Metabolism of fluorodifen by soil microorganisms

The metabolism of fluorodifen (p-nitrophenyl α,α,α,-trifluoro-2-nitro-p-tolyl ether) by soil microorganisms in the presence or absence of other carbon and nitrogen sources was studied. The degradation of this herbicide continued for 5 days, when benzoate or acetate and ammonium sulphate were included in the cultures, and for more than 5 weeks when fluorodifen was used as a sole source of carbon and nitrogen.Under all conditions nitrite ions were produced at concentrations ranging between 5 and 80 per cent of the nitro-nitrogen of the fluorodifen present. The highest concentration of nitrite was obtained when added carbon sources were used with fluorodifen. The lowest nitrite concentration accumulated when the fluorodifen was used as sole source of carbon and nitrogen. The nitrite reached a maximum value after a few days of incubation, followed by rapid disappearance.p-Nitrophenol and quinol were identified in the acid-ether extract of cultures. It is suggested that the first step in the degradation of fluorodifen is the hydrolysis of the ether linkage followed by the direct elimination of the nitro-groups as nitrite ions.     

Effects of urease inhibitors on nitrification in soils

The effects of 10 urease inhibitors on nitrification in soils were studied by determining the effects of 10 and 50 parts/10⁶ (soil basis) of each inhibitor on the amounts of nitrate and nitrite produced when soils treated with ammonium sulfate (200 μg of ammonium N/g of soil) were incubated (30°C) under aerobic conditions for 14 days. The urease inhibitors used (catechol. hydroquinone, p-benzoquinone, 2,3-dimethyl-p-benzoquinone, 2,5-dimethyl-p-benzoquinone. 2,6-dimethyl-p-benzoquinone. 2,5-dichloro-p-benzoquinone, 2,6-dichloro-p-benzoquinone. sodium p-chloromercuribenzoate, and phenylmercuric acetate) were those found most effective in previous work to evaluate more than 130 compounds as soil urease inhibitors. Their effects on nitrification were compared with those of three compounds patented as soil nitrification inhibitors (N-Serve. AM. and ST).Most of the urease inhibitors studied had little effect on nitrification when applied at the rate of 10 μg/g of soil. but had marked inhibitory effects when applied at the rate of 50 μg/g of soil. None inhibited nitrification as effectively as N-Serve. but phenylmercuric acetate inhibited nitrification more effectively than did AM or ST when applied at the rate of 10 μg/g of soil. Phenylmercuric acetate, 2,5-dimethyl-p-benzoquinone, and 2,6-dimethyl-p-benzoquinone had very marked effects on nitrification when applied at the rate of 50 μg/g of soil.     

Kocuria rosea HN01, a newly alkaliphilic humus-reducing bacterium isolated from cassava dreg compost

Purpose

The aims of this study were to isolate an alkaliphilic humus-reducing bacterium, investigate the fastest microbial reduction of humus analog as affected by different cultivation, and examine its ability for iron(III) oxide reduction and organochlorine pollutants (OCPs) degradation.

Materials and methods

A strain of pure culture, designated as HN01, was isolated from cassava dreg compost using anaerobic enrichment procedure with glucose as the electron donor and anthraquinone-2,6-disulphonate (AQDS) as the sole terminal electron acceptor. The isolate strain was identified using phenotypic and phylogenetic analysis. Iron(III) oxides and OCPs were chosen as potential electron acceptors. Strict anaerobic techniques and sterile conditions were applied throughout the incubation experiments, purged with O₂-free N₂ for 15 min. The concentration of reduced AQDS and Fe(II) was then quantified using a UV–vis spectrophotometer. The concentration of OCPs was analyzed by gas chromatography with a micro-electron capture detector. Cell number was determined by direct plate counting on aerobic Luria–Bertani medium agar medium at pH 9.

Results and discussion

(1) Strain HN01 was identified as Kocuria rosea, and the AQDS reduction by HN01 was observed in NaCl concentrations below 12 % (w/v) (optimum, 10 %) and pH ranges of 6.0–10.0 (optimum, 9.0) with sucrose as electron donor at 30 °C; (2) glucose, sucrose, methanol, ethanol, glycerol, and acetate were the favorable electron donors for AQDS reduction by strain HN01; (3) the strain had the ability of reducing iron(III) oxides in the presence of sucrose at pH 9.0 and its Fe(III)-reducing capacity ranked as goethite (α-FeOOH) > lepidocrocite (γ-FeOOH) > haematite(α-Fe₂O₃); and (4) the strain could effectively dechlorinate p,p′-DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane), and the dechlorination rate reached 71.3 %.

