Isolation and Characterization of Mercury Resistant Bacillus sp. from Soils with an Extensive History as Substrates for Mercury Extraction in Mexico

Metal phytoextraction assisted by bacteria plays an important role in bioremediation systems. In this work, mercury-resistant bacterial strains were isolated from soils with high levels of mercury (San Joaquin, Queretaro State, Mexico) and identified as Bacillus sp. based on the 16S rDNA gene sequence analysis. The bacterial strains were found to exhibit different multiple mercury-resistance and carbon source utilization characteristics. The mercury reduction ability was tested through a volatilization assay. The bacterial isolates were also evaluated for their ability to promote growth and mercury uptake in tomato plants. In a roll towel assay, the maximum vigor index of tomato plants was obtained with the inoculation of Bacillus sp. A2, A12, B11, B15 and C1, while in a pot assay, the maximum vigor index was obtained with the inoculation of Bacillus sp. A6, A7 and B20, compared with un-inoculated controls in the presence of HgCl₂. Maximum Hg accumulation in the roots and shoots of tomato plants was obtained only with Bacillus sp. A7 in the roll towel assay, whereas in the pot assay, maximum accumulation was obtained with Bacillus sp. A12 compared with un-inoculated controls. Our results show that mercury accumulation in tissue is enhanced by these plant growth promoting bacterial strains, which recommends their possible use as microbe-assisted phytoremediation systems in mercury-polluted soils.     

Bacillus probiotics: an alternative to antibiotics for livestock production

The use of probiotics as feed supplements in animal production has increased considerably over the last decade, particularly since the ban on antibiotic growth promoters in the livestock sector. Several Bacillus sp. are attractive for use as probiotic supplements in animal feed due to their ability to produce spores. Their heat stability and ability to survive the low pH of the gastric barrier represent an advantage over other probiotic micro‐organisms. This review discusses important characteristics required for selection of Bacillus probiotic strains and summarizes the beneficial effect of Bacillus‐based feed additives on animal production. Although the mechanism of action of Bacillus probiotics has not been fully elucidated, they are effective in improving the growth, survival and health status of terrestrial and aquatic livestock. Bacillus strains also have utility in bioremediation and can reduce nitrogenous waste, thereby improving environmental conditions and water quality. Finally, recent innovative approaches for using Bacillus spores in various applications are discussed.     

Oily sludge degradation by bacteria from Ankleshwar, India

Three bacterial strains, Bacillus sp. SV9, Acinetobacter sp. SV4 and Pseudomonas sp., SV17 from contaminated soil in Ankleshwar, India were tested for their ability to degrade the complex mixture of petroleum hydrocarbons (such as alkanes, aromatics, resins and asphaltenes), sediments, heavy metals and water known as oily sludge. Gravimetric analysis showed that Bacillus sp. SV9 degraded approx. 59% of the oily sludge in 5 days at 30 °C whereas Acinetobacter sp. SV4 and Pseudomonas sp. SV17 degraded 37% and 35%. Capillary gas chromatographic analysis revealed that after 5 days the Bacillus strain was able to degrade oily sludge components of chain length C₁₂–C₃₀ and aromatics more effectively than the other two strains. Maximum drop in surface tension (from 70 to 28.4 mN/m) was accompanied by maximum biosurfactant production (6.7 g l⁻¹) in Bacillus sp. SV9 after 72 h, these results collectively indicating that this bacterial strain has considerable potential for bioremediation of oily sludge.     

Promising Strategies for the Mineralisation of 2,4,6-trinitrotoluene

2,4,6-trinitrotoluene (TNT) is known to be one of the most common military explosives. In spite of its established toxicity and mutagenicity for many organisms, soils and groundwater are still being frequently contaminated at manufacturing, disposal and TNT destruction sites. The inability of natural aquatic and soil biota to use TNT as growth substrate has been recognized as the primary limitation in the application of bioremediation processes to contaminated environments. However, promising degradation pathways have been recently discovered which may lead to the mineralisation of TNT. Significant advances have been made in studying the mechanism of TNT denitration, which can be considered as the major reaction and the driving force towards beneficial biodegradation. The possibilities to favour TNT denitration are discussed based on current knowledge of the enzymology and genetics of denitration in nitroaromatic degrading organisms. The literature survey demonstrates that the only enzymes characterized so far for their denitrase activity towards TNT belong to the class I flavin-dependent β/α barrel oxidoreductases, also known as the “Old Yellow Enzyme” family. In addition, this review provides an overview of strategies and future directions towards a rational search for new catabolic activities, including metagenomic library screening, plus new possibilities to improve the activity of known catabolic enzymes acting on TNT, such as DNA shuffling.     

