Identification and catabolic activity of well-derived gasoline-degrading bacteria from a contaminated aquifer

Phenotypic and Genomic Characterization of Pseudomonas wuhanensis sp. nov., a Novel Species with Promising Features as a Potential Plant Growth-Promoting and Biocontrol Agent

Plant growth-promoting rhizobacterial strain FP607T was isolated from the rhizosphere of beets in Wuhan, China. Strain FP607T exhibited significant antagonism toward several phytopathogenic bacteria, indicating that FP607T may produce antimicrobial metabolites and has a stronger biocontrol efficacy against plant pathogens. Growth-promoting tests showed that FP607T produced indole-3-acetic acid (IAA), NH3, and ferritin. The genome sequence of strain FP607T was 6,590,972 bp long with 59.0% G + C content. The optimum temperature range was 25-30 °C, and the optimum pH was 7. The cells of strain FP607T were Gram-negative, short, and rod-shaped, with polar flagella. The colonies on the King's B (KB) agar plates were light yellow, smooth, and circular, with regular edges. A phylogenetic analysis of the 16S rRNA sequence and a multilocus sequence analysis (MLSA) showed that strain FP607T was most closely related to the type of strain Pseudomonas farris SWRI79T. Based on a polyphasic taxonomic approach, strain FP607T was identified as a novel species within the genus Pseudomonas, for which the name Pseudomonas wuhanensis sp. nov. was proposed. The type of strain used was FP607T (JCM 35688, CGMCC 27743, and ACCC 62446).

Isolation, identification, and optimization of conditions for the degradation of four sulfonamide antibiotics and their metabolic pathways in Pseudomonas stutzeri strain DLY-21

Overuse of sulfonamides in aquaculture and agriculture leads to residual drugs that cause serious pollution of the environment. However, the residues of sulfonamides in the environment are not unique, and the existing microbial degradation technology has a relatively low degradation rate of sulfonamides. Therefore, in this study, a Pseudomonas stutzeri strain (DLY-21) with the ability to degrade four common SAs was screened and isolated from aerobic compost. Under optimal conditions, the DLY-21 strain degraded four sulfonamides simultaneously within 48 h, and the degradation rates were all over 90%, with the average degradation rates of SAs being sulfoxide (SDM) ≈ sulfachloropyridazine (SCP) > sulfa quinoxaline (SQ) > sulfadiazine (SQ). In addition, the main compounds of the strain DLY-21-degrading SAs were identified by LC-MS analysis. On this basis, four detailed reaction pathways for SA degradation were deduced. This is the first report of the use of a P. stutzeri strain to degrade four sulfonamide antibiotics (SQ, SDM, SCP, and SM1), which can improve the removal efficiency of sulfonamide antibiotic pollutants and thus ameliorate environmental pollution. The results showed that DLY-21 had a good degradation effect on four SAs (SQ, SDM, SCP, and SM1).

Pseudomonas benzopyrenica sp. nov., isolated from soil, exhibiting high-efficiency degradation of benzo(a)pyrene

A Gram-negative, yellow-pigmented, aerobic and rod-shaped bacterium, designated as strain BaP3T, was isolated from the soil. Strain BaP3T grew at 16-37℃ (optimum, 30 °C) and pH 6.0-8.0 (optimum, pH 7.0). Additionally, strain BaP3T could tolerate NaCl concentrations in the range 0-6 % (optimum, 1%). Moreover, strain BaP3T was motile by flagella. The phylogenetic analysis of 16S rRNA sequences showed that strain BaP3T belonged to the genus Pseudomonas, and the sequence was most closely related to Pseudomonas oryzihabitans CGMCC 1.3392T and Pseudomonas psychrotolerans DSM 15758T, with 99.66 % sequence similarity. Pseudomonas rhizoryzae RY24T was the next closely related species, exhibiting 99.38 % 16S rRNA gene sequence similarity. The DNA-DNA hybridization and average nucleotide identity values between strain BaP3T and its closely related types were below 50 and 92 %, respectively. Both results were below the cut-off for species distinction. The genomic DNA G+C content of strain BaP3T was 65.30 mol%. The predominant quinone in strain BaP3T was identified as ubiquinone Q-9. The major cellular fatty acids were summed feature 8 (C18 : 1  ω7c and/or C18 : 1  ω6c), summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c) and C16 : 0. These results indicated that strain BaP3T represents a novel species in the genus Pseudomonas. The type strain is BaP3T (CCTCC AB 2022379T=JCM 35914T), for which the name Pseudomonas benzopyrenica sp. nov. is proposed.

Isolation of Pseudomonas aromaticivorans sp. nov from a hydrocarbon-contaminated groundwater capable of degrading benzene-, toluene-, m- and p-xylene under microaerobic conditions

Members of the genus Pseudomonas are known to be widespread in hydrocarbon contaminated environments because of their remarkable ability to degrade a variety of petroleum hydrocarbons, including BTEX (benzene, toluene, ethylbenzene and xylene) compounds. During an enrichment investigation which aimed to study microaerobic xylene degradation in a legacy petroleum hydrocarbon-contaminated groundwater, a novel Gram-stain-negative, aerobic, motile and rod-shaped bacterial strain, designated as MAP12T was isolated. It was capable of degrading benzene, toluene, meta- and para- xylene effectively under both aerobic and microaerobic conditions. The 16S rRNA gene sequence analysis revealed that strain MAP12T belongs to the genus Pseudomonas, with the highest 16S rRNA gene similarity to Pseudomonas linyingensis LYBRD3-7T (98.42%), followed by Pseudomonas sagittaria JCM 18195T (98.29%) and Pseudomonas alcaliphila JCM 10630T (98.08%). Phylogenomic tree constructed using a concatenated alignment of 92 core genes indicated that strain MAP12T is distinct from any known Pseudomonas species. The draft genome sequence of strain MAP12T is 4.36 Mb long, and the G+C content of MAP12T genome is 65.8%. Orthologous average nucleotide identity (OrthoANI) and digital DNA–DNA hybridization (dDDH) analyses confirmed that strain MAP12T is distinctly separated from its closest neighbors (OrthoANI < 89 %; dDDH < 36%). Though several members of the genus Pseudomonas are well known for their aerobic BTEX degradation capability, this is the first report of a novel Pseudomonas species capable of degrading xylene under microaerobic conditions. By applying genome-resolved metagenomics, we were able to partially reconstruct the genome of strain MAP12T from metagenomics sequence data and showed that strain MAP12T was an abundant member of the xylene-degrading bacterial community under microaerobic conditions. Strain MAP12T contains ubiquinone 9 (Q9) as the major respiratory quinone and diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine as major polar lipids. The major cellular fatty acids of strain MAP12T are summed feature 3 (C16:1ω6c and/or C16:1ω7c), C16:0 and summed feature 8 (C18:1ω6c and/or C18:1ω7c). The results of this polyphasic study support that strain MAP12T represents a novel species of the genus Pseudomonas, hence the name of Pseudomonas aromaticivorans sp. nov. is proposed for this strain considering its aromatic hydrocarbon degradation capability. The type strain is MAP12T (=LMG 32466, =NCAIM B.02668).

