MESOPHILIC CELLULOLYTIC CLOSTRIDIA FROM FRESH-WATER ENVIRONMENTS

Eight strains of obligately anaerobic, mesophilic, cellulolytic bacteria were isolated from mud of freshwater environments. The isolates (C strains) were rod-shaped, gram negative, and formed terminal spherical to oval spores that swelled the sporangium. The guanine plus cytosine content of the DNA of the C strains ranged from 30.7 to 33.2 mol% (midpoint of thermal denaturation). The C strains fermented cellulose with formation primarily of acetate, ethanol, CO(2), and H(2). Reducing sugars accumulated in the supernatant fluid of cultures which initially contained ≥0.4% (wt/vol) cellulose. The C strains resembled Clostridium cellobioparum in some phenotypic characteristics and Clostridium papyrosolvens in others, but they were not identical to either of these species. The C strains differed from thermophilic cellulolytic clostridia (e.g., Clostridium thermocellum) not only in growth temperature range but also because they fermented xylan and five-carbon products of plant polysaccharide hydrolysis such as d-xylose and l-arabinose. At 40°C, cellulose was degraded by cellulolytic mesophilic cells (strain C7) at a rate comparable to that at which C. thermocellum degrades cellulose at 60°C. Substrate utilization and growth temperature data indicated that the C strains contribute to the anaerobic breakdown of plant polymers in the environments they inhabit

THERMAL HISTORY, CHEMICAL-COMPOSITION AND RELATIONSHIP OF COMETS TO THE ORIGIN OF LIFE

It is generally believed that a comet consists basically of a loose conglomeration of frozen gases with embedded material similar to that found in the carbonaceous chondritic meteorites, and consequently that comets may be nearly pristine samples of the original solar nebula1−5. We show here that thermal processing within comets could have played an important part in determining their present state; in particular, we find that liquid water might have been available in some comets over geologically and biologically significant spans of time. It follows that a cometary origin is not excluded for some thermally metamorphosed meteorites and asteroids, that comets may contain quite complex organic molecules, and that comets may have played a role in the origin and conceivably even in the subsequent evolution of terrestrial life