Biodegradation Kinetics of Phenanthrene by a Fusant Strain

The fusant strain (F14), which produced by protoplast fusion between Sphingomonas sp. GY2B (GenBank DQ139343) and Pseudomonas sp. GP3A (GenBank EU233280), was tested for phenanthrene biodegradation at 30 °C and pH of 7.0. The kinetics of phenanthrene biodegradation by F14 was investigated over a wide range of initial concentration (15-1,000 mg l(-1)). The rate and the extent of phenanthrene degradation increased with the increase of concentration up to 230 mg l(-1), which indicated negligible inhibition effect at low concentrations. The non-competitive inhibition model was found to be fit for the process. GC-MS analysis showed that biodegradation of phenanthrene by F14 was via dioxygenation at both 1,2- and 3,4-positions and followed by 2-hydroxy-1-naphthoic acid and 1-hydroxy-2-naphthoic acid. The relative intensity of 2-hydroxy-1-naphthoic acid was approximately 3-4 times higher than that of 1-hydroxy-2-naphthoic acid, indicating the 2-hydroxy-1-naphthoic acid was the predominant product in the phenanthrene degradation by fusant strain F14.     

A phenanthrene-degrading strain Sphingomonas sp. GY2B isolated from contaminated soils

This study systematically characterized an aerobic bacterial strain Sphingomonas sp. GY2B for biotransformation of phenanthrene. The strain was isolated from soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and was shown to efficiently use phenanthrene as the sole carbon and energy source. The antibiotics discs susceptibility test revealed that the bacterium was susceptible to some commonly used antibiotics, such as cefuroxime, chloramphenicol, erythromycin and tetracycline. It showed better growth at pH 7.4 and 30 °C and in a mineral salts medium (MSM) with phenanthrene at 100 mg L⁻¹ as the substrate. The results indicated that 99.8% of the substrate had been degraded and that salicylate route was likely the metabolic pathway. When added as the second organic chemical, glucose could enhance the bacterial growth at low concentration (10–200 mg L⁻¹), but could inhibit cell growth at high concentration (>500 mg L⁻¹). Further study showed that strain GY2B could also use naphthalene, phenol, 1-hydroxy-2-naphthoic acid, 2-naphthol, salicylic acid and catechol as the sole carbon and energy source, but did not grow on 1-naphthol which could be co-metabolized in the present of phenanthrene or 1-hydroxy-2-naphthoic acid.     

Isolation of phenanthrene-degrading bacteria and characterization of phenanthrene metabolites

Three aerobic bacterial consortia GY2, GS3 and GM2 were enriched from polycyclic aromatic hydrocarbon-contaminated soils with water-silicone oil biphasic systems. An aerobic bacterial strain utilizing phenanthrene as the sole carbon and energy source was isolated from bacterial consortium GY2 and identified as Sphingomonas sp. strain GY2B. Within 48 h and at 30°C the strain metabolized 99.1% of phenanthrene (100 mg/l) added to batch culture in mineral salts medium and the cell number increased by about 40-fold. Three metabolites 1-hydroxy-2-naphthoic acid, 1-naphthol and salicylic acid, were identified by gas chromatographic mass spectrometry and UV–visible spectroscopy analysis. A degradation pathway was proposed based on the identified metabolites. In addition to phenanthrene, strain GY2B could use other aromatic compounds such as naphthalene, 2-naphthol, salicylic acid, catechol, phenol, benzene and toluene as a sole source of carbon and energy.     

Paracoccus pacificus sp. nov., isolated from the Western Pacific Ocean

A Gram-stain negative, short rod-shaped, non-motile, catalase- and oxidase-positive, aerobic bacterium, designated F14^T, was isolated from the Western Pacific Ocean. Phylogenetic and phenotypic properties of the organism supported that it belongs to the genus Paracoccus. The levels of 16S rRNA gene sequences similarity between strain F14^T and other type strains of recognized members of the genus Paracoccus were 93.6–96.5 %. Growth of strain F14^T was observed at 4–40 °C (optimum, 28–30 °C), pH 6.0–10.0 (optimum, pH 7.0–8.0) and in the presence of 0–7 % (w/v) NaCl (optimum, 1–2 %). The major cellular fatty acid was summed feature 8 (C_18:1 ω6c and/or C_18:1 ω7c). The major respiratory quinone was ubiquinone-10. The polar lipid pattern indicated the presence of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine and three unknown lipids. The DNA G+C content was 61.4 mol%. On the basis of polyphasic characterization, strain F14^T represents a novel species, for which the name Paracoccus pacificus sp. nov. is proposed. The type strain is F14^T (=CGMCC 1.12755^T=LMG 28106^T=MCCC 1A09947^T).     