Response relationship of environmental factors caused by toluene concentration during leaching of capillary zone

Due to the leaching of capillary water, the petroleum pollutants initially trapped in vadose zone may migrate to lower aquifer, thus increasing the risk of groundwater pollution. In order to explore the effect of capillary leaching on toluene-contaminated soil and the relationship between toluene concentration (TC) and environmental factors (EFs) during the leaching process, the sterilized and non-sterilized soil column experiments were designed. The EFs were used to estimate TC. The results showed that the difference between leaching and volatilization rates directly determined the changing trend of toluene concentration in capillary water. The toluene concentration in the medium always showed decreasing trend due to leaching. The indigenous microbial community structure of the non-sterilized soil column was analyzed by 16S rRNA sequencing. It was found that indigenous microorganisms could degrade toluene after 33.0 days of acclimatation. The microbial population was dominated by bacteria, among them the Ellin6055 strain and Pseudomonas, Pseudoxanthomonas, Cupriavidus, Bdellovibrio, Sphingobium, Phenylobacterium, Ramlibacter, Bradyrhizobium, Shinella genera. The Pseudomonas was the most crucial bacterial genus that degraded toluene. Indigenous microbial degradation was the fundamental reason for strong response relationship. Furthermore, we suggested a relationship of function between environmental factors (pH, DO, ORP) and time (t) for toluene attenuation: C₀+ln(e^Atα^Bγ^Cβ)=C_Toluene, (α, β, γ represent the pH, DO, and ORP in leaching capillary water, respectively; A, B, and C represent undetermined coefficients), and the fitting coefficient R² > 0.950. This relationship can only characterize the attenuation process of capillary zone leaching on toluene. However, it may still be utilized to give a theoretical foundation for understanding the dynamic of pollutant concentration change processes under specific environmental factors.

Polycyclic Aromatic Hydrocarbons Degradation by Aquatic Bacteria Isolated from Khazar Sea, the World’s Largest Lake

Background: Aquatic microorganisms have an important role in the bioremediation of environmental pollutants. Polycyclic Aromatic Hydrocarbons (PAHs) are described as dangerous pollutants that can bind covalently to the nucleic acids, causing mutations. Therefore, they have carcinogenic and toxic properties. Also, are involved in diseases such as asthma, lung dysfunction, and chronic bronchitis. This study aimed to isolate and characterize aquatic bio-degrading bacteria from the world’s largest lake, Khazar, with the ability to use PAHs as only carbon source. Methods: Samples were taken from the estuary of Siah Rud River (Mazandaran province, Iran) and Fereydunkenar beach leading to isolation of twenty-three bacteria on marine agar and sea water media. The isolates were cultured on separate ONR7a medium, each supplemented with only one PAH; as the sole carbon source; including naphthalene, phenanthrene, and anthracene. Results: Eleven bacterial isolates were able to grow on supplemented media: TBZ-E1, TBZ-E2, TBZ-E3, TBZ-S12, TBZ-S16, TBZ-E20, TBZ-SF2, TBZ-F1, TBZ-F2, TBZ-F3 and TBZ2. These isolates belong to Alteromonas, Marivivens, Pseudoalteromonas, Vibrio, Shewanella, Photobacterium, Mycobacterium and Pseudomonas genera. The qualitative analysis showed that the consortium of isolates TBZ-F1, TBZ-F2, TBZ-F3, TBZ-SF2, and TBZ2 displayed the highest degradation rate for phenanthrene and naphthalene. Naphthalene, phenanthrene, and anthracene were potently degraded by TBZ2 and TBZ-SF2 and accordingly were subjected to measure degradation potential of mentioned PAHs. Conclusion: The bacterial isolates of Caspian lake have a critical duty in biodegradation of PAHs. These isolates are representative samples of the bacterial population of this lake, participating in the purification process of this habitat.

The Fate of MTBE and BTEX in Constructed Wetlands

Hydrocarbon contamination of water resources is a global issue. These compounds are generated and discharged into the environment in industrial areas from chemical and petrochemical plants, oil refineries, power plants, and so forth. Fuel hydrocarbons, namely, BTEX (benzene, toluene, ethylbenzene, and xylenes) and MTBE (methyl tert-butyl ether), are commonly found in groundwater, posing environmental and health risks to humans and ecosystems. Nature-based technologies represent an alternative solution, providing high efficiency, an environmentally friendly character, simple operation, and cost efficiency, which are characteristics particularly desired by the international petroleum industry. This article discusses the use of the green technology of constructed wetlands to remediate water polluted with hydrocarbons. Although the number of related international experiences and studies is limited, the article presents the latest developments of wetland technology for the removal of MTBE and benzene-BTEX. The discussion includes the overall efficiency of the different wetland types that have been tested and used, the main transformation and removal processes that regulate the fate of BTEX and MTBE in constructed wetlands, and the potential for future investigations.

Metataxonomic analyses reveal differences in aquifer bacterial community as a function of creosote contamination and its potential for contaminant remediation

Metataxonomic approach was used to describe the bacterial community from a creosote-contaminated aquifer and to access the potential for in situ bioremediation of the polycyclic aromatic hydrocarbons (PAHs) by biostimulation. In general, the wells with higher PAH contamination had lower richness and diversity than others, using the Shannon and Simpson indices. By the principal coordinate analysis (PCoA) it was possible to observe the clustering of the bacterial community of most wells in response of the presence of PAH contamination. The significance analysis using edgeR package of the R program showed variation in the abundance of some Operational Taxonomic Units (OTUs) of contaminated wells compared to uncontaminated ones. Taxons enriched in the contaminated wells were correlated positively (p < 0.05) with the hydrocarbons, according to redundancy analysis (RDA). All these enriched taxa have been characterized as PAH degrading agents, such as the genus Comamonas, Geobacter, Hydrocarboniphaga, Anaerolinea and Desulfomonile. Additionally, it was possible to predict, with the PICRUSt program, a greater proportion of pathways and genes related to the degradation of PAHs in the wells with higher contamination levels. We conclude that the contaminants promoted the enrichment of several groups of degrading bacteria in the area, which strengthens the feasibility of applying biostimulation as an aquifer remediation strategy.

