Properties of mutacin b, an antibacterial substance produced by Streptococcus mutans strain BHT

An antibacterial substance produced by strain BHT of Streptococcus mutans (mutacin b) was found to be a small molecule (MW 3,500-6,000) with remarkable resistance to temperature, alkali and various solvents. Enzyme sensitivity tests of partially purified preparations indicated that mutacin b is a peptide. It is sensitive to several proteolytic enzymes and its lethal effects on sensitive cells can be prevented by adding trypsin to cells exposed to mutacin b. High concentrations of mutacin b inhibited the growth of producer cells, indicating that strain BHT is only partially immune to this substance.     

Diversity of CTX-M beta-lactamases and their promoter regions from Enterobacteriaceae isolated in three Parisian hospitals

Nine clinical isolates of Enterobacteriaceae (six Escherichia coli and three Proteus mirabilis) isolated in three Parisian hospitals between 1989 and 2000 showed a particular extended-spectrum cephalosporin-resistance profile characterized by resistance to cefotaxime and aztreonam but not to ceftazidime. CTX-M-1, CTX-M-2, CTX-M-9, CTX-M-14 and two novel plasmid-mediated CTX-M beta-lactamases (CTX-M-20, and CTX-M-21) were identified by polymerase chain reaction and isoelectric focusing (pI>8) and were associated in eight cases with TEM-1 (pI=5.4) or TEM-2 (pI=5.6) beta-lactamases. We used internal ISEcp1 and IS26 forward primers and the CTX-M consensus reverse primer to characterize the CTX-M beta-lactamase promoter regions and showed their high degree of structure diversity. We found upstream of some bla(CTX-M) genes, a 266-bp sequence 100% identical to the sequence upstream of the Kluyvera ascorbata beta-lactamase gene, suggesting that this chromosomal enzyme is the progenitor of the CTX-M-2/5 cluster.     

Characteristics of three phages infectious for psychrophilic fishery isolates ofPseudomonas putrefaciens

Three phages capable of infecting at 2 C strains ofPseudomonas putrefaciens from fish were isolated and characterized. Two phages were extremely sensitive to 55 C. DNA base composition of the three phages, based on Tm measurements, were 36.4, 40.0 and 48.8% G+C. Only one phage plaqued at a lower efficiency in the presence of citrate, none were inhibited by indole, while the plating efficiency of all three was reduced by oxalate. One phage was found to be obligately psychrophilic on its original propagating host and was unable to plaque at 20 C even though the host grew well up to 27 C. This investigation was supported by Public Health Service research grant EF-00863-2. We would like to thank Dr. S. C. Holt for assistance in the electron microscopy portion of this work.     

Bacteriophages of psychrophilic pseudomonads. II. Host range of phage active againstPseudomonas putrefaciens

Forty phages active against 4 terrestrial and against 10 of 24 marine strains ofP. putrefaciens were isolated from raw municipal sewage, fish-pier water, and refrigerated haddoch fillets. With one exception, phages active against marine strains were obtained only from pier water and fish fillets. Only two strains were attacked solely by their homologous phage while five of the marine strains were not attacked by any phage. Lytic reactions revealed no obvious differences between marine and terrestrial strains.Detectable bacteriocins were not produced by any of the strains and only one strain was found to be lysogenic. Most of the phages were capable of forming plaques at 2 G, regardless of the temperature at which they were isolated.The present work represents part of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at the University of Massachusetts.This investigation was supported by Public Health Service Grant EF-00873-2 from the Division of Environmental Engineering and Food Protection.     

Sensitivity of respiratory metabolism and efficiency to foliar nitrogen during growth and maintenance

Scaling of respiration from the leaf to the canopy level currently depends on identification of physiological parameters that are tightly linked to respiration and that can readily be determined. Several recent studies have helped provide guides to predicting whole canopy respiration on the basis of foliar nitrogen (N). This approach is potentially powerful owing to the well‐described patterns of allocation of N that follow interception of radiation. In the present study, we investigated the sensitivity of the N–respiration correlation to environmental and developmental factors, in order to evaluate its usage for attempts to scale respiration to the organism and ecosystem level. We studied fully expanded, 1 and 2‐year‐old, and current‐year needles from canopies of Pinus radiata that had been treated (unthinned, thinned and thinned+fertilized treatments) in ways likely to induce a wide range of growth and respiratory responses. We examined respiration in detail during the growth period in spring and again at the end of summer, using calorespirometric methods (combined measurements of CO₂ and heat rates) to determine the respiration rates , instantaneous enthalpic growth rates (R_SGΔH_B, a measure of the conservation of electrons in anabolic products) and the enthalpy conversion efficiency (η_H) of needles differing in age. A general linear model revealed that was positively correlated with needle N, but this correlation was strongly dependent on the season and the needle age – indicating an important physiological difference between expanding young needles and fully expanded old needles. Furthermore, the strength of the correlation between needle N and respiration was comparatively weak for the current year, expanding foliage, indicating that factors other than foliage N significantly influenced the respiration of young needles. The analysis of instantaneous growth rates revealed two general processes. Older, nonexpanding foliage showed considerable rates of enthalpic growth (increases in enthalpy) that was mainly caused by the increment of lignin during secondary growth. Secondly, canopy development appeared dynamic and to be optimized according to environmental drivers and constraints – such as light and water availability. In late spring, needle extension slowed in the upper, but not the lower canopy, because the upper canopy appeared to be affected first by the onset of drought stress in late spring. Growth rates were reduced in the upper canopy despite greater rates of respiration, indicating higher demand of ATP for the maintenance of protein and for export of sugars. Consequently, the enthalpy conversion efficiency and enthalpic N productivity (enthalpic growth per unit N) were comparatively poor indicating advanced development of needles in the upper canopy. We suggest that the growth and maintenance paradigm of respiration is, at best, only moderately useful when applied to whole trees, and is not valid at the cellular level or that of the plant organ. A different concept, namely that of respiratory efficiency, seems a more suitable way to represent respiration in carbon (C) balance models and should help provide a better mechanistic understanding of how respiration affects the C conversion efficiency of plants, and ultimately the net primary productivity of ecosystems.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.