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      Diversity of Xenorhabdus and Photorhabdus spp. and Their Symbiotic Entomopathogenic Nematodes from Thailand

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          Abstract

          Xenorhabdus and Photorhabdus spp. are bacterial symbionts of entomopathogenic nematodes (EPNs). In this study, we isolated and characterized Xenorhabdus and Photorhabdus spp. from across Thailand together with their associated nematode symbionts, and characterized their phylogenetic diversity. EPNs were isolated from soil samples using a Galleria-baiting technique. Bacteria from EPNs were cultured and genotyped based on recA sequence. The nematodes were identified based on sequences of 28S rDNA and internal transcribed spacer regions. A total of 795 soil samples were collected from 159 sites in 13 provinces across Thailand. A total of 126 EPNs isolated from samples taken from 10 provinces were positive for Xenorhabdus (n = 69) or Photorhabdus spp. (n = 57). Phylogenetic analysis separated the 69 Xenorhabdus isolates into 4 groups. Groups 1, 2 and 3 consisting of 52, 13 and 1 isolates related to X. stockiae, and group 4 consisting of 3 isolates related to X. miraniensis. The EPN host for isolates related to X. stockiae was S. websteri, and for X. miraniensis was S. khoisanae. The Photorhabdus species were identified as P. luminescens (n = 56) and P. asymbiotica (n = 1). Phylogenenic analysis divided P. luminescens into five groups. Groups 1 and 2 consisted of 45 and 8 isolates defined as subspecies hainanensis and akhurstii, respectively. One isolate was related to hainanensis and akhurstii, two isolates were related to laumondii, and one isolate was the pathogenic species P. asymbiotica subsp. australis. H. indica was the major EPN host for Photorhabdus. This study reveals the genetic diversity of Xenorhabdus and Photorhabdus spp. and describes new associations between EPNs and their bacterial symbionts in Thailand.

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          Most cited references 21

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          A METHOD FOR OBTAINING INFECTIVE NEMATODE LARVAE FROM CULTURES.

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            Mutualism and pathogenesis in Xenorhabdus and Photorhabdus: two roads to the same destination.

            Photorhabdus and Xenorhabdus bacteria colonize the intestines of the infective soil-dwelling stage of entomophagous nematodes, Heterorhabditis and Steinernema, respectively. These nematodes infect susceptible insect larvae and release the bacteria into the insect blood. The bacteria kill the insect larvae and convert the cadaver into a food source suitable for nematode growth and development. After several rounds of reproduction the nematodes are recolonized by the bacteria before emerging from the insect cadaver into the soil to search for a new host. Photorhabdus and Xenorhabdus bacteria therefore engage in both pathogenic and mutualistic interactions with different invertebrate hosts as obligate components of their life cycle. In this review we aim to describe current knowledge of the molecular mechanisms utilized by Photorhabdus and Xenorhabdus to control their host-dependent interactions. Recent work has established that there is a trade-off between pathogenicity and mutualism in both these species of bacteria suggesting that the transition between these interactions must be under regulatory control. Despite the superficial similarity between the life cycles of these bacteria, it is now apparent that the molecular components of the regulatory networks controlling pathogenicity and mutualism in Photorhabdus and Xenorhabdus are very different.
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              Photorhabdus and a host of hosts.

              Photorhabdus is a member of the family Enterobacteriaceae that lives in a mutualistic association with a Heterorhabditis nematode worm. The nematode worm burrows into insect prey and regurgitates Photorhabdus, which goes on to kill the insect. The nematode feeds off the growing bacteria until the insect tissues are exhausted, whereupon they reassociate and leave the cadaver in search of new prey. This highly efficient partnership has been used for many years as a biological crop protection agent. The dual nature of Photorhabdus as a pathogen and mutualist makes it a superb model for understanding these apparently exclusive activities. Furthermore, recently identified clinical isolates of Photorhabdus are helping us to understand how human pathogens can emerge from the enormous reservoir of invertebrate pathogens in the environment. As Photorhabdus has never been found outside a host animal, its niche represents an entirely biotic landscape. In this review we discuss what molecular adaptations allow this bacterium to complete this fascinating and complex life cycle.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2012
                12 September 2012
                : 7
                : 9
                Affiliations
                [1 ]Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
                [2 ]Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
                [3 ]Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom
                [4 ]Vietnam National Museum of Nature, Vietnam Academy of Science and Technology, Caugiay, Hanoi, Vietnam
                [5 ]Molecular Biotechnology, Institute for Molecular Biosciences, Goethe University Frankfurt, Frankfurt, Germany
                [6 ]Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom
                Universidad Pública de Navarra, Spain
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: AT NC ST PKL HBB SJP NS NRW. Performed the experiments: AT NC ST NS PKL. Analyzed the data: AT NC ST SJP. Contributed reagents/materials/analysis tools: AT ST NS NC PKL. Wrote the paper: AT NC ST PKL HBB SJP NS NRW.

                Article
                PONE-D-12-12171
                10.1371/journal.pone.0043835
                3440396
                22984446

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Page count
                Pages: 9
                Funding
                This work was funded by the European Commission under the seventh Framework Programme Grant HEALTH-F3-2009-223328-GAMEXP. AT is supported by a scholarship under a PhD Sandwich Program of Commission on Higher Education, Ministry of Education of Thailand. NC is supported by a Wellcome Trust Career Development award in Public Health and Tropical Medicine, UK (grant 087769/Z/08/Z). SJP is supported by the NIHR Cambridge Biomedical Research Centre. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology
                Ecology
                Community Ecology
                Species Interactions
                Microbial Ecology
                Evolutionary Biology
                Evolutionary Ecology
                Microbiology
                Applied Microbiology
                Bacteriology
                Microbial Ecology
                Microbial Evolution
                Parasitology
                Population Biology

                Uncategorized

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