Conclusions

This is the first report of a strain of K. rosea capable of reducing AQDS, iron (III) oxides, and p,p′-DDT, which extends the diversity of the alkaliphilic and halotolerant humus/Fe(III)-reducing bacterium associated with dechlorination. The strain may have the potential to be used for bioremediation of an anoxic alkaline wastewater or site contaminated with OCPs.     

Enzymatic binding of the pollutant 2,6-xylenol to a humus constituent

Dimeric and polymeric hybrid oliogmers were obtained by the reaction of 2,6-xylenol and syringic acid in the presence of an enzyme from the fungus Trametes versicolor. Three hybrid dimers were formed in an assay at pH 4.5, while at pH 6.5, the formation of additional higher polymers with a phenyl-ether bond (tail to head linkage) was detected. The major product was identified as 3,5-dimethyl-3′,5′-dimethoxydiphenoquinone (4,4′), and it amounted to approximately 45% of the applied 2,6-xylenol after 3.5 hr incubation at pH 4.5. About 8% of the 2,6-xylenol was transformed to 4,4′-dihydroxy-3,5-dimethyl-3′,5′-dimethoxydiphenol and 22% to 3-methoxy-5-(2′,6′-dimethylphenoxy)-benzoquinone (1,2).     

Removal of Mixed Pesticides from Drinking Water System Using Surfactant-Assisted Nano-TiO2

The present study focused on the degradation of mixed pesticides using UV-induced photocatalytic degradation of lindane (1α,2α,3β,4α,5α,6β-hexachlorocyclohexane), methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate), and dichlorvos (2,2-dichlorovinyl-O-O-dimethyl phosphate). Different grades of TiO₂ were prepared through the acid route (AR), alcohol route (AlR), and surfactant route (SR) and their photocatalytic activity were compared with commercially available Degussa P-25 TiO₂. The rate of degradation of pesticides was high for TiO₂ prepared through the SR compared to the other three catalysts. The crystalline structure and morphology of SR TiO₂ was identified with scanning electron microscope, energy dispersive X-ray analyzer, UV, and transmission electron microscope analyses and was compared with that of Degussa P-25 TiO₂. Degradation studies of individual as well as mixed pesticides were carried out. The intermediate formed during the photodegradation of methyl parathion, lindane, and dichlorvos were identified by gas chromatography–mass spectrometry analysis.     

Biodegradation and persistence of several acetamide,acylanilide, azide,carbamate, and organophosphate pesticide combinations

The effect of potassium azide (KN₃), O,O-diethyl O-(2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate (diazinon), O,O-diethyl S-[(ethylthio)- methyl] phosphorodithioate (phorate), 1-naphthyl methylcarbamate (carbaryl), and p-chlorophenyl methylcarbamate (PCMC) on the biodegradation and persistence of several amide, carbamate, and urea herbicides in soil and microbial culture systems was examined. KN₃ inhibited the biodegration of isopropyi m-chlorocarbanilate (chlorpropham) in both soil perfusion and microbial culture system, but was limited in increasing chlorpropham persistence in soil under greenhouse conditions. PCMC and diazinon, inhibited the metabolism of chlorpropham by isolated cultures of soil bacteria (Pseudonwnas striata Chester and Achromobacter sp). Phorate inhibited chlorpropham metabolism by P. striata, but did not inhibit chlorpropham metabolism by Achromobacter sp. Carbaryl, PCMC, and diazinon increased the persistence of chlorpropham in soil under greenhouse conditions. PCMC also inhibited the microbial metabolism of isopropyl carbanilate (propham), 3',4'-dichloropropionanilide (propanil), 2-chloro-N,N-diallylacetamide (CDAA), 1,1-dimethyl-3 (α,ga,α-trifluoro-m-tolyl)urea (fluometuron) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), but not that of 2-chloro-N-isopropylacetanilide (propachlor) in isolated culture systems.     

