Streamer initiation in atmospheric pressure gas discharges by direct particle simulation.

A two-dimensional particle code that simulates electrical breakdown of gases by modeling avalanche evolution from the initial ion-electron pair up to the development of a streamer is presented. Trajectories of individual particles are followed, the self-field is included consistently and collision processes are accurately modeled using experimentally determined cross sections. It is emphasized that the tadpolelike structure of well-formed streamer heads is present throughout the avalanche phase, and that the transition to the self-similar evolution characteristic of the streamer phase merely reflects the continued development of this structure.

Identification and sequence of an unstable DNA element in the entomopathogenic bacteria Photorhabdus temperata strain K122.

Aims: A search was conducted for a difference in genome composition between phenotypic variants of the insect pathogenic bacteria, Photorhabdus temperata.

Methods: An unstable 300 bp fragment of DNA was identified by amplified fragment length polymorphism (AFLP) analysis, which was not, however, associated with phenotypic variation.

Results: During prolonged culturing of the bacteria, one copy of the repeated fragment was deleted and a restriction site linked to one of the copies was lost or gained.

The ner gene of Photorhabdus: effects on primary-form-specific phenotypes and outer membrane protein composition.

The nematode-bacterium complex of Heterorhabditis-Photorhabdus is pathogenic to insect larvae. The bacteria undergo a form of phenotypic switching whereby the primary form, at the stationary phase of the growth cycle, makes a range of products and has the capacity to support nematode growth, whereas the secondary form does not express these phenotypes. The work described here investigated the mechanism regulating phenotypic variation by transforming the primary cells with secondary-form DNA on a low-copy-number vector and screening for colonies which did not produce the yellow pigment characteristic of primaries.

Acid stress in the food pathogen Bacillus cereus.

Aims: The pathogen Bacillus cereus, which is associated with a number of foods including dairy products, was studied for its response to acid stress during the exponential phase.

Methods And Results: Bacillus cereus was found to adapt to acid stress (pH 4.6) when pre-exposed to a non-lethal, inducing pH of 6.

Heat and salt stress in the food pathogen Bacillus cereus.

Aims: The effects of stresses imposed on bacterial contaminants during food processing and treatment of packaging material were evaluated on the food pathogen Bacillus cereus.

Methods And Results: Conditions were established which allowed the cells to adapt to heat, ethanol and hydrogen peroxide stresses, but not to osmotic shock. Cross protection between stresses indicated a clear hierarchy of resistance with salt protecting against hydrogen peroxide, which protected against ethanol, which protected against heat shock.