Sphingopyxis Sp Research Articles

The detoxification activities and mechanisms of microcystinase towards MC-LR

Microcystins (MCs) are the most common and toxic cyanotoxins that are hazardous to human health and ecosystems. Microcystinase is the enzyme in charge of the initial step in the biodegradation of MCs. The characterization, application conditions, and detoxification mechanisms of microcystinase from an indigenous bacterium Sphingopyxis sp. YF1 towards MC-LR were investigated in the current study. The microcystinase gene of strain YF1 was most similar to Sphingomonas sp. USTB-05 and contained a CAAX-family conversed abortive Infection (ABI) domain. The microcystinase was successful obtained and purified by overexpression in Escherichia coli. The highest degradation rate of MC-LR was 1.0 μg/mL/min under the optimal condition of 30 ℃, pH 7, 20 μg/mL MC-LR, and 400 μg/mL microcystinase. The MC-degrading product was identified as linearized MC-LR, which possessed a much lower inhibitory activity against protein phosphatase 2A than MC-LR. Microcystinase interacted with MC-LR via amino acid residues involved in through the formation of conventional Hydrogen Bond, Pi-Pi T-shapes, Van der Waals force, and so on. The optimal MC-degrading condition of pure microcystinase and its detoxification mechanisms against MC-LR were revealed. The toxicity of purified linearized MC-LR was explored for the first time. These findings suggest that pure microcystinase may efficiently detoxify MCs and it is promising in the bioremediation of MC-polluted environments.

Optimization of Biodegradation Characteristics of Sphingopyxis sp. YF1 against Crude Microcystin-LR Using Response Surface Methodology.

Sphingopyxis sp. YF1 has proven to be efficient in biodegrading microcystin (MC)-leucine (L) and arginine (R) (MC-LR); however, the optimal environmental factors to biodegrade the toxin have not been investigated. In this study, the biodegrading characteristics of strain YF1 against MC-LR were assessed under diverse environmental factors, including temperature (20, 30 or 40 °C), pH (5, 7 or 9) and MC-LR concentration (1, 3 or 5 µg/mL). Data obtained from the single-factor experiment indicated that MC-LR biodegradation by strain YF1 was temperature-, pH- and MC-LR-concentration-dependent, and the maximal biodegradation rate occurred at 5 µg/mL/h. Proposing Box-Behnken Design in response surface methodology, the influence of the three environmental factors on the biodegradation efficiency of MC-LR using strain YF1 was determined. A 17-run experiment was generated and carried out, including five replications performed at the center point. The ANOVA analysis demonstrated that the model was significant, and the model prediction of MC-LR biodegradation was also validated with the experimental data. The quadratic statistical model was established to predict the interactive effects of the environmental factors on MC-LR biodegradation efficiency and to optimize the controlling parameters. The optimal conditions for MC-LR biodegradation were observed at 30 °C, pH 7 and 3 µg/mL MC-LR, with a biodegradation efficiency of 100% after 60 min. The determination of the optimal environmental factors will help to unveil the detailed biodegradation mechanism of MC-LR by strain YF1 and to apply it into the practice of eliminating MC-LR from the environment.

Characteristics and Mechanisms of a Novel Salt-Tolerant Heterotrophic Nitrification-Aerobic Denitrification Strain Sphingopyxis Sp. Cy-10

Characteristics and Mechanisms of a Novel Salt-Tolerant Heterotrophic Nitrification-Aerobic Denitrification Strain Sphingopyxis Sp. Cy-10

Mycrocystin-LR degradation by indigenous bacterial community of Rybinsk Reservoir

The fate of microcystin-LR (MC-LR) in water samples of Rybinsk Reservoir taken before and during water bloom was assessed. The decrease in the MC-LR concentration in the both samples was due to its biodegradation by indigenous bacterial community. The highest biodegradation rate and shortest half-life of MC-LR in the water sample taken during water bloom were observed. A microcystin degrading bacterium was isolated and shown be 98.92% similar to Sphingopyxis sp. based on a fragment of 16S rRNA gene sequence. The rate of MC-LR biodegradation by Sphingopyxis sp. S7 was strongly dependent on initial concentration of toxin and temperature.