Membrane fatty acids adaptive profile in the simultaneous presence of arsenic and toluene in <Emphasis Type="Italic">Bacillus</Emphasis> sp. ORAs2 and <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. ORAs5 strains

Bacillus sp. ORAs2 and Pseudomonas sp. ORAs5, two arsenic-resistant bacterial strains previously isolated from sediments of the Orbetello Lagoon, Italy, were tested for their adaptation to mixed contaminants on the level of membrane fatty acid composition. The two bacterial strains were characterized by high levels of arsenic resistance, and Pseudomonas sp. ORAs5 was also shown to be solvent-tolerant. The bacterial strains were exposed to mixtures of two toxic compounds: arsenic at fixed concentrations and toluene in variable amounts or, alternatively, toluene at constant values along with arsenic added at variable concentrations. Both strains react to the contaminants by changing the composition of their membrane fatty acids. Bacillus sp. strain ORAs2 showed a correlation between growth rate decreases and fatty acids degree of saturation increases in both cases, although pointedly in the presence of 1, 2, and 3 mM of toluene and different additions of arsenic, counteracting membranes fluidity induced by toxic compounds. In Pseudomonas sp. ORAs5, adaptive changes in membrane composition was observed both in terms of increases in the degree of saturation and in the trans/cis ratio of unsaturated fatty acids in the presence of varying toluene and constant arsenic concentrations, whereas only minor changes occurred with increasing arsenic and constant toluene concentrations. Thus, on the level of membrane composition, Bacillus sp. ORAs2 showed a higher potential for adaptation to the presence of mixed pollutants, suggesting its probable suitability for bioremediation purposes.     

Isolation and characterization of chromium(VI)-reducing Bacillus sp. FY1 and Arthrobacter sp. WZ2 and their bioremediation potential

Two native bacterial strains, FY1 and WZ2, that showed high chromium(VI)-reducing ability were respectively isolated from electroplating and tannery effluent–contaminated sites and identified as Bacillus and Arthrobacter. The objective of the present study was to evaluate their potential for future application in soil bioremediation. The results showed that both Bacillus sp. FY1 and Arthrobacter sp. WZ2 were tolerant to 1000 mg L^?1 Cr(VI) and capable of reducing 78–85% and 75–82% of Cr(VI) (100–200 mg L^?1) within 24 h, respectively. The Cr(VI) reduction rate decreased with increasing levels of Cr(VI) concentration (200–1000 mg L^?1). The optimum pH, temperature, and inoculum concentration for Cr(VI) reduction were found to be between pH 7.0 and 8.0; 30 and 35°C; and 1 × 10⁸ cells ml^?1, respectively. Further evidence for the bioremediation potential of Bacillus sp. FY1 and Arthrobacter sp. WZ2 was provided by the high capacity to reduce 100, 200, and 500 mg kg^?1 Cr(VI) in contaminated soil by 83–91%, 78–85%, and 71–78% within 7 days, respectively. These findings demonstrated the high potential of Bacillus sp. FY1 and Arthrobacter sp. WZ2 for application in future soil bioremediation.     

Toxicity of Hexavalent Chromium and Its Reduction by Bacteria Isolated from Soil Contaminated with Tannery Waste

An Arthrobacter sp. and a Bacillus sp., isolated from a long-term tannery waste contaminated soil, were examined for their tolerance to hexavalent chromium [Cr(VI)] and their ability to reduce Cr(VI) to Cr(III), a detoxification process in cell suspensions and cell extracts. Both bacteria tolerated Cr(VI) at 100 mg/ml on a minimal salts agar medium supplemented with 0.5% glucose, but only Arthrobacter could grow in liquid medium at this concentration. Arthrobacter sp. could reduce Cr(VI) up to 50 μg/ml, while Bacillus sp. was not able to reduce Cr(VI) beyond 20 μg/ml. Arthrobacter sp. was distinctly superior to the Bacillus sp. in terms of their Cr(VI)-reducing ability and resistance to Cr(VI). Assays with permeabilized (treated with toluene or Triton X 100) cells and crude extracts demonstrated that the Cr(VI) reduction was mainly associated with the soluble protein fraction of the cell. Arthrobacter sp. has a great potential for bioremediation of Cr(VI)-containing waste. Received: 13 June 2002 / Accepted: 13 September 2002     