An Investigation of Petrol Metabolizing Bacteria Isolated from Contaminated Soil Samples Collected from Various Fuel Stations

The present study aimed to isolate the high-efficiency petrol metabolizing thermophilic bacteria from petrol contaminated soil samples. Isolation was carried out through enrichment culture, serial dilution and pour plate methods using the petrol supplemented minimal salt media. The isolated bacteria were analyzed to document growth behavior, petrol removal efficiencies, antibiotic resistance profile, and biochemical characteristics. The 16S rRNA based phylogenetic analysis helped to reveal the identity of isolated bacterial species and construct the phylogenetic trees. Total nine bacteria were isolated, out of which three (IUBP2, IUBP3, IUBP5) were identified as Brevibacillus formosus, one (IUBP1) was found similar to Brevibacillus agri, four (IUBP7, IUBP8, IUBP13, and IUBP14) shared homology with Burkholderia lata, and one (IUBP15) with Burkholderia pyrrocinia. All the isolates were fast growing and exhibited considerable petrol degradation potential. The highest petrol removal efficiency (69.5% ± 13.44/6 days) was recorded for the strain IUBP15 at a petrol concentration of 0.1% (v/v). All bacteria studied (100%) were positive for esculinase and phosphatase. Many strains exhibited positive responses for arginine dehydrolase (22%), β-naphthylamidase (11%), β-D-glucosaminide (33%), mannitol (55%), sorbitol (66%) and inulin (88%) fermentation test. While all were sensitive to the antibiotics, some of them were found resistant against chloramphenicol and oxacillin. The remarkable biochemical characteristics and considerable petrol removal potential (40–70%) highlights utilization of the bacteria isolated for petrol bioremediation, mineralization of organophosphates, dairy and food industry, and also as biofertilizers and biocontrol agents.

Effect of the nitrification inhibitor (3, 4-dimethylpyrazole phosphate) on the activities and abundances of ammonia-oxidizers and denitrifiers in a phenanthrene polluted and waterlogged soil

Through a 60-day microcosm incubation, the effect of 3, 4-dimethylpyrazole phosphate (DMPP) on the activities and abundances of ammonia-oxidizers and denitrifiers in phenanthrene-polluted soil was investigated. Five treatments were conducted for clean soil (CK), phenanthrene added (P), phenanthrene and DMPP added (PD), phenanthrene and urea added (PU), and phenanthrene, urea, and DMPP added (PUD) soils. The results indicate that the potential nitrification rate (PNR) in the P treatment was significantly higher than that in the PD treatment only on day 7, whereas the PNR in the PU treatment was significantly higher than that in the PUD treatment on each sampling day. The abundance of soil ammonia-oxidizing bacteria (AOB) in the PU treatment was significantly higher than that in the PUD treatment on each sampling day. Moreover, the abundance of AOB but rather than the ammonia-oxidizing archaea (AOA) had significantly positive correlation with soil PNR (P < 0.05). DMPP showed no obvious effect on the soil denitrification enzyme activity (DEA), which could have inhibited the abundances of denitrification-related narG, nirS, and nirK genes. The results of this study should provide a deeper understanding of the interaction between soil polycyclic aromatic hydrocarbons (PAH) contamination, ammonia oxidization, and denitrification, and offer valuable information for assessing the potential contribution of denitrification for soil PAH elimination.

Effects of null mutation of the heat-shock gene htpG on the production of virulence factors by Pseudomonas aeruginosa

AIM

Pseudomonas aeruginosa is one of the most clinically important opportunistic pathogen in humans. The aim of the project was to study effects of HtpG on the selected virulence factors responsible for pathogenesis and biofilm formation of P. aeruginosa.

METHODOLOGY

By characterizing a htpG null mutant of P. aeruginosa, we have identified the role of HtpG in the production of selected factors.

RESULTS

We showed that ΔhtpG mutant affects many physiological processes containing: decreased activity of the LasA protease, reduction of biofilm formation, decreased motility, and diminished amount of rhamnolipids and pyoverdine/pyocyanin. These defects were most evident when the ΔhtpG strain was cultured at 42°C.

CONCLUSION

Our findings demonstrate the unexplored role of HtpG in the pathogenicity of P. aeruginosa, and indicate potential targets for antibacterial therapeutics. [Formula: see text].

Draft genome sequence of a caprolactam degrader bacterium: Pseudomonas taiwanensis strain SJ9

Pseudomonas taiwanensis strain SJ9 is a caprolactam degrader, isolated from industrial wastewater in South Korea and considered to have the potential for caprolactam bioremediation. The genome of this strain is approximately 6.2 Mb (G + C content, 61.75%) with 6,010 protein-coding sequences (CDS), of which 46% are assigned to recognized functional genes. This draft genome of strain SJ9 will provide insights into the genetic basis of its caprolactam-degradation ability.

Antibiotic multiresistance analysis of mesophilic and psychrotrophic Pseudomonas spp. isolated from goat and lamb slaughterhouse surfaces throughout the meat production process

The aim of this study was to investigate the phenotypic and genotypic antibiotic resistance profiles of pseudomonads isolated from surfaces of a goat and lamb slaughterhouse, which were representative of areas that are possible sources of meat contamination. Mesophilic (85 isolates) and psychrotrophic (37 isolates) pseudomonads identified at the species level generally were resistant to sulfamethoxazole, erythromycin, amoxicillin, ampicillin, chloramphenicol, trimethoprim, rifampin, and ceftazidime (especially mesophiles), as well as colistin and tetracycline (especially psychrotrophes). However, they generally were sensitive to ciprofloxacin, gentamicin, imipenem, and kanamycin regardless of species identity. Worryingly, in the present study, we found multidrug resistance (MDR) to up to 13 antibiotics, which was related to intrinsic and acquired resistance mechanisms. Furthermore, a link between various antimicrobial resistance genes was shown for beta-lactams and tetracycline, trimethoprim, and sulfonamides. The distribution and resistome-based analysis of MDR pseudomonads in different slaughterhouse zones indicated that the main sources of the identical or related pseudomonad strains were the animals (feet and wool) and the slaughterhouse environment, being disseminated from the beginning, or entrance environment, to the environment of the finished meat products. Those facts must be taken into consideration to avoid cross-contamination with the subsequent flow of mobile resistance determinants throughout all slaughterhouse zones and then to humans and the environment by the application of adequate practices of hygiene and disinfection measures, including those for animal wool and feet and also the entrance environment.