Simultaneous Removal of the Freshwater Bloom-Forming Cyanobacterium Microcystis and Cyanotoxin Microcystins via Combined Use of Algicidal Bacterial Filtrate and the Microcystin-Degrading Enzymatic Agent, MlrA.

Freshwater cyanobacterial blooms (e.g., Microcystis blooms) constitute a major global environmental problem because of their risks to public health and aquatic ecological systems. Current physicochemical treatments of toxic cyanobacteria cause the significant release of cyanotoxin microcystins from damaged cells. Biological control is a promising eco-friendly technology to manage harmful cyanobacteria and cyanotoxins. Here, we demonstrated an efficient biological control strategy at the laboratory scale to simultaneously remove Microcystis and microcystins via the combined use of the algicidal bacterial filtrate and the microcystin-degrading enzymatic agent. The algicidal indigenous bacterium Paenibacillus sp. SJ-73 was isolated from the sediment of northern Lake Taihu, China, and the microcystin-degrading enzymatic agent (MlrA) was prepared via the heterologous expression of the mlrA gene in the indigenous microcystin-degrading bacterium Sphingopyxis sp. HW isolated from Lake Taihu. The single use of a fermentation filtrate (5%, v/v) of Paenibacillus sp. SJ-73 for seven days removed the unicellular Microcystis aeruginosa PCC 7806 and the native colonial Microcystis strain TH1701 in Lake Taihu by 84% and 92%, respectively, whereas the single use of MlrA removed 85% of microcystins. Used in combination, the fermentation filtrate and MlrA removed Microcystis TH1701 and microcystins by 92% and 79%, respectively. The present biological control thus provides an important technical basis for the further development of safe, efficient, and effective measures to manage Microcystis blooms and microcystins in natural waterbodies.

Bioinformatic analyses and enzymatic properties of microcystinase

Microcystinase (MlrA) is a key protease in the microcystin (MC) degradation pathway identified in bacterial strains. MlrA hydrolyzes the Adda-arginine peptide bond of cyclic MCs, leading to linearized MCs and a significant reduction in the toxicity of cyanobacteria. In this study, the major biological characteristics of this class of enzymes were analyzed by utilizing the amino acid sequence information of MlrA from Sphingopyxis sp. USTB-05. The encoded gene mlrA was expressed heterologously and its enzymatic properties were characterized. The results showed that MlrA has a highly conserved Abi domain, which participates in immunity via degradation of bacteria through MCs and transmits genetic information through horizontal gene transfer. Enzymatic analysis showed that MlrA is a neutral protease (enzyme activity was highest when pH = 7.4), and it had good stability at 40 °C and pH of ~6.2–8.6. In addition, the effects of metal ions on MlrA revealed that Cu2+ and Zn2+ inactivated MlrA. This research expands the knowledge about MC biodegradation and provides broad scope for future research.

Primary biodegradation and mineralization of aryl organophosphate flame retardants by Rhodococcus-Sphingopyxis consortium

In this study, the biodegradation towards aryl organophosphate flame retardants (aryl-OPFRs) was investigated by the Rhodococcus-Sphingopyxis consortium, mixture of strain Rhodococcus sp. YC-JH2 and Sphingopyxis sp. YC-JH3. The optimal ratio between the two composition strains was determined as 1:1. Under the optimum condition (pH 8, 35 °C and 0% salinity), the consortium could utilize aryl-OPFRs as sole carbon source and degrade them rapidly with half-life of 4.53, 21.11 and 23.0 h for triphenyl phosphate (TPhP), tricresyl phosphate (TCrP) and 2-ethylhexyl diphenyl phosphate (EHDPP) respectively. The consortium maintained high degrading efficiency under a wide of range of pH (6–10), temperature (20–40 °C) and salinity (0–6%). Besides, the consortium could rapidly degrade high concentration of TPhP and no inhibitory effect towards degradation speed was observed up to 500 mg/L. The effect of metal ions and surfactants was estimated. Most metal ions exhibited significant inhibition, except Zn2+ and Pb2+, which showed no effect or slight promotion. Ionic surfactants could severely reduce the degrading capacity, while nonionic surfactants showed no effect. With abundant inoculation of the consortium, mineralization higher than 75% could be achieved within a week. This study provides efficient microorganisms for bioremediation of aryl-OPFRs contamination.

