A chloramphenicol-streptomycin-resistance plasmid from a clinical strain of Staphylococcus sciuri and its structural relationships to other staphylococcal resistance plasmids

A 5.1-kb plasmid, designated pSCS12, isolated from a naturally occurring Staphylococcus sciuri conferred resistance to chloramphenicol (CmR) and streptomycin (SmR). Restriction endonuclease analyses of pSCS12 revealed partial structural homologies to the CmR-plasmids pC221 from S. aureus and pSCS1 from S. intermedius, to the SmR-plasmids pSAI-1 from S. hyicus and pS194 from S. aureus, as well as to the CmR/SmR plasmid pSK68 from S. aureus. Southern-blot hybridization with specific CmR- and SmR-gene probes confirmed these similarities and allowed the mapping of the CmR- and SmR-determinants in the S. sciuri plasmid pSCS12. These observations lead to the suggestion that CmR/SmR-plasmids, such as pSCS12, may have evolved from CmR- and SmR-plasmids by interplasmidic recombination.     

Resistance in the wild crop relatives Avena macrostachya and Hordeum bogdani to the aphid Rhopalosiphum padi

In previous screening tests the two wild crop relatives Avena macrostachya (Bal., ex Coss. et Dur.) and Hordeum bogdani (Wil.) demonstrated a high degree of resistance to the aphid Rhopalosiphum padi (L.). In a choice situation using wild and cultivated oats and barley, alate aphids settled in lower numbers on the wild species. The results were, however, variable in the Avena combination. Nymph production was significantly higher, development time shorter and adult weight higher on the cultivated varieties. From the third instar and onwards the excretion of honeydew was significantly lower on the resistant plants. In general the honeydew contained less than 1% free amino acids although excreta from H. vulgare contained 3.5%. The percentage of free amino acids found in the honeydew was similar for all plant species (5.2–7.6%) except for H. vulgare, on which the aphids excreted 22% of the amounts ingested. Amino acids excreted in high proportions on all plants included asparagine, -aminobutyric acid, glutamic acid, and glycine. Tissue sectioning did not reveal any obvious mechanical barriers to stylet penetration. The potential use of these wild species as sources for aphid resistance breeding in oats and barley is considered.

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Résumè Lors d'examens systématiques antérieurs, Avena macrostachya (Bal. ex Coss. & Dur.) et Hordeum bogdani (Wil.) ont présenté une résistance élevée au puceron Rhopalosiphum padi (L.). Lorsqu'ils avaient un choix comprenant de l'avoine et de l'orge cultivés, les pucerons ailés ont atterri en nombres moins importants sur les espèces sauvages. Les résultats étaient cependant variables dans le complexe avoine. La production de nymphes et le poids des adultes étaient plus élevés sur espèces cultivées, ainsi que la durée du développement était plus longue sur les espèces sauvages. A partir du troisième stade, l'excrétion de miellat a été significativement plus faible sur les espèces résistantes. En général, le miellat y contenait moins de 1% d'acides aminés bien que sur H. vulgare il en contînt 3,5%. Les pourcentages d'acides aminés libres du miellat étaient semblables sur toutes les plantes (5,2–7,6%), à l'exception de H. vulgare sur lequel les pucerons excrétaient 22% des taux ingérés. Les acides aminés excrétés en fortes quantités sur les différentes plantes, comprenaient l'asparagine, l'acide -aminobutyrique, l'acide glutamique et la glycine. Des coupes de tissus n'ont révélé aucun obstacle mécanique clair à la pénétration des stylets. Les possibilités d'utiliser ces espèces sauvages comme source de résistance aux pucerons dans la sélection de l'avoine et de l'orge ont été examinées.

