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1.
Stimulation of the multiplication of Micrococcus luteus by an autocrine growth factor 总被引:12,自引:0,他引:12
Galina V. Mukamolova Svetlana S. Kormer Douglas B. Kell A. S. Kaprelyants 《Archives of microbiology》1999,172(1):9-14
Viable cells of Micrococcus luteus secrete a proteineous growth factor (Rpf) which promotes the resuscitation of dormant, nongrowing cells to yield normal,
colony-forming bacteria. When washed M. luteus cells were used as an inoculum, there was a pronounced influence of Rpf on the true lag phase and cell growth on lactate
minimal medium. In the absence of Rpf, there was no increase in colony-forming units for up to 10 days. When the inoculum
contained less than 105 cells ml–1, macroscopically observable M. luteus growth was not obtained in succinate minimal medium unless Rpf was added. Incubation of M. luteus in the stationary phase for 100 h resulted in a failure of the cells to grow in lactate minimal medium from inocula of small
size although the viability of these cells was close to 100% as estimated using agar plates made from lactate minimal medium
or rich medium. The underestimation of viable cells by the most-probable-number (MPN) method in comparsion with colony-forming
units was equivalent to the requirement that at least 105 cells grown on succinate medium, 103 cells from old stationary phase, or approximately 10–500 washed cells are required per millilitre of inoculum for growth
to lead to visible turbidity. The addition of Rpf in the MPN dilutions led to an increase of the viable cell numbers estimated
to approximately the same levels as those determined by colony-forming units. Thus, a basic principle of microbiology –“one
cell-one culture”– may not be applicable in some circumstances in which the metabolic activity of “starter” cells is not sufficient
to produce enough autocrine growth factor to support cell multiplication.
Received: 7 December 1998 / Accepted: 7 April 1999 相似文献
2.
Anna Rita Migliaccio Giovanni Migliaccio Brigitte Durand GianCarlo Mancini John W. Adamson 《Cytotechnology》1993,11(2):107-113
We have analyzed the effect of stem cell factor (SCF), alone or in combination with other growth factors, on the generation of colony-forming cells (CFC) and on the expansion of hematopoiesisin vitro from light density, soybean agglutinin–, CD34+ cord blood cells under serum-deprived conditions. The growth factors were either added only once at the onset of the culture or added every few days when the cultures were demidepopulated and refed with fresh medium. No growth factor, alone, generated CFC or expanded hematopoiesis under these conditions. However, SCF, in combination with interleukin 3 (IL-3) or with late-acting factors (granulocyte colony-stimulating factor (G-CSF) or erythropoietin (Epo)), generated large numbers of mature cells as well as CFC. The number of CFC generated depended on the refeeding procedure adopted. In cultures never refed, the CFC numbers increased from > 160 CFC/culture at day 0 to > 3000 CFC at day 10. The CFC numbers stayed above the input levels for 25 days before declining. Almost no CFC were detectable after one month. In contrast, in cultures regularly refed, CFC were detectable for at least 40 days. The lineages of the mature cells and the types of CFC generated varied with the different growth factors. In the presence of SCF plus IL-3, erythroid burst-forming cells (BFU-E) and granulocyte/macrophage colony-forming cells (GM-CFC) were generated and erythroid as well as myelomonocytic precursors were present among the differentiated cells. In contrast, in the presence of SCF and G-CSF or Epo, the progenitor cells as well as the differentiated cells were dictated by the late-acting growth factor (i.e. mostly G-CFC and myeloid cells in the presence of SCF and G-CSF vs. BFU-E, erythroid colony-forming cells (CFU-E) and erythroblasts in the presence of SCF and Epo). Thus, marked expansion of erythropoiesis and granulopoiesis can be achievedin vitro by as few as two factors — SCF acting as the early factor along with the appropriate late-acting factor.Paper presented in part at the World Congress on Cell Cultures, Washington D.C., 21–24 June 1992. 相似文献
3.
Growing cells of a thermophilic strain ofBacillus brevis, producer of thermostable α-amylase, were immobilized by entrapment in agar gel. Optimum immobilization conditions for effective
α-amylase production in batch fermentations were established (gel concentration 3%, initial biomass concentration in the gel
0.8% (W/V), and preculture age—late exponential phase). The dynamics of α-amylase synthesis by the biocatalysts obtained under the
optimal conditions was compared with that of free cells and the operational stability of the biocatalysts was studied in semicontinuous
cultivation experiments. Maximum α-amylase yields (252% of the control) were achieved after the second cycle of cultivation.
