- Volume 137, Issue 1, 1991

Summary: Helicobacter pylori is the major aetiological agent of gastroduodenitis in humans. Due to the potential importance of catalase in the growth and survival of Helicobacter pylori on the surface of inflamed mucosae, we have characterized catalase from H. pylori as a prelude to further studies on the function of the enzyme in vivo. The catalase activity of H. pylori was significantly affected by the presence of blood, serum or erythrocytes in the growth medium: the greatest activity was expressed when the bacterium was grown on medium containing serum. H. pylori catalase is a tetramer with a subunit M r of 50000. The enzyme had a pI of 9·0–9·3, was active over a broad pH range and was stable at 56 °C. It was non-competitively inhibited by sodium azide, and had no detectable peroxidase activity. The K m for the purified catalase was measured as 43 · 3 mm-H2O2 and the V as 60 ± 3 mmol H2O2 min-1 (mg protein)-1. The native catalase has absorption maxima at 280 nm and 405 nm with further minor shoulders or peaks at 510 nm, 535 nm and 625 nm, consistent with the presence of an iron-porphyrin prosthetic group.

Standardized experimental conditions were established to test the role of sucrose in the regulation and control of its metabolism in Streptococcus salivarius. A fresh isolate of S. salivarius was used. The extracellular dextranase activity of cells grown on sucrose was 10-fold higher than that of cells grown on glucose, fructose or galactose. This activity increased in less than 5 min following the addition of sucrose to galactose-grown cells, a phenomenon which was affected by neither rifampicin nor chloramphenicol which inhibit transcription and translation, respectively. Extracellular fructanase activity was 2-fold higher when cells were grown on sucrose than when they were grown on the other sugars. This increase also occurred within 5 min, but was diminished by transcriptional and translational inhibitors. De novo synthesis was required for the production of extracellular glucosyltransferase (GTF) activity which, upon the addition of sucrose, became associated with the cell surface. Conversely, cell-associated fructosyltransferase (FTF) activity appeared to require genetic induction for its production and cell-surface association, but required sucrose for its release from the surface framework. Versatility in the control mechanisms of this complex set of enzymes allows their expression and function to be regulated at several widely separated stages in the life histories of these proteins.

The level and pattern of rhizosphere competence of a strain of Trichoderma harzianum (1295-22) derived from fusing protoplasts of auxotrophic mutants of the prototrophic strains T12 and T95 were studied and compared with those of the original strains. Colonization of the rhizosphere by the three strains was tested after treating seeds of cotton and maize with conidia and planting them in soil at a constant moisture content. Propagules of the fungi were removed by a washing technique, Trichoderma spp. were isolated by plating serial dilutions on a selective medium, and individual strains were identified by their characteristic growth on differential media. Both strains T12 and T95 colonized the entire length of maize roots, but strain 1295-22 was more effective in colonizing the middle sections of the roots than either parental strain. All strains colonized cotton roots more poorly than maize roots; strains T12 and T95 were not detected on some root segments of this crop. Strain T95 was, however, found on the root tip, while T12 was absent from this root portion. Conversely, strain 1295-22 colonized all root sections of this crop, and its population levels were higher in the middle root portions than those of either parental strain.

This study describes a computer-based technique for classifying and identifying bacterial samples using Fourier-transform infrared spectroscopy (FT-IR) patterns. Classification schemes were tested for selected series of bacterial strains and species from a variety of different genera. Dissimilarities between bacterial IR spectra were calculated using modified correlation coefficients. Dissimilarity matrices were used for cluster analysis, which yielded dendrograms broadly equated with conventional taxonomic classification schemes. Analyses were performed with selected strains of the taxa Staphylococcus, Streptococcus, Clostridium, Legionella and Escherichia coli in particular, and with a database containing 139 bacterial reference spectra. The latter covered a wide range of Gram-negative and Gram-positive bacteria. Unknown specimens could be identified when included in an established cluster analysis. Thirty-six clinical isolates of Staphylococcus aureus and 24 of Streptococcus faecalis were tested and all were assigned to the correct species cluster. It is concluded that: (1) FT-IR patterns can be used to type bacteria; (2) FT-IR provides data which can be treated such that classifications are similar and/or complementary to conventional classification schemes; and (3) FT-IR can be used as an easy and safe method for the rapid identification of clinical isolates.