Cloning of a gene from Bacillus cereus with homology to the mreB gene from Escherichia coli

How to Build a Bacterial Cell: MreB as the Foreman of E. coli Construction

Cell shape matters across the kingdoms of life, and cells have the remarkable capacity to define and maintain specific shapes and sizes. But how are the shapes of micron-sized cells determined from the coordinated activities of nanometer-sized proteins? Here, we review general principles that have surfaced through the study of rod-shaped bacterial growth. Imaging approaches have revealed that polymers of the actin homolog MreB play a central role. MreB both senses and changes cell shape, thereby generating a self-organizing feedback system for shape maintenance. At the molecular level, structural and computational studies indicate that MreB filaments exhibit tunable mechanical properties that explain their preference for certain geometries and orientations along the cylindrical cell body. We illustrate the regulatory landscape of rod-shape formation and the connectivity between cell shape, cell growth, and other aspects of cell physiology. These discoveries provide a framework for future investigations into the architecture and construction of microbes.

Complex regulatory pathways coordinate cell-cycle progression and development in Caulobacter crescentus

Caulobacter crescentus has become the predominant bacterial model system to study the regulation of cell-cycle progression. Stage-specific processes such as chromosome replication and segregation, and cell division are coordinated with the development of four polar structures: the flagellum, pili, stalk, and holdfast. The production, activation, localization, and proteolysis of specific regulatory proteins at precise times during the cell cycle culminate in the ability of the cell to produce two physiologically distinct daughter cells. We examine the recent advances that have enhanced our understanding of the mechanisms of temporal and spatial regulation that occur during cell-cycle progression.

Proteomic and microscopic analysis of biofilms formed by Listeria monocytogenes 568

Biofilm formation may be important in the colonization of the food-processing environment by the food-borne pathogen Listeria monocytogenes. Listeria monocytogenes 568 formed adherent multicellular layers on a variety of test surfaces following growth at 37 degrees C with multiple transfers of the test surface into fresh medium. Microscopic examination of these adherent layers suggest that the cells were surrounded by extracellular material. The presence of a carbohydrate containing extracellular polymeric matrix was confirmed by labelling hydrated adherent layers with fluorescein-conjugated concanavalin A, indicating that these adherent layers are biofilms. To gain insight into the physiological state of cells in these biofilms, the proteomes from biofilm- and planktonic-grown cells from the same cultures were compared using 2-dimensional polyacrylamide gel electrophoresis. Nineteen proteins, which exhibited higher levels of expression in biofilm-grown cells, were successfully identified from the 2-D gels using a combination of MALDI-TOF and MS/MS. Proteins that were found to be more highly expressed in biofilm-grown cells were involved in stress response, envelope and protein synthesis, biosynthesis, energy generation, and regulatory functions. In biofilm-grown cells, many proteins in the pH range 4-6 ran as multiple spots arranged horizontally across the 2-D gels.

Identification of proteins involved in the heat stress response of Bacillus cereus ATCC 14579

To monitor the ability of the food-borne opportunistic pathogen Bacillus cereus to survive during minimal processing of food products, we determined its heat-adaptive response. During pre-exposure to 42 degrees C, B. cereus ATCC 14579 adapts to heat exposure at the lethal temperature of 50 degrees C (maximum protection occurs after 15 min to 1 h of pre-exposure to 42 degrees C). For this heat-adaptive response, de novo protein synthesis is required. By using two-dimensional gel electrophoresis, we observed 31 heat-induced proteins, and we determined the N-terminal sequences of a subset of these proteins. This revealed induction of stress proteins (CspB, CspE, and SodA), proteins involved in sporulation (SpoVG and AldA), metabolic enzymes (FolD and Dra), identified heat-induced proteins in related organisms (DnaK, GroEL, ClpP, RsbV, HSP16.4, YflT, PpiB, and TrxA), and other proteins (MreB, YloH, and YbbT). The upregulation of several stress proteins was confirmed by using antibodies specific for well-characterized heat shock proteins (HSPs) of B. subtilis. These observations indicate that heat adaptation of B. cereus involves proteins that function in a variety of cellular processes. Notably, a 30-min pre-exposure to 4% ethanol, pH 5, or 2.5% NaCl also results in increased thermotolerance. Also, for these adaptation processes, protein synthesis is required, and indeed, some HSPs are induced under these conditions. Collectively, these data show that during mild processing, cross-protection from heating occurs in pathogenic B. cereus, which may result in increased survival in foods.