Effects of substituted p-benzoquinones on urease activity in soils

The effectiveness of substituted p-benzoquinones as inhibitors of urease activity in soils depends largely upon their substituent groups. Methyl, chloro-, bromo- and fluoro-substituted p-benzoquinones have a marked inhibitory effect on soil urease activity, whereas phenyl-, r-butyl-and hydroxy-substituted p-benzoquinones have little, if any, effect. Methyl-substituted p-benzoquinones differ from other substituted p-benzoquinones in that their effects on soil urease activity usually increase markedly with increase in their time of contact with soil.A study of the effects of selected substituted p-benzoquinones on urea hydrolysis and volatilization of urea N as ammonia in a sandy soil treated with urea showed that methyl- and chloro-substituted p-benzoquinones had very marked effects, whereas hydroxy- and phenyl-substituted p-benzoquinones had little or no effect. Gaseous loss of urea N as ammonia when this soil was incubated at 20°C for 14 days was reduced from 62.8 to 0.1 per cent by addition of 2,3-dimethyl-, 2,5-dimethyl-, or 2,6-dimethyl-p-benzoquinone (2.3 parts/100 parts of urea).The work reported indicates that, of the 34 substituted p-benzoquinones studied, 2,3-dimethyl-, 2, 5-dimethyl- and 2,6-dimethyl-p-benzoquinone are likely to prove the most effective for retardation of urea decomposition in soils and reduction of the problems caused by the normally rapid hydrolysis of fertilizer urea by soil urease.     

Structural elucidation of phototransformation products of azimsulfuron in water

The photodegradation of the sulfonylurea herbicide azimsulfuron, N-[[(4,6-dimethoxypyrimidin-2-yl)amino]carbonyl]-1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (AZS), was studied in water at different wavelengths and in the presence of photocatalysts. AZS was rapidly degraded by UV light, affording three photoproducts. The main product, accounting for about 70% of photodegraded herbicide, was identified as 6-amino-5-[(4,6-dimethoxypyrimidin-2-yl)methylamino]-1,5,6,8-tetrahydro-7-oxa-8lambda(6)-tia-1,2,5,6-tetraza-azulen-4-one (ADTA) by single-crystal X-ray diffraction. With simulated sunlight irradiation, the reaction was slower and 2-amino-4,6-dimethoxypyrimidine (DPA) and 1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (MPS), arising from a photohydrolytic cleavage of the sulfonylurea bridge, were the only byproducts observed. The reactions followed first-order kinetics. The addition of dissolved organic matter (DOM) did not modify significantly the AZS photodegradation rate. The presence of Fe2O3 accelerated more than twice the reaction rate affording two major products, DPA and MPS, together with minor amounts of N-[[(5-hydroxy-4,6-dimethoxypyrimidin-2-yl)amino]carbonyl]-1-methyl-4-(2-methyl-2H-tetrazole-5-yl)-1H-pyrazole-5-sulfonamide (AZS-OH). The greatest degradation rate was detected in the presence of TiO2. Only the photohydroxylation product AZS-OH was observed, which was transformed rapidly into oxalic acid.     

TNT nitroreductase from a Pseudomonas aeruginosa strain isolated from TNT-contaminated soil

Microbial degradation and detoxification of TNT (2,4,6-trinitrotoluene) in soils ultimately depends on the presence of effective intracellular or extracellular enzymes. TNT was rapidly degraded by an enzyme obtained from a Pseudomonas aeruginosa strain isolated from TNT-contaminated soil. The nitroreductase enzyme was purified to apparent electrophoretic homogeneity by sequential chromatography on phenyl-sepharose, hydroxyapatite, and ion exchange resins. The TNT-nitroreductase catalyzed reduction of TNT to 4-hydroxylamino-4,6-dinitrotoluene (4HADNT) and 4-amino-2,6-dinitrotoluene (4ADNT). TNT reduction to 4ADNT in cell-free enzyme preparations corresponded to 2ADNT production by intact cells. The enzyme required NADH as a cosubstrate and the optimal pH for the reaction was approximately 6.5. The purified enzyme also exhibited NADH diaphorase activity and its denatured molecular weight was approximately 54 kDa.     

Co-remediation of DDT-contaminated soil using white rot fungi and laccase extract from white rot fungi

Purpose

2,2-Bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT), one of the most widely used organochlorine pesticides in soil, was banned in the 1970s for agricultural use because of its detrimental impacts on wildlife and harmful effects on human health via the food chain. However, high levels of DDT are frequently detected in agricultural soils in China. Considering this situation, this study investigated the use of white rot fungi and laccase derived from white rot fungi to co-remediate DDT-contaminated soil.