Sphingopyxis sp. Strain OPL5, an Isoprene-Degrading Bacterium from the Sphingomonadaceae Family Isolated from Oil Palm Leaves.

The volatile secondary metabolite, isoprene, is released by trees to the atmosphere in enormous quantities, where it has important effects on air quality and climate. Oil palm trees, one of the highest isoprene emitters, are increasingly dominating agroforestry over large areas of Asia, with associated uncertainties over their effects on climate. Microbes capable of using isoprene as a source of carbon for growth have been identified in soils and in the tree phyllosphere, and most are members of the Actinobacteria. Here, we used DNA stable isotope probing to identify the isoprene-degrading bacteria associated with oil palm leaves and inhabiting the surrounding soil. Among the most abundant isoprene degraders of the leaf-associated community were members of the Sphingomonadales, although no representatives of this order were previously known to degrade isoprene. Informed by these data, we obtained representatives of the most abundant isoprene degraders in enrichments, including Sphingopyxis strain OPL5 (Sphingomonadales), able to grow on isoprene as the sole source of carbon and energy. Sequencing of the genome of strain OPL5, as well as a novel Gordonia strain, confirmed their pathways of isoprene degradation and broadened our knowledge of the genetic and taxonomic diversity of this important bacterial trait.

Universality and Potential Application of Mn(Ⅱ) Oxidation Triggered by Microbial Interspecies Interactions

Mn(Ⅱ)-oxidizing microorganisms can catalytically increase the oxidation rate of divalent manganese by several orders of magnitude, and affect the valence state and fate of elemental manganese. In addition to Mn(Ⅱ)-oxidization by a single microbial strain, our previous studies revealed that interspecies interactions between two bacterial strains (Sphingopyxis sp. QXT-31 and Arthrobacter sp. QXT-31) could trigger the Mn(Ⅱ)-oxidizing activities of Arthrobacter sp. QXT-31. In order to further explore its universality, mechanism, and potential engineering applications, research was conducted on three other Sphingopyxis strains using culture-dependent experiments, comparative genomic analysis, and transcriptome analysis. The results showed that one Sphingopyxis strain could also trigger the Mn(Ⅱ)-oxidizing activity of Arthrobacter sp. QXT-31, which could be regarded as a hint for the prevalence of Mn(Ⅱ) oxidation triggered by microbial interspecies interactions in the natural environment. Furthermore, the upregulation of the antibiotic synthesis pathway in Sphingopyxis was observed just before the Mn(Ⅱ)-oxidizing activity of Arthrobacter sp. QXT-31 was triggered, thus suggesting its possible involvement in stimulating the Mn(Ⅱ)-oxidizing activity of Arthrobacter sp. QXT-31. Finally, we demonstrated that using microbial interspecies interactions to enhance the oxidative removal of Mn(Ⅱ) in a manganese removal reactor is potentially feasible.

Enantioselective Catabolism of the Two Enantiomers of the Phenoxyalkanoic Acid Herbicide Dichlorprop by Sphingopyxis sp. DBS4.