Application of micronucleus test and comet assay to evaluate BTEX biodegradation

The BTEX (benzene, toluene, ethylbenzene and xylene) mixture is an environmental pollutant that has a high potential to contaminate water resources, especially groundwater. The bioremediation process by microorganisms has often been used as a tool for removing BTEX from contaminated sites. The application of biological assays is useful in evaluating the efficiency of bioremediation processes, besides identifying the toxicity of the original contaminants. It also allows identifying the effects of possible metabolites formed during the biodegradation process on test organisms. In this study, we evaluated the genotoxic and mutagenic potential of five different BTEX concentrations in rat hepatoma tissue culture (HTC) cells, using comet and micronucleus assays, before and after biodegradation. A mutagenic effect was observed for the highest concentration tested and for its respective non-biodegraded concentration. Genotoxicity was significant for all non-biodegraded concentrations and not significant for the biodegraded ones. According to our results, we can state that BTEX is mutagenic at concentrations close to its water solubility, and genotoxic even at lower concentrations, differing from some described results reported for the mixture components, when tested individually. Our results suggest a synergistic effect for the mixture and that the biodegradation process is a safe and efficient methodology to be applied at BTEX-contaminated sites.

Aerobic denitrification by novel isolated strain using NO-₂-N as nitrogen source

Biological denitrification reaction can be achieved under aerobic environment. Few aerobic denitrifiers using nitrite as sole nitrogen source were identified. Using nitrite as the sole nitrogen source, this work assessed the denitrification activity of yy7, an aerobic heterotrophic denitrifier identified as Pseudomonas sp. (94% similarity) by 16S rRNA sequencing analysis. The logistic equation describes the cell growth curve, yielding a generation time of 2.9h at an initial 18 mg l(-1)NO(-)₂-N. Reduction of NO(-)₂-N was primarily achieved during its logarithmic growth phase, and was accompanied by an increase in suspension pH and near complete consumption of dissolved oxygen. Three genes relating to nirK, norB, and nosZ were noted to involve in isolate strain. Isolate yy7 can survive and remove up to 40 mg l(-1)NO(-)₂-N and, hence, can be applied as an effective aerobic denitrifier during simultaneous nitrification and denitrification via nitrite processes.

Hetero-oligomeric cell wall channels (porins) of Nocardia farcinica

The cell wall of Nocardia farcinica contains a cation-selective cell wall channel, which may be responsible for the limited permeability of the cell wall of N. farcinica for negatively charged antibiotics. Based on partial sequencing of the protein responsible for channel formation derived from N. farcinica ATTC 3318 we were able to identify the corresponding genes (nfa15890 and nfa15900) within the known genome of N. farcinica IFM 10152. The corresponding genes of N. farcinica ATTC 3318 were separately expressed in the Escherichia coli BL21DE3Omp8 strain and the N-terminal His10-tagged proteins were purified to homogeneity using immobilized metal affinity chromatography. The pure proteins were designated NfpANHis and NfpBNHis, for N. farcinica porin A and N. farcinica porin B. The two proteins were checked separately for channel formation in lipid bilayers. Our results clearly indicate that the proteins NfpANHis and NfpBNHis expressed in E. coli could only together form a channel in lipid bilayer membranes. This means that the cell wall channel of N. farcinica is formed by a heterooligomer. NfpA and NfpB form together a channel that may structurally be related to MspA of Mycobacterium smegmatis based on amino acid comparison and renaturation procedure.

BTEX biodegradation by bacteria from effluents of petroleum refinery

Groundwater contamination with benzene, toluene, ethylbenzene and xylene (BTEX) has been increasing, thus requiring an urgent development of methodologies that are able to remove or minimize the damages these compounds can cause to the environment. The biodegradation process using microorganisms has been regarded as an efficient technology to treat places contaminated with hydrocarbons, since they are able to biotransform and/or biodegrade target pollutants. To prove the efficiency of this process, besides chemical analysis, the use of biological assessments has been indicated. This work identified and selected BTEX-biodegrading microorganisms present in effluents from petroleum refinery, and evaluated the efficiency of microorganism biodegradation process for reducing genotoxic and mutagenic BTEX damage through two test-systems: Allium cepa and hepatoma tissue culture (HTC) cells. Five different non-biodegraded BTEX concentrations were evaluated in relation to biodegraded concentrations. The biodegradation process was performed in a BOD Trak Apparatus (HACH) for 20 days, using microorganisms pre-selected through enrichment. Although the biodegradation usually occurs by a consortium of different microorganisms, the consortium in this study was composed exclusively of five bacteria species and the bacteria Pseudomonas putida was held responsible for the BTEX biodegradation. The chemical analyses showed that BTEX was reduced in the biodegraded concentrations. The results obtained with genotoxicity assays, carried out with both A. cepa and HTC cells, showed that the biodegradation process was able to decrease the genotoxic damages of BTEX. By mutagenic tests, we observed a decrease in damage only to the A. cepa organism. Although no decrease in mutagenicity was observed for HTC cells, no increase of this effect after the biodegradation process was observed either. The application of pre-selected bacteria in biodegradation processes can represent a reliable and effective tool in the treatment of water contaminated with BTEX mixture. Therefore, the raw petroleum refinery effluent might be a source of hydrocarbon-biodegrading microorganisms.

Novel aerobic benzene degrading microorganisms identified in three soils by stable isotope probing

The remediation of benzene contaminated groundwater often involves biodegradation and although the mechanisms of aerobic benzene biodegradation in laboratory cultures have been well studied, less is known about the microorganisms responsible for benzene degradation in mixed culture samples or at contaminated sites. To address this knowledge gap, DNA based stable isotope probing (SIP) was utilized to identify active benzene degraders in microcosms constructed with soil from three sources (a contaminated site and two agricultural sites). For this, replicate microcosms were amended with either labeled (¹³C) or unlabeled benzene and the extracted DNA samples were ultracentrifuged, fractioned and subject to terminal restriction fragment length polymorphism (TRFLP). The dominant benzene degraders (responsible for ¹³C uptake) were determined by comparing relative abundance of TRFLP phylotypes in heavy fractions of labeled benzene (¹³C) amended samples to the controls (from unlabeled benzene amended samples). Two phylotypes (a Polaromonas sp. and an Acidobacterium) were the major benzene degraders in the microcosms constructed from the contaminated site soil, whereas one phylotype incorporated the majority of the benzene-derived ¹³C in each of the agricultural soils ("candidate" phylum TM7 and an unclassified Sphingomonadaceae).