Materials and methods

A culture of white rot fungi was used to inoculate soil samples and also to extract laccase from. Soil was contaminated with four components of DDT (p,p′-DDE, o,p′-DDT, p,p′-DDD, and p,p′-DDT). Individual DDT components and the sum of the DDT components (p,p′-DDE, o,p′-DDT, p,p′-DDD, and p,p′-DDT—collectively referred to as DDTs) were both analyzed by GC at various stages during the incubation period. The efficacy of co-remediating DDT-contaminated soil using white rot fungi and laccase was tested by investigating how degradation varied with varying amounts of white rot fungi, sterilizing soil, temperature, soil pH, concentrations of DDT, and concentration of the heavy metal ion Cd²⁺.

Results and discussion

“”It was concluded that the reduction of DDTs in soil using white rot fungi and laccase was higher than reduction using only white rot fungi or laccase by nearly 14 and 16 %, respectively. Five milliliters fungi per 15 g soil and 6 U laccase per gram soil were the optimal application rates for remediation, as shown by a reduction in DDTs of 66.82 %. The difference in the reduction of individual DDT components and DDTs between natural and sterilized soils was insignificant. The optimal temperature and pH in the study were 28 °C and 4.5, respectively. In addition, reduction of individual DDT components and DDTs increased with increasing concentrations of DDT and decreased with increasing concentrations of Cd²⁺.

Conclusions

Compared with the remediation of DDT using only white rot fungi or laccase, the co-remediation of DDT using white rot fungi and laccase degraded DDT in soil more rapidly and efficiently; the highest reduction of DDTs was 66.82 %.     

Isolation and identification of iron-reducing bacteria from gley soils

Seventy-one facultative anaerobic bacteria, capable of reducing iron oxide in pure culture, were isolated from three differently gleyed subsoils. The bacteria were picked at random from poured plates (10⁻⁵ and 10⁻⁶) inoculated with serially diluted soil samples. An attempt was made to identify these strains by morphological and biochemical tests. Among these 71 iron-reducing bacteria, all except three were capable of reducing nitrate to nitrite and 35 reduced nitrite further into gaseous compounds (denitrification), but only one strain (Bacillus subtilis) produced H₂S. Based upon their physiological and morphological properties, 38 strains were allotted to the genus Pseudomonas, 31 sporeformers to the genus Bacillus and two were regarded to be coryneform (Arthrobacter?) bacteria. Species identified were Ps. denitrificans (23), ps. stutzeri (8) ps. fluorescens-putida (5), Bacillus cereus (6), B. cereus var. mycoides (14) and Bacillus subtilis (9). Two spore-forming bacilli, two non-pigmented pseudomonads and two coryneform type of bacteria could not be identified. The significance of the enzyme nitrate reductase (nitratase) of these bacteria for anaerobic respiration and as a mechanism of iron reduction is discussed.     

Methyl parathion degradation and metabolism in soil: Influence of high soil-water contents

Mineralization of [¹⁴C]methyl parathion (MP) in Cecil sandy loam was considerably reduced when soil-water content was near saturation. Despite the fact that amounts of MP residue in soil held at 10?0 kPa after 35 days were about the same, larger amounts of metabolites were accumulated and higher amounts of non-extractable ¹⁴C-activity were formed in soil held at ? 2.5 kPa than held at ? 6 kPa. Three principal metabolites, p-nitrophenol (PNP), p-aminophenol (PAP) and a water-soluble polar product ($\text{R}{}_{\mathrm{?}}\text{= 0}$), were detected in soil held at ? 2.5 kPa but only PNP and PAP were detected in soil held at ? 6 kPa. The major metabolite PNP behaved like parent MP, in that it was rapidly mineralized in soil held at ? 6kPa. Much slower mineralization was observed in soil held at ? 2.5kPa.     