Dichlorprop [(RS)-2-(2,4-dichlorophenoxy)propanoic acid; DCPP], an important phenoxyalkanoic acid herbicide (PAAH), is extensively used in the form of racemic mixtures (Rac-DCPP), and the environmental fates of both DCPP enantiomers [(R)-DCPP and (S)-DCPP] mediated by microorganisms are of great concern. In this study, a bacterial strain Sphingopyxis sp. DBS4 was isolated from contaminated soil and was capable of utilizing both (R)-DCPP and (S)-DCPP as the sole carbon source for growth. Strain DBS4 preferentially catabolized (S)-DCPP as compared to (R)-DCPP. The optimal conditions for Rac-DCPP degradation by strain DBS4 were 30 °C and pH 7.0. In addition to Rac-DCPP, other PAAHs such as (RS)-2-(4-chloro-2-methylphenoxy)propanoic acid, 2,4-dichlorophenoxyacetic acid, 4-chloro-2-methylphenoxyacetic acid, and 2,4-dichlorophenoxyacetic acid butyl ester could also be catabolized by strain DBS4. Bioremediation of Rac-DCPP-contaminated soil by inoculation of strain DBS4 exhibited an effective removal of both (R)-DCPP and (S)-DCPP from the soil. Due to its broad substrate spectrum, strain DBS4 showed great potential in the bioremediation of PAAH-contaminated sites.

Purification and activity of the first recombinant enzyme for biodegrading hepatotoxin by Sphingopyxis sp. USTB-05

Cyanobacterial hepatotoxins which are produced and released by bloom-forming cyanobacteria may threaten the safety of drinking water for human beings and animals. Microcystinase (MlrA) catalyzes the first and most important step for biodegrading hepatotoxic microcystins (MCs) and nodularin (NOD), which hydrolyzes the cyclic hepatotoxin into the linear hepatotoxin as the first product. Here the recombinant MlrA of Sphingopyxis sp. USTB-05 for biodegrading hepatotoxins was firstly purified and its activity was also investigated. The purification process of MlrA was comprised of four steps, affinity purification of glutathione S-transferase (GST)-tagged MlrA, thrombin cleavage of GST tag, GST tag removal and thrombin removal with the benzamidine sepharose. The purified recombinant MlrA was found to have a strong ability to catalyze hepatotoxins, and initial microcystin-LR (MC-LR) of 19.9 mg/L and NOD of 25.2 mg/L were removed within 10 min and 12 h at the protein concentration of 60 mg/L, respectively. The results indicated that the enzyme MlrA with a high activity could be purified and obtained with the biotechnology process of expression and purification described here, which is very important in further studies on the enzyme structure and the enzymatic mechanism for biodegrading hepatotoxins.

A complete route for biodegradation of potentially carcinogenic cyanotoxin microcystin-LR in a novel indigenous bacterium

Microcystin-leucine-arginine (MC-LR), a cyclic potentially carcinogenic hepatotoxin, occurs frequently in aquatic habitats worldwide and seriously threatens ecosystem and public health. Limited effectiveness of physicochemical treatments to remove MC-LR from drinking water has led to a search for alternative cost-effective and environment friendly biodegradation strategies. Obtaining MC-degrading bacteria and understanding their MC-degrading mechanisms are outstanding challenges. Here, a novel indigenous bacterium named Sphingopyxis sp. YF1 with a high efficient capacity for MC-degradation was successfully isolated from eutrophic Lake Taihu. Through integrating mass spectrometer and multi-omics analyses accompanied by functional verification of certain genes and proteins, a complete MC-degradation pathway was firstly identified, in which MC-LR was sequentially degraded into linearized MC-LR, tetrapeptide, Adda, phenylacetic acid, and finally potential product CO2. Some specific proteins such as microcystinase, linearized-microcystinase, tetrapeptidease and PAAase responsible for this pathway were identified. This study pioneeringly demonstrated that MC-LR can be completely degraded through natural remediation processes and revealed a significant potential for MC-LR biodegradation in both natural environment and engineered systems.

