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Copyright of Canadian Journal of Microbiology is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In short-season production areas, cool soil temperature is a major factor potentially limiting soybean [Glycine max (L.) Merr.] plant growth and yield. Genistein (4,5,7-trihydroxyisoflavone) is a signal compound secreted from soybean roots and is essential to establishment of the soybean-Bradyrhizobiumjaponicum N-fixing symbiosis. The addition of genistein to soybean inocula has proven to be an effective means of generating increases in N fixation and yield; however, genistein is costly. We used ultraviolet (UV) mutagenesis to make 10 mutants of USDA 110 that express the nod genes without exposure to genistein. A field experiment was conducted at the Lods Agronomy Research Centre in southwestern Quebec in 1998 and 1999. The treatments consisted of factorial combinations of inoculant type [no inoculant (control) and inoculants containing the mutants or the wildtypes 532 C or USDA 110] and soybean cultivar (OAC Bayfield and Maple Glen). Inoculation with mutant strains Bj 30055 and Bj 30058 resulted in greater soybean yields than inoculation with 532 C (6.2% increase, averaged across the 2 yr) or the wildtype USDA 110 (9.9% increase, averaged across the 2 yr). These increases were largely due to increases in pod and seed number. These results showed that mutants that express nod genes in the absence of plant-to-bacteria signal compounds can help to overcome the low temperature limitation of soybean nodulation leading to improved growth and yield of soybean crops grown in areas with cool spring soils., THE FORMATION OF EFFECTIVE SOYBEAN nodules is a complex and highly regulated process that requires production and exchange of specific molecular signals between the host plant and the bacterial symbiont. [...]

Researchers report the first known identification of nitrogen-fixing bacteria in pulp and paper mill primary clarifiers. About half of the culturable cells contained nitrogenase and 90% of these cells were identified as Klebsiella strains.

Results reveal that mutations affecting the degradation pathway of poly-3-hydroxybutyrate occur on the chromosome and the megaplasmid of the bacterium. Data on the chromosomal loci are presented.

Mutations that mediated the ability of Pck-deficient Rhizobium meliloti mutants to utilize succinate and tricarboxylic acid (TCA) intermediates were analyzed to characterize the biosynthesis of phosphoenolpyruvate (PEP). The activity of pyruvate orthophosphate dikinase (PPDK) in Rhizobium (Sinorhizobium) meliloti was enhanced by pckA suppressor mutations. Gluconeogenesis from malate in the pckA suppressor strain was also mediated by the combined activities of malic enzyme and PPDK.

Diphosphopyridine-nucleotide-dependent malic enzyme (DME) of Rhizobium meliloti is needed for symbiotic nitrogen fixation since it forms a pathway in which malate is converted to acetyl-CoA in bacteroids. This enzyme shows maximal activity with NAD+ as cofactor but has reduced activity when NADP+ is used. Acetyl-CoA strongly inhibited DME activity but not TME activity. The dme gene was expressed in free-living cells and in nitrogen-fixing bacteroids while tme gene was repressed in bacteroids.

The tme gene of Rhizobium meliloti which encodes the triphosphopyridine nucleotide (NADP+)-dependent malic enzyme was cloned and localized to a 3.7-kb region. It was discovered that (NADP+)-dependent malic enzyme activity was not needed for N2 fixation, as tme mutants induced N2-fixing root nodules on alfalfa. Also, the apparent (NADP+)-dependent malic enzyme activity observed in wild-type activity appeared to be caused by the utilization of NADP+ by (NAD+)-dependent malic enzyme.

Tn5 insertion and subcloning of the phosphoenolpyruvate carboxykinase (pckA) gene of Rhizobium meliloti helps map and analyze the DNA sequence and expression of this gene. A 536-amino-acid protein is encoded by pckA, which is expressed in enhanced levels in cells with succinate or arabinose as carbon sources. Primer extension analysis of this gene's promoter suggests that it belongs to the sigma70 class of promoters.

Research has been conducted on replicated river biofilms cultivated in rotating annular reactors. The effect of seasonal variations and nutrient inputs on biofilms' genetic compositions and physiological activities has been investigated via the use of physiological and molecular biology techniques.

Examines the effect of cool soil temperature on soybean plant growth and yield in Quebec. Increase in nitrogen fixation and yield due to the addition of genistein to soybean inocula; Details on the law temperature limitation of soybean nodulation; Improvement of growth and yields of soybean grown in cool spring soils.