Thermostable Flavin Reductase That Couples with Dibenzothiophene Monooxygenase,from Thermophilic Bacillus sp. DSM411: Purification,Characterization, and Gene Cloning

Flavin reductase is essential for the oxygenases involved in microbial dibenzothiophene (DBT) desulfurization. An enzyme of the thermophilic strain, Bacillus sp. DSM411, was selected to couple with DBT monooxygenase (DszC) from Rhodococcus erythropolis D-1. The flavin reductase was purified to homogeneity from Bacillus sp. DSM411, and the native enzyme was a monomer of M_r 16 kDa. Although the best substrates were flavin mononucleotide and NADH, the enzyme also used other flavin compounds and acted slightly on nitroaromatic compounds and NADPH. The purified enzyme coupled with DszC and had a ferric reductase activity. Among the flavin reductases so far characterized, the present enzyme is the most thermophilic and thermostable. The gene coded for a protein of 155 amino acids with a calculated mass of 17,325 Da. The enzyme was overproduced in Escherichia coli, and the specific activity in the crude extracts was about 440-fold higher than that of the wild-type strain, Bacillus sp. DSM411.     

Biodegradation of trinitrotoluene (TNT) by indigenous microorganisms from TNT-contaminated soil,and their application in TNT bioremediation

Soil and groundwater contaminated by munitions compounds is a crucial issue in environmental protection. Trinitrotoluene (TNT) is highly toxic and carcinogenic; therefore, the control and remediation of TNT contamination is a critical environmental issue. In this study, the authors characterized the indigenous microbial isolates from a TNT-contaminated site and evaluated their activity in TNT biodegradation. The bacteria Achromobacter sp. BC09 and Citrobacter sp. YC4 isolated from TNT-contaminated soil by enrichment culture with TNT as the sole carbon and nitrogen source (strain BC09) and as the sole nitrogen but not carbon source (strain YC4) were studied for their use in TNT bioremediation. The efficacy of degradation of TNT by indigenous microorganisms in contaminated soil without any modification was insufficient in the laboratory-scale pilot experiments. The addition of strains BC09 and YC4 to the contaminated soil did not significantly accelerate the degradation rate. However, the addition of an additional carbon source (e.g., 0.25% sucrose) could significantly increase the bioremediation efficiency (ca. decrease of 200 ppm for 10 days). Overall, the results suggested that biostimulation was more efficient as compared with bioaugmentation. Nevertheless, the combination of biostimulation and bioaugmentation using these indigenous isolates is still a feasible approach for the development of bioremediation of TNT pollution.     

Plant growth-promoting Bacillus sp. strain SDA-4 confers Cd tolerance by physio-biochemical improvements,better nutrient acquisition and diminished Cd uptake in Spinacia oleracea L.

Cadmium (Cd) is highly toxic metal for plant metabolic processes even in low concentration due to its longer half-life and non-biodegradable nature. The current study was designed to assess the bioremediation potential of a Cd-tolerant phytobeneficial bacterial strain Bacillus sp. SDA-4, isolated, characterized and identified from Chakera wastewater reservoir, Faisalabad, Pakistan, together with spinach (as a test plant) under different Cd regimes. Spinach plants were grown with and without Bacillus sp. SDA-4 inoculation in pots filled with 0, 5 or 10 mg kg⁻¹ CdCl₂-spiked soil. Without Bacillus sp. SDA-4 inoculation, spinach plants exhibited reduction in biomass accumulation, antioxidative enzymes and nutrient retention. However, plants inoculated with Bacillus sp. SDA-4 revealed significantly augmented growth, biomass accumulation and efficiency of antioxidative machinery with concomitant reduction in proline and MDA contents under Cd stress. Furthermore, application of Bacillus sp. SDA-4 assisted the Cd-stressed plants to sustain optimal levels of essential nutrients (N, P, K, Ca and Mg). It was inferred that the characterized Cd-tolerant PGPR strain, Bacillus sp. SDA-4 has a potential to reduce Cd uptake and lipid peroxidation which in turn maintained the optimum balance of nutrients and augmented the growth of Cd-stressed spinach. Analysis of bioconcentration factor (BCF) and translocation factor (TF) revealed that Bacillus sp. SDA-4 inoculation with spinach sequestered Cd in rhizospheric zone. Research outcomes are important for understanding morpho-physio-biochemical attributes of spinach-Bacillus sp. SDA-4 synergy which might provide efficient strategies to decrease Cd retention in edible plants and/or bioremediation of Cd polluted soil colloids.     

