Isolation, characterization, and identification of Geobacillus thermodenitrificans HRO10, an alpha-amylase and alpha-glucosidase producing thermophile.

Thermophilic and amylolytic aerobic bacteria were isolated from soil through a selective enrichment procedure at 60 degrees C with starch as the carbon source. One of the isolates designated as HRO10 produced glucose aside from limit dextrin as the only hydrolysis product from starch and was characterized in detail. The starch-degrading enzymes produced by strain HRO10 were determined to be alpha-amylase and alpha-glucosidase. Whereas the alpha-amylase activity was detected exclusively in the culture supernatant, alpha-glucosidase occurred intracellular, extracellular, or on the surface of the bacteria depending on the growth phase. The optimum temperature and pH required for the growth of strain HRO10 were about 50 degrees C and pH 6.5 to 7.5. The strain used different carbohydrates as the carbon source, but the maximum production of alpha-amylase occurred when 1.0% (w/v) starch or dextrin was used. The use of organic vs. inorganic nitrogen favored the production of alpha-amylase in strain HRO10. The metal ions Li+, Mg2+, and Mn2+ stimulated the production of both enzymes. Identification of strain HRO10 by physiological and molecular methods including sequencing of the 16S rDNA showed that this strain belongs to the species Geobacillus thermodenitrificans. Biochemically, strain HRO10 differs from the type strain DSM 465 only in its ability to hydrolyze starch.

Wide geographic distribution of bacteriophages that lyse the same indigenous freshwater isolate (Sphingomonas sp. strain B18).

An indigenous freshwater bacterium (Sphingomonas sp. strain B18) from Lake Plubetasee (Schleswig-Holstein, Germany) was used to isolate 44 phages from 13 very different freshwater and brackish habitats in distant geographic areas. This bacterial strain was very sensitive to a broad spectrum of phages from different aquatic environments. Phages isolated from geographically distant aquatic habitats, but also those from the same sample, were diverse with respect to morphology and restriction pattern. Some phages were widely distributed, while different types coexisted in the same sample. It was concluded that phages could be a major factor in shaping the structure of bacterial communities and maintaining a high bacterial diversity.

Stenotrophomonas rhizophila sp. nov., a novel plant-associated bacterium with antifungal properties.

A polyphasic taxonomic study was performed on 16 Stenotrophomonas strains from environmental and clinical sources. A group of three plant-associated isolates were shown to be phenotypically different from the other strains. This group formed a separate physiological cluster (B1) with 42% heterogeneity to the other isolates. The defining characteristics of the new species were as follows: growth at 4 degrees C and the absence of growth at 40 degrees C; the utilization of xylose as a carbon source; lower osmolytic tolerance (< 4.5% NaCl, w/v), although the isolates can produce trehalose and glucosylglycerol as osmoprotective substances; the absence of lipase and beta-glucosidase production; and antifungal activity against plant-pathogenic fungi. The whole-cell fatty acid profile of this group was different and characterized by the main fatty acids iso-C15:0 and anteiso-C15:0. Numerical analysis of the fatty acid profiles of the strains examined supports the differentiation of the physiological B1 group. By 16S rDNA analysis, three clusters were distinguished. The three strains of the B1 group formed a separate environmental cluster (E1). They showed a mean similarity of 99.5% within the cluster, and differed from strains of a second environmental cluster (E2) by 2.2% and from the clinical cluster (C) by about 3.0%. DNA-DNA hybridization data supported the taxonomic differentiation. All results led to the proposal of a new species, Stenotrophomonas rhizophila sp. nov., with strain e-p10(T) (= DSM 14405(T) = ATCC BAA-473(T)) as the type strain.