Toxicity of a secondary metabolite produced by Simplicillium chinense Snef5 against the root-knot nematode Meloidogyne incognita

ABSTRACT

We studied the bioactive compound of the fungus Simplicillium chinense strain Snef5, isolated from its culture filtrate. Following purification by chromatography, the structure of the secondary metabolite, identified as 2,6-pyridinedicarboxylic acid, was determined by spectroscopic methods (IR, ¹H, and ¹³C NMR) and scanning electron microscopy (SEM). The metabolite exhibited antimicrobial activity against M. incognita with an LD50 of 0.229?mg/ml. The light microscope was used to observe the surface and internal cellular micro-structure of the nematodes. The results of the microscopy indicated that the anatomy of the J₂ of M. incognita was disrupted following exposure to 2,6-pyridinedicarboxylic acid. This is the first report on the activity of 2,6-pyridinedicarboxylic acid of S. chinense metabolites on the root knot nematode. It showed a high level of nematicidal activity. Our data on the inhibitory effects of 2,6-pyridinedicarboxylic acid suggest that secondary metabolites from Snef5 have potential use as novel biological control agents.     

Studies of the number concentration and size distribution of the suspended dust particles in the atmosphere of Qena/Egypt

Studies of particle number concentration, size, shape and distribution of the dust particles suspended in the atmosphere of Qena (upper Egypt) have been conducted. The results show that the concentration of these particles decreases with increasing size according to the Junge power law size distribution: n(d_p) = C/ln10 (d _p)^?(α+1. The values of the exponent α range from 1.3 to 2. The largest number of particles have sizes less than 2 μm with irregular shape. The effect of some weather conditions on the total number of particles was considered. The total number of particles and effective mean diameters were calculated.     

Methane flux and regulatory variables in soils of three equal-aged Japanese cypress (Chamaecyparis obtusa) forests in central Japan

To compare factors that control methane flux in forest soils, we studied three equal-aged Japanese cypress (Chamaecyparis obtusa) forests in Chubu district, central Japan. The three sites are located at different altitudes: 630 m (SET), 1010 m (INB), and 1350 m (OSK). Methane was absorbed at every site. The highest uptake rate was observed in the middle-altitude soil (INB, 5.89 mg CH₄ m⁻² d⁻¹), which was the only site where methane uptake rate was correlated with air and soil surface temperatures. Methane flux in the field was not correlated with water content, inorganic N content, or water-soluble organic carbon. C/N ratio was correlated with methane flux (r=0.64,p<0.001). The results suggest that some organic inhibitors might be produced through decomposition of organic matter. There was a negative correlation between methane uptake rate and water-soluble Al (r=−0.63,p<0.001). Inhibition of methane consumption by 1 and 5 mM Al solutions was observed in laboratory incubation. This result suggests that water-soluble Al may be a factor controlling methane uptake. Multiple regression with a backward-elimination procedure identified three variables that were significantly associated with methane flux in the field (p<0.05): air temperature, C/N ratio, and the concentration of water-soluble Al.     

Development of a Two-Phase Cosolvent Washing-Fungal Biosorption Process for the Remediation of DDT-Contaminated Soil

A bench scale, two-phase soil washing-biosorption process was developed for the remediation of p,p′-DDT-contaminated soil (containing 990 and 7750 mg kg^-1 of p,p′-DDT). Removal of p,p′-DDT from contaminated soil was achieved by washing the soil with low molecular weight primary alcohols (ethanol or 1-propanol). An improved efficiency of p,p′-DDT removal was observed with increasing C-chain length of the cosolvent and by increasing the cosolvent volume fraction. When 40 or 80% 1-propanol were used, greater than 93% of p,p′-DDT was desorbed from the respective soils. p,p′-DDT was partitioned from the cosolvent solutions using biomass of Cladosporium sp. strain AJR³18,501 as the sorptivematrix. When studies were conducted using a cosolvent-recycling regime (with 80% 1-propanol) greater than 95% of p,p′-DDT was removed from Soil A (990 mg kg^-1 p,p′-DDT) and Soil B (7750 mg kg^-1 p,p′-DDT) with the majority of the desorbed organochlorine repartitioning onto the fungal biomass. Less than 2.4 μg mL^-1 p,p′-DDT was detected in the cosolvent wash solution of Soil A after 80 hr: potentially the cosolvent could be further reused to treat other soil. A higher concentration of p,p′-DDT was detected in the cosolvent wash solution of soil B after 120 hr (13.3 μg mL^-1) indicating that the p,p′-DDT sorption sites on the fungal biomass were fully saturated.     