Insertional inactivation of hblC encoding the L2 component of Bacillus cereus ATCC 14579 haemolysin BL strongly reduces enterotoxigenic activity, but not the haemolytic activity against human erythrocytes

Haemolysin BL (HBL) is a Bacillus cereus toxin composed of a binding component, B, and two lytic components, L1 and L2. HBL is also the enterotoxin responsible for the diarrhoeal food poisoning syndrome caused by several strains of B. cereus. The three genes encoding the HBL components constitute an operon and are transcribed from a promoter 608 bp upstream of the hblC translational start site. The first gene of the hbl operon, hblC, in the B. cereus type strain, ATCC 14579, was inactivated in this study. Inactivation of hblC strongly reduced both the enterotoxigenic activity of B. cereus ATCC 14579 and the haemolytic activity against sheep erythrocytes, while maintaining full haemolytic activity against human erythrocytes.

Cloning and characterization of a Bacillus thuringiensis homolog of the spoIIID gene from Bacillus subtilis

The SpoIIID protein of Bacillus subtilis (Bs) is a small DNA-binding protein that is essential for gene expression of the mother cell compartment during sporulation. We have cloned a DNA fragment from Bacillus thuringiensis (Bt) that showed a specific hybridization with the Bs spoIIID gene. Sequence analysis found an open reading frame encoding 90 amino acids (aa), which are 89% identical to the deduced aa sequence of Bs spoIIID. Upstream from the transcription start point (tsp), a nucleotide sequence highly homologous to the consensus sequence motif for the sigma 35-recognized promoters was found. Northern blot analysis has indicated that the expression of the gene is induced only at the midsporulation stage, and that the gene constitutes an operon with a downstream gene, mreB. The Bs strain carrying the spoIIID delta erm or spoIIID83 mutation completely restored sporulation ability upon introduction of the spoIIID homologous gene from Bt. These results strongly suggest that the gene we have cloned is a Bt homolog of spoIIID.

Bacillus subtilis possesses a second determinant with extensive sequence similarity to the Escherichia coli mreB morphogene

A gene with substantial sequence similarity to the mreB morphogene of Bacillus subtilis has been identified at 302 degrees on the chromosomal map by A. Decatur, B. Kunkel, and R. Losick (Harvard University; personal communication). Our characterization has revealed that the protein product of this determinant (termed mbl for mreB-like) is 55 and 53% identical in sequence to the MreB proteins of B. subtilis and Escherichia coli, respectively. The protein is 86% identical to a protein identified as MreB from Bacillus cereus, suggesting that the B. cereus protein is actually Mbl. Insertional inactivation of mbl indicated that this gene is not essential for cell viability or sporulation. Cells bearing mutant mbl alleles display a decreased growth rate and an altered cellular morphology. The cells appear bloated and are frequently twisted. Intergenic suppressor mutations which restore the growth rate to an approximately normal level arise within the mutant population. A second site mutation, designated som-1, was mapped to the hisA-mbl region of the chromosome by transduction.

A small (2.4 Mb) Bacillus cereus chromosome corresponds to a conserved region of a larger (5.3 Mb) Bacillus cereus chromosome

We have determined the sizes of the chromosomes of six Bacillus cereus strains (range 2.4-4.3 Mb) and constructed a physical map of the smallest B. cereus chromosome (2.4 Mb). This map was compared to those of the chromosomes of four B. cereus strains and one B. thuringiensis strain previously determined to be 5.4-6.3 Mb. Of more than 50 probes, 30 were localized to the same half of the larger B. cereus and B. thuringiensis chromosomes. All 30 were also present on the small chromosome. Twenty of the probes present on the other half of the larger chromosomes were either present on extrachromosomal DNA, or absent from the B. cereus strain carrying the small chromosome. We propose that the genome of B. cereus/B. thuringiensis has one constant part and another less stable part which is more easily mobilized into other genetic elements. This part of the genome is localized to one region of the chromosome and may be subject to deletions or more frequent relocations between the chromosome and episomal elements of varying sizes up to the order of megabases.

A complete physical map of a Bacillus thuringiensis chromosome

Bacillus thuringiensis is the source of the most widely used biological pesticide, through its production of insecticidal toxins. The toxin genes are often localized on plasmids. We have constructed a physical map of a Bacillus thuringiensis chromosome by aligning 16 fragments obtained by digestion with the restriction enzyme NotI. The fragments ranged from 15 to 1,350 kb. The size of the chromosome was 5.4 Mb. The NotI DNA fingerprint patterns of 12 different B. thuringiensis strains showed marked variation. The cryIA-type toxin gene was present on the chromosome in four strains, was extrachromosomal in four strains, and was both chromosomal and extrachromosomal in two strains. A Tn4430 transposon probe hybridized to 5 of the 10 cryIA-positive chromosomal fragments, while cryIA and the transposon often hybridized to different extrachromosomal bands. Ten of the strains were hemolytic when grown on agar plates containing human erythrocytes. Nine of the strains were positive when assayed for the presence of Bacillus cereus enterotoxin. We conclude that B. thuringiensis is very closely related to B. cereus and that the distinction between B. cereus and B. thuringiensis should be reconsidered.