     

Resistance of different lucerne cultivars to the pea aphid Acyrthosiphon pisum: influence of phloem composition on aphid fecundity

Sugars and amino acids were analysed in the phloem sap (sampling by the exudation method) of four clones of lucerne (Medicago sativa L.) characterized by their resistance to the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae). Differences in the qualitative amino acid balance are shown and a negative correlation between the reproductive rate of the aphid and the sugars/amino acids ratio is underlined. To demonstrate any causal relationship between these two variables, the reproduction of A. pisum on artificial diets copying the sap of the two extreme clones (resistant and susceptible) was measured. The results show that the resistance is not a simple nutritional effect; however, the amino acid balance contributes to the resistance exhibited by some cultivars.

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Résumé L'analyse (sucres et acides aminés) de la sève de 4 cultivars de luzerne (Medicago sativa) caractérisés pour leur résistance au puceron du pois (Acyrthosiphon pisum (Harris)) (Homoptera: Aphididae), est réalisée sur des exsudats de phloème. La teneur en sucres (exprimée en équivalent saccharose) montre d'importantes différences: rapport de 1 à 3 respectivement entre les clones sensible et résistant. La teneur globale en acides aminés exsudés varie en sens inverse, entraînant une corrélation négative pour les 4 clones étudiés entre le rapport sucre/acides aminés (0,6 à 3,6) et la résistance mesurée par le taux net de reproduction à 14 jours (78,5 à 11,2 larves/femelle). L'analyse des acidses aminés révèle de plus des différences qualitatives entre cultivars, notamment pour certains acides aminés essentiels méthionine, histidine, lysine, aromatiques.Le rôle de l'équilibre en acides aminés et en sacharose dans la résistance de certains cultivars au puceron du pois est apprécié par des mesures de la reproduction de A. pisum sur des milieux artificiels reproduisant le rapport sucre/acides aminés et/ou le spectre des acides aminés des 2 clones extrêmes (sensible et résistant). La résistance n'apparaît pas être le résultat d'une simple différence de la qualité nutritionnelle de la sève; la balance en acides aminés doit cependant participer pour une part à la résistance au puceron.

     

Negative interactions between Willamette mites and Pacific mites: possible management strategies for grapes

Willamette mites and Pacific mites are often negatively associated on grape vines. In particular, vineyards with early season infestations of the less damaging Willamette mite rarely develop high populations of the economically important Pacific mite. We report that Willamette mites had a negative effect on Pacific mite populations in both the greenhouse and field. In some experiments, the negative effect was more pronounced when vines had been damaged by previous feeding of Willamette mites and in other experiments concurrent feeding by both mite species was necessary to demonstrate a negative effect. Therefore, we cannot conclude if the mechanism of the response involves induced resistance against Pacific mites, more conventional interspecific competition, or both. Since predators were uncommon in our experiments, predator build up on Willamette mites did not cause the low Pacific mite population that we observed, although this mechanism may be important in many vineyards. Further, larger scale experiments are necesary to determine if growers can introduce Willamette mites to help control Pacific mites.

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Résumé E. willametti et T. pacificus sont souvent antagonistes dans les vignobles. En particulier, dans les vignobles contaminés tôt dans la saison par E. willametti,-dont les dégâts sont moins conséquents-, on observe rarement des populations élevées de T. pacificus, dont les dégâts sont économiquement importants. Nous avons constaté que E. Willametti a réduit les populations de T. pacificus, tant en serres qu'à l'extérieur. Dans quelques cas, l'effet antagoniste était plus marqué quand les vignes avaient été préalablement endommagées par l'alimentation de E. willametti. Dans d'autres expériences, la compétition alimentaire entre les deux espèces d'acariens était nécessaire pour produire un effet antagoniste. Cependant, nous ne pouvons pas en conclure que la réponse implique une résistance induite contre T. pacificus, ou une compétition interspécifique plus classique, ou les deux à la fois. Puisque les prédateurs étaient rares dans nos expériences, une explosion des prédateurs sur E. willametti n'a pu provoquer le faible niveau de population observé avec T. pacificus, bien qu'un tel méchanisme puisse être important dans certains vignobles. Quoi qu'il en soit, des expériences à plus grande échelle sont nécessaires pour déterminer si les vignerons peuvent introduire Eotetranychus willametti afin de limiter les populations de Tetranychus pacificus.