Microbial Degradation of Fipronil in Clay Loam Soil

Fipronil, (±)-5-amino-1-(2,6-dichloro-∝,∝,∝-trifluoro-p-tolyl)-4-trifluoromethysulfinylpyrazole-3-carbonitrile, is used as an effective insecticide for the control of rice pests in China. Although many studies examining the fate of fipronil in the soilenvironment have been conducted, there are no studies on the microbial degradation of fipronil in the soil environment. Fipronil was degradedby microorganisms in the non-sterile clay loam soil, which resulted in the formation of metabolite, MB45950. The degradation of fipronil in non-sterile clay loam soil was mainly influenced by the soil microbes. The half-lives in non-sterile clay loam soil were 9.72 and 8.78 d at 25 and 35 °C, respectively compared to 33.51 and 32.07 d at 25 and 35 °C, respectively in the sterile soil. The microbial viability test showed that non-sterile clay loam soil had viable microorganisms throughout the experiment. Fipronil did not adversely affect the microbes once soil microbes adapted to the presence of fipronil in the clay loam soil.     

Nitrogen-fixing activities associated with rhizomes and roots of Equisetum species

High rates of nitrogen fixation (acetylene reduction) were associated with Equisetum arvense L. and three other species of the same genus. Excised rhizomes and roots were assayed by incubation under ambient air and N₂-enriched air (pO₂ 0.10atm), using the acetylene reduction method. There was a lag of about 1 day before high activity was observed under a pO₂ of 0.10 atm, but under ambient air the lag was longer and varied from sample to sample. The duration of this lag usually coincided with that required for the establishment of a definite pO₂ level (a threshold value) in the incubation atmosphere. The threshold pO₂ value was about 0.15 atm for E. arvense, E. palustre, and E. hyemale, and 0.10 atm for E. ramosissimum. On incubation of the plant materials, acetylene reduction activity (ARA) increased gradually as the atmospheric pO₂ decreased, and maximum ARA was observed under a definite pO₂ value in the range from 0.04 to 0.01 atm.The highest value was 69nmol C₂H₄4 formed g^?1 fresh wt h^?1 with a sample of E. arvense atpO₂ 0.03 atm. When the pO₂ decreased below 0.01 atm, ARA decreased very rapidly and finally ceased. Several strains of N₂-fixing bacteria were isolated from rhizomes and roots of E. arvense and all were classified as members of the family Enterobacteriaceae.     

Degradation of ioxynil by a soil fungus, Fusarium solani

A fungus, Fusarium solani, isolated from the soil, degraded ioxynil (3,5-diiodo-4-hydroxyben-zonitrile) in pure culture into at least eight products. Five products were detected in the organic fractions extracted from a culture grown in [¹⁴C]cyano-labeled ioxynil. Three additional products were separated by ion-exchange chromatography of the acidified aqueous phase. Cultures grown in the presence of [¹⁴C]ring-labeled ioxynil produced the same products in the organic extract and four to five products in the aqueous phase. The cyano-carbon of ioxynil was released as CO₂ at a faster rate than that of ring-carbons and was released after the initial ring cleavage. Two of the metabolites were identified as 3,5-diiodo-4-hydroxybenzamide and 3,5-diiodo-4-hydroxybenzoic acid.     

Effects of oxygen tension on growth,respiration, and types of bacteria isolated from soil suspensions

Fifty-seven bacteria were isolated from soil suspensions incubated under pO₂ of 1.5 or 159 mm Hg and their growth and generic characteristics were elucidated.The isolates were cultured under both high (159 mm Hg) and low (3 mm Hg) pO₂. On the basis of their growth responses to the different pO₂, the isolates were classified into two types; (A-type) the lag time, specific growth rate, and/or maximum growth depended on pO₂, and (B-type) these three growth characteristics did not depend on pO₂. B-types were found only among isolates from soil suspensions incubated under the low pO₂. The respiration of some B-type isolates was inhibited by higher pO₂. No A-type isolates were inhibited by high pO₂.The isolates were classified into eight generic groups: Under 159 mm Hg O₂, Groups I(Bacillus spp) and IV(Pseudomonas spp etc.) dominated the others; under 1.5 mm Hg O₂, Group I, III(coryneform bacteria) and V(Alcaligenes spp etc.) dominated. Microaerophilic isolates (isolated only from the soil suspension incubated under 1.5 mm Hg O₂) were classified into Group V. Isolates belonging to the B-type were classified into the coryneform and Group V bacteria.