Scanning electron microscopy was used to characterize the bacteria entrapped in agar gel. 相似文献
4.
The strain Penicillium purpurogenum P-26 was subjected to UV irradiation and N-methyl-N′-nitro-N-nitrosoguanidine treatment and mutants were isolated capable of synthesizing cellulase under the conditions of a high concentration
of glucose. Initially mutants resistant to catabolite repression by 2-deoxy-D-glucose were isolated on Walseth’s cellulose/agar plates containing 15–45 mM 2-deoxy-D-glucose. These mutants were again screened for resistance to catabolite repression by glycerol or glucose on Walseth’s cellulose/agar
plates containing 50 g/l glycerol or 50 g/l glucose respectively. Four mutants with different sizes of clearing zone on Walseth’s
cellulose/agar plates containing 50 g/l glucose were selected for flask culture. Among them, the mutant NTUV-45-4 showed better
carboxymethylcellulase activity in flask culture containing 1% Avicel plus 3% glucose than did the parental strain.
Received: 9 October 1995/Received revision: 27 November 1995/Accepted: 8 January 1996 相似文献
5.
Kristůfek V Elhottová D Chronáková A Dostálková I Picek T Kalcík J 《Folia microbiologica》2005,50(5):427-435
The bacterial population of brown coal colliery spoil (Sokolov coal mining district, Czechia) was characterized by measuring
viable bacterial biomass, the culturable to total cell ratio (C:T), colony-forming curve (CFC) analysis and species and/or
biotype diversity. Bacterial representatives that differed in colony-forming growth (fast and/or slow growers) were used for
growth-strategy investigation of heterotrophic bacteria. Spoil substrates from the surface (0–50 mm) and the mineral (100–150
mm) layers were sampled on 4 sites undergoing spontaneous succession corresponding to 1, 11, 21 and 43 years after deposition
(initial, early, mid and late stages). The bacterial biomass of the surface layer increased during the initial and early stages
with a maximum at mid stage and stabilized in the late stage while mineral layer biomass increased throughout the succession.
The maxima of C:T ratios were at the early stage, minima at the late stage. Depending on the succession stage the C:T ratio
was 1.5–2 times higher in the mineral than the surface layer of soil. An increase in the fraction of nonculturable bacteria
was associated with the late succession stage. CFC analysis of the surface layer during a 3-d incubation revealed that the
early-succession substrate contained more (75 %) rapidly colonizing bacteria (opportunists, r-strategists) than successively
older substrates. The culturable bacterial community of the mineral layer maintained a high genera and species richness of
fast growers along the succession line in contrast to the surface layer community, where there was a maximum in the abundance
of fast growers in the early stage. There was a balanced distribution of Grampositive and Gram-negative representatives of
fast growers in both layers. A markedly lower abundance of slow growers was observed in the mineral in contrast to the surface
layer. Gram-positive species dominated the slow growers at the surface as well as in the mineral layers. The growth strategy
of the heterotrophic bacterial population along four successional stages on spoil of brown coal colliery substrate in the
surface layer displayed a trend indicative of a r-K continuum in contrast to the mineral layer, where an r-strategy persisted.
This research was funded by theCzech Science Foundation grant no. 526/03/1259 and by theResearch Plan of the Institute of Soil Biology, Academy of Sciences of the Czech Republic, project no. AV 0Z 6066 0521. 相似文献
6.
Viability of soil bacteria: Optimization of plate-counting technique and comparison between total counts and plate counts within different size groups 总被引:11,自引:0,他引:11
Viable counts of heterotropic soil bacteria were 3–5 times higher on low-nutrient agar media compared with a series of conventional agar media. Substantial amounts of monosaccharides and amino acids were present in solid media made from distilled water and agar powder, and a salt-solution agar medium (without organic substrates added) gave practically the same colony counts as the low nutrient soil extract agar medium. MPN values were comparable to or lower than plate counts. A search for slow-growing cells in the negative MPN tubes by fluorescence microscopical examination after 3 months incubation was negative.The viable counts were 2–4% of the total microscopical counts in different soils. Assuming that the colony-forming cells did not derive from the numerous dwarf cells present in soil, a calculated percent viability of the larger cells was about 10%. The ecological significance of the plate-counting technique is discussed. 相似文献
7.