Biodegradation of 2-Nitrotoluene by <Emphasis Type="Italic">Micrococcus</Emphasis> sp. strain SMN-1

A bacterial consortium capable of degrading nitroaromatic compounds was isolated from pesticide-contaminated soil samples by selective enrichment on 2-nitrotoluene as a sole source of carbon and energy. The three different bacterial isolates obtained from bacterial consortium were identified as Bacillus sp. (A and C), Bacillus flexus (B) and Micrococcus sp. (D) on the basis of their morphological and biochemical characteristics and by phylogenetic analysis based on 16S rRNA gene sequences. The pathway for the degradation of 2-nitrotoluene by Micrococcus sp. strain SMN-1 was elucidated by the isolation and identification of metabolites, growth and enzymatic studies. The organism degraded 2-nitrotoluene through 3-methylcatechol by a meta-cleavage pathway, with release of nitrite.     

Application of Bacillus sp. strain VT-8 for decontamination of TNT-polluted sites

Bacterial strain Bacillus sp. VT-8 was shown to use trinitrotoluene (TNT) as the sole source of carbon, nitrogen, and energy, as well as to carry out its co-oxidation. Resistance of Bacillus sp. VT-8 to high TNT concentrations was shown. Efficient detoxification of TNT-contaminated soil and water samples was demonstrated. This strain may be recommended for TNT biodegradation at concentrations of up to 140 mg/L due to its high degradation activity and the absence of toxic effect of TNT on Bacillus sp. VT-8.     

Hydride-mediated reduction of 2,4,6-trinitrotoluene by yeasts as the way to its deep degradation

Broad screening of microorganisms from natural and anthropogenic ecological niches has revealed strains Candida sp. AN-L15 and Geotrichum sp. AN-Z4 which transform, 2,4,6-trinitrotoluene (TNT) via alternative pathways (with the domination of hydride ion-mediated reduction of the aromatic ring) and produce relatively high amounts of nitrites. According to the spectrophotometry data, the hydride attack of TNT by Candida sp. AN-L15 and Geotrichum sp. AN-Z4 grown at pH 5.0–8.0 leads to the mono-and dihydride complexes of TNT (H^?-TNT and 2H^?-TNT, respectively) and to protonated forms of the latter. Analysis by HPLC, GC-mass spectrometry, and ion chromatography revealed the products of deep conversion of TNT. The growth of the yeast strains in a weakly acidic medium with TNT (440 μM) is accompanied by formation of 2,4-dinitrotoluene (2,4-DNT, up to 18.2 μM). Together with accumulation of nitrites (up to 76.0 μM, depending on pH of the medium), these findings demonstrate the capacity of both strains for TNT denitration. Formation of 2,4-DNT reflects the realization of one of the possible mechanisms of TNT ortho-nitro group elimination and switching over to the pathways of metabolism of dinitrotoluenes, which are much more easily biodegradable than TNT. Simultaneously with the dominating TNT hydride attack, the mechanism of 4-and 6-electron reduction of the nitro group also functions in Candida sp. AN-L15 and Geotrichum sp. AN-Z4. Realization of the studied mechanisms of TNT transformation under growth of Candida sp. AN-L15 on n-alkane is important for bioremediation in the cases of combined pollution by oil products and explosives.     

Purification and characterization of NAD(P)H-dependent nitroreductase I from Klebsiella sp. C1 and enzymatic transformation of 2,4,6-trinitrotoluene

Three NAD(P)H-dependent nitroreductases that can transform 2,4,6-trinitrotoluene (TNT) by two reduction pathways were detected in Klebsiella sp. C1. Among these enzymes, the protein with the highest reduction activity of TNT (nitroreductase I) was purified to homogeneity using ion-exchange, hydrophobic interaction, and size exclusion chromatographies. Nitroreductase I has a molecular mass of 27 kDa as determined by SDS-PAGE, and exhibits a broad pH optimum between 5.5 and 6.5, with a temperature optimum of 30–40°C. Flavin mononucleotide is most likely the natural flavin cofactor of this enzyme. The N-terminal amino acid sequence of this enzyme does not show a high degree of sequence similarity with nitroreductases from other enteric bacteria. This enzyme catalyzed the two-electron reduction of several nitroaromatic compounds with very high specific activities of NADPH oxidation. In the enzymatic transformation of TNT, 2-amino-4,6-dinitrotoluene and 2,2′,6,6′-tetranitro-4,4′-azoxytoluene were detected as transformation products. Although this bacterium utilizes the direct ring reduction and subsequent denitration pathway together with a nitro group reduction pathway, metabolites in direct ring reduction of TNT could not easily be detected. Unlike other nitroreductases, nitroreductase I was able to transform hydroxylaminodinitrotoluenes (HADNT) into aminodinitrotoluenes (ADNT), and could reduce ortho isomers (2-HADNT and 2-ADNT) more easily than their para isomers (4-HADNT and 4-ADNT). Only the nitro group in the ortho position of 2,4-DNT was reduced to produce 2-hydroxylamino-4-nitrotoluene by nitroreductase I; the nitro group in the para position was not reduced.     