Evidence for surfactant production by the haloarchaeon Haloferax sp. MSNC14 in hydrocarbon-containing media

The potential for surfactant production by the extreme halophilic archaeon Haloferax sp. MSNC14 in the presence of individual hydrocarbon substrates was studied. This strain was selected for its ability to grow on different types of hydrocarbons at high NaCl concentrations. Linear (n-heptadecane or C17) and isoprenoid (pristane) alkanes, a polyaromatic hydrocarbon (phenanthrene) and ammonium acetate (highly water-soluble control compound) were used as growth substrates. The adherence potential was demonstrated by the ability of the cells to adhere to liquid or solid hydrocarbons. The biosurfactant production was indicated by the reduction of the surface tension (ST) and by the emulsification activity (EA) of cell-free supernatants. Growth on acetate was accompanied by a low EA (lower than 0.1) and a high ST (~70 mN/m), whereas an important EA (up to 0.68 ± 0.08) and a reduction of ST (down to 32 ± 2.3 mN/m) were observed during growth on the different hydrocarbons. Both ST and EA varied with the growth phase. The adhesion to hydrocarbons was higher when cells were grown on C17 (by 60–70 %) and pristane (by 30–50 %) than on phenanthrene (~25 %). The results demonstrated that strain MNSC14 was able to increase the bioavailability of insoluble hydrocarbons, thus facilitating their uptake and their biodegradation even at high salt concentration.     

Identification of protoplast fusion strain Fhhh by randomly amplified polymorphic DNA

A functional strain Fhhh was constructed through protoplast fusion of three parental strains (Phanerochaete chrysosporium, Saccharomyces cerevisiae and native bacterium YZ) to improve the degradation efficiency of purified terephthalic acid wastewater. Randomly amplified polymorphic DNA (RAPD) and scanning electron microscope (SEM) analysis were applied to identify and confirm the fusant Fhhh through phenotypic and genetic relationship. The result of SEM analysis demonstrated that the cell shape of fusant Fhhh differed from all three parental strains. RAPD analysis of 40 arbitrary primers generated a total of 1,135 bands. The genetic similarity indices between Fhhh and parental strains Phanerochaete chrysosporium (PC), Saccharomyces cerevisiae (SC) and native bacterium (YZ) were 34.01%, 33.16%, and 35.97%, respectively. The targeted-gene PCR results showed that Fhhh inherited the DNA fragments of mnp and lip genes from parental strain PC and FLO1 gene fragment from parental strain SC. Our results suggested protoplast fusion technique may be considered as a promising technique in environmental pollution control.     

Isolation and characterization of marine diesel oil-degrading Acinetobacter sp. strain Y2

The marine diesel oil-degrading bacterium Acinetobacter sp. strain Y2 was isolated from oil-polluted seawater sampled from Dinghai port, Zhoushan City, Zhejiang Province, China. The isolated bacterium was identified as Acinetobacter sp. based on its 16S rDNA gene sequence as well as various morphological and physiological characteristics. The degradation characteristics of strain Y2 were studied and its parameters for oil degradation optimized. These optimal conditions were determined to be an initial pH of 7.5, an incubation temperature of 30 °C, an initial diesel oil concentration of 2 % (v/v), and an initial inoculating bacteria concentration of 3?×?10⁷ cells/mL. The results from the gas chromatography–mass spectrometry analysis showed that strain Y2 could almost completely degrade all components of diesel oil, with a degradation ratio of up to 80 % after 10 days of incubation at the optimal conditions.     

Biodegradation and metabolite transformation of pyrene by basidiomycetes fungal isolate Armillaria sp. F022