     

A nonconjugative mobilizable broad host range plasmid of Acinetobacter sp. that determines HgCl2 resistance

Summary HgCl₂-resistant strains of Acinetobacter sp. obtained from the soil at the Khaidarkan mercury mine (Kirghiz SSR) were found to contain, apart from large plasmids (60 kb), a small plasmid (7.5 kb) designated pKL1. It was established by conjugative crosses and transformation that pKL1 is a broad host range mobilizable plasmid and that it carries the Hg^r determinant. The restriction map of pKL1 was constructed; the site of the Hg^r determinant and the regions essential to replication were localized. A comparison of these results with earlier data suggests that microorganisms belonging to one microbiocenosis may carry Hg^r determinants on plasmids with highly different structures and properties.Deceased on July 16, 1985     

Interdependence of growth, water relations and abscisic acid level in Phaseolus vulgaris during waterlogging

The interdependence between changes in growth and water relations after waterlogging was investigated by recording simultaneously growth, transpiration, water potential, turgor, leaf diffusion resistance and abscisic acid content in Phaseolus vulgaris L. cv. bruine Noord-Hollandse. Growth was inhibited immediately after flooding, whereas transpiration decreased gradually to a low level in about three days. The first two days after flooding a small increase in abscisic acid content in the leaves was observed which was accompanied by an increase in diffusion resistance. The increase in abscisic acid content could result from an inhibited export from the leaves. After the first two days a decrease in water potential and turgor was accompanied by a drastic increase in both abscisic acid content and diffusion resistance. This large increase in abscisic acid content occurred before the turgor had reached its minimum value. The change in diffusion resistance kept showing a lag of about one day with the change in abscisic acid content. The possibility is discussed that besides abscisic acid also its metabolite phaseic acid is involved in stomatal closure. After the formation of adventitious roots on the hypocotyl, abscisic acid level, diffusion resistance, water potential and turgor returned to the control values. Transpiration showed a slow recovery from the sixth day after flooding, whereas growth was inhibited for at least nine days. A remarkable similarity exists between our observations on the responses of bean plants to flooding and the well known responses to drought.     

Isolation and cryopreservation of O-methylthreonine-resistant Rosa cell lines altered in the feedback sensitivity of l-threonine deaminase

O-Methylthreonine (OMT) inhibits the growth of plated Rosa cells (ID₅₀6·10^-6M). Isoleucine is able to reverse efficiently and specifically this OMT toxicity. From OMT-resistant colonies occurring at a frequency of 1.58·10^-7 variants per cell plated at 10^-4M OMT, the variant strains OMT^R-1 and OMT^R-2 were isolated, cloned via protoplasts and characterized. Both variants were ten times more resistant to OMT than the wildtype and were cross-resistant to another isoleucine analog, dl-4-thiaisoleucine. The resistant variants retained their resistance after storage for three years in liquid nitrogen. Both resistant strains were stable for several months when subcultured in the absence of OMT although it was shown in a reconstitution experiment that wildtype cells overgrow OMT^R-2 variant cells if co-cultivated for many passages in drug-free medium. One case of instability was observed upon long-term subculturing in drug-free medium: the strain OMT^R-1D^* partially lost phenotypic properties. Resistance to OMT was followed qualitatively by a new method based on inhibition-zone formation in cell suspensions plated in agar medium. The OMT-resistant variants showed a reduction in sensitivity of the enzyme l-threonine deaminase to feedback inhibition by isoleucine, a decreased stability of l-threonine deaminase when stored at-18°C or incubated at +55°C and a two- to threefold increase of the free isoleucine pool within the cells. The genetical events and the biochemical mechanisms which might lead to the observed stable and biochemically defined character are discussed with particular reference to the high ploidy level of the Rosa cell line.Abbreviations OMT l-O-methylthreonine - TD l-threonine deaminase