The fliK Gene Is Required for the Resistance of Bacillus thuringiensis to Antimicrobial Peptides and Virulence in Drosophila melanogaster

Antimicrobial peptides (AMPs) are essential effectors of the host innate immune system and they represent promising molecules for the treatment of multidrug resistant microbes. A better understanding of microbial resistance to these defense peptides is thus prerequisite for the control of infectious diseases. Here, using a random mutagenesis approach, we identify the fliK gene, encoding an internal molecular ruler that controls flagella hook length, as an essential element for Bacillus thuringiensis resistance to AMPs in Drosophila. Unlike its parental strain, that is highly virulent to both wild-type and AMPs deficient mutant flies, the fliK deletion mutant is only lethal to the latter's. In agreement with its conserved function, the fliK mutant is non-flagellated and exhibits highly compromised motility. However, comparative analysis of the fliK mutant phenotype to that of a fla mutant, in which the genes encoding flagella proteins are interrupted, indicate that B. thuringiensis FliK-dependent resistance to AMPs is independent of flagella assembly. As a whole, our results identify FliK as an essential determinant for B. thuringiensis virulence in Drosophila and provide new insights on the mechanisms underlying bacteria resistance to AMPs.

Spores and soil from six sides: interdisciplinarity and the environmental biology of anthrax (Bacillus anthracis)

Environmentally transmitted diseases are comparatively poorly understood and managed, and their ecology is particularly understudied. Here we identify challenges of studying environmental transmission and persistence with a six-sided interdisciplinary review of the biology of anthrax (Bacillus anthracis). Anthrax is a zoonotic disease capable of maintaining infectious spore banks in soil for decades (or even potentially centuries), and the mechanisms of its environmental persistence have been the topic of significant research and controversy. Where anthrax is endemic, it plays an important ecological role, shaping the dynamics of entire herbivore communities. The complex eco-epidemiology of anthrax, and the mysterious biology of Bacillus anthracis during its environmental stage, have necessitated an interdisciplinary approach to pathogen research. Here, we illustrate different disciplinary perspectives through key advances made by researchers working in Etosha National Park, a long-term ecological research site in Namibia that has exemplified the complexities of the enzootic process of anthrax over decades of surveillance. In Etosha, the role of scavengers and alternative routes (waterborne transmission and flies) has proved unimportant relative to the long-term persistence of anthrax spores in soil and their infection of herbivore hosts. Carcass deposition facilitates green-ups of vegetation to attract herbivores, potentially facilitated by the role of anthrax spores in the rhizosphere. The underlying seasonal pattern of vegetation, and herbivores' immune and behavioural responses to anthrax risk, interact to produce regular 'anthrax seasons' that appear to be a stable feature of the Etosha ecosystem. Through the lens of microbiologists, geneticists, immunologists, ecologists, epidemiologists, and clinicians, we discuss how anthrax dynamics are shaped at the smallest scale by population genetics and interactions within the bacterial communities up to the broadest scales of ecosystem structure. We illustrate the benefits and challenges of this interdisciplinary approach to disease ecology, and suggest ways anthrax might offer insights into the biology of other important pathogens. Bacillus anthracis, and the more recently emerged Bacillus cereus biovar anthracis, share key features with other environmentally transmitted pathogens, including several zoonoses and panzootics of special interest for global health and conservation efforts. Understanding the dynamics of anthrax, and developing interdisciplinary research programs that explore environmental persistence, is a critical step forward for understanding these emerging threats.

ORF 2 from the Bacillus cereus linear plasmid pBClin15 encodes a DNA binding protein

AIMS

To isolate and identify DNA-binding protein(s) with affinity for the mobile chromosomal repeat element bcr1 in Bacillus cereus group bacteria.

METHODS AND RESULTS

A biotinylated bcr1 element was immobilized to streptavidin-coated magnetic beads and used to pull out a 20 kDa DNA-binding protein from a whole cell protein extract of B. cereus ATCC 14579. The protein was identified as the product of ORF 2 encoded by the bacteriophage-related autonomously replicating linear genetic element pBClin15 carried by the strain. DNA binding was not bcr1-specific. By Northern blotting ORF 2 was co-transcribed with ORF 1, and also in certain instances with ORF 3 by transcriptional readthrough of the terminator located between ORF 2 and ORF 3.

CONCLUSIONS

ORF 2 from pBClin15 encodes a DNA-binding protein. ORF 2 is co-transcribed with its upstream gene ORF 1, and in a subset of the transcripts also with the downstream gene ORF 3 through alternative transcription termination.

