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Myxococcus xanthus DK1622 contains two paralogous groEL gene loci that possess both different sequences and different organizations within the genome. Deletion of either one of these two genes alone does not affect cell viability. However, deletion of both groEL genes results in cell death unless a complemented groEL1 or groEL2 gene is present. The groEL1 gene was determined to be essential for cell survival under heat shock conditions; a strain with mutant groEL2 caused cells to be more sensitive than the wild-type strain to higher temperatures. Mutants with a single deletion of either groEL1 (MXAN_4895) or groEL2 (MXAN_4467) had a growth curve similar to that of the wild-type strain DK1622 in medium containing hydrolyzed proteins as the substrate. However, when cells were cultured on medium containing either Escherichia coli cells or casein as the substrate, deletion of groEL2, but not groEL1, led to a deficiency in cell predation and macromolecular feeding. Furthermore, groEL1 was found to play an indispensable role in the development and sporulation of cells, but deletion of groEL2 had no visible effects. Our results suggest that, although alternatively required for cell viability, the products of the two groEL genes have divergent functions in the multicellular social life cycle of M. xanthus DK1622. doi:10.1128/JB.01458-09

The X S gene encodes a holin, S105, and an antiholin, S107, which differs by its Met-Lys N-terminal extension. The model for the lysis-defective character of S107 stipulates that the additional N-terminal basic residue keeps S107 from assuming the topology of S105, which is N-out, C-in, with three transmembrane domains (TMDs). Here we show that the N terminus of S105 retains its fMet residue but that the N terminus of S107 is fully deformylated. This supports the model that in S105, TMD1 inserts into the membrane very rapidly but that in S107, it is retained in the cytoplasm. Further, it reveals that, compared to S105, S107 has two extra positively charged moieties, Lys2 and the free N-terminal amino group, to hinder its penetration into an energized membrane. Moreover, an allele, [S105.sub.[DELTA]TMD1], with TMD1 deleted, was found to be defective in lysis, insensitive to membrane depolarization, and dominant to the wild-type allele, indicating that the lysis-defective, antiholin character of S107 is due to the absence of TMD1 from the bilayer rather than to its ectopic localization at the inner face of the cytoplasmic membrane. Finally, the antiholin function of the deletion protein was compromised by the substitution of early-lysis missense mutations in either the deletion protein or parental S105 but restored when both [S105.sub.[DELTA]TMD1] and holin carried the substitution. doi: 10.1128/JB.01263-09

Escherichia coli mazEF is a toxin-antitoxin gene module that mediates cell death during exponential-phase cellular growth through either reactive oxygen species (ROS)-dependent or ROS-independent pathways. Here, we found that the stationary-phase sigma factor [[sigma].sup.s] was responsible for the resistance to mazEF-mediated cell death during stationary growth phase. Deletion of rpoS, the gene encoding [[sigma].sup.s] from the bacterial chromosome, permitted mazEF-mediated cell death during stationary growth phase.

Enterococci are major contributors of hospital-acquired infections and have emerged as important reservoirs for the dissemination of antibiotic resistance traits. The ability to form biofilms on medical devices is an important aspect of pathogenesis in the hospital environment. The Enterococcusfaecalis Fsr quorum system has been shown to regulate biofilm formation through the production of gelatinase, but the mechanism has been hitherto unknown. Here we show that both gelatinase (GelE) and serine protease (SprE) contribute to biofilm formation by E. faecalis and provide clues to how the activity of these proteases governs this developmental process. Confocal imaging of biofilms suggested that [GelE.sup.-] mutants were significantly reduced in biofilm biomass compared to the parental strain, whereas the absence of SprE appeared to accelerate the progression of biofilm development. The phenotype observed in a [SprE.sup.-] mutant was linked to an observed increase in autolytic rate compared to the parental strain. Culture supernatant analysis and confocal microscopy confirmed the inability of mutants deficient in GelE to release extracellular DNA (eDNA) in planktonic and biofilm cultures, whereas cells deficient in SprE produced significantly more eDNA as a component of the biofilm matrix. DNase I treatment of E. faecalis biofilms reduced the accumulation of biofilm, implying a critical role for eDNA in biofilm development. In conclusion, our data suggest that the interplay of two secreted and coregulated proteases--GelE and SprE--is responsible for regulating autolysis and the release of high-molecular-weight eDNA, a critical component for the development of E. faecalis biofilms.

Bacteria growing in biofilms often develop multicellular, three-dimensional structures known as microcolonies. Complex differentiation within biofilms of Pseudomonas aeruginosa occurs, leading to the creation of voids inside microcolonies and to the dispersal of cells from within these voids. However, key developmental processes regulating these events are poorly understood. A normal component of multicellular development is cell death. Here we report that a repeatable pattern of cell death and lysis occurs in biofilms of P. aeruginosa during the normal course of development. Cell death occurred with temporal and spatial organization within biofilms, inside microcolonies, when the biofilms were allowed to develop in continuous-culture flow cells. A subpopulation of viable cells was always observed in these regions. During the onset of biofilm killing and during biofilm development thereafter, a bacteriophage capable of superinfecting and lysing the P. aeruginosa parent strain was detected in the fluid effluent from the biofilm. The bacteriophage implicated in biofiim killing was closely related to the filamentous phage Pf1 and existed as a prophage within the genome of P. aeruginosa. We propose that prophage-mediated cell death is an important mechanism of differentiation inside microcolonies that facilitates dispersal of a subpopulation of surviving cells.

Research has been conducted on Salmonella enterica serovar Typhimurium hemA gene. Results demonstrate that hemA-deficient cell exposure to hydrogen peroxide leads to the iron-dependent DNA damage and cell death.

Research has been conducted on the anthraquinone-2,6-disulfonate (AQDS) used as an electron shuttle during extracellular electron transfer. Results indicate that AQDS enters the Shewanella oneidensis strain MR-1 and causes cell death, and that there may be functional and structural relationship between quinone-containing electron shuttles and antibiotics.

This review discusses mouse polyomavirus transformation and their natural life cycle in vertebrate species with reference to the role played by the middle T antigen in the viral replication and transcription, apoptosis, signal transduction pathways, development of transgenic mice, and mechanistic aspects of tumor development.

Results demonstrate that P1-mediated phd-doc module postsegregationl killing by the P1 prophage is dependent on the presence of Escherichia coli mazEF toxin-antitoxin system. Data indicate that the Doc toxin protein initiates cell death via mazEGF system by inhibiting E.coli protein synthesis

A chromosome expression system was used to investigate the relative contribution of four genes belonging to the PBSX operon, xepA, xhlA, xhlB and xlyA and their respective products, exporter protein, membrane-associated protein, holin and endolysin to cell lysis in Bacillus subtilis. Results indicate that the PBSX lysis system is different from those of other phage systems.

Immunoelectron microscopy was utilized to determine the protein products of atl gene to determine the role of the bacterolytic enzyme gene in wall perforation in penicillin G (PNG)-treated Staphylococcus aureus. Analysis of atl gene products during the autolytic process in PNG-treated Staphylococcus aureus indicated the presence of atl-generated wall hydrolases that promoted the formation of wall defects due to PNG. The wall defects created by atl gene products during the autolytic process released internal pressure which led to the formation of murosomes.