The occurrence of multidrug-resistant Pseudomonas aeruginosa on hydrocarbon-contaminated sites

The main aim of this paper was the comprehensive estimation of the occurrence rate and the antibiotic-resistance conditions of opportunistic pathogen Pseudomonas aeruginosa in hydrocarbon-contaminated environments. From 2002 to 2007, 26 hydrocarbon-contaminated sites of Hungary were screened for the detection of environmental isolates. Altogether, 156 samples were collected and examined for the determination of appearance, representative cell counts, and antibiotic-resistance features of P. aeruginosa. The detected levels of minimal inhibitory concentrations of ten different drugs against 36 environmental strains were compared to the results of a widely used reference strain ATCC 27853 and four other clinical isolates of P. aeruginosa. Based on our long-term experiment, it can be established that species P. aeruginosa was detectable in case of 61.5% of the investigated hydrocarbon-contaminated sites and 35.2% of the examined samples that shows its widespread occurrence in polluted soil-groundwater systems. In the course of the antibiotic-resistance assay, our results determined that 11 of the examined 36 environmental strains had multiple drug-resistance against several clinically effective antimicrobial classes: cephalosporins, wide spectrum penicillins, carbapenems, fluoroquinolones, and aminoglycosides. The fact that these multiresistant strains were isolated from 8 different hydrocarbon-contaminated sites, mainly from outskirts, confirms that multiple drug-resistance of P. aeruginosa is widespread not only in clinical, but also in natural surroundings as well.

Isolation and characterization of a monoaromatic hydrocarbon-degrading bacterium, Pseudomonas aeruginosa from crude oil

The present study reports on the isolation and characterization of a Pseudomonas aeruginosa strain PTz-5 from crude oil from oil field sampled in Assam, India. It was capable to utilize hexadecane, benzene or toluene as a sole source of carbon aerobically. Strain PTz-5 was able to produce extracellular lipase that catalyzed triglycerides to free fatty acid and glycerol. The lipase activity was stable in the temperature range of 40 to 60 degrees C. Strain PTz-5 avidly adhered to the surface of hydrocarbon droplets during their growth in liquid culture medium. These properties could play an essential role in hydrocarbon degradation. The results presented here highlight the metabolic versatility and hydrocarbon biodegradative capability of strain PTz-5, signifying its great potential for the bioremediation of various hydrocarbon-contaminated environments.

Toluene degradation kinetics for planktonic and biofilm-grown cells of Pseudomonas putida 54G

Toluene degradation kinetics by biofilm and planktonic cells of Pseudomonas putida 54G were compared in this study. Batch degradation of (14)C toluene was used to evaluate kinetic parameters for planktonic cells. The kinetic parameters determined for toluene degradation were: specific growth rate, micro(max) = 10.08 +/- 1.2/day; half-saturation constant, K(S) = 3.98 +/- 1.28 mg/L; substrate inhibition constant, K(I) = 42.78 +/- 3.87 mg/L. Biofilm cells, grown on ceramic rings in vapor phase bioreactors, were removed and suspended in batch cultures to calculate (14)C toluene degradation rates. Specific activities measured for planktonic and biofilm cells were similar based on toluene degrading cells and total biomass. Long-term toluene exposure reduced specific activities that were based on total biomass for both biofilm and planktonic cells. These results suggest that long-term toluene exposure caused a large portion of the biomass to become inactive, even though the biofilm was not substrate limited. Conversely, specific activities based on numbers of toluene-culturable cells were comparable for both biofilm and planktonically grown cultures. Planktonic cell kinetics are often used in bioreactor models to model substrate degradation and growth of bacteria in biofilms, a procedure we found to be appropriate for this organism. For superior bioreactor design, however, changes in cellular activity that occur during biofilm development should be investigated under conditions relevant to reactor operation before predictive models for bioreactor systems are developed.

Biodegradation aspects of polycyclic aromatic hydrocarbons (PAHs): a review

PAHs are aromatic hydrocarbons with two or more fused benzene rings with natural as well as anthropogenic sources. They are widely distributed environmental contaminants that have detrimental biological effects, toxicity, mutagenecity and carcinogenicity. Due to their ubiquitous occurrence, recalcitrance, bioaccumulation potential and carcinogenic activity, the PAHs have gathered significant environmental concern. Although PAH may undergo adsorption, volatilization, photolysis, and chemical degradation, microbial degradation is the major degradation process. PAH degradation depends on the environmental conditions, number and type of the microorganisms, nature and chemical structure of the chemical compound being degraded. They are biodegraded/biotransformed into less complex metabolites, and through mineralization into inorganic minerals, H(2)O, CO(2) (aerobic) or CH(4) (anaerobic) and rate of biodegradation depends on pH, temperature, oxygen, microbial population, degree of acclimation, accessibility of nutrients, chemical structure of the compound, cellular transport properties, and chemical partitioning in growth medium. A number of bacterial species are known to degrade PAHs and most of them are isolated from contaminated soil or sediments. Pseudomonas aeruginosa, Pseudomons fluoresens, Mycobacterium spp., Haemophilus spp., Rhodococcus spp., Paenibacillus spp. are some of the commonly studied PAH-degrading bacteria. Lignolytic fungi too have the property of PAH degradation. Phanerochaete chrysosporium, Bjerkandera adusta, and Pleurotus ostreatus are the common PAH-degrading fungi. Enzymes involved in the degradation of PAHs are oxygenase, dehydrogenase and lignolytic enzymes. Fungal lignolytic enzymes are lignin peroxidase, laccase, and manganese peroxidase. They are extracellular and catalyze radical formation by oxidation to destabilize bonds in a molecule. The biodegradation of PAHs has been observed under both aerobic and anaerobic conditions and the rate can be enhanced by physical/chemical pretreatment of contaminated soil. Addition of biosurfactant-producing bacteria and light oils can increase the bioavailability of PAHs and metabolic potential of the bacterial community. The supplementation of contaminated soils with compost materials can also enhance biodegradation without long-term accumulation of extractable polar and more available intermediates. Wetlands, too, have found an application in PAH removal from wastewater. The intensive biological activities in such an ecosystem lead to a high rate of autotrophic and heterotrophic processes. Aquatic weeds Typha spp. and Scirpus lacustris have been used in horizontal-vertical macrophyte based wetlands to treat PAHs. An integrated approach of physical, chemical, and biological degradation may be adopted to get synergistically enhanced removal rates and to treat/remediate the contaminated sites in an ecologically favorable process.

