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Ammonia-oxidizing archaea (AOA) play an important role in nitrification and many studies exploit their amoA genes as marker for their diversity and abundance. We present an archaeal amoA consensus phylogeny based on all publicly available sequences (status June 2010) and provide evidence for the diversification of AOA into four previously recognized(More)
Six closely related N2-fixing bacterial strains were isolated from surface-sterilized roots and stems of four different rice varieties. The strains were identified as Serratia marcescens by 16S rRNA gene analysis. One strain, IRBG500, chosen for further analysis showed acetylene reduction activity (ARA) only when inoculated into media containing low levels(More)
The invasive properties of Azoarcus sp. strain BH72, an endorhizospheric isolate of Kallar grass, on gnotobiotically grown seedlings of Oryza sativa IR36 and Leptochloa fusca (L.) Kunth were studied. Additionally, Azoarcus spp. were localized in roots of field-grown Kallar grass. To facilitate localization and to assure identity of bacteria, genetically(More)
Burkholderia phytofirmans PsJN is a naturally occurring plant-associated bacterial endophyte that effectively colonizes a wide range of plants and stimulates their growth and vitality. Here we analyze whole genomes, of PsJN and of eight other endophytic bacteria. This study illustrates that a wide spectrum of endophytic life styles exists. Although we(More)
N2-fixing bacteria such as Azoarcus spp., Herbaspirillum spp, and Acetobacter diazotrophicus can infect the interior of gramineous plants without causing symptoms of plant disease but do not survive in soil. Like phytopathogens, they can penetrate into central tissues and spread systemically. There is no evidence for an endosymbiosis in living plant cells;(More)
The taxonomic structure of members of the genus Azoarcus sensu lato was reassessed in a polyphasic approach. Two species, Azoarcus communis and Azoarcus indigens, three unnamed species containing diazotrophs associated with Kallar grass roots (groups C, D) and a group of strains (E) isolated from fungi were analysed. They were compared by PAGE analyses of(More)
In addition to forming symbiotic nodules on legumes, rhizobial strains are members of soil or rhizosphere communities or occur as endophytes, e.g., in rice. Two rhizobial strains which have been isolated from root nodules of the aquatic legumes Aeschynomene fluminensis (IRBG271) and Sesbania aculeata (IRBG74) were previously found to promote rice growth. In(More)
Terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR-amplified nitrogenase gene (nifH) fragments is a rapid technique for profiling of diazotrophic microbial communities without the necessity of cultures for study. Here, we examined the impact of N-fertilization, plant genotype and environmental conditions on diazotrophic microbial(More)
A gfp (green fluorescent protein) cassette for transcriptional fusions has been developed to study gene expression in Azoarcus sp. BH72 in association with plant roots. The bacteria expressed nitrogenase genes (nifHDK) in the rhizosphere, on root tips, and in epidermal cells of rice seedlings. Green fluorescent protein fusions also visualized promoter(More)
We report the discovery of novel subcellular structures related to bacterial nitrogen fixation in the strictly respiratory diazotrophic bacterium Azoarcus sp. BH72, which was isolated as an endophyte from Kallar grass. Nitrogenase is derepressed under microaerobic conditions at O2 concentrations in the micromolar range. With increasing O2 deprivation,(More)