VIRUS LIKE PARTICLES FROM THE SEA: NEW PARTICLES AND NEW CONCEPT
Within the frame of a study on intergeneric phage-mediated gene transfer between marine bacteria and enteric bacteria, namely an auxotrophic mutant of Escherichia coli AB1157 we used virus like particles (VLPs) from an oligotrophic marine environment (Mediterranean Sea, West coast of Corsica) and obtained gene transfer frequencies ranging between 10-2 to 10-6 per particle. Consequently we had to assume that an important fraction of the VLPs obtained via ultrafiltration from surface seawater have the capability to induce horizontal gene transfer into E. coli. In the process of this investigation we made a number of new observations which were not compatible either with the concept of gene transfer by phages nor by gene transfer due to other known mechanisms (e.g. membran vesicles). The obtained bacteria got the ability to produce new VLPs which had again the capability to induce horizontal gene transfer. Neither plaque formation nor cell lysis was observed - thus the observed particles cannot be classified as viruses. Using molecularbiological and microbiological methods we are about to analyze and characterize those VLPs.
Processed by: Sylvia Hagemann, Branko Velimirov, Lisa Stöger, Melanie Kappelmann, Ingrid Gerstl
ENTEROVIRUSES IN OUR AQUEOUS ENVIRONMENT
(RNA-viruses, human pathogens and emerging pathogens in aquatic ecosystems)
Aquatic sediments serve as a reservoir for a multitude of viruses. Virus like particles (VLPs) of aquatic as well as of terrestric origin can be found in those sediments, among them a significant number of human pathogens - mainly RNA-viruses. It is reasonable to assume that aquatic sediments also harbour significant numbers of emerging pathogens. It is therefore essential not only for ecosystem research but also for the improvement of public health to assess the diversity of RNA-viruses in aquatic systems and to estimate their potential to become human pathogens.
Processed by: Branko Velimirov, Sylvia Hagemann, Armin Loeckher
MONITORING BACTERIAL SECONDARY PRODUCTION IN THE ALTE DONAU
Within the frame of a monitoring program for the assessment of the water quality of a main recreational site of Vienna, the Alte Donau, bacterial abundance, morphometry and production is quantified at regular time intervals within a year. While the practical aspect of the project is the field of hygienic, the scientific aspects encompass the understanding of the functioning of the microbial and viral loop in both the water column and the bottom sediment system of the habitat.
Processed by: Branko Velimirov in Cooporation with the MA45
MOLECULAR BIOLOGY AND EVOLUTION OF DNA TRANSPOSONS
A substantial fraction of vertebrate and invertebrate genomes is composed of mobile elements and their derivatives. The P elements of Drosophila belong to the class of DNA transposons. Autonomous elements are about 3 kb long and consist of four exons, three introns and terminal non coding sequences ending in terminal inverted repeats. Their transposition follows a cut and paste mechanism generating a 8 bp target site duplication. The transposition event is catalyzed by the 87 kDa transposase which is translated in germ line cells from a mRNA transcribed from the four exons. In somatic cells, a 66 kDa protein is synthesized from an mRNA which retains the third intron leading to a premature stop of translation. This truncated protein acts as a repressor of P element transposition. P elements were first discovered in Drosophila melanogaster due to their ability to induce hybrid dysgenesis. Subsequently, P homologous sequences were identified in many drosophilid species and some dipteran species outside the drosophilid family.. Sequence analyses of different P element subfamilies within the Drosophilidae revealed that their sequence relationships are not in accordance with the phylogeny of their host species. These findings resulted in the generally accepted model that P elements are not merely vertically inherited but can also be transmitted horizontally. The first horizontal transmission identified was the transfer from D. willistoni to D. melanogaster. This rather recent event was followed by the rapid spread of P elements through the natural populations of D. melanogaster. A considerable number of horizontal transfer events must be considered to explain the present distribution pattern of P element subfamilies within the Drosophilidae. In some drosophila species, in the blowfly Lucilia cuprina, and in the housefly Musca domestica terminally truncated and therefore immobile P transposons have been detected. In Drosophila these stationary sequences have retained the coding capacity of the first three exons thus expressing a repressor-like protein with unknown function. This change from a parasitic element to a beneficial host gene has been described as molecular domestication.
In humans at least 45% of the genome belong to transposable elements and a number of single copy genes seem to have originated from them. Until now, 48 domesticated human genes probably originating from up to 39 different transposon copies could be identified. Most of them originated from DNA transposons, although only about 6% of the human transposable elements belong to this transposon type.
In 2001 we reported for the first time the detection of a P homologous sequence in the human genome, which we subsequently named Phsa (‘P homologue of Homo sapiens’). It is a stationary, single-copy gene, located on the long arm of chromosome 4 and encodes a hypothetical protein of 903 amino acids, with still unknown function. Such stationary, single-copy P-homologous sequences have been detected in several other vertebrate species at orthologous positions to Phsa, but only as rudiments in rodents In contrast, several P-homologous sequences have been found in the genome of zebrafish, named Pdre (P homolog of Danio rerio). Some of these have structural features typical of transposable elements and large open reading frames (ORFs) that suggest coding capacity. Recently (2009) we published the P elements from Ciona intestinalis, a species of the most primitive chordates, and compared them with those from Ciona savignyi. They showed typical DNA transposon structures, namely terminal inverted repeats (TIRs) and target site duplications (TSDs) indicating that P elements with typical features of transposable DNA elements may be found already at the base of the chordate lineage and it can be speculated that P elements were present in a common ancestor of the urochordata and vertebrates, or considering the well-known Drosophila P elements, even within the common ancestor of protostomia and deuterostomia.
Processed by: Sylvia Hagemann, Branko Velimirov, Ingrid Gerstl