useful information about the stability of these pathogens in the Nile River water and could serve as an early warning when considering the water of the river for agricultural irrigation or household use in areas with limited or no access to potable water.