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Brominated phenols are listed as priority pollutants together with nitrophenol and chlorophenol are the key components of paper pulp wastewater. However, the biodegradation of bromophenol in a mixed substrate system is very scanty. In the present investigation, simultaneous biodegradation kinetics of three substituted phenols 4-bromophenol (4-BP), 4-nitrophenol (4-NP), and 4-chlorophenol (4-CP) were investigated using Arthrobacter chlorophenolicus A6. A 23 full factorial design was applied with varying 4-BP and 4-CP from 75–125 mg/L and 4-NP from 50–100 mg/L. Almost complete degradation of this mixture of substituted phenols was achieved at initial concentration combinations of 125, 125, and 100 mg/L of 4-CP, 4-BP, and 4-NP, respectively, in 68 h. Statistical analysis of the results revealed that, among the three variables, 4-NP had the most prominent influence on the degradation of both 4-CP and 4-BP, while the concentration of 4-CP had a strong negative interaction effect on the biodegradation of 4-NP. Irrespective of the concentration levels of these three substrates, 4-NP was preferentially biodegraded over 4-CP and 4-BP. Furthermore, 4-BP biodegradation rates were found to be higher than those of 4-CP, followed by 4-NP. Besides, the variation of the biomass yield coefficient of the culture was investigated at different initial concentration combinations of these substituted phenols. Although the actinomycetes consumed 4-NP at a faster rate, the biomass yield was very poor. This revealed that the microbial cells were more stressed when grown on 4-NP compared to 4-BP and 4-CP. Overall, this study revealed the potential of A. chlorophenolicus A6 for the degradation of 4-BP in mixed substrate systems.

Among known microbial species, Arthrobacter chlorophenolicus A6 has shown very good potential to treat phenolic wastewaters. In this study, the levels of various culture conditions, namely initial pH, agitation (rpm), temperature (°C), and inoculum age (h) were optimized to enhance 4-chlorophenol (4-CP) biodegradation and the culture specific growth rate. For optimization, central composite design of experiments followed by response surface methodology (RSM) was applied. Results showed that among the four independent variables, i.e., pH, agitation (rpm), temperature (°C), and inoculum age (h) investigated in this study, interaction effect between agitation and inoculum age as well as that between agitation and temperature were significant on both 4-CP biodegradation efficiency and culture specific growth rate. Also, at the RSM optimized settings of 7.5 pH, 207 rpm, 29.6°C and 39.5 h inoculum age, 100% biodegradation of 4-CP at a high initial concentration of 300 mg l −1 was achieved within a short span of 18.5 h of culture. The enhancement in the 4-CP biodegradation efficiency was found to be 23% higher than that obtained at the unoptimized settings of the culture conditions. Results of batch growth kinetics of A. chlorophenolicus A6 for various 4-CP initial concentrations revealed that the culture followed substrate inhibition kinetics. Biokinetic constants involved in the process were estimated by fitting the experimental data to several models available from the literature.

The present study reports the kinetics of p-nitrophenol (PNP) biodegradation by Arthrobacter chlorophenolicus A6 in batch shake flasks for initial PNP concentrations in the range of 25–225 mg l −1 . Results of batch growth kinetics of A. chlorophenolicus A6 at various initial PNP concentrations revealed that the culture followed substrate inhibition kinetics with estimated decay coefficient value of 0.0132 h −1 . Biokinetic constants involved in the process were estimated by fitting the experimental data to several substrate inhibition kinetics models available from the literature. Among the models tested, Webb model fitted the experimental data best with the least root mean square error value, and the estimated model constants values were μ  = 0.161 h −1 , K i  = 128 mg l −1 , K s  = 60.15 mg l −1 , and K  = 100 mg l −1 . In addition, observed and theoretical yield coefficients, maintenance energy, and specific growth rate of the culture at various initial PNP concentrations were also investigated in the study.

The Arthrobacter sp. strain AK-YN10 is an s-triazine pesticide degrading bacterium isolated from a sugarcane field in Central India with history of repeated atrazine use. AK-YN10 was shown to degrade 99 % of atrazine in 30 h from media supplemented with 1000 mg L-1 of the herbicide. Draft genome sequencing revealed similarity to pAO1, TC1, and TC2 catabolic plasmids of the Arthrobacter taxon. Plasmid profiling analyses revealed the presence of four catabolic plasmids. The trzN, atzB, and atzC atrazine-degrading genes were located on a plasmid of approximately 113 kb. The flagellar operon found in the AK-YN10 draft genome suggests motility, an interesting trait for a bioremediation agent, and was homologous to that of Arthrobacter chlorophenolicus. The multiple s-triazines degradation property of this isolate makes it a good candidate for bioremediation of soils contaminated by s-triazine pesticides.

Chlorophenols are widespread and of environmental concern due to their toxic and carcinogenic properties. Development of less costly and less technically challenging remediation methods are needed; therefore, we developed a formulation based on micronized vermiculite that, when air-dried, resulted in a granular product containing the 4-chlorophenol (4-CP)-degrading Gram-positive bacterium Arthrobacter chlorophenolicus A6. This formulation and stabilization method yielded survival rates of about 60% that remained stable in storage for at least 3 months at 4 °C. The 4-CP degradation by the formulated and desiccated A. chlorophenolicus A6 cells was compared to that of freshly grown cells in controlled-environment soil microcosms. The stabilized cells degraded 4-CP equally efficient as freshly grown cells in two different set-ups using both hygienized and non-treated soils. The desiccated microbial product was successfully employed in an outdoor pot trial showing its effectiveness under more realistic environmental conditions. No significant phytoremediation effects on 4-CP degradation were observed in the outdoor pot experiment. The 4-CP degradation kinetics from both the microcosms and the outdoor pot trial were used to generate a predictive model of 4-CP biodegradation potentially useful for larger-scale operations, enabling better bioremediation set-ups and saving of resources. This study also opens up the possibility of formulating and stabilizing also other Arthrobacter strains possessing different desirable pollutant-degrading capabilities.

Trehalose is a non-reducing disaccharide with beneficial physiological properties and commercial potential. Trehalose synthase (EC 5.4.99.16) catalyzes the reversible conversion between maltose and trehalose. A recombinant trehalose synthase from Arthrobacter chlorophenolicus SK 33.001 (ACTS) was cloned, expressed, and characterized. The recombinant enzyme encoded a protein of 598 amino acids with a molecular mass of 66 kDa. Gel filtration showed that ACTS is a tetramer in sodium phosphate buffer. The enzyme was metal ion independent and exhibited maximal activity in sodium phosphate buffer (pH 7.5) at 30 °C. The kinetic investigations resulted in a KM value of 120.