Ammonia-oxidizing chemoautotrophic Nitrosomonas europaea ATCC 25978 exhibited remarkable oxaloacetate-oxidative activity. Citrate(si)-synthase [EC 4.1.3.7.] was purified as an electrophoretic homogeneous protein. The molecular weight of the enzyme was estimated to be about 295, 000 (α_xβ_y) by gel filtration, suggesting that the enzyme consisted of two different subunits (α; 65, 000, β; 75, 000), as demonstrated by SDS-PAGE. The N-terminal sequences of α and β type enzyme proteins were Ala-Leu-Val-Ser-Leu-Arg-Gln-Leu-Leu. The isoelectric point of the enzyme was pH 5.2. The enzyme was stable up to 35°C and in a pH range between 6.0-8.0. The optimum pH for the reaction was 6.5-8.5 and the optimum temperature was 30-40°C. The apparent K_m values for oxaloacetate and acetyl-CoA were about 0.025 and 0.080mM, respectively. The enzyme was not inhibited by ATP (1mM), NADH (1mM) or 2-oxoglutamic acid (10mM). Activation by metal ions (0.1mM) was not observed.

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Seedlings of Picea jezoensis (Yezo spruce) are known to survive well on decayed wood whereas those on the ground are apt to die off due to the attack of plant pathogens. Therefore, microfloral characteristics in the decayed P. jezoensis wood were examined in respect to natural regeneration of the forest.
Microbial examination of the decayed wood indicated that Gram-positive but not spore-forming bacteria were dominant As the decayed wood was strongly acidic, the presence of acidophilic microorganisms was surveyed. Actinomycetes was shown to predominate in the surface layer of the deccayed wood. All of the isolates grew in the liquid medium of pH 4.5, but not above 7.5. However, the growth responses to the pH between 3.5 and 6.5 were different among the isolates. Diaminopimelic acid of all the isolates was LL, and menaquinone system was MK-9 with H₈, or H₈ and H₆. Therefore, all of the isolates were regarded to belong to group streptomycetes. Two thirds of the isolates had cellulolytic activity, and some of them showed antifungal activity against several strains of Fusarium.

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This paper reviews our studies on the protozoan distribution and their behaviour within and among soil aggregates. Our studies were performed with the idea that the aggregate structure involving pores of various size is the key concept in the analysis of microenvironment of soil microorganisms. Aggregates (1-2mm in diameter) taken from sandy clay loam soil were used throughout these studies. The main results are as follows: (1) Detected protozoan groups differed noticeably from aggregate to aggregate. This suggests that protozoa cannot migrate easily from aggregate to aggregate under field conditions. (2) As most protozoan cells were easily washed out into the water, we consider that these organisms usually inhabit on the surface or in non-capillary pores opened to the surface. Some of amoebae, flagellates and small ciliates cells, however, persisted in being washed out. These cells are considered to have inhabited in closed non-capillary pores inside the aggregates. (3) When Colpoda sp. (protozoa) and Klebsiella pneumoniae (bacterium) were introduced to sterilized aggregates, Colpoda sp. ate the bacterial cells anchored at the surface and in the open pores. The protozoa were not able to consume the bacterial cells in non-capillary pores. (4) In sterilized aggregates, the percentage of eaten bacterial cells at the surface and in the open pores increased with the amount of added protozoan cells in a range from ca. 0.3 to ca. 50 cells per aggregate at 60% W. H. C. Protozoan movement between and within soil aggregates is limited under this moisture condition. (5) Under higher conditions of moisture, however, the protozoa ate a much higher percentage of bacterial cells than at 60% W. H. C. The increase in the moisture content must facilitate the movement of the protozoa within and among aggregates.

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