Ribosomes, Polyribosomes, and Deoxyribonucleic Acid from Thermophilic, Mesophilic, and Psychrophilic Clostridia

Abstract

Analysis of deoxyribonucleic acid (DNA) from four species of Clostridium , including two thermophiles, a mesophile, and a psychrophile, revealed no obvious relationship between growth temperature and DNA base composition. The melting temperatures (T m ) of the DNA from the four species varied no more among the thermophilic, mesophilic, and psychrophilic species than among many related mesophilic species. Characterization of ribosomes from the clostridia by means of optical rotatory dispersion yielded similar spectra in common with other unrelated organisms. Only small differences were noted in the base composition of ribosomal ribonucleic acid (RNA) and in the amino acid composition of ribosomal proteins, including half-cystine content, as determined by cysteic acid analysis, and accessible sulfhydryl groups, as determined by titration with dithiobis (2-nitrobenzoic acid). Except for the two thermophiles, the ribosomal protein electrophoretic patterns were dissimilar. No unusual thermal stability was manifested in the T m values of thermophile ribosomal RNA. However, thermophile ribosome T m values (69 C) were higher than were mesophile and psychrophile T m values (64 C). Ribosomes from the four clostridial species were also examined in regard to the effect of heat on their functional integrity, measured by their activity in poly U-directed 14 C-phenylaline incorporation, and their gross physical integrity, measured by sucrose gradient analysis. The T d, 5 values (temperature which produces 50% inactivation after 5 min) was found to be 70 and 72 C for the two thermophiles C. tartarivorum and C. thermosaccharolyticum , respectively; 57 C for a mesophile, C. pasteurianum ; and 53 C for a psychrophile, Clostridium sp. strain 69. At 55 C, little effect was seen on the thermophile ribosomes, but the mesophile ribosomes lost 90% of their activity in 1 hr, and psychrophile ribosomes lost 100% of their activity within 10 min. According to sucrose gradient profiles, heating at 55 C results in dissociation of mesophile ribosomes and aggregation of psychrophile ribosomes. Thermophile S-100 fractions were also more thermostable than were mesophile or psychrophile S-100 fractions. The T d, 5 values were 69 C for C. tartarivorum and C. thermosaccharolyticum S-100 and 41 C for C. pasteurianum and Clostridium sp. strain 69 S-100. The effect of heat on the endogenous incorporation of 14 C-valine by polysomes was also examined. In the case of thermophile polysomes, the extent of incorporation at 55 and 37 C was about equal. In the case of mesophile and psychrophile polysomes, the extent at 55 C was 44 and 39%, respectively, of the value at 37 C. The initial rates of incorporation in all four cases were greater at 55 C than at 37 C.