Endophytic bacteria reside within plant tissues and have often been found to promote plant growth. Fourteen strains of putative endophytic bacteria, not including endosymbiotic Bradyrhizobium strains, were isolated from surface-sterilized soybean (Glycine max. (L.) Merr.) root nodules. These isolates were designated as non-Bradyrhizobium endophytic bacteria (NEB). Three isolates (NEB4, NEB5, and NEB17) were found to increase soybean weight when plants were co-inoculated with one of the isolates and Bradyrhizobium japonicum under nitrogen-free conditions, compared with plants inoculated with B. japonicum alone. In the absence of B. japonicum, these isolates neither nodulated soybean, nor did they affect soybean growth. All three isolates were Gram-positive spore-forming rods. While Biolog tests indicated that the three isolates belonged to the genus Bacillus, it was not possible to determine the species. Phylogenetic analysis of 16S rRNA gene hypervariant region sequences demonstrated that both NEB4 and NEB5 are Bacillus subtilis strains, and that NEB17 is a Bacillus thuringiensis strain.Key words: root nodule, endophytic bacteria, plant-growth-promoting bacteria, Bacillus subtilis, Bacillus thuringiensis.Les bactéries endophytes sont des bactéries qui résident à l'intérior des tissus végétaux. Plusieurs études ont démontré la capacité de ces bactéries à favoriser la croissance des plantes. Quatorze souches de bactéries endophytes ont été isolées à partir de nodules de soya (Glycinemax (L.) Merr.) stérilisés en surface. Ces isolats ont été désignées comme étant des bactéries endophytes n'appartenant pas au genre Bradyrhizobium (NEB). Lorsque co-inoculés avec Bradyrhizobium japonicum, trois isolats (NEB4, NEB5 et NEB17) se sont avérées capable d'augmenter le poids de plantes soya. En absence de la souche de B. japonicum, ces même isolats ont été incapable d'affecter la croissance des plants ou de noduler. NEB4, NEB5 et NEB17 sont des bactéries Gram positives formant des spores. Des essais Biolog n'ont pas permis l'obtention d'une identification au niveau de l'espèce, mais ont quand même indiqué que les trois souches appartiennent au genre Bacillus. L'analyse phylogénétique des séquences d'une région très variable du gène 16S rARN a démontré que NEB4 et NEB5 sont des souches appartenant à l'espèce Bacillus subtilis, et que NEB17 est une souche appartnenant à l'espèce Bacillus thuringiensis.Mots clés : nodosités racinaires, bactérie endophyte, bactérie favorisant la croissance des plantes, Bacillus subtilis, Bacillus thuringiensis.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

DEAE-cellulose chromatography of extracts of free-living Rhizobium meliloti cells revealed separate NAD+-dependent and NADP+-dependent malic enzyme activities. The NAD+ malic enzyme exhibited more activity with NAD+ as cofactor, but also showed some activity with NADP+. The NADP+ malic enzyme only showed activity when NADP+ was supplied as cofactor. Three independent transposon-induced mutants of R. meliloti which lacked NAD+ malic enzyme activity (dme-) but retained NADP+ malic enzyme activity were isolated. In an otherwise wild-type background, the dine mutations did not alter the carbon utilization phenotype; however, nodules induced by these mutants failed to fix N2. Structurally, these nodules appeared to develop like wild-type nodules up to the stage where N2-fixation would normally begin. These results support the proposal that NAD+ malic enzyme, together with pyruvate dehydrogenase, functions in the generation of acetyl-CoA required for TCA cycle function in N2-fixing bacteroids which metabolize C4-dicarboxylic acids supplied by the plant. [ABSTRACT FROM AUTHOR]

The goal of this study was to initiate investigation of the genetics of bacterial poly-3-hydroxybutyrate (PHB) metabolism at the community level. We constructed metagenome libraries from activated sludge and soil microbial communities in the broad-host-range IncP cosmid pRK7813. Several unique clones were isolated from these libraries by functional heterologous complementation of a Sinorhizobium meliloti bdhA mutant, which is unable to grow on the PHB cycle intermediate D-3-hydroxybutyrate due to absence of the enzyme D-3-hydroxybutyrate dehydrogenase activity. Clones that conferred D-3-hydroxybutyrate utilization on Escherichia coli were also isolated. Although many of the S. meliloti bdhA mutant complementing clones restored D-3-hydroxybutyrate dehydrogenase activity to the mutant host, for some of the clones this activity was not detectable. This was also the case for almost all of the clones isolated in the E. coli selection. Further analysis was carried out on clones isolated in the S. meliloti complementation. Transposon mutagenesis to locate the complementing genes, followed by DNA sequence analysis of three of the genes, revealed coding sequences that were broadly divergent but lay within the diversity of known short-chain dehydrogenase/reductase encoding genes. In some cases, the amino acid sequence identity between pairs of deduced BdhA proteins was <35%, a level at which detection by nucleic acid hybridization based methods would probably not be successful. [ABSTRACT FROM AUTHOR]

When nano-sized titanium dioxide (nano-TiO 2 ) absorbs ultra-violet (UV-A) radiation, it produces reactive oxygen species that can be toxic to bacteria. We used the agronomically beneficial nitrogen-fixing bacterium Sinorhizobium meliloti strain 1021 as a model microorganism to detect nano-TiO 2 toxicity. Sinorhizobium meliloti was exposed to aqueous dispersions of micrometer-sized TiO 2 (micron-TiO 2 , 44 μm) or nanometer-sized TiO 2 (nano-TiO 2 , 21 nm) at nominal concentrations of 0, 100, 300, 600, 900, and 1800 mg TiO 2 /L. There were fewer viable S. meliloti cells after exposure to nano-TiO 2 under dark and UV-A light conditions. Nano-TiO 2 was more toxic to S. meliloti with UV-A irradiation (100% mortality at 100 mg TiO 2 /L) than under dark conditions (100% mortality at 900 mg TiO 2 /L). Micron-TiO 2 concentrations less than 300 mg TiO 2 /L had no effect on S. meliloti viability under dark or UV-A light conditions. Exposure to 600 mg/L or more of micron-TiO 2 under UV-A light could also photo-kill S. meliloti cells (100% mortality). Further studies are needed to ascertain whether nano-TiO 2 interferes with the growth of N 2 -fixing microorganisms in realistic agricultural environments.