In situ bioremediation of groundwater contaminated with petroleum constituents using oxygen release compounds (ORCs)

Over the past 5 years, the use of in situ biological remediation methods has gained acceptance for the biological degradation of petroleum hydrocarbons and chlorinated solvents in the groundwater. Application of slow-release compounds such as Oxygen Release Compound (ORC) and Hydrogen Releasing Compounds have been used routinely as remediation tools. This paper describes the implementation of an in situ bioremediation scheme to address the petroleum constituents in the groundwater at the site of a former gasoline station. Site investigations had indicated that groundwater beneath the site was contaminated with up to 34,300 microg/L benzene, toluene, ethylbenzene and xylenes (BTEX). The remedial scheme involved the installation of the four monitoring wells, monitoring and sampling of the wells and the application of ORCs into the Area of Concern (AOC). The results indicate that levels of petroleum constituents continue to be present in groundwater beneath the site after ORC injection. However, over time the levels of BTEX have significantly decreased. Kinetic study showed that the removal of BTEX fits a zero-order kinetic model for each monitoring well under enhanced oxidized conditions. The compound with the highest biodegradation rate constant was m,p-xylene in monitoring wells MW-2, MW-3 and MW-4.

The primary aerobic biodegradation of gasoline hydrocarbons

We describe the primary aerobic biodegradation of an unleaded, unoxygenated, regular gasoline by inocula from unacclimated fresh and sea water, and from a domestic sewage treatment plant. Biodegradation was rapid and complete in all inocula, with an overall median "half-life", at approximately 70 ppm gasoline and low levels of inorganic nutrients, of 5 days. The biodegradation of 131 individual hydrocarbons in the gasoline followed a relatively consistent pattern. The larger n-alkanes and iso-alkanes, and simple and alkylated aromatic compounds were the most readily degraded compounds, followed by the smaller n-alkanes and isoalkanes and the naphthenes. The last compounds to be degraded were butane, iso-butane, and 2,2-dimethylbutane, but even these disappeared with an apparent half-life of <30 days. The fact that the aqueous concentration of many of the individual components was in the sub ppb level is a remarkable demonstration of the ability of unadapted indigenous aerobic microorganisms to respond to and effectively biodegrade gasoline range hydrocarbons.

Spatial distribution and physiological state of bacteria in a sand column experiment during the biodegradation of toluene

Toxic organic contaminants frequently serve as growth substrates for bacteria. However, long-term exposure to the organic contaminants can result in significant stress or "injury" to bacterial cells such that bacteria may lose, either temporarily or permanently, their capacity to degrade a specific toxic organic contaminant. In order to understand the relationship between biodegradability and physiological conditions of bacteria after a prolonged exposure to a contaminant, biomass samples collected from a sand column experiment, with toluene as the carbon source, were analyzed for bacterial physiology and spatial population distribution in the porous media. The column was seeded with three bacterial isolates that perform aerobic (Pseudomonas putida F1), denitrifying (Thauera aromatica T1), and facultative (Ralstonia pickettii PKO1) degradation of toluene were analyzed. Total, viable but not culturable with toluene, and toluene-culturable cells were enumerated using 4'6-diamidino-2-phenylindole (DAPI) staining and plate counting methods. Comparison of three types of cell counts showed that toluene-culturable cells were less than 40% of the total cell numbers. However, viable colonies transferred to a toluene media after cultivation on rich media regained their ability to degrade toluene. This implies that the temporary loss of their toluene degradation capacity is either due to an intracellular accumulation of degradation by-products, which have to be consumed in order for the cells to degrade toluene, or it is possible that cells have shifted to degrade other substrates such as toluene degradation intermediates or organic materials resulting from cell turnover. Comparison of cell counts with toluene concentration showed no exponential increase in total and viable cell numbers, as reported for flat bed biofilm reactor experiments. The overall fraction of toluene-culturable cells was highest at the highest toluene concentration near the column inlet, which indicates that the observed temporary loss of toluene culturability was not solely caused by a direct toxic effect from the long-term exposure to toluene.

Effect of dissolved oxygen regime on growth dynamics of Pseudomonas spp during benzene degradation

We investigated the effect of different oxygen regimes on growth patterns of Pseudomonas spp. during benzene degradation in microcosm batch studies. Benzene degradation was induced by limiting oxygen available for microbial activity, which consists of three initial-dissolved oxygen (DO) levels of oxic, hypoxic, and anoxic conditions. Batch experiments were performed for cell growth and benzene degradation by inoculating three strains of Pseudomonas spp. (Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas putida) in mineral salt medium containing aqueous benzene. Results showed that all strains were capable to grow and degrade benzene under all oxygen regimes but in a different manner. The highest cell growth of P. aeruginosa and P. fluorescens was achieved under oxic and anoxic condition, respectively, but there was no substantial difference on benzene degradation between the oxygen treatments with about 25% reduction for both strains. P. putida showed a facultative process for both cell growth and benzene degradation. This reveals that care should be taken in selection of microorganisms with regard to environmental studies since they exhibit different responses for given environmental conditions such as DO levels.

Biology of Pseudomonas stutzeri

Pseudomonas stutzeri is a nonfluorescent denitrifying bacterium widely distributed in the environment, and it has also been isolated as an opportunistic pathogen from humans. Over the past 15 years, much progress has been made in elucidating the taxonomy of this diverse taxonomical group, demonstrating the clonality of its populations. The species has received much attention because of its particular metabolic properties: it has been proposed as a model organism for denitrification studies; many strains have natural transformation properties, making it relevant for study of the transfer of genes in the environment; several strains are able to fix dinitrogen; and others participate in the degradation of pollutants or interact with toxic metals. This review considers the history of the discovery, nomenclatural changes, and early studies, together with the relevant biological and ecological properties, of P. stutzeri.

Study of a hexane-degrading consortium in a biofilter and in liquid culture: biodiversity, kinetics and characterization of degrading strains

A gasoline-degrading consortium, originating from a Mexican soil, was used to study its hexane-degradation kinetics in liquid culture and in a biofilter with mineral support. The biodiversity of the consortium depending on the culture conditions and electron and energy source (gasoline, hexane in liquid or hexane in the biofilter) was analyzed using a 16S rRNA-based approach. Significant differences between the populations were observed, indicating a probable adaptation to the substrate. Two strains, named SP2B and SP72-3, isolated from the consortium, belonged to Actinomycetes and demonstrated a high metabolic potential in hexane degradation. Even though the SP2B strain was related to Rhodococcus ruber DSM 43338(T) by phylogenetic studies, it displayed enlarged metabolic properties in hexane and other short-alkane degradation compared with the collection strain.

