The dominant rumen bacteria in high-arctic Svalbard reindeer were characterized, their population densities were estimated, and ruminal pH was determined in summer, when food quality and availability are good, and in winter, when they are poor. In summer the total cultured viable population density was (2.09 1.26) x 1010 cells ml-1, whereas in winter it was (0.36 ± 0.29) x 1010 cells ml-', representing a decrease to 17% of the summer population density. On culture, Butyrivibriofibrisolvens represented 22% of the bacterial population in summer and 30% in winter. Streptococcus bovis represented 17% of the bacterial population in summer but only 4% in winter. Methanogenic bacteria were present at 104 cells ml-' in summer and 107 cells mlV1 in winter. In summer and winter, respectively, the proportions of the viable population showing the following activities were as follows: starch utilization, 68 and 63%; fiber digestion, 31 and 74%; cellulolysis, 15 and 35%; xylanolysis, 30 and 58%; proteolysis, 51 and 28%; ureolysis, 40 and 54%; and lactate utilization, 13 and 4%. The principal cellulolytic bacterium was B. fibnisolvens, which represented 66 and 52% of the cellulolytic population in summer and winter, respectively. The results indicate that the microflora of the rumen of Svalbard reindeer is highly effective in fiber digestion and nitrogen metabolism, allowing the animals to survive under the austere nutritional conditions typical of their high-arctic habitat.

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The microbial populations of the rumens of seaweed-fed and pasture-fed Orkney sheep were examined. The populations in the pasture-fed sheep were similar to those of other domestic ruminants fed on land plants, but those of the seaweed-fed animals showed major differences in the dominant species. Total ciliate populations were quantitatively similar, but in the seaweed-fed animals Dasytricha ruminantium was one of the most dominant species. No phycomycete fungi or cellulolytic bacteria were found in the seaweed-fed animals, and the bacterial population was dominated by Streptococcus bovis, Selenomonas ruminantium, Butyrivibrio fibrisolvens and lactate-utilizing species. Electron microscopy revealed that spirochaetes and an unidentified filamentous bacterium were probably of major significance in seaweed digestion. The ability of bacterial strains from both groups of animals to metabolize plant and algal constituents was examined.

The dominant cecal bacteria in the high-arctic Svalbard reindeer were characterized, their population densities were estimated, and cecal pH was determined in summer, when food quality and availability is good, and in winter, when it is very poor. In summer the total culturable viable bacterial population was (8.9 ± 5.3) x 108 cells mn1-1, whereas in winter it was (1.5 ± 0.7) x 108 cells ml-, representing a decrease to 17% of the summer population density. Of the dominant species of cultured bacteria, Butyrivibriofibrisolvens represented 23% in summer and 18% in winter. Streptococcus bovis represented 17% in summer and 5% in winter. Bacteroides ruminicola represented 10% in summer and 26% in winter. In summer and winter, respectively, the proportion of the viable population showing the following activities was as follows: fiber digestion, 36 and 48%; cellulolysis, 10 and 6%; xylanolysis, 33 and 48%;, and starch utilization, 77 and 71%. The most abundant cellulolytic species in summer was Butyrivibrio fibrisolvens, representing 62% of the total cellulolytic population, and in winter it was Ruminococcus albus, representing 80% of the total cellulolytic population. The most abundant xylanolytic species in summer was Butyrivibrio fibrisolvens, and in winter it was Bacteroides ruminicola, representing 59 and 54% of the xylanolytic isolates in summer and winter, respectively. The cecal bacterial of the Svalbard reindeer have the ability to digest starch and the major structural carbohydrates of the diet that are not digested in the rumen. The cecum in these animals has the potential to contribute very substantially to the digestion of the available plant material in both summer and winter. Svalbard reindeer (Rangifer tarandus platyrhynchus) survive utnder the most austere nutritional conditions on the high-arctic archipelago of Svalbard (770 to 810 N) (see Orpin et al. [19]). To survive under such conditions it is imperative for the animals to digest the poor-quality, fibrous plants which are available in winter as well as to make maximum use of the summer forage rich in seed heads (21, 23). Recently, Orpin et al. (19) have shown that a highly specialized rumen microflora, which is particularly effective in fiber digestion, probably contribute substantially to this end. During the summer these animals feed for more than 50 to 60% of the 24-h day (18), and it is likely that the flow rate of digesta from the rumen is high, containing plant tissues which are not digested in the rumen. Indeed, we have observed large fragments of plant tissues, including nearly intact mosses, in the cecal contents of Svalbard reindeer in summer.

~ ~~ ~The haem requirement for growth of the rumen chytridiomycete Neocalfimastix frontalis H8 was satisfied by haem, haemin, haematin, mesoporphyrin IX, coproporphyrins I and 111, uroporphyrins I and 111, but not deuteroporphyrin IX. Porphyrin degradation products and precursors of porphyrin synthesis did not support growth. Protoporphyrin IX and haematoporphyrin IX supported growth, indicating that the organism contains ferrochetalase, but was unable to synthesize the porphyrin ring. Haem could be provided by catalase and peroxidase, but not by cytochrome c. Zoosporogenesis was induced in N . frontalis H8 in rumen fluid principally by haem, haemin and haematin, and to a smaller extent by catalase, peroxidase and protoporphyrin IX. Haem precursors and degradation products were ineffective. Chlorophylls a and b and their ruminal degradation products, plant fraction 1 protein and chelated iron neither stimulated growth nor induced zoosporogenesis. Haem induced partial zoosporogenesis in haemlimited cultures and suspensions of sporangia grown in vitro.