Aromatic hydrocarbon compound degradation of phenylacetic acid by indigenous bacterial Sphingopyxis isolated from Lake Taihu

ABSTRACTThe aromatic compound phenylacetic acid (PAA) is present in the environment, and released in the catabolism of phenylalanine, 2-phenylethylamine, or environmental contaminants such as ethylbenzene and styrene. PAA was also proposed to be involved in human chronic kidney disease development. Several bacteria and fungi utilize these aromatic acids as sole carbon source either during aerobic or anaerobic conditions. The aromatic structure of PAA makes this compound resistant toward oxidation or reduction, because the stabilizing resonance energy of the aromatic ring system is difficult to overcome. In the case of bacteria that utilize aromatic compounds as growth substrates, the aromatic ring system limits survival due to a lack of carbon source. Sphingopyxis sp. YF1 isolated from Lake Taihu was found to be beneficial in bioremediation of aromatic compounds. This study thus aimed to examine the influence of environmental factors such as temperature, PAA concentration, and pH on the effectiveness of Sphingopyxis sp. YF1 to degrade aromatic compounds using PAA as model compound. Data showed the highest PAA-degrading rate of strain Sphingopyxis sp. YF1 was 7.6 mg/L·h under the condition of 20°C, pH 9 with a 1000 μg/ml concentration of PAA. Evidence indicates that PAA-degrading ability of strain Sphingopyxis sp. YF1 appears to be primarily influenced by the concentration of PAA, followed by temperature and pH. PAA-degrading gene PAAase was identified in this strain using polymerase chain reaction (PCR) method. These results illustrate that the bacteria Sphingopyxis sp. YF1 removes PAA effectively at certain environmental conditions and this proves beneficial in bioremediation of aromatic compounds.

Comparative genomics of Sphingopyxis spp. unravelled functional attributes

Members of genus Sphingopyxis are known to thrive in diverse environments. Genomes of 21 Sphingopyxis strains were selected. Phylogenetic analysis was performed using GGDC, AAI and core-SNP showed agreement at sub-species level. Based on our results, we propose that both S. baekryungensis DSM16222 and Sphingopyxis sp. LPB0140 strains should not be included under genus Sphingopyxis. Core-analysis revealed, 1422 genes were shared which included essential pathways and genes for conferring adaptation against stress environment. Polyhydroxybutyrate degradation, anaerobic respiration, type IV secretion were notable abundant pathways and exopolysaccharide, hyaluronic acid production and toxin-antitoxin system were differentially present families. Interestingly, genome of S. witflariensis DSM14551, Sphingopyxis sp. MG and Sphingopyxis sp. FD7 provided a hint of probable pathogenic abilities. Protein-Protein Interactome depicted that membrane proteins and stress response has close integration with core-proteins while aromatic compounds degradation and virulence ability formed a separate network. Thus, these should be considered as strain specific attributes.

High-efficient and sustainable biodegradation of microcystin-LR using Sphingopyxis sp. YF1 immobilized Fe3O4@chitosan

The microcystin-LR (MC-LR) produced due to harmful cyanobacterial blooms have brought great harm to human and aquatic organisms, attracting a wide public health attention. To deal with MC-LR contamination, we synthesized a novel bio-functionalized composite for the high-efficient and sustainable biodegradation of microcystin-LR by covalent immobilizing Sphingopyxis sp. YF1 onto chitosan-grafted Fe3O4 magnetic particles (Fe3O4@CTS). The Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) were utilized to characterize the structural properties of Fe3O4@CTS/Sphingopyxis sp. YF1. The immobilization conditions were optimized. And the MC-LR-degrading capabilities of Fe3O4@CTS/Sphingopyxis sp. YF1 were assessed under various conditions. The results showed that the optimal immobilization conditions containing 1.0 % (v/v) glutaraldehyde, immobilization for 4 h at 30 ℃. The Fe3O4@CTS/Sphingopyxis sp. YF1 showed an attractive degradation performance which possesed a wide torlerance to pH (6.0–9.0) and temperature (25–35 ℃). More interesting is that the Fe3O4@CTS/Sphingopyxis sp. YF1 exhibited significantly increased MC-LR-degrading capabilities after recycling and reusing which degradation rate reached 1.50 μg/mL/h in the sixth cycle, and it was easily recycled by using a magnet (Ms 21.5 emug-1). Two intermediates (tetrapeptide and Adda) and three degradation related genes (mlrA, mlrB and mlrC) were obtained in this study and the pathway for the degradation was proposed. These results revealed that Fe3O4@CTS/Sphingopyxis sp. YF1 can be potentially used for treatment of MC-LR contaminated environment.

