dictyNews Electronic Edition Volume 33, number 6 August 28, 2009 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ========= Abstracts ========= Xpf and not the Fanconi anaemia proteins or Rev3 accounts for the extreme resistance to cisplatin in Dictyostelium discoideum Xiao-Yin Zhang, Judith Langenick, David Traynor, M. Madan Babu, Rob R. Kay and Ketan J. Patel Medical Research Council, Laboratory for Molecular Biology, Hills Road, Cambridge CB2 0QH, UK PLoS Genetics, in press Organisms like Dictyostelium discoideum, often referred to as DNA damage "extremophiles", can survive exposure to extremely high doses of radiation and DNA crosslinking agents. These agents form highly toxic DNA crosslinks that cause extensive DNA damage. However little is known about how Dictyostelium and the other “extremophiles” can tolerate and repair such large numbers of DNA crosslinks. Here we describe a comprehensive genetic analysis of crosslink repair in Dictyostelium discoideum. We analyse three gene groups that are crucial for a replication coupled repair process that removes DNA crosslinks in higher eukarya: The Fanconi anaemia pathway (FA), translesion synthesis (TLS), and nucleotide excision repair. Gene disruption studies unexpectedly reveal that the FA genes and the TLS enzyme Rev3 play minor roles in tolerance to crosslinks in Dictyostelium. However, disruption of the Xpf nuclease subcomponent results in striking hypersensitivity to crosslinks. Genetic interaction studies reveal that although Xpf functions with FA and TLS gene products, most Xpf mediated repair is independent of these two gene groups. These results suggest that Dictyostelium utilises a distinct Xpf nuclease-mediated repair process to remove crosslinked DNA. Other DNA damage resistant organisms and chemoresistant cancer cells might adopt a similar strategy to develop resistance to DNA crosslinking agents. Submitted by Judith Langenick [jlange@mrc-lmb.cam.ac.uk] -------------------------------------------------------------------------------- Phase variation has a role in Burkholderia ambifaria niche adaptation Ludovic Vial(1), Marie-Christine Groleau(1), Martin G Lamarche(1), Geneviève Filion(2), Josée Castonguay-Vanier(1), Valérie Dekimpe(1), France Daigle(3), Steve J Charette(2,4) and Eric Déziel(1) 1INRS-Institut Armand Frappier, Laval, Québec, Canada 2Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec (Hôpital Laval), Québec, Canada 3Department of Microbiology and Immunology, University of Montreal, Montréal, Québec, Canada 4Département de microbiologie et de biochimie, Faculté des sciences et de génie, Université Laval, Québec, Canada ISME Journal, in press Members of the Burkholderia cepacia complex (Bcc), such as B. ambifaria, are effective biocontrol strains, for instance, as plant growth-promoting bacteria; however, Bcc isolates can also cause severe respiratory infections in people suffering from cystic fibrosis (CF). No distinction is known between isolates from environmental and human origins, suggesting that the natural environment is a potential source of infectious Bcc species. While investigating the presence and role of phase variation in B. ambifaria HSJ1, an isolate recovered from a CF patient, we identified stable variants that arose spontaneously irrespective of the culture conditions. Phenotypic and proteomic approaches revealed that the transition from wild-type to variant types affects the expression of several putative virulence factors. By using four different infection models (Drosophila melanogaster, Galleria mellonella, macrophages and Dictyostelium discoideum), we showed that the wild-type was more virulent than the variant. It may be noted that the variant showed reduced replication in a human monocyte cell line when compared with the wild-type. On the other hand, the variant of isolate HSJ1 was more competitive in colonizing plant roots than the wild-type. Furthermore, we observed that only clinical B. ambifaria isolates generated phase variants, and that these variants showed the same phenotypes as observed with the HSJ1 variant. Finally, we determined that environmental B. ambifaria isolates showed traits that were characteristic of variants derived from clinical isolates. Our study therefore suggest that B.ambifaria uses phase variation to adapt to drastically different environments: the lung of patients with CF or the rhizosphere. Submitted by Steve Charette [steve.charette@bcm.ulaval.ca] ============================================================== [End dictyNews, volume 33, number 6]