SummaryIron is an important nutrient in N 2 -®xing legume root nodules. Iron supplied to the nodule is used by the plant for the synthesis of leghemoglobin, while in the bacteroid fraction, it is used as an essential cofactor for the bacterial N 2 -®xing enzyme, nitrogenase, and iron-containing proteins of the electron transport chain. The supply of iron to the bacteroids requires initial transport across the plant-derived peribacteroid membrane, which physically separates bacteroids from the infected plant cell cytosol. In this study, we have identi®ed Glycine max divalent metal transporter 1 (GmDmt1), a soybean homologue of the NRAMP/Dmt1 family of divalent metal ion transporters. GmDmt1 shows enhanced expression in soybean root nodules and is most highly expressed at the onset of nitrogen ®xation in developing nodules. Antibodies raised against a partial fragment of GmDmt1 con®rmed its presence on the peribacteroid membrane (PBM) of soybean root nodules. GmDmt1 was able to both rescue growth and enhance 55 Fe(II) uptake in the ferrous iron transport de®cient yeast strain (fet3fet4). The results indicate that GmDmt1 is a nodule-enhanced transporter capable of ferrous iron transport across the PBM of soybean root nodules. Its role in nodule iron homeostasis to support bacterial nitrogen ®xation is discussed.

The importance of zinc in organisms is clearly established, and mechanisms involved in zinc acquisition by plants have recently received increased interest. In this report, the identification, characterization and location of GmZIP1, the first soybean member of the ZIP family of metal transporters, are described. GmZIP1 was found to possess eight putative transmembrane domains together with a histidine-rich extra-membrane loop. By functional complementation of zrt1zrt2 yeast cells no longer able to take up zinc, GmZIP1 was found to be highly selective for zinc, with an estimated K m value of 13.8 M. Cadmium was the only other metal tested able to inhibit zinc uptake in yeast. An antibody raised against GmZIP1 specifically localized the protein to the peribacteroid membrane, an endosymbiotic membrane in nodules resulting from the interaction of the plant with its microsymbiont. The specific expression of GmZIP1 in nodules was confirmed by Northern blot, with no expression in roots, stems, or leaves of nodulated soybean plants. Antibodies to GmZIP1 inhibited zinc uptake by symbiosomes, indicating that at least some of the zinc uptake observed in isolated symbiosomes could be attributed to GmZIP1. The orientation of the protein in the membrane and its possible role in the symbiosis are discussed.Zinc is an essential micronutrient for all organisms, including plants. More than 3% of the proteins of Saccharomyces cerevisiae and Caenorhabditis elegans are predicted to contain sequence motifs characteristic of zinc binding structural domains (1). Zinc deficiency is a widespread micronutrient deficiency limiting crop production (2). In recent years, genes encoding zinc transporters have been identified in various organisms (3-11). These studies have shed some light on zinc uptake and regulation, particularly at the plasma membrane level. However, with the exception of the recently identified Zrt3p transporter on the vacuole membrane in yeast (9), little is known about intracellular zinc transport systems, nor about the mechanisms of the transporters identified. Here we investigate zinc transport at the symbiotic interface between legumes and rhizobia, which presents an additional level of complexity.Many legumes form a symbiosis with nitrogen-fixing soil bacteria (rhizobia) that enables the plants to utilize atmospheric N 2 for growth. Infection of the legume root by rhizobia results in the formation of specialized organs called nodules that provide the microaerobic conditions required for operation of the nitrogenase enzyme. Within the infected cells of nodules, the N 2 -fixing bacteroids are enclosed in a plant membrane to form an organelle-like structure termed the symbiosome (12). The envelope of the symbiosome is called the peribacteroid membrane (PBM) 1 and effectively controls the exchange of metabolites between the symbiotic partners. The PBM, although originating from the plasma membrane of root cells, evolves over the course of nodule organogenesis to become a new and specialized membrane containing symbiosi...

We evaluated a ready-to-use real-time quantitative Legionella pneumophila PCR assay system by testing 136 hot-water-system samples collected from 55 sites as well as 49 cooling tower samples collected from 20 different sites, in parallel with the standard culture method. The PCR assay was reproducible and suitable for routine quantification of L. pneumophila. An acceptable correlation between PCR and culture results was obtained for sanitary hot-water samples but not for cooling tower samples. We also monitored the same L. pneumophilacontaminated cooling tower for 13 months by analyzing 104 serial samples. The culture and PCR results were extremely variable over time, but the curves were similar. The differences between the PCR and culture results did not change over time and were not affected by regular biocide treatment. This ready-to-use PCR assay for L. pneumophila quantification could permit more timely disinfection of cooling towers.Legionellosis can be acquired by inhalation of Legionella pneumophila bacteria dispersed by environmental sources, such as hot-water systems and cooling towers. Legionellosis outbreaks are often associated with high mortality rates (15 to 20%) (10). Legionella pneumophila serogroup 1 is responsible for up to 80% of cases (9,11,30). The density of Legionella cells in water is theoretically associated with the risk of legionellosis (5, 15): cell densities above 10 4 to 10 5 CFU per liter of water have been shown to represent a potential health risk to humans (20,23). Environmental Legionella monitoring is recommended in several countries (7,16), and regular treatment of cooling tower installations is obligatory in France (7).In France, conventional culture is the only approved technique for the detection and quantification of Legionella in water samples (2). However, definitive culture results take 10 days to obtain and may have decreased sensitivities due to Legionella growth characteristics (3, 6). Several authors have developed real-time-PCR-based methods for rapid detection of Legionella in water samples (3,12,27,29). However, Joly et al. recently reported that quantitative real-time PCR is influenced by the type of water sample and that the results may be laboratory dependent (12). Several commercial real-time PCR kits are currently available, such as the iQ-check real-time PCR kit (Bio-Rad, France), the Aqua Screen Lp-qDual kit (Minerva Biolabs, Germany), and the GeneDisc Legionella kit (GeneSystems, France). The main differences between these kits are based on the degrees of standardization of the three critical steps: DNA extraction, PCR preparation, and data analysis.In this study, we compared a standardized real-time quantitative PCR assay system with the conventional culture method. The PCR system, developed by GeneSystems (Bruz, France), is the first ready-to-use PCR instrument dedicated to routine Legionella detection in water samples that includes a dedicated filtration unit and DNA extraction instrument. The two methods were both applied to 136 hot-water-system sam...