SIGNIFICANCE AND IMPACT OF THE STUDY

The B. cereus group contains bacterial species of medical and economic importance. Bacteriophages or phage-encoded proteins from these bacteria have been suggested as potential therapeutic agents. Understanding the biology of bacteriophage-related genetic elements through functional characterization of their genes is of high relevance.

The Bacillus cereus group: novel aspects of population structure and genome dynamics

AIMS

To provide new insights into the population and genomic structure of the Bacillus cereus group of bacteria.

METHODS AND RESULTS

The genetic relatedness among B. cereus group strains was assessed by multilocus sequence typing (MLST) using an optimized scheme based on seven chromosomal housekeeping genes. A set of 48 strains from different clinical sources was included, and six clonal complexes containing several genetically similar isolates from unrelated patients were identified. Interestingly, several clonal groups contained strains that were isolated from similar human sources. Furthermore, comparative whole genome sequence analysis of 16 strains led to the discovery of novel ubiquitous genome features of the B. cereus group, such as atypical group II introns, IStrons, and hitherto uncharacterized repeated elements.

CONCLUSIONS

The B. cereus group constitutes a coherent population unified by the presence of ubiquitous and specific genetic elements which do not show any pattern, either in their sequences or genomic locations, which allows to differentiate between the member species of the group. Nevertheless, the population is very dynamic, as particular lineages of clinical origin can evolve to form clonal complexes. At the genome level, the dynamic behaviour is indicated by the presence of numerous mobile and repeated elements.

SIGNIFICANCE AND IMPACT OF THE STUDY

The B. cereus group of bacteria comprises species that are of medical and economic importance. The MLST data, along with the primers and protocols used, will be available in a public, web-accessible database (http://mlstoslo.uio.no).

Sequence analysis of three Bacillus cereus loci carrying PIcR-regulated genes encoding degradative enzymes and enterotoxin

PIcR is a pleiotropic regulator of extracellular virulence factors in the opportunistic human pathogen Bacillus cereus and the entomopathogenic Bacillus thuringiensis, and is induced in cells entering stationary phase. Among the genes regulated by PIcR are: pIcA, encoding phosphatidylinositol-specific phospholipase C (PI-PLC); plc, encoding phosphatidylcholine-preferring phospholipase C (PC-PLC); nhe, encoding the non-haemolytic enterotoxin; hbl, encoding haemolytic enterotoxin BL (HBL); and genes specifying a putative S-layer like surface protein and a putative extracellular RNase. By analysing 37.1 kb of DNA sequence surrounding hbl, plcA and plcR, 28 ORFs were predicted. Three novel genes putatively regulated by PlcR and encoding a neutral protease (NprB), a subtilase family serine protease (Sfp) and a putative cell-wall hydrolase (Cwh) were identified. The corresponding sfp and cwh genes were located in the immediate upstream region of plcA and could both be regulated by a putative PlcR-binding site positioned between the inversely transcribed genes. Similarly, nprB was positioned directly upstream and transcribed in the opposite orientation to plcR. Genes surrounding plcA, plcR and hblCDAB that were lacking an upstream PlcR regulatory sequence did not appear to serve functions apparently related to PlcR and did not exhibit a conserved organization in Bacillus subtilis.

Genome organization is not conserved between Bacillus cereus and Bacillus subtilis

The opportunistic pathogen Bacillus cereus is the genetically stable member of a group of closely related bacteria including the insect pathogen Bacillus thuringiensis and the mammalian pathogen Bacillus anthracis. Physical maps of B. cereus and B. thuringiensis strains show considerable variations in discrete parts of the chromosome, suggesting that certain genome regions are more prone to rearrangements. B. cereus belongs to the same subgroup of Bacillus species as Bacillus subtilis, by both phenotypic and rRNA sequence classification. The analysis of 80 kb of genome sequence sampled from different regions of the B. cereus ATCC 10987 chromosome is reported. Analysis of the sequence and comparison of the localization of the putative genes with that of B. subtilis orthologues show the following: (1) gene organization is not conserved between B. cereus and B. subtilis; (2) several putative genes are more closely related to genes from other bacteria and archaea than to B. subtilis, or may be absent in B. subtilis 168; (3) B. cereus contains a 155 bp repetitive sequence that is not present in B. subtilis. By hybridization, this repeat is present in all B. cereus and B. thuringiensis strains so far investigated.