An experimental investigation was carried out to determine the agreement between two methods of viable bacteria aerosol detection.
Various amounts of Bacillus globigii (BG) spores were aerosolized in 1-s bursts into a HEPA-filtered air stream and sampled simultaneously with a fluorescence
aerosol particle sensor (FLAPS) and a slit to agar biological air sampler. The slit sampler incorporated 150-mm malt extract
culture plates, which were incubated at 37°C for at least 12 h before culturable BG particles were counted in terms of colony-forming
units (CFU). A relationship between CFU and optically detected viable bacteria particles was determined as culturable particle
concentrations decreased. Through further analytical procedures, the FLAPS showed a limit of detection (LOD) of 4.2 bacterial
particle/2.5 l of sampled air or 1.7 × 103 m−3. This real-time bacteria aerosol monitor could be used to detect burst contamination events during a surgical procedure.
The technology may be used for developing a dose–response relationship between bacterial particle exposure and infection,
a tool potentially helpful in determining patient risk. 相似文献
8.
Christiane Baschien Georg Rode Uta Böckelmann Peter Götz Ulrich Szewzyk 《Microbial ecology》2009,58(3):642-650
We investigated microbial interactions of aquatic bacteria associated with hyphae (the hyphosphere) of freshwater fungi on
leaf litter. Bacteria were isolated directly from the hyphae of fungi from sedimented leaves of a small stream in the National
Park “Lower Oder,” Germany. To investigate interactions, bacteria and fungi were pairwise co-cultivated on leaf-extract medium
and in microcosms loaded with leaves. The performance of fungi and bacteria was monitored by measuring growth, enzyme production,
and respiration of mono- and co-cultures. Growth inhibition of the fungus Cladosporium herbarum by Ralstonia pickettii was detected on leaf extract agar plates. In microcosms, the presence of Chryseobacterium sp. lowered the exocellulase, endocellulase, and cellobiase activity of the fungus. Additionally, the conversion of leaf
material into microbial biomass was retarded in co-cultures. The respiration of the fungus was uninfluenced by the presence
of the bacterium. 相似文献
9.
Jufang Wang Yinying Tao Zhinan Xu Rong Xu Peilin Cen Xiaoning Wang 《World journal of microbiology & biotechnology》2008,24(9):1885-1891
An integrated high-throughput screening (HTS) strategy was developed to screen large numbers of polymyxin E-producing mutants
of Paenibacillus polymyxa. Various types of mutants were transferred onto the surfaces of solidified agar in 96-well microtiter plates, and then inoculated
to 96-deep-well microtiter plates for micro-cultivation. The culture conditions were optimized for the production of polymyxin
E. The supernatants from the micro-culture plates were transferred to 96-well bioassay microtiter plates containing Escherichia coli JM109 for high-throughput bioassay. By using this high-throughput screening (HTS) procedure, one best producer P. polymyxa PE 5.808 was identified from a large NTG mutated library with about 5,000 isolates. The volumetric productivity of polymyxin
E of P. polymyxa PE 5.808 was 1,200 μg/ml in shake flasks, about 140% improvement compared with that of the wild type strain. 相似文献
10.
Characterization of Bdellovibrio- and like organisms (BALOs) from environmental samples involves growing them in the presence of Gram-negative prey bacteria
and isolation of BALO plaques. This labor-intensive enrichment and isolation procedure may impede the detection and phylogenetic
characterization of uncultivable BALOs. In this article, we describe a simple slide biofilm assay to improve detection and
characterization of BALO microbiota. Agar spiked with biostimulants such as yeast extract (YE), casamino acids (CA), or concentrated
cells of Vibrio parahaemolyticus P5 (most widely used prey bacteria for isolation of halophilic BALOs) was plated onto buffed glass slides and exposed to
water samples collected from Apalachicola Bay, Florida. After incubating for a week, diversity of the biofilm bacterial community
was studied by culture-dependent and culture-independent molecular methods. The results revealed that most probable numbers
(MPNs) of BALOs and total culturable bacteria recovered from YE agar slide were significantly higher than the numbers on CA-
or P5-spiked agar slides. Polymerase chain reaction–restriction fragment length polymorphism followed by 16S rDNA sequencing
of clones from different biostimulants resulted in identification of a plethora of Gram-negative bacteria predominantly from
the alpha, gamma, delta-proteobacteria, and the Cytophaga–Flavobacterium–Bacteroides group. Corresponding to the higher biomass on the YE agar slide, the BALO clone library from YE was most diverse, consisting
of Bacteriovorax spp. and a novel clade representing Peredibacter spp. Microbiota from all three biostimulated biofilms were exclusively Gram-negative, and each bacterial guild represented
potential prey for BALOs. We propose the use of this simple yet novel slide biofilm assay to study oligotrophic aquatic bacterial
diversity which could also potentially be utilized to isolate marine bacteria with novel traits. 相似文献
11.
