Nutrition and Growth Characteristics of Trichomitopsis termopsidis, a Cellulolytic Protozoan from Termites

Putatively axenic cultures of Trichomitopsis termopsidis 6057, isolated by M. A. Yamin (J. Protozool. 25:535-538, 1978) from the hindgut of Zootermopsis termites, apparently contained methanogenic bacteria, inasmuch as small amounts of CH₄ were produced during growth. However, T. termopsidis could be “cured” of methanogenic activity by incubation in the presence of bromoethanesulfonate. Both the cured derivative (6057C) and the parent strain (6057) required NaHCO₃ and fetal bovine serum for good growth; the presence of yeast extract in media was stimulatory. Growth of both strains was markedly improved by substituting heat-killed cells of Bacteroides sp. strain JW20 (a termite gut isolate) for heat-killed rumen bacteria in media as a source of bacterial cell material. Heat-killed Bacteroides sp. strain JW20 was the best of a number of bacteria tested, and under these conditions H₂ was a major protozoan fermentation product. Growth of T. termopsidis strains was further improved by co-cultivation in the presence of Methanospirillum hungatii. M. hungatii was the best of a number of H₂-consuming bacteria tested, and under these conditions CH₄, but not H₂, was produced, indicating interspecies transfer of H₂ between the protozoa and M. hungatii. Both strains of T. termopsidis used powdered, particulate forms of cellulose (e.g., pure cellulose, corncob, cereal leaves) as fermentable energy sources, although powdered wood, chitin, or xylan supported little or no growth. Cells of the cellulose-forming coccus Sarcina ventriculi also served as a fermentable energy source, but these were used poorly as a source of bacterial cell material. The only substantial difference between T. termopsidis 6057 and 6057C was that the latter grew poorly or not at all with rumen bacteria as a source of bacterial cell material. The improved growth of T. termopsidis in vitro should facilitate further studies on the cell biology and biochemistry of these symbiotic, anaerobic protozoa.