Cloning and Expression of Genes for Biodegrading Nodularin by Sphingopyxis sp. USTB-05.

Biodegradation is efficient for removing cyanobacterial toxins, such as microcystins (MCs) and nodularin (NOD). However, not all the microbial strains with the microcystin-biodegrading enzymes MlrA and MlrC could biodegrade NOD. Studies on genes and enzymes for biodegrading NOD can reveal the function and the biodegradation pathway of NOD. Based on successful cloning and expression of the USTB-05-A and USTB-05-C genes from Sphingopyxis sp. USTB-05, which are responsible for the biodegradation of MCs, the pathway for biodegrading NOD by these two enzymes was investigated in this study. The findings showed that the enzyme USTB-05-A converted cyclic NOD (m/z 825.4516) into its linear type as the first product by hydrolyzing the arginine and Adda peptide bond, and that USTB-05-C cut off the Adda and glutamic acid peptide bond of linearized NOD (m/z 843.4616) and produced dimeric Adda (m/z 663.4377) as the second product. Further, based on the homology modeling of enzyme USTB-05-A, site-directed mutants of USTB-05-A were constructed and seven crucial sites for enzyme USTB-05-A activity were found. A complete enzymatic mechanism for NOD biodegradation by USTB-05-A in the first step was proposed: glutamic acid 172 and histidine 205 activate a water molecule facilitating a nucleophilic attack on the arginine and Adda peptide bond of NOD; tryptophan 176 and tryptophan 201 contact the carboxylate side chain of glutamic acid 172 and accelerate the reaction rates; and histidine 260 and asparagine 264 function as an oxyanion hole to stabilize the transition states.

Effects of chlorine disinfection on the membrane fouling potential of bacterial strains isolated from fouled reverse osmosis membranes

Biofouling of reverse osmosis (RO) membranes is an inevitable issue in wastewater reclamation and limits the application of RO systems. Chlorine disinfection is widely used as a pretreatment to control biofouling. However, the extracellular polymeric substances (EPS) and cellular inclusions released during chlorine disinfection might also cause membrane fouling. Furthermore, little is known regarding the chlorine resistance of bacterial strains found on fouled RO membranes. In this study, four bacterial strains isolated from fouled RO membranes were used as testing subjects to investigate the bacterial inactivation performance of chlorine disinfection. The effects of chlorine disinfection on the RO membrane fouling potential of these strains were also revealed. The chlorine resistance ability of Sphingopyxis sp. BM1-1 was strongest among the four strains as it secretes the highest amount of EPS per cell. The log inactivation efficiency of this strain was 1-log by 0.2 mg-Cl2/L in 30 min, which was one to three orders of magnitude lower than that of the other strains. Although chlorine disinfection inactivated most bacterial cells (>90%), the reaction with chlorine significantly increased the RO membrane fouling potential of all bacterial solutions. To elucidate the main mechanism behind the increase in the fouling potential, we further investigated the changes in the properties of EPS, and the release of EPS and cellular inclusions during chlorine disinfection. Chlorine disinfection did not significantly affect the RO membrane fouling potential of the EPS secreted by these bacterial strains. However, dissolved organic carbon (DOC), protein, polysaccharide, and DNA concentration of all bacterial solutions increased by one to nine times after chlorine disinfection. These results indicate that large amounts of EPS and cellular inclusions were released into the solutions after the reaction with chlorine, which was the main cause of the increase in RO membrane fouling potential of the bacterial solution after chlorine disinfection.