Flagella-based motility of extremely alkaliphilic Bacillus species is completely dependent upon Na+. Little motility is observed at pH values < ∼8.0. Here we examine the number of flagella/cell as a function of growth pH
in the facultative alkaliphile Bacillus pseudofirmus OF4 and a derivative selected for increased motility on soft agar plates. Flagella were produced by both strains during growth
in a pH range from 7.5 to 10.3. The number of flagella/cell and flagellin levels of cells were not strongly dependent on growth
pH over this range in either strain although both of these parameters were higher in the up-motile strain. Assays of the swimming
speed indicated no motility at pH < 8 with 10 mM Na+, but significant motility at pH 7 at much higher Na+ concentrations. At pH 8–10, the swimming speed increased with the increase of Na+ concentration up to 230 mM, with fastest swimming at pH 10. Motility of the up-motile strain was greatly increased relative
to wild-type on soft agar at alkaline pH but not in liquid except when polyvinylpyrrolidone was added to increase viscosity.
The up-motile phenotype, with increased flagella/cell may support bundle formation that particularly enhances motility under
a subset of conditions with specific challenges. 相似文献
12.
Growth of alkaliphilic Bacillus halodurans C-125 both on agar plates and in liquid culture was inhibited by methyl-β-cyclodextrin (CD). Furthermore, resting cells of
the strain were lysed by contact with methyl-β-CD higher than 10 mM. α-CD also showed lysis activity against Bacillus and related strains. The activity was not observed with Gram-negative and Gram-positive bacteria except for Bacillus strains. Fluorescence staining and scanning electron microscopy of cells revealed that methyl-β-CD disrupted cell membranes,
and consequently, the cells were lysed. This is a novel physiological property of CDs. 相似文献
13.
N. Nishihara S. Horiike T. Takahashi T. Kosaka Y. Shigenaka H. Hosoya 《Protoplasma》1998,203(1-2):91-99
Summary The green parameciumParamecium bursaria has many endosymbiotic algae in its cytoplasm. Here, we cloned and characterized endosymbiotic algae fromP. bursaria and examined in detail the interaction between the cloned algae and algae-free paramecia. Homogenates ofP. bursaria were cultured on agar plates containing various kinds of media to establish clones of the endosymbiotic algae. Many algal colonies were obtained from poorly nutritious medium (CA medium) after one month in culture. Algae were picked up from these colonies and inoculations were repeated 9 times on agar plates containing CA medium. On enriched media including bacto-peptone, glucose, proteose-peptone and/or yeast extract, however, bacteria and mold grew rapidly and no algal colonies were formed. When the cloned algae were cultured in liquid CA medium, they grew faster than on agar plates and the numbers stayed constant at 1 × 107 algae/ml after 7 days in culture. They revealed high infectivity to algae-free paramecia, and an incubation period of 24 h and at least 1 × 103 algae/paramecium were required to achieve successful infection (80–90%). The growth and infection rate did not change through 74 repeated inoculations of algae in liquid CA medium. Optical microscopic observations revealed marked morphological similarity between endosymbiotic algae and free-livingChlorella, but the latter showed no infectivity to algae-free paramecia. The cloned endosymbiotic algae presented here will provide an excellent opportunity to examine the mechanism of symbiont-host interaction. 相似文献
14.