Armillaria sp. F022 is a white-rot fungus isolated from a tropical rain forest in Indonesia that is capable of utilizing pyrene as a source of carbon and energy. Enzymes production during the degradation process by Armillaria sp. F022 was certainly related to the increase in biomass. In the first week after incubation, the growth rate rapidly increased, but enzyme production decreased. After 7 days of incubation, rapid growth was observed, whereas, the enzymes were produced only after a good amount of biomass was generated. About 63 % of pyrene underwent biodegradation when incubated with this fungus in a liquid medium on a rotary shaker (120 rpm, 25 °C) for 30 days; during this period, pyrene was transformed to five stable metabolic products. These metabolites were extracted in ethyl acetate, isolated by column chromatography, and then identified using thin layer chromatography (TLC) and gas chromatography–mass spectrometry (GC–MS). 1-Hydroxypyrene was directly identified by GC–MS, while 4-phenanthroic acid, 1-hydroxy-2-naphthoic acid, phthalic acid, and protocatechuic acid were identified to be present in their derivatized forms (methylated forms and silylated forms). Protocatechuic acid was the end product of pyrene degradation by Armillaria sp. F022. Dynamic profiles of two key enzymes, namely laccase and 1,2-dioxygenase, were revealed during the degradation process, and the results indicated the presence of a complicated mechanism in the regulation of pyrene-degrading enzymes. In conclusion, Armillaria sp. F022 is a white-rot fungus with potential for application in the degradation of polycyclic aromatic hydrocarbons such as pyrene in the environment.     

Overproduction and biological activity of prodigiosin-like pigments from recombinant fusant of endophytic marine Streptomyces species

Thirty-four endophytic marine Actinomycetes isolates were recovered from the Egyptian marine sponge Latrunculia corticata, out of them 5 isolates (14.7 %) showed red single colonies on yeast-CzAPEK plates. Isolates under the isolation code NRC50 and NRC51 were observed with the strongest red biomass. After application of protoplast fusion between NRC50 and NRC51 isolates, 26 fusants were selected and produced widely different amounts of prodigiosin-like pigments (PLPs) on different fermentation media. Among them fusant NRCF69 produced 79 and 160.4 % PLPs more than parental strains NRC50 and NRC51, respectively. According to the analysis of 16S rDNA sequence (amplified, sequenced, and submitted to GenBank under Accession no. JN232405 and JN232406, respectively), together with their morphological and biochemical characteristics, parental strains NRC50 (P1) and NRC51 (P2) were identified as Streptomyces sp. and designated as Streptomyces sp. NRC50 and Streptomyces sp. NRC51. This study describes a low cost, effective production media by using peanut seed broth, sunflower oil broth or dairy processing wastewater broth alone, or supplemented with 0.5 % mannitol that supports the production of PLPs by the Streptomyces fusant NRCF69 under study (42.03, 40.11, 36.7 and 47 g L^?1, respectively). PLPs compounds exhibited significant cytotoxic activities against three human cancer cell lines: colon cancer cell line (HCT-116), liver cancer cell line (HEPG-2) and breast cancer cell line (MCF-7) and antimycotic activity against clinical dermatophyte isolates of Trichophyton, Microsporum and Epidermophyton.     

Kinetics of growth and caffeine demethylase production of Pseudomonas sp. in bioreactor

The effect of various initial caffeine concentrations on growth and caffeine demethylase production by Pseudomonas sp. was studied in bioreactor. At initial concentration of 6.5 g l^?1 caffeine, Pseudomonas sp. showed a maximum specific growth rate of 0.2 h^?1, maximum degradation rate of 1.1 g h^?1, and caffeine demethylase activity of 18,762 U g CDW^?1 (CDW: cell dry weight). Caffeine degradation rate was 25 times higher in bioreactor than in shake flask. For the first time, we show highest degradation of 75 g caffeine (initial concentration 20 g l^?1) in 120 h, suggesting that the tested strain has potential for successful bioprocess for caffeine degradation. Growth kinetics showed substrate inhibition phenomenon. Various substrate inhibition models were fitted to the kinetic data, amongst which the double-exponential (R ² = 0.94), Luong (R ² = 0.92), and Yano and Koga 2 (R ² = 0.94) models were found to be the best. The Luedeking–Piret model showed that caffeine demethylase production kinetics was growth related. This is the first report on production of high levels of caffeine demethylase in batch bioreactor with faster degradation rate and high tolerance to caffeine, hence clearly suggesting that Pseudomonas sp. used in this study is a potential biocatalyst for industrial decaffeination.     

Intergeneric protoplast fusion between Acinetobacter sp. A3 and Pseudomonas putida DP99 for enchanced hydrocarbon degradation

Summary Polyethylene glycol 6000 mediated protoplast fusion between an alkane degrader Acinetobacter sp. A3, and a naphthalene degrader, Pseudomonas putida DP99 , resulted in fusants capable of degrading both hydrocarbons and were morphologically similar to Acinetobacter sp. A3. While fusant F4/13 and Pseudomonas putida DP99 degraded over 98% of naphthalene provided by the end of five days, tetradecane degradation by fusant F4/13 was 82% compared to 77% by Acinetobacter sp. A3 in the same time period. Also, while from naphthalene +tetradecane mixture, fusant F4/13 could degrade 99% and 53% of naphthalene and tetradecane respectively, both the parent strains together could degrade over 99% naphthalene but only about 16% tetradecane.     