Characterization and 16S metagenomic analysis of organophosphorus flame retardants degrading consortia

Three bacterial consortia, named YC-SY1, YC-BJ1 and YC-GZ1, were enriched from different areas of China. Bacterial consortia YC-SY1, YC-BJ1 and YC-GZ1 could efficiently degrade triphenyl phosphate (TPhP) (100 mg/L) by approximately 79.4%, 99.8% and 99.6%, tricresyl phosphate (TCrP) by 90.6%, 91.9% and 96.3%, respectively, within 4 days. And they could retain high degrading efficiency under a broad range of temperature (15–40 ℃), pH (6.0–10.0) and salinity (0–4%). A total of 10 bacterial isolates were selected and investigated their degradation capacity. Among these isolates, two were significantly superior to the others. Strain Rhodococcus sp. YC-JH2 could utilize TPhP (50 mg/L) as sole carbon source for growth with 37.36% degradation within 7 days. Strain Sphingopyxis sp. YC-JH3 could efficiently degrade 96.2% of TPhP (50 mg/L) within 7 days, except that no cell growth was observed. Combined with 16S diversity analysis, our results suggest that the effective components of three bacterial consortia responsible for TPhP and TCrP degradation were almost the same, that is, bacteria capable of degrading TPhP and TCrP are limited, in this study, the most efficient component is Sphingopyxis. This study provides abundant microorganism sources for research on organophosphorus flame retardants (OPFRs) metabolism and bioremediation towards OPFRs-contaminated environments.

Isolation and Characterization of a Bacterial Strain Capable of Efficient Berberine Degradation.

Background: Berberine (BBR) is a pharmaceutical chemical with a broad antibacterial spectrum, and its biological treatment has been of research and practical interest. In this study, a pure bacterial strain B16 was isolated from the activated sludge in a pharmaceutical wastewater treatment plant. The aim of the study is to characterize the properties of the strain B16, especially its BBR degradation capability. Methods: The identification of strain B16 was conducted by visual observation, as well as biochemical and phylogenetic analysis. The degradation kinetics of strain B16 was tentatively described by Haldane model. Results: The strain B16 was 100% determined as a Sphingopyxis sp. The kinetic parameters of BBR degradation by strain B16 were as follows: Vmax 54.73 ± 5.54 mg (g MLSS · h)−1, Km 66.68 ± 8.95 mg L−1, and Ki 43.16 ± 5.92 mg L−1, with an R2 of 0.996. Stain B16 exhibited considerable capability of BBR degradation. BBR of initial concentration 40 mg L−1 could be completely degraded in 48 h under optimal conditions. Conclusions: strain B16 was the first pure culture found with the ability to totally mineralize BBR, indicating the potential of B16 application in real industrial processes.

Distribution and characterization of N-acylhomoserine lactone (AHL)-degrading activity and AHL lactonase gene (qsdS) in Sphingopyxis

N-Acylhomoserine lactone (AHL)-degrading enzyme is identified from the various environments and applied for quorum-sensing inhibition. In this study, we isolated two AHL-degrading strains, Sphingopyxis sp. EG6 and FD7, from the industrial cooling water samples. When the eight Sphingopyxis type strains were checked for the AHL-degrading activity, two strains, Sphingopyxis alaskensis DSM 13593 and Sphingopyxis bauzanensis DSM 22271, showed high AHL-degrading activity. The complete genome sequences of EG6 and FD7 revealed the presence of gene homolog of qsdS, which encodes AHL-lactonase in Sphingomonas ursincola. The qsdS gene is seated between putative gene homologs involved in 3-isopropylmalate dehydratase large (leuC2) and small (leuD) subunits in the genome of EG6, FD7, DSM 13593, and DSM 22271, but completely disappeared between leuC2 and leuD in the genome sequences of Sphingopyxis type strains without AHL-degrading activity. Purified His-tagged QsdS showed high AHL-degrading activity and catalyzed AHL ring opening by hydrolyzing lactones. In addition, heterologous expression of qsdS in Pseudomonas aeruginosa resulted in reduction of biofilm formation. These results suggested that the AHL-degrading activity in Sphingopyxis is useful as an effective agent for biofilm inhibition.