Together with colleagues, including Esther Zimmer (to whom he was then married) and Norton Zinder, he discovered that viruses that infect bacteria can transfer genetic information between their hosts. This mechanism — transduction — was an unexpected way of altering the host's genetic make-up, and later assumed special significance with the recognition that viral sequences can be inserted in the human genome and can presumably be inherited. The discovery of transduction opened a vast area for research on the role of viruses in evolution and disease, and — even more intriguing — into the non-pathological characteristics of microorganisms. Another surprise was the finding that small, ring-shaped pieces of DNA, termed plasmids, reside in microbial cells and are distinct from chromosomal DNA, being capable of autonomous replication. Plasmids can be introduced into other cells to produce vast amounts of useful proteins such as human insulin and the hepatitis B virus vaccine. Lederberg's work was seminal in initiating a new approach to biology based on the genome and its interactions with the environment. This was recognized by the award of the Nobel prize in 1958, at the age of 33, which he shared with George Beadle and Edward Tatum.

The diplomonad parasite Giardia intestinalis contains two functionally equivalent nuclei that are inherited independently during mitosis. Although presumed to be asexual, Giardia has low levels of allelic heterozygosity, indicating that the two nuclear genomes may exchange genetic material. Fluorescence in situ hybridization performed with probes to an episomal plasmid suggests that plasmids are transferred between nuclei in the cyst, and transmission electron micrographs demonstrate fusion between cyst nuclei. Green fluorescent protein fusions of giardial homologs of meiosis-specific genes localized to the nuclei of cysts, but not the vegetative trophozoite. These data suggest that the fusion of nuclei, or karyogamy, and subsequently somatic homologous recombination facilitated by the meiosis gene homologs, occur in the giardial cyst.

A large-scale, double-stream gas puff target has been illuminated by sub-kJ, near-infrared (NIR) focused laser pulses at the PALS facility (Prague Asterix Laser System) to produce high-energy pulses of soft X rays from hot, dense plasma. The double-puff arrangement ensures high gas density and conversion efficiency from NIR to X rays approaching that typical for solid targets. In addition, its major advantage over solid targets is that it is free of debris and has substantially suppressed charged-particle emission. The X-ray emission characteristics of the source were determined for a range of gases that included krypton, xenon, N(2), CO and N(2)-CO. A demonstrated application of the xenon-based source is a single-shot damage induction to plasmid DNA. The yields of single-strand breaks (SSBs) and double-strand breaks (DSBs) were determined as a function of energy fluence adjusted by varying distance of sample from the source and thickness of aluminum filters.

Lactobacillus salivarius subsp. salivarius strain UCC118 is a bacteriocin-producing strain with probiotic characteristics. The 2.13-Mb genome was shown by sequencing to comprise a 1.83 Mb chromosome, a 242-kb megaplasmid (pMP118), and two smaller plasmids. Megaplasmids previously have not been characterized in lactic acid bacteria or intestinal lactobacilli. Annotation of the genome sequence indicated an intermediate level of auxotrophy compared with other sequenced lactobacilli. No single-copy essential genes were located on the megaplasmid. However, contingency amino acid metabolism genes and carbohydrate utilization genes, including two genes for completion of the pentose phosphate pathway, were megaplasmid encoded. The megaplasmid also harbored genes for the Abp118 bacteriocin, a bile salt hydrolase, a presumptive conjugation locus, and other genes potentially relevant for probiotic properties. Two subspecies of L. salivarius are recognized, salivarius and salicinius, and we detected megaplasmids in both subspecies by pulsed-field gel electrophoresis of sizes ranging from 100 kb to 380 kb. The discovery of megaplasmids of widely varying size in L. salivarius suggests a possible mechanism for genome expansion or contraction to adapt to different environments.

Times Cited: 2 Article English Hegemann, J. H Univ Dusseldorf, Inst Mikrobiol, Univ Str 1,Geb 26-12-64, D-40225 Dusseldorf, Germany Cited References Count: 43 532HH GREAT CLARENDON ST, OXFORD OX2 6DP, ENGLAND OXFORD

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