The complete genomic sequence of Pseudomonas syringae pv. syringae B728a (Pss B728a) has been determined and is compared with that of P. syringae pv. tomato DC3000 (Pst DC3000). The two pathovars of this economically important species of plant pathogenic bacteria differ in host range and other interactions with plants, with Pss having a more pronounced epiphytic stage of growth and higher abiotic stress tolerance and Pst DC3000 having a more pronounced apoplastic growth habitat. The Pss B728a genome (6.1 Mb) contains a circular chromosome and no plasmid, whereas the Pst DC3000 genome is 6.5 mbp in size, composed of a circular chromosome and two plasmids. Although a high degree of similarity exists between the two sequenced Pseudomonads, 976 protein-encoding genes are unique to Pss B728a when compared with Pst DC3000, including large genomic islands likely to contribute to virulence and host specificity. Over 375 repetitive extragenic palindromic sequences unique to Pss B728a when compared with Pst DC3000 are widely distributed throughout the chromosome except in 14 genomic islands, which generally had lower GC content than the genome as a whole. Content of the genomic islands varies, with one containing a prophage and another the plasmid pKLC102 of Pseudomonas aeruginosa PAO1. Among the 976 genes of Pss B728a with no counterpart in Pst DC3000 are those encoding for syringopeptin, syringomycin, indole acetic acid biosynthesis, arginine degradation, and production of ice nuclei. The genomic comparison suggests that several unique genes for Pss B728a such as ectoine synthase, DNA repair, and antibiotic production may contribute to the epiphytic fitness and stress tolerance of this organism.virulence genes ͉ epiphyte ͉ plant pathogen

The room-temperature reaction of lithium hydroxide with aluminum hydroxide (bayerite) in the ratio of 1:2 produces lithium dialuminate, LiA12(OH),*2H20. Rietveld refinement of X-ray and neutron powder diffraction patterns indicate that the structure is composed of [LiAlZ-(OH),]+ layers separated by water molecules and hydroxide ions. Disorder in the stacking sequence leads to indexing the diffraction pattern on a hexagonal cell (a = 5.0972(3) A, c = 7.5524(9) A X 3n layers); however, the structure is better described by a C-centered monoclinic cell with the constraints the b = a d 3 and cos / 3 = -a/3c ( a = 5.097 A, b = 8.829 A, c = 7.741 A, and /3 = 103.0'). The diffraction patterns were refined using a model of up to 54 layers (-400 A). The layer stacking vector, which defines the angle between layers, is less than expected based on the position of the diffraction peaks. The structural complexities present in lithium dialuminate have their origins in the conditions of synthesis and the layered nature of the material.

This review focuses on the use of designed reactants, consisting of ultrathin elemental layers sequentially deposited in ultrahigh vacuum, to control reaction pathways and the structure of compounds formed. Two reaction pathways are discussed. The first uses controlled nucleation of an amorphous intermediate to kinetically access compounds under conditions where they may be thermodynamically unstable. The second approach takes advantage of the controlled diffusion lengths in elementally modulated reactants and slow diffusion rates at low temperatures to prepare superlattice and heterostructure compounds with controlled composition and structure.