Hong Jun Choi Joo Bin Hong Jeong Joon Park Won-Jae Chi Mu-Chan Kim Yong-Keun Chang Soon-Kwang Hong 《Biotechnology and Bioprocess Engineering》2011,16(1):81-88
The agar degrading bacterial strain GNUM-08124 was isolated from Enteromorpha compressa collected in the East Sea of Korea by using a selective artificial sea water (ASW) agar plate containing agar as the sole
carbon source. GNUM-08124 grows to produce a circular, smooth, yellow-colored, and raised colony. Its ability to hydrolyze
agar was confirmed by staining the ASW agar plate with Lugol’s solution. In liquid culture, the cell density (A600) increased exponentially and reached a maximum level on the third day of cultivation. The specific agarase activity also
increased in proportion to the cell density and reached maximum agarolytic activity on the third day. The 16S rRNA sequence
of GNUM-08124 showed a close relationship to Micrococcus luteus (99.65%) and Micrococcus endophyticus (99.15%), which led us to assign it to the genus Micrococcus. Physiological studies indicated that optimal growth conditions were between 30 and 40°C, pH 4 and 7, using media containing
between 5 and 10% NaCl (w/v), respectively. The GNUM-08124 strain was a grampositive, urease-positive, and catalase-positive
bacterium. It could not hydrolyze gelatin, cellulose, xylan, or starch, but fermented a broader range of substrates, including
Dglucose, D-galactose, D-fructose, D-lactose, D-trehalose, D-mannitol, D-melibiose, D-raffinose, D-xylose, methyl-α-D-glucopyranoside,
N-acetyl-glucosamine, and xylitol, than those fermented by M. luteus or M. endophyticus, suggesting GNUM-08124 is a novel agar hydrolyzing microorganism belonging to Genus Micrococcus. Micrococcus sp. GNUM-08124 showed the highest agarase activity when it was cultured in ASW-YP medium supplemented with 0.4% glucose,
but demonstrated lower activity in rich media (LB or TSB), in spite of superior cell growth, implying that agarase production
is tightly regulated in an agar-dependent manner and repressed in rich conditions. 相似文献
15.
Takashi Yamanaka 《Mycoscience》1994,35(2):187-189
Lyophyllum tylicolor, which forms mycelial basidia (and basidiospores), produced fruit-bodies when cultivated at 20°C under continuous illumination
of 400–700 lux on agar plates containing Bacto-Soytone and glucose or an extract from urea-treated soil. Under these conditions,
mycelial basidia were also observed on the Soytone-glucose agar, but not on the soil extract agar. In darkness, fruit-bodies
and mycelial basidia were not observed on either medium. In culture on the soil extract agar, fruit-body primordia were produced
at the position of the margin of the colony when it was transferred from darkness to continuous light; stipes did not elongate
under illumination of ca. 2000 lux; and mycelial basidia and basidiospores, but not fruit-bodies, developed when glucose concentration
in the medium was as high as 1% (w/v). 相似文献
16.
Containment of a genetically engineered microorganism during a field bioremediation application 总被引:6,自引:0,他引:6
A field release of a genetically engineered microorganism was performed at the Field Lysimeter Site on the Oak Ridge Reservation.
Six large lysimeters were filled with soil that had been contaminated with a mixture of naphthalene, phenanthrene, and anthracene.
A genetically engineered bacterial strain, Pseudomonas fluorescens HK44, was sprayed onto the surface of the soil during soil loading. This strain contains a fusion between the lux genes of Vibrio fischeri and the promoter for the lower pathway of naphthalene degradation, enabling the strain to become bioluminescent when it is
degrading naphthalene. Release of the bacteria outside the lysimeters was monitored, using selective agar plates and one-stage
Anderson air samplers. Although approximately 1014 bacteria were sprayed during the loading process, escape was only detected sporadically; the highest incidence of bacterial
escape was found when the relative humidity and wind speed were low.
Received: 6 March 1998 /thinsp;Received revision: 16 September 1998 / Accepted: 16 October 1998 相似文献
17.
Flores-Guzmán P Martínez-Jaramillo G Montesinos JJ Valencia I Mayani H 《Cytotherapy》2006,8(3):299-307
BACKGROUND: During long-term culture of primitive hematopoietic cells large numbers of mature cells are generated that, on the one hand, consume nutrients and cytokines present in the medium and, on the other hand, may produce or elicit the production of soluble factors that limit the growth of primitive cells. Thus it is possible that under standard culture conditions hematopoietic stem and progenitor cells are unable to display their true proliferation and expansion potentials. METHODS: Hematopoietic cell populations, enriched for CD34+ cells, were obtained from both umbilical cord blood (UCB) and mobilized peripheral blood (MPB), and cultured in cytokine-supplemented liquid culture, under continuous removal of mature cells by means of weekly re-selection of primitive, lineage-negative (Lin-) cells. Proliferation and expansion capacities of such cells were determined weekly for a 42-day culture period. RESULTS: As expected, based on our previous studies in standard liquid cultures, throughout the culture period there was a continuous decrease in the proportion of progenitor cells; however, after every re-selection on days 7, 14 and 21, there was a significant enrichment for both CD34+ cells and colony-forming cells (CFC). As a result of such an enrichment, the cumulative increase in the numbers of total cells and CFC in cultures with two, three or four selections was significantly higher than the increments observed in standard cultures, in which only a single selection was performed on day 0. Cultures of UCB cells showed consistently higher levels of both total cells and CFC than cultures of MPB cells. DISCUSSION: Taken together, these results indicate that continuous removal of mature cells from liquid cultures of primitive progenitors results in higher increments in the levels of both total cells and CFC. 相似文献
18.