Competition between oxygen and nitrate respirations in continuous culture ofPseudomonas aeruginosa performing aerobic denitrification

Continuous culture of P. aeruginosa was conducted with nitrate-containing media under the dilution rates (D) of 0.026, 0.06, and 0.13/h and the dissolved oxygen concentrations (DO) of 0-2.2 mg/L. The bacterium performed simultaneous O(2) and nitrate respiration in all of the systems studied. For each D, the (apparent) cell yield from glucose (Y(X/S)) was lower at zero DO, but did not change substantially with non-zero DO. In non-zero DO systems, Y(X/S) increased with increasing D, and when fit with a model considering cell death, gave the following parameters: maximum cell yield Y(X/S) (m) = 0.49, maintenance coefficient M(S) = 0.029 (/h), and cell decay constant k(d) = 0.014/h. The same model failed to describe the behaviors of zero-DO systems, where neither glucose nor nitrate was limiting and the limiting factor(s) remained unknown. The cell yield from accepted electron (Y(X/e)) was however relatively constant in all systems, and the energy yield per electron accepted via denitrification was estimated at approximately 69% of that via O(2) respiration. A closer examination revealed that increasing DO enhanced O(2) respiration only at extremely low DO ( <0.05 mg/L), beyond which the increasing DO only slightly increased its weak inhibition on denitrification. While O(2) was the preferred electron acceptor, the fraction of electrons accepted via denitrification increased with increasing D.

Monitoring microaerobic denitrification of Pseudomonas aeruginosa by online NAD(P)H fluorescence

Defined as the transition conditions in which the organism(s) performs simultaneous aerobic and anaerobic respiration or fermentation, microaerobic conditions are commonly present in the nature. Microaerobic metabolism of microorganisms is however poorly characterized. Being extremely sensitive to the change in cellular electron-accepting mechanisms, NAD(P)H fluorescence provides a useful ways for online monitoring of microaerobic metabolism. Its application to studies of microbial nitrate respiration and particularly, denitrification of Pseudomonas aeruginosa is reviewed here, centering on four topics: (1) online monitoring of anaerobic nitrate respiration by NAD(P)H fluorescence, (2) effects of denitrification on P. aeruginosa phenotypes, (3) microaerobic denitrification of P. aeruginosa in continuous culture, and (4) correlation between NAD(P)H fluorescence and denitrification-to-respiration ratio. Online NAD(P)H fluorescence is shown to sensitively detect the changes of cellular metabolism. For example, it revealed the intermediate nitrite accumulation in C-limited Escherichia coli performing anaerobic nitrate respiration via dissimilative ammonification, by exhibiting two-stage profiles with intriguing fluorescence oscillation. When applied to continuous culture studies of P. aeruginosa (ATCC 9027), the online fluorescence helped to identify that the bacterium conducted denitrification even at DO > 1 mg/l. In addition, the fluorescence profile showed a unique correlation with the fraction of electrons accepted by denitrification (out of all the electrons accepted by aerobic and anaerobic respiration). The applicability of online NAD(P)H fluorescence in monitoring and quantitatively describing the sensitive microaerobic state of microorganisms is clearly demonstrated.

Assessing degradation capability of aerobic indigenous microflora in PAH-contaminated brackish sediments

A study was conducted to determine polycyclic aromatic hydrocarbons (PAHs) distribution and microbial population changes in brackish sediments from an Italian lagoon included in the Ramsar List of Wetlands of International Importance. The presence and level of PAH-degrading bacteria were estimated by the most probable number (MPN) enumeration technique, whereas degradation capability towards target compounds was checked against loss of spiked PAHs (Phenanthrene, Anthracene and Fluoranthene) in MPN tubes after incubation in optimal conditions. Chemical analyses and microbiological counts suggested a potential for PAHs biodegradation by natural occurring populations of sediment microorganisms, thus indicating an "optimal range" in sediment PAHs concentrations, outside of which the natural selection of the indigenous microflora did not occur. The MPN procedure here described, provided an effective and reliable way to simultaneously determine microbial population densities and subsequent confirmation of the biodegradation capability of sediment indigenous microflora when exposed to laboratory and environmental concentrations of PAHs.

Link between spatial structure of microbial communities and degradation of a complex mixture of volatile organic compounds in peat biofilters

AIMS

To investigate the relationships between the operation of the volatile organic compound (VOC) removal biofilter and the structure of microbial communities, and to study the impact on degradation activities and the structuring of microbial communities of biofilter malfunctions related to the qualitative composition of the polluted air.

METHODS AND RESULTS

A microbiological study and a measurement of biodegradation activities were simultaneously carried out on two identical peat-packed columns, seeded with two different inocula, treating polluted air containing 11 VOCs. For both reactors, the spatial structure of the microbial communities was investigated by means of single-strand conformation polymorphism (SSCP) analysis. For both reactors, stratification of degradation activities in function of depth was observed. Oxygenated compounds were removed at the top of the column and aromatics at the bottom. Comparison of SSCP patterns clearly showed a shift in community structure in function of depth inside both biofilters. This distribution of biodegradation activities correlates with the spatialization of microbial density and diversity. Although the operating conditions of both reactors were identical and the biodegradation activities similar, the composition of microflora differed for biofilters A and B. Subdivision of biofilter B into two independent parts supplied with polluted air containing the complex VOC mixture showed that the microflora having colonized the bottom of biofilter B retained their potential for degrading oxygenated compounds.

CONCLUSIONS

This work highlights the spatialization of biodegradation functions in a biofilter treating a complex mixture of VOCs. This distribution of biodegradation activities correlates with the spatialization of microbial density and diversity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This vertical structure of microbial communities must be taken into consideration when dealing with the malfunctioning of bioreactors. These results are also useful information about changes in microbial communities following natural or anthropogenic alterations in different ecosystems (soils and sediments) where structuring of microbial communities according to depth has been observed.

Stimulating in-soil rhamnolipid production in a bioslurry reactor by limiting nitrogen

A soil with aged contamination from lubricating oil (LO) and polychlorinated biphenyls (PCBs) was treated in a bioslurry reactor to investigate in-soil biosurfactant production by Pseudomonas aeruginosa, the most abundant indigenous, culturable, hydrocarbon-degrading microorganism. After 2 days of growth on LO, a depletion of nitrogen stimulated the production and accumulation of rhamnolipids to levels roughly 20 times the critical micelle concentration. Surface tensions and concentrations of monorhamnolipid and dirhamnolipid, PCBs, and total petroleum hydrocarbons (TPH) were measured in a slurry filtrate. Soil-bound PCBs and TPH were also quantified. Rhamnolipid production was observed within 1 to 2 days after nitrogen depletion in each of the 10 batches tested. By day 6, total rhamnolipid concentrations increased from below detection to average values over 1,000 mg/L, which caused over 98% of soil-bound PCBs and over 99% of TPH to be emulsified and recovered in the filtrate. After 70 days, rhamnolipid concentrations were only reduced by 15%, because of nitrogen-limited rates of rhamnolipid biodegradation. The results show that in-soil biosurfactant production can be stimulated in a controlled way with nutrient limitation and can be used to achieve soil washing.