Role of heavy metal resistant Ochrobactrum sp. and Bacillus spp. strains in bioremediation of a rice cultivar and their PGPR like activities

The present study demonstrates the metal toxicity ameliorating and growth promoting abilities of three different bacterial isolates when applied to rice as host plant. The three bacterial strains included a cadmium resistant Ochrobactrum sp., a lead resistant Bacillus sp. and an arsenic resistant Bacillus sp. designated as CdSP9, PbSP6, and AsSP9, respectively. When these isolates were used as inocula applied to metal-treated rice plants of variety Satabdi, the germination percentage, relative root elongation (RRE), amylase and protease activities were increased. The toxic effect of metal was reduced in presence of these bacteria. The overall biomass and root/shoot ratio were also enhanced by bacterial inoculation. Hydroponic studies showed that the superoxide dismutase (SOD) activity and malondialdehyde (MDA) level, which had been increased in the presence of metal stress in rice roots, were lowered by the bacterial inoculation. In addition, all three strains were 1-aminocyclopropane-1-carboxylate (ACC) deaminase and catalase positive, whereas siderophore producing ability was lacking in PbSP6. However, both PbSP6 and AsSP9 were protease positive and could hydrolyse starch. The data indicate that these bacteria have promise for bioremediation as well as for plant growth promotion.     

Application of Biofilm-Forming Bacteria on the Enhancement of Organophosphorus Fungicide Degradation

This study aimed to develop technology enhancing the biodegradation efficacy against organophosphorus fungicide with biofilm-forming bacteria in situ. Using the crystal violet staining method, two bacterial strains having biofilm formation capability were isolated and identified as Pseudomonas sp. C7 and Bacillus sp. E5. Compared with the culture of tolclofos-methyl degrader Sphingomonas sp. 224, biofilm formation was improved by co-inoculation with biofilm-forming bacterium Bacillus sp. E5. Evaluated in liquid culture conditions, this two-species mixed consortium was observed to degrade tolclofos-methyl more effectively than Sphingomonas sp. 224 alone, with an approximately 90% degradation efficiency within 48 h of dosing. The improved effectiveness of the consortium biofilm was reflected using soil in situ with an approximately 7% increased degradation ratio over Sphingomonas sp. 224 alone. This is the first report demonstrating improved bioremediation degradation efficacy against tolclofos-methyl exhibited by a consortium biofilm. This work presents a possible effective bioremediation strategy using a specific biofilm composition against pollutants containing organophosphorus compounds in situ.     

Exploring the application of biostimulation strategy for bacteria in the bioremediation of industrial effluent

The purpose of this study was to isolate and characterise toxic element-resistant bacteria from acid mine drainage water and to apply them in the bioremediation of industrial effluent, as well as to identify optimal effluent:nutrient concentration for onsite biostimulation strategy. Wastewater samples were collected from acid mine drainage and industry. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was employed for elemental composition analysis. Isolated bacterial strains were characterised using molecular methods. Bioremediation assays were employed to determine the extent of bacterial tolerance and removal of toxic elements using a biostimulation strategy employing minimal salt medium (MSM) at varied concentrations and positive and negative controls of only MSM and industrial effluent, respectively. Two bacterial strains demonstrated resistance to toxic elements, Bacillus sp. MGI101 and Lysinibacillus sp. MGI102 both isolated from the AMD sites. However, no observable growth of toxic metal-resistant bacteria was obtained from the industrial effluents. Bacterial strains MGI101 and MGI102 demonstrated high resistance to target toxic elements during the screening and tolerance assays. Remarkably, Bacillus sp. MGI101 demonstrated greater ability to remove toxic elements including arsenic, chromium, zinc, copper and aluminium in undiluted solutions of the industrial effluent, with its highest removal capacity observed at > 60% for arsenic and aluminium. Both Bacillus sp.MGI101 and Lysinibacillus sp. MGI102 demonstrated varied abilities for the removal of toxic elements from dilution concentration of effluent mixed with MSM. However, the optimal dilution ratio observed in this experiment was 5:15 (effluent:MSM). Overall results demonstrated that isolated bacterial strains have the potential to be employed in bioremediation programmes of acid mine drainages and multi-element contaminated water.