Ya-Wei Zhu Yu-Hua Zhao Xiao-Yan Lin Li Yang 《World journal of microbiology & biotechnology》2005,21(6-7):1195-1200
Summary An aerobic bacterium named strain BH was isolated from soil samples based on its bensulfuronmethyl-degrading characteristics
using continuous enrichment cultures. The cells of the strain were non-motile, gram-positive short rods. Colonies formed on
agar medium were round, smooth, sticky, white-yellow in colour and of butyrous consistency. Analyses of nutritional utilization
in Biolog microplates, conventional phenotypic characteristics and 16S rRNA gene sequencing were consistent with assigning
strain BH to the genus Brevibacterium. Growth of the cells and their ability to degrade bensulfuronmethyl were simultaneously monitored under different liquid
medium conditions during 7 days of incubation. They degraded bensulfuronmethyl from 100 to 70.6 mg l−1 in mineral M9 medium and exhibited more effective degradation in the presence of yeast extract, completely removing an initial
concentration of 100 mg l−1 and at best 80% of an initial concentration of 200 mg l−1. Further studies are required to determine the potential use of the isolate in the disposal of bensulfuronmethyl residues
in agriculture and industry. 相似文献
19.
Rosa Margesin 《Extremophiles : life under extreme conditions》2009,13(2):257-262
Three bacterial (Pedobacter heparinus, Pedobacter piscium, Pedobacter cryoconitis) and three yeast strains (Saccharomyces cerevisiae, Leucosporidiella creatinivora, Rhodotorula glacialis) of different thermal classes (mesophiles and psychrophiles) were tested for the effect of temperature on a range of growth
parameters, including optical density, viable cell numbers, and cell dry mass, in order to determine the temperature conditions
under which maximum biomass formation is obtained. Maximum values of growth parameters obtained at the stationary growth phase
of the strains were used for statistical calculation. Temperature had a significant (P ≤ 0.05) effect on all growth parameters for each strain; correlations between the growth parameters were significant (P ≤ 0.05–0.01). The maximum growth temperature or the temperature at which microbial growth was fastest was in no case the temperature
at which the investigated strains produced the highest amount of biomass. All tested psychrophilic bacteria and yeast strains
produced highest amounts of cells (as calculated per mg cell dry mass or per OD600 unit) at 1°C, while cell numbers of mesophiles were highest at 20°C. Thus, cultivation temperatures close to the maximum
growth temperature are not appropriate for studying psychrophiles. 相似文献
20.
Analysis of bacterial populations in a grassland soil according to rates of development on solid media 总被引:3,自引:0,他引:3
Abstract The process of colony formation by bacteria from grassland soil sampled in April, July and September was simulated by a colony-forming curve (CFC). The CFC was a super-imposition of several component curves (cCFC) given theoretically by the first order reaction (FOR) model [3,6]. The pattern of FOR model curves was not influenced by the time of sampling and four cCFCs were always recognized during an incubation period of 160 h. It was considered that the CFC describes an inherent property of the bacterial population of the field. Bacterial isolates were obtained from colonies produced in each of four cCFCs on agar plates. Isolates corresponding to one cCFC were classified as one group. The bacterial isolates were characterized by morphological and physiological tests and subsequently clustered. Few oligotrophic bacteria were obtained among bacteria which produced visible colonies within 63 h of incubation time. On the other hand, approx. 50% of bacteria which produced v colonies after 63 h were oligotrophic bacteria. The time required for the appearance of the first colony, t r of the FOR model, was very similar in the isolates belonging to one group. A close linear relationship was observed between t r value and doubling time of isolates. 相似文献