Microbial response and elimination capacity in biofilters subjected to high toluene loadings

Elimination capacity (EC) is frequently used as a performance and design criterion for vapor-phase biofilters without further verification of the microbial quantity and activity. This study was conducted to investigate how biofilters respond to high pollutant loadings and ultimately how this affects the EC of the biofilter. Two identical laboratory-scale biofilters were maintained at an initial toluene loading rate of 46 g m-3 h-1 for a period of 24 days. After the initial biofilm development stage, the loading rates were increased to 91 g m-3 h-1 and 137 g m-3 h-1, respectively. Following a short period of pseudo-steady state, toluene removal efficiencies rapidly declined in both biofilters, with a concurrent decline in both critical and maximum ECs. The decline was mainly due to deterioration in the biodegradation activity of the biofilm and a decline in the toluene-degrading bacterial population within the biofilm phase. The findings imply that high toluene loadings accelerated the deterioration in overall performance due to a rapid accumulation of inactive biomass. As a result, care must be used when relying on EC values for biofilter design and operational purposes, since the values do not appropriately reflect the temporal changes in biodegradation activity and active biomass quantities that can occur in biofilters subjected to high inlet loadings.

Simultaneous enumeration of different bacteria using reverse sample genome probing technique

Quantitative reverse sample genome probing (RSGP) with lambdaDNA as an internal standard was used to enumerate the total numbers of Rhizobium sp. CCRC 13560, Rhizobium meliloti CCRC 13516 and Bradyrhizobium sp. CCRC 13585. K(lambda)/Kx ratios varied between the three species but also in response to the amounts of lambdaDNA or genomic DNA used in the labeling mixture or fixed upon the membrane. Comparative enumerations of pure cultures revealed higher counts using genomic probing as compared with growth-based colony forming units (CFU; 3.4+/-1.7-fold higher for R. meliloti, 6.4+/-7.8-fold higher for Rhizobium sp. and 0.34+/-0.17-fold higher for Bradyrhizobium sp.). In mixed cultures, the estimated cell numbers using genomic probing were 126+/-172-, 85+/-83- and 4.0+/-3.4-fold higher (same respective order) than the growth-based assay. By replacing the klambda/kx ratio with k'lambda/k'x (slope from signal intensity of differently diluted lambdaDNA/slope from signal intensity of differently diluted target DNAxf(x)/flambda), significant improvement in the accuracy of the estimation was achieved. The calculated cell numbers via the genomic probe technique were 0.99+/-0.13-, 1.25+/-0.23- and 0.18+/-0.11-fold higher than the respective CFUs in pure cultures of R. meliloti, Rhizobium sp. and Bradyrhizobium sp. In samples containing mixed populations, the estimated numbers from genomic probing were 1.25+/-0.51-, 45.9+/-14.8- and 0.27+/-0.07-fold higher than the CFU-derived cell count (same respective order).

Degradation of isooctane by Mycobacterium austroafricanum IFP 2173: growth and catabolic pathway

AIMS

Isooctane (2,2,4-trimethylpentane), a major component of gasoline formulations, is recalcitrant to biodegradation probably because of the quaternary carbon group it contains. Information on the biodegradability of this hydrocarbon is essential to evaluate its fate in the environment. For these reasons, the degradation kinetics and the catabolic pathway of isooctane were investigated in Mycobacterium austroafricanum IFP 2173, the only strain characterized to use it as sole carbon and energy source.

METHODS AND RESULTS

The selected strain exhibited a rather moderate maximum growth rate (micromax = 0.053 h(-1)) but degraded isooctane up to 99% with a mineralization yield of 45%, indicating attack of the quaternary carbon group. The GC/MS identification of metabolites, 2,4,4-trimethylpentanoic and dimethylpropanoic (pivalic) acids, which transiently accumulated in the cultures indicated that degradation started from the isopropyl extremity of the molecule and subsequently proceeded by catabolism of the tert-butyl moiety. The degradation of putative metabolic intermediates was investigated. The initial isooctane oxidation system was tentatively characterized.

CONCLUSIONS

The isooctane-degrading strain harboured two candidate systems for initial alkane oxidation. Although a cytochrome P450 was induced by isooctane degradation, the functional oxidation system was probably a nonheme alkane monooxygenase as indicated by PCR amplification and RT-PCR expression of an alkB gene.

SIGNIFICANCE AND IMPACT OF THE STUDY

Isooctane is a recalcitrant branched alkane. A plausible pathway of its degradation by Myco. austroafricanum was put forward.

Aerobic denitrification of Pseudomonas aeruginosa monitored by online NAD(P)H fluorescence

Continuous cultures of Pseudomonas aeruginosa (ATCC 9027) maintained at different dissolved oxygen concentrations (DO) were studied for the effects of DO on various culture properties, especially aerobic respiration and denitrification. The DO was varied from 0 mg/liter (completely anoxic conditions) to 1.3 mg/liter and measured with optical sensors that could accurately determine very low DO based on oxygen-quenched luminescence. The strain was found to perform aerobic denitrification; while the specific rate decreased with increasing DO, denitrification persisted at approximately 1/8 of the maximum rate (1.7 mmol/g of cells/h) even at relatively high DO (1 to 1.3 mg/liter). In the presence of nitrate, the culture's Monod half-rate saturation constant for O(2) was very small, <0.1 mg/liter. Aerobic denitrification appeared to function as an electron-accepting mechanism supplementary to or competitive with aerobic respiration. The shift of the culture's respiratory mechanism was also clearly detected with a fluorometer targeting intracellular NAD(P)H, i.e., the reduced forms of the NAD(P) coenzymes. Comparatively, the NAD(P)H fluorescence under the anoxic, denitrifying conditions (NFU(DN)) was highest, that under fully aerobic conditions (NFU(OX)) was lowest, and that under conditions in which both denitrification and aerobic respiration occurred (NFU) was intermediate. Representing a quantitative measure of the culture's "fractional approach" to the fully denitrifying state, the normalized fraction (NFU - NFU(OX))/(NFU(DN) - NFU(OX)) was correlated with DO and the calculated fraction of electrons accepted by denitrification. The NFU fraction decreased with increasing DO, following an empirical exponential relationship. The fraction of denitrification-accepted electrons increased with the NFU fraction: the increase was gradual and approximately linear at DO of >/==" BORDER="0">0.1 mg/liter but much sharper at lower DO. Online NAD(P)H fluorescence was demonstrated as a feasible technique for effective monitoring and quantitative description of the microaerobic state of microorganisms.