     

Pyrene Biodegradation by Bacillus spp. Isolated from Coal Tar–Contaminated Soil

Aerobic, mesophilic bacteria from coal tar–contaminated soil were analyzed for pyrene utilization capacity and identified by 16S ribosomal DNA sequencing as members of three genera: Bacillus spp., Pseudomonas sp., and Rhodococcus sp. The soil contained nine different hazardous polyaromatic hydrocarbons (PAHs): benzo[g, h, i]perylene, dibenzo[a, h]anthracene, indeno[1,2,3-c,d]pyrene, pyrene, acenaphthylene, fluorene, phenanthrene, benzo[k]fluoranthene, and benzo[b]fluoranthene. Bacillus spp. (PK-6) MTCC 1005 showed 56.4% utilization of pyrene (C₁₆H₁₀) (50 μg ml^?1) in 4 days, with growth associated biosurfactant activity and resulted in the formation of five new intermediates: phenanthrene (C₁₄H₁₀), 9,10-diphenylphenanthrene (C₂₆H₁₈), 9-methoxyphenanthrene (C₁₅H₁₂O), 5,6,7,8-tetrahydro-1-naphthoic acid (C₁₁H₁₂O₂), and 1,6,7-trimethylnaphthalene (C₁₃H₁₄). The results suggested that Bacillus spp. could be found suitable for practical field application for effective in situ PAH bioremediation.     

Microbial degradation of explosives: biotransformation versus mineralization

The nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) is a reactive molecule that biotransforms readily under both aerobic and anaerobic conditions to give aminodinitrotoluenes. The resulting amines biotransform to give several other products, including azo, azoxy, acetyl and phenolic derivatives, leaving the aromatic ring intact. Although some Meisenheimer complexes, initiated by hydride ion attack on the ring, can be formed during TNT biodegradation, little or no mineralization is encountered during bacterial treatment. Also, although the ligninolytic physiological phase and manganese peroxidase system of fungi can cause some TNT mineralization in liquid cultures, little to no mineralization is observed in soil. Therefore, despite more than two decades of intensive research to biodegrade TNT, no biomineralization-based technologies have been successful to date. The non-aromatic cyclic nitramine explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) lack the electronic stability enjoyed by TNT or its transformed products. Predictably, a successful enzymatic change on one of the N–NO₂ or C–H bonds of the cyclic nitramine would lead to a ring cleavage because the inner C–N bonds in RDX become very weak (<2 kcal/mol). Recently this hypothesis was tested and proved feasible, when RDX produced high amounts of carbon dioxide and nitrous oxide following its treatment with either municipal anaerobic sludge or the fungus Phanaerocheate chrysosporium. Research aimed at the discovery of new microorganisms and enzymes capable of mineralizing energetic chemicals and/or enhancing irreversible binding (immobilization) of their products to soil is presently receiving considerable attention from the scientific community. Received: 14 February 2000 / Received revision: 9 June 2000 / Accepted: 13 June 2000     

Metabolism of nitrophenols by bacteria isolated from parathion-amended flooded soil

Two bacterial isolates from parathion-amended flooded soil, Pseudomonas sp. and Bacillus sp., were examined for their ability to decompose nitrophenols. Uniformly labelled ¹⁴C-p-nitrophenol was metabolized by both bacteria, ¹⁴CO₂ and nitrite being end products. A substantial portion (23% for Pseudomonas sp. and 80% for Bacillus sp.) of radioactivity applied as p-nitrophenol was accounted for as ¹⁴CO₂ at the end of a 72-h period; 8 to 16% remained in the water phase after solvent extraction. Pseudomonas sp. produced nitrite also from 2,4-dinitrophenol, but only after a lag, and not from o- and m-nitrophenols. Interestingly, m-nitrophenol, known for its resistance to biodegradation because of meta substitution, was decomposed by Bacillus sp., resulting in the formation of nitrite and phenol; o-nitrophenol and 2,4-dinitrophenol resisted degradation by this bacterium.