A previously undescribed plant-microbe interaction between a root-colonizing Streptomyces species, S. lydicus WYEC108, and the legume Pisum sativum is described. The interaction is potentially of great importance to the health and growth in nature of this nodulating legume. The root-colonizing soil actinomycete S. lydicus WYEC108 influences pea root nodulation by increasing root nodulation frequency, possibly at the level of infection by Rhizobium spp. S. lydicus also colonizes and then sporulates within the surface cell layers of the nodules. Colonization leads to an increase in the average size of the nodules that form and improves the vigor of bacteroids within the nodules by enhancing nodular assimilation of iron and possibly other soil nutrients. Bacteroid accumulation of the carbon storage polymer, poly-␤-hydroxybutyrate, is reduced in colonized nodules. Root nodules of peas taken from agricultural fields in the Palouse hills of northern Idaho were also found to be colonized by actinomycete hyphae. We hypothesize that root and nodule colonization is one of several mechanisms by which Streptomyces acts as a naturally occurring plant growth-promoting bacterium in pea and possibly other leguminous plants.Streptomyces lydicus WYEC108 is a root-colonizing actinomycete originally isolated and studied for its properties as an antifungal biocontrol agent. This strain is capable of mycoparasitic colonization of fungal root pathogens and excretion of antifungal metabolites within plant rhizospheres (16,62). Recently, we demonstrated that strain WYEC108 is also a plant growth-promoting bacterium in the absence of fungal pathogen challenge. This may be due to the ability of strain WYEC108 to produce hydroxamate-type siderophores and/or other plant growth-promoting metabolites in the rhizosphere (25). Streptomyces spp. have been previously described as rhizosphere-colonizing bacteria (37, 38), antifungal biocontrol agents useful in controlling fungal root diseases (51), in vitro siderophore producers, and in vitro producers of plant growthpromoting hormones (25). Plant root exudates stimulate rhizosphere growth of actinomycetes that are strongly antagonistic to fungal pathogens, while the actinomycetes utilize root exudates for growth and synthesis of antimicrobial substances (16,62). In addition, actinomycetes synthesize an array of biodegradative enzymes, including chitinases (9, 23, 35), glucanases (18,26,29,32,59,60), peroxidases (48), and other enzymes possibly involved in mycoparasitic activity. Yet, the overall importance, physiological activities, and symbiotic roles of actinomycetes in situ within plant rhizospheres remain little studied at the biochemical or mechanistic levels. We believe that Streptomyces are far more important rhizosphere bacteria than has been generally recognized.Important to the symbiotic relationship between plants and microbes is the acquisition of iron. Although abundant in nature, under aerobic conditions at a neutral or alkaline pH, iron is found in highly insoluble forms not readil...

Resveratrol (3,5,4'-trihydroxy-trans-stilbene), an antifungal phytoalexin produced by grapes, peanuts, and Japanese knotweeds, is thought to be a beneficial dietary phytochemical in red wine and grape juice. Information on its antibacterial properties and biotransformation, however, is limited. We surveyed the interactions of resveratrol with 43 strains of bacterial species that are often animal- or human-associated. Resveratrol at 50 mg L(-1) reduced the growth rates of most of the bacteria tested, but did not totally prevent growth even at much higher levels. Eleven of the 43 bacteria were capable of transforming at least 20% of the resveratrol. Three major metabolites were identified as resveratroloside, piceid, and dihydroresveratrol, and three other metabolites were partially characterized.

Several microorganisms have been isolated that can transform hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a cyclic nitramine explosive. To better characterize the microbial genes that facilitate this transformation, we sequenced and annotated a 182-kb plasmid, pGKT2, from the RDX-degrading strain Gordonia sp. KTR9. This plasmid carries xplA, encoding a protein sharing up to 99% amino acid sequence identity with characterized RDX-degrading cytochromes P450. Other genes that cluster with xplA are predicted to encode a glutamine synthase-XplB fusion protein, a second cytochrome P450, Cyp151C, and XplR, a GntR-type regulator. Rhodococcus jostii RHA1 expressing xplA from KTR9 degraded RDX but did not utilize RDX as a nitrogen source. Moreover, an Escherichia coli strain producing XplA degraded RDX but a strain producing Cyp151C did not. KTR9 strains cured of pGKT2 did not transform RDX. Physiological studies examining the effects of exogenous nitrogen sources on RDX degradation in strain KTR9 revealed that ammonium, nitrite, and nitrate each inhibited RDX degradation by up to 79%. Quantitative real-time PCR analysis of glnA-xplB, xplA, and xplR showed that transcript levels were 3.7-fold higher during growth on RDX than during growth on ammonium and that this upregulation was repressed in the presence of various inorganic nitrogen sources. Overall, the results indicate that RDX degradation by KTR9 is integrated with central nitrogen metabolism and that the uptake of RDX by bacterial cells does not require a dedicated transporter.

Aims:  To isolate environmental bacteria capable of transforming fluoroquinolones to inactive molecules. Methods and Results:  Bacteria were isolated from the aerobic liquor of a wastewater treatment plant on a medium containing norfloxacin (100 mg l−1). Twenty‐two isolates were highly resistant (minimal inhibitory concentration: 6·25−200 μg ml−1) to five fluoroquinolones and six of them were positive by PCR amplification for the aminoglycoside resistance gene aac(6′)‐Ib. Of these, only Escherichia coli strain LR09 had the ciprofloxacin‐acetylating variant gene aac(6′)‐Ib‐cr; HPLC and mass spectrometry showed that this strain transformed both ciprofloxacin and norfloxacin by N‐acetylation. This bacterium also had mutations in the quinolone‐resistance determining regions of the gyrA and parC genes. Conclusions:  An E. coli isolate from wastewater, which possessed at least two distinct fluoroquinolone resistance mechanisms, inactivated ciprofloxacin and norfloxacin by N‐acetylation. Significance and Impact of the Study:  This is the first report of N‐acetylation of fluoroquinolones by an aac(6′)‐Ib‐cr‐containing bacterium from an environmental source.