Nine polymorphic mer loci carried by 185 gram-negative fecal bacterial strains from humans and nonhuman primates are described. The loci were characterized with specific intragenic and intergenic PCR primers to amplify distinct regions covering approximately 80% of the typical gram-negative mer locus. These loci were grouped phylogenetically with respect to each other and with respect to seven previously sequenced mer operons from gram-negative bacteria (the latter designated loci 1, 2, 3, 6, 7, 8, and ⌬8 by us here for the purpose of this analysis). Six of the mer loci recovered from primates are similar either to these previously sequenced mer loci or to another locus recently observed in environmental isolates (locus 4), and three are novel (loci 5, 9, and 10). We have observed merC, or a merC-like gene, or merF on the 5 side of merA in all of the loci except that of Tn501 (here designated mer locus 6). The merB gene was observed occasionally, always on the 3 side of merA. Unlike the initial example of a merB-containing mer locus carried by plasmid pDU1358 (locus 8), all the natural primate loci carrying merB also had large deletions of the central region of the operon (and were therefore designated locus ⌬8). Four of the loci we describe (loci 2, 5, 9, and 10) have no region of homology to merB from pDU1358 and yet strains carrying them were phenylmercury resistant. Two of these loci (loci 5 and 10) also lacked merD, the putative secondary regulator of operon expression. Phylogenetic comparison of character states derived from PCR product data grouped those loci which have merC into one clade; these are locus 1 (including Tn21), locus 3, and locus 4. The mer loci which lack merC grouped into a second clade: locus 6 (including Tn501) and locus 2. Outlying groups lacked merD or possessed merB. While these mer operons are characterized by considerable polymorphism, our ability to discern coherent clades suggests that recombination is not entirely random and indeed may be focused on the immediate 5 and 3 proximal regions of merA. Our observations confirm and extend the idea that the mer operon is a genetic mosaic and has a predominance of insertions and/or deletions of functional genes immediately before and after the merA gene. chi sites are found in several of the sequenced operons and may be involved in the abundant reassortments we observe for mer genes.

Gram-negative fecal bacteria from three longitudinal Hg exposure experiments and from two independent survey collections were examined for their carriage of the mercury resistance (mer) locus. The occurrence of antibiotic resistance was also assessed in both mercury-resistant (Hg r) and mercury-susceptible (Hg s) isolates from the same collections. The longitudinal studies involved exposure of the intestinal flora to Hg released from amalgam "silver" dental restorations in six monkeys. Hg r strains were recovered before the installation of amalgams, and frequently these became the dominant strains while amalgams were installed. Such persistent Hg r strains always carried the same mer locus throughout the experiments. In both the longitudinal and survey collections, certain mer loci were preferentially associated with one genus, whereas other mer loci were recovered from many genera. In general, strains with any mer locus were more likely to be multiresistant than were strains without mer loci; this clustering tendency was also seen for antibiotic resistance genes. However, the association of antibiotic multiresistance with mer loci was not random; regardless of source, certain mer loci occurred in highly multiresistant strains (with as many as seven antibiotic resistances), whereas other mer loci were found in strains without any antibiotic resistance. The majority of highly multiresistant Hg r strains also carried genes characteristic of an integron, a novel genetic element which enables the formation of tandem arrays of antibiotic resistance genes. Hg r strains lacking antibiotic resistance showed no evidence of integron components.

We used metalloregulated luciferase reporter fusions and spectroscopic quantification of soluble Hg(II) to determine that the hydroperoxidase-catalase, KatG, of Escherichia coli can oxidize monatomic elemental mercury vapor, Hg(0), to the water-soluble, ionic form, Hg(II). A strain with a mutation inkatG and a strain overproducing KatG were used to demonstrate that the amount of Hg(II) formed is proportional to the catalase activity. Hg(0) oxidation was much decreased in stationary-phase cells of a strain lacking KatG, suggesting that the monofunctional hydroperoxidase KatE is less effective at this reaction. Unexpectedly, Hg(0) oxidation also occurred in a strain lacking both KatE and KatG, suggesting that activities other than hydroperoxidases may carry out this reaction. Two typical soil bacteria,Bacillus and Streptomyces, also oxidize Hg(0) to Hg(II). These observations establish for the first time that bacteria can contribute, as do mammals and plants, to the oxidative phase of the global Hg cycle.

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Icebox watermelons first appeared in the United States about 50 years ago. They weigh between 6 and 12 pounds and come in a variety of shapes and colors. With a rising interest in local production, organic produce, and direct marketing, farmers in Washington are looking to diversify crop varieties to meet these demands. Icebox watermelons offer a means of locally producing high-quality watermelons. In 2004 and 2005, we evaluated icebox watermelon varieties to determine which are most suitable for production in our region. In 2004, we evaluated 44 varieties of icebox watermelon and in 2005 we evaluated 100 varieties at WSU Vancouver REU. Varieties were seeded in the greenhouse mid-April and transplanted to the field by mid-June. The greenhouse and field were managed organically. The study design was a randomized complete-block with three replications. Plots were single rows, 6.1 m long, with seven plants per plot. Spacing was 1 m between plants and 3 m between rows. Plants were mulched with black plastic and drip-irrigated 2.5 cm per week. Melons were harvested twice weekly, from mid-August through mid-October. Fruit weight, number, and size were measured, and percentage of soluble solids was measured using a °Brix meter. General eating quality was also evaluated. Summaries of selected varieties will be presented here. To view other varieties included in the trial, see our website, http://agsyst.wsu.edu. Results of this study show significant differences among icebox watermelon varieties in total yield, number of fruit per plot, average fruit weight, number of days to harvest, and percentage of soluble solids. These preliminary findings indicate that more than 80 varieties of icebox watermelon can be grown productively in our region.