Phylogenetic analysis of the genes for naphthalene and phenanthrene degradation in Burkholderia sp. strains

The genetic systems responsible for naphthalene and phenanthrene catabolism have been analyzed in the five strains of Burkholderia sp. isolated from soil samples (West Siberia) contaminated by heavy residual fuel and in the laboratory collection strain Burkholderia sp. BS3702 isolated from soil samples of the coke gas plant (Vidnoe, Moscow oblast). The results of this work demonstrate that naphthalene and phenanthrene degradation in the above strains is encoded by the sequences not homologous to the classical nah genes of pseudomonades. In the Burkholderia sp. BS3702 strain, the initial stages of phenanthrene degradation and the subsequent stages of salicylate degradation are controlled by the sequences of different evolutionary descent (phn and nag genes).     

Hyphomonas beringensis sp. nov. and Hyphomonas chukchiensis sp. nov., isolated from surface seawater of the Bering Sea and Chukchi Sea

Two Gram-negative, non-spore-forming, oval to pear shaped motile strains, designated 25B14_1^T and BH-BN04-4^T, isolated from surface seawater from the Bering Sea and Chukchi Sea, respectively, were subjected to polyphasic taxonomic study. Phylogenetic analysis based on 16S rRNA gene sequences demonstrated that strains 25B14_1^T and BH-BN04-4^T clustered together with Hyphomonas atlanticus 22II1-22F38^T and Hyphomonas oceanitis DSM 5155^T, respectively, within genus Hyphomonas. Based on whole genome sequence analysis, the calculated DDH and ANIm values between strain 25B14_1^T and BH-BN04-4^T are 18.8 and 83.19 % respectively. The calculated DDH values of strain 25B14_1^T and BH-BN04-4^T with seven type strains ranged from 18.2 to 19.9 % and from 18.4 to 40.4 %, respectively. The ANIm values of strain 25B14_1^T and BH-BN04-4^T with seven type strains ranged from 83.00 to 84.67 % and from 83.14 to 90.58 %, respectively. Both isolates were found to contain Q-11 as the predominant respiratory quinone. The major fatty acids of strain 25B14_1^T were identified as C_16:0, C_17:0, C_18:1 ω7c-methyl and Summed Feature 8 (C_18:1 ω6c/ω7c as defined by MIDI), while in the case of strain BH-BN04-4^T they were identified as C_16:0, C_18:1 ω7c-methyl and Summed Feature 8 (C_18:1 ω6c/ω7c). The G+C contents of 25B14_1^T and BH-BN04-4^T were determined to be 58.4 and 61.0 mol%, respectively. The combined phenotypic and genotypic data show that the two isolates each represent novel species of the genus Hyphomonas, for which the names Hyphomonas beringensis sp. nov. and Hyphomonas chukchiensis sp. nov. are proposed, with the type strain 25B14_1^T (=MCCC 1A07321^T = LMG 27914^T) and BH-BN04-4^T (=MCCC 1A07481^T = LMG 27915^T), respectively.     

Polyphasic characterization of four soil-derived phenanthrene-degrading Acidovorax strains and proposal of Acidovorax carolinensis sp. nov.

Four bacterial strains identified as members of the Acidovorax genus were isolated from two geographically distinct but similarly contaminated soils in North Carolina, USA, characterized, and their genomes sequenced. Their 16S rRNA genes were highly similar to those previously recovered during stable-isotope probing (SIP) of one of the soils with the polycyclic aromatic hydrocarbon (PAH) phenanthrene. Heterotrophic growth of all strains occurred with a number of organic acids, as well as phenanthrene, but no other tested PAHs. Optimal growth occurred aerobically under mesophilic temperature, neutral pH, and low salinity conditions. Predominant fatty acids were C_16:1ω7c/C_16:1ω6c, C_16:0, and C_18:1ω7c, and were consistent with the genus. Genomic G + C contents ranged from 63.6 to 64.2%. A combination of whole genome comparisons and physiological analyses indicated that these four strains likely represent a single species within the Acidovorax genus. Chromosomal genes for phenanthrene degradation to phthalate were nearly identical to highly conserved regions in phenanthrene-degrading Delftia, Burkholderia, Alcaligenes, and Massilia species in regions flanked by transposable or extrachromosomal elements. The lower degradation pathway for phenanthrene metabolism was inferred by comparisons to described genes and proteins. The novel species Acidovorax carolinensis sp. nov. is proposed, comprising the four strains described in this study with strain NA3^T as the type strain (=LMG 30136, =DSM 105008).     

Degradation and transformation of anthracene by white-rot fungus Armillaria sp. F022

Characterization of anthracene metabolites produced by Armillaria sp. F022 was performed in the enzymatic system. The fungal culture was conducted in 100-mL Erlenmeyer flask containing mineral salt broth medium (20 mL) and incubated at 120 rpm for 5–30 days. The culture broth was then centrifuged at 10,000 rpm for 45 min to obtain the extract. Additionally, the effect of glucose consumption, laccase activity, and biomass production in degradation of anthracene were also investigated. Approximately, 92 % of the initial concentration of anthracene was degraded within 30 days of incubation. Dynamic pattern of the biomass production was affected the laccase activity during the experiment. The biomass of the fungus increased with the increasing of laccase activity. The isolation and characterization of four metabolites indicated that the structure of anthracene was transformed by Armillaria sp. F022 in two routes. First, anthracene was oxidized to form anthraquinone, benzoic acid, and second, converted into other products, 2-hydroxy-3-naphthoic acid and coumarin. Gas chromatography–mass spectrometry analysis also revealed that the molecular structure of anthracene was transformed by the action of the enzyme, generating a series of intermediate compounds such as anthraquinone by ring-cleavage reactions. The ligninolytic enzymes expecially free extracellular laccase played an important role in the transformation of anthracene during degradation period.     

Characterisation of a thermostable catechol-2,3-dioxygenase from phenanthrene-degradingPseudomonas sp. strain ZJF08

Four strains with high phenanthrene-degrading ability were isolated from petroleum badly polluted soil. The strainPseudomonas sp. ZJF08 demonstrated the highest rate of degradation (138. 1 mg·L^?1·day^?1) among them and degraded 97.1% of the phenanthrene in one week. The activities of two key enzymes of ZJF08, polycyclic aromatic hydrocarbon dioxygenase and catechol-2,3-oxygenase (C23O), were also assayed during the degradation of phenanthrene. Both of them reached their maximums on the 2^nd day of degradation. The C23O gene (C7) ofPseudomonas sp. ZJF08 was cloned and expressed inEscherichia coli, and its gene product was purified by a Ni-NTA-agarose column. The optimum temperature for the purified C23O was 40°C at pH 7.5 and the C23O activity could be still detected when the temperature reached 70°C. The results showed that the C23O fromPseudomonas sp. strain ZJF08 exhibited better thermostability than its homologs reported.     

Biodegradaon of phenanthrene in soil microcosms stimulated by an introduced Alcaligenes sp.

Abstract A phenanthrene degrading strain of Alcaligenes sp. was isolated from oil polluted soil. Addition of Alcaligenes sp. to soil microcosms supplemented with phenanthrene (1 mg/g dry soil) resulted in degradation of the added phenanthrene within 11 days. The phenanthrene concentration declined only 12% in uninoculated soil during 42 days. The total phenanthrene degradation potential of Alcaligenes sp. was 2.3 mg/g dry soil during a period of 22 days. The amount of CO₂ evolved during 22 days corresponded to the conversion of 91% of the degraded phenanthrene to CO₂. The Alcaligenes sp. were not able to degrade phenanthrene in sterile soil.     

Comparison of Thraustochytrids Aurantiochytrium sp., Schizochytrium sp., Thraustochytrium sp., and Ulkenia sp. for Production of Biodiesel,Long-Chain Omega-3 Oils,and Exopolysaccharide

Heterotrophic growth of thraustochytrids has potential in coproducing biodiesel for transportation, as well as producing a feedstock for omega-3 long-chain (≥C20) polyunsaturated fatty acids (LC-PUFA), especially docosahexaenoic acid (DHA) for use in nutraceuticals. In this study, we compared eight new endemic Australian thraustochytrid strains from the genera Aurantiochytrium, Schizochytrium, Thraustochytrium, and Ulkenia for the synthesis of exopolysaccharide (EPS), in addition to biodiesel and LC-PUFA. Aurantiochytrium sp. strains readily utilized glucose for biomass production, and increasing glucose from 2 to 4 % w/v of the culture medium resulted in increased biomass yield by an average factor of 1.7. Ulkenia sp. strain TC 010 and Thraustochytrium sp. strain TC 033 did not utilize glucose, while Schizochytrium sp. strain TC 002 utilized less than half the glucose available by day 14, and Thraustochytrium sp. strain TC 004 utilized glucose at 4 % w/v but not 2 % w/v of the culture suggesting a threshold requirement between these values. Across all strains, increasing glucose from 2 to 4 % w/v of the culture medium resulted in increased total fatty acid methyl ester content by an average factor of 1.9. Despite an increasing literature demonstrating the capacity of thraustochytrids for DHA synthesis, the production of EPS from these organisms is not well documented. A broad range of EPS yields was observed. The maximum yield of EPS was observed for Schizochytrium sp. strain TC 002 (299 mg/L). High biomass-producing strains that also have high lipid and high EPS yield may be better candidates for commercial production of biofuels and other coproducts.     

Biodegradation of sulfonamides by <Emphasis Type="Italic">Shewanella oneidensis</Emphasis> MR-1 and <Emphasis Type="Italic">Shewanella</Emphasis> sp. strain MR-4

Because of extensive sulfonamides application in aquaculture and animal husbandry and the consequent increase in sulfonamides discharged into the environment, strategies to remediate sulfonamide-contaminated environments are essential. In this study, the resistance of Shewanella oneidensis MR-1 and Shewanella sp. strain MR-4 to the sulfonamides sulfapyridine (SPY) and sulfamethoxazole (SMX) were determined, and sulfonamides degradation by these strains was assessed. Shewanella oneidensis MR-1 and Shewanella sp. strain MR-4 were resistant to SPY and SMX concentrations as high as 60 mg/L. After incubation for 5 days, 23.91 ± 1.80 and 23.43 ± 2.98% of SPY and 59.88 ± 1.23 and 63.89 ± 3.09% of SMX contained in the medium were degraded by S. oneidensis MR-1 and Shewanella sp. strain MR-4, respectively. The effects of the initial concentration of the sulfonamides and initial pH of the medium on biodegradation, and the degradation of different sulfonamides were assessed. The products were measured by LC–MS; with SPY as a substrate, 2-AP (2-aminopyridine) was the main stable metabolite, and with SMX as a substrate, 3A5MI (3-amino-5-methyl-isoxazole) was the main stable metabolite. The co-occurrence of 2-AP or 3A5MI and 4-aminobenzenesulfonic acid suggests that the initial step in the biodegradation of the two sulfonamides is S–N bond cleavage. These results suggest that S. oneidensis MR-1 and Shewanella sp. strain MR-4 are potential bacterial resources for biodegrading sulfonamides and therefore bioremediation of sulfonamide-polluted environments.     

Pelagibacterium nitratireducens sp.nov., A Marine Alphaproteobacterium Isolated from the East China Sea

A Gram-negative, rod-shaped, non-spore-forming aerobic bacterium, motile with a single polar flagellum, strain JLT2005^T, was isolated from surface seawater collected from the East China Sea and formed ivory white colonies on a rich organic medium. The strain was positive for catalase, oxidase, and urease. It grew in the presence of 0–12 % (w/v) NaCl (optimum 5 %), at 20–35 °C (optimum 25 °C), or at pH 6–10 (optimum pH 9). The major fatty acids (>10 %) were C_18:1ω7c, C_19:0ω8c cyclo, C_16:0, and C_18:0. The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol, and five unidentified glycolipids. Ubiquinone-10 and Ubiquinone-11 were present as the major quinones. The DNA G+C content was 74.3 mol%. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain JLT2005^T belongs to the genus Pelagibacterium in the family Hyphomicrobiaceae, class Alphaproteobacteria. The closest neighbors were Pelagibacterium halotolerans B2^T (98.7 % similarity) and Pelagibacterium luteolum 1_C16_27^T (97.1 % similarity). DNA–DNA relatedness values of strain JLT2005^T with P. halotolerans B2^T and with P. luteolum 1_C16_27^T were 31.6 and 25 %. Evidence from genotypic, chemotaxonomic, and phenotypic data shows that strain JLT2005^T represents a novel species of the genus Pelagibacterium, for which the name Pelagibacterium nitratireducens sp. nov is proposed. The type strain is JLT2005^T (=CGMCC 1.10829^T =JCM 17767^T).