Twenty-four thermophilic bacteriophages have been isolated from diverse sources such as compost, soil, silage and rotting straw. Although considerable individual host specificity was observed, the phages were able to infect most of the major taxonomic groups of Bacillus thermophiles. The phages varied considerably in morphology and size; the phage heads were either cylindrical or polyhedral with tails varying in length between 15 and 500 nm. Most of the phages were stable at 50 degrees C for 4-5 h but at 70 degrees C the plaque-forming units decreased by between 10(2)- and 10(7)-fold in 2 h. The DNA of morphologically similar phages was examined by restriction enzyme analysis, and some differences in the DNA fragment patterns were found. Efficiency of plating data indicated that 'B. caldotenax' has a restriction and modification system. These phages may be valuable for the study of the genetics of thermophilic bacilli: transduction of 'B. caldotenax' and 'B. caldovelox' by phage JS017 has been observed.
Several closely related, xylanolytic, thermophilic bacilli were isolated from local soils on xylose-containing minimal medium. On the basis of morphology and biochemical characteristics, one of the isolates, designated strain S1812 T (T l type strain), was studied further. Strain S1812 T was a xylanolytic, sporulating, Gram-positive, rod-shaped bacterium. Its Gram-positive nature was confirmed by electron microscopic examination of thin sections of the cells. The isolate was a thermophilic (optimum temperature for growth, 65 SC), facultative anaerobe that grew on a wide range of carbon sources including glucose, lactose, starch and xylose. It expressed high levels of both xylose isomerase and xylulokinase on xylose and also on glucose. The DNA GMC content was 44 mol %. rRNA gene sequence analysis placed strain S1812 T in Bacillus cluster 5 ; it was more closely related to Saccharococcus thermophilus than to thermophilic Bacillus species. DNA-DNA hybridization also indicated its close relationship to S. thermophilus. Based on the evidence presented, it is proposed that strain S1812 T be designated Saccharococcus caldoxylosilyticus sp. nov. Strain S1812 T is the type strain (l ATCC 700356 T l DSM 97-987 T ).
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