Recent studies on the colony formation of soil bacteria opened the way to categorize soil bacteria into colony forming curve (CFC) groups of different growth rates. A bacterial culture collection comprising organisms from every CFC group is called an ecocollection (EC). Outlines of ECs of paddy soil 1992 and grassland soil 1987 and 1992 were described. Phylogenetic studies by 16S rDNA sequencing showed a great diversity of culture strains of the ecocollections. A set of alternative concepts was proposed; the active and the quiescent forms of bacterial cells in soil. The former is able to be cultivated and thus counted by the plate method, while the latter is not unless it transforms into the former. Based on the results several points required for extensive cataloguing of soil bacteria were noted.

The colony-forming process of bacteria in a paddy field soil on 100-fold diluted nutrient broth (DNB) plates containing As(III) (250-1,000 ppm) was analyzed by the first-order reaction (FOR) model. The process on plates with 250 ppm As(III) was simulated by a superimposition of three FOR model curves, which are respectively referred to as component colony-forming curve (cCFC) I, II, or III. Bacterial isolates from the 250 ppm As(III) plates were divided into three groups according to cCFC, along which each respective bacterium produced its colony. The three cCFC groups showed different trends of physiological properties: (1) the range of tr, which is the waiting time for the appearance of the first colony of each single population in the presence or absence of As(III), (2) the range of the maximal tolerant As(III) concentration for each isolate and some of its taxonomic properties. Twelve out of 72 strains examined harbored one or more plasmids, suggesting location of As(III)-tolerant genes on the chromosomal DNA.A variety of bacteria which are tolerant to biologically inhibitory elements, including both heavy metals and metals, inhabit soils. The bacterial tolerance to the many inhibitory elements results often from the presence of plasmids in cells (20). The plasmids, a series of extrachromosomal tolerance factors, are thought to be distributed widely in natural environments such as soils, water, plants, and animals and to be propagated among a wide range of microorganisms (17). The grouping of soil bacteria tolerant to toxic elements and the detection of plasmids responsible

The effects of holding temperature, time and cooling rate on the microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si (at.%) alloys are studied. Three kinds of segregations are found in the as-cast material. In back scattered electron images these segregations are observed as dark regions formed by the solidification process, bright regions with irregular shaped blocks and imaged regions of lighter contrast formed by the cooling process from β phase to α phase and from α phase to (β + γ) two phase or (α + β + γ) three phase, respectively. Addition of small amounts of Cr, Ni and Si to the Ti-45Al-7Nb alloy shifts the (β + γ) two phase state and (α + γ + β) three phase state to a lower Nb concentration range. While cooling from the α single phase state to the (β + γ) two phase or (α + β + γ) three phase states, sequential type phase transformation occurs. The amounts of Cr, Ni and Si are too small to induce the pearlitic mode of transformation. Therefore, the sequential mode of the ternary alloy containing Nb occurs. The microstructures change depending on the cooling rate from α single phase region. Massive transformation occurs in the range of 300 K s−1 to 50 K s−1. However, the α phase is partially retained at the cooling rate of 300 K s−1. A fully lamellar structure appears at cooling rates lower than 10 K s−1.