From cholera to corals: viruses as drivers of virulence in a major coral bacterial pathogen

Disease is an increasing threat to reef-building corals. One of the few identified pathogens of coral disease is the bacterium Vibrio coralliilyticus. In Vibrio cholerae, infection by a bacterial virus (bacteriophage) results in the conversion of non-pathogenic strains to pathogenic strains and this can lead to cholera pandemics. Pathogenicity islands encoded in the V. cholerae genome play an important role in pathogenesis. Here we analyse five whole genome sequences of V. coralliilyticus to examine whether virulence is similarly driven by horizontally acquired elements. We demonstrate that bacteriophage genomes encoding toxin genes with homology to those found in pathogenic V. cholerae are integrated in V. coralliilyticus genomes. Virulence factors located on chromosomal pathogenicity islands also exist in some strains of V. coralliilyticus. The presence of these genetic signatures indicates virulence in V. coralliilyticus is driven by prophages and other horizontally acquired elements. Screening for pathogens of coral disease should target conserved regions in these elements

Analytical solution of generalized Burton--Cabrera--Frank equations for growth and post--growth equilibration on vicinal surfaces

We investigate growth on vicinal surfaces by molecular beam epitaxy making use of a generalized Burton--Cabrera--Frank model. Our primary aim is to propose and implement a novel analytical program based on a perturbative solution of the non--linear equations describing the coupled adatom and dimer kinetics. These equations are considered as originating from a fully microscopic description that allows the step boundary conditions to be directly formulated in terms of the sticking coefficients at each step. As an example, we study the importance of diffusion barriers for adatoms hopping down descending steps (Schwoebel effect) during growth and post-growth equilibration of the surface.Comment: 16 pages, REVTeX 3.0, IC-DDV-94-00

Comment on "A new mechanism for reentrant behaviour in semiconductor epitaxy: A reflection high-energy electron diffraction study of the growth of GaAs(1 1 1)A thin films" [Surf. Sci. 459 (2000) 277-286]

10.1016/S0039-6028(02)01918-0Surface Science5151263-265SUSC

Phosphorus incorporation during InP(0 0 1) homoepitaxial growth by solid source molecular beam epitaxy

10.1016/S0039-6028(03)00535-1Surface Science5313L383-L387SUSC

DEEP STATES AND SURFACE PROCESSES IN GaAs GROWN BY MOLECULAR BEAM EPITAXY

Nous avons utilisé les mesures de DLTS pour étudier l'influence des conditions de croissance sur les pièges à électrons désignés par M1, M2, M3 et M4 présents dans le GaAs élaboré par EJM dans un domaine de températures de 520°C à 650°C. Pour un rapport As : Ga de 5:1, les concentrations de M1, M3 et M4 tombent de 2 décades pour des températures de croissance passant de 520°C à 650°C, tandis que M2 a un comportement plus complexe et est le piège principal dans les couches déposées à 650°C. A une température de croissance fixée à 550°C, les concentrations de M1 et M4 diminuent quand le rapport As:Ga augmente alors que les concentrations de M2 et M3 augmentent. Les concentrations de M1 et M4 sont également réduites d'un facteur de 25 quand Pb ou l'hydrogène interagissent avec la surface pendant la croissance. Nous concluons que M1 et M4 sont reliés, bien que n'étant pas le même centre, et peuvent être associés à une lacune As. M2 et M3 sont des entités différentes, reliées ni à M1 ni à M4.We have used DLTS measurements to study the influence of growth conditions on the electron traps designated M1, M2, M3 and M4 which occur in MBE GaAs grown in the temperature range 520°C to 650°C. At an As:Ga ratio of 5:1 the concentrations of M1, M3 and M4 fall by two decades for growth temperatures increasing from 520°C to 650°C, whereas M2 has a more complex behaviour and is the dominant trap in 650°C grown layers. At a fixed growth temperature of 550°C concentrations of M1 and M4 fall with increasing As:Ga ratio whereas concentrations of M2 and M3 increase. The concentrations of M1 and M4 are also reduced by a factor 25 when Pb or hydrogen interact with the surface during growth. We argue that M1 and M4 are related, though not the same centre, and may be associated with As vacancies. M2 and M3 are different entities, neither of them related to M1 nor M4

Missing "sheets" in the reciprocal space representation of the disordered surface with one-dimensional domain boundaries

10.1016/S0218-625X(01)00130-0Surface Review and Letters85509-511SRLE

Growth and structural characterisation of Si/SiGe hetero structures for optoelectronic applications

The availability of compliant substrates has opened new avenues to exploit SiGe materials for optoelectronic applications. In this paper, relevant issues including fabrication of compliant substrates through compositionally graded buffer layers, strain (stress) balance in active layer design and X-ray characterisation are discussed. Quantum cascade structures designed for light emitting devices at THz range are grown using a combination of low pressure chemical vapour deposition and gas source molecular beam epitaxy in a single growth system. The results of structural characterisation by X-ray diffraction and transmission electron microscopy show that by following stringent design criteria, active layer structures more than 4 μm thick with low threading dislocation density can be achieved. Electroluminance in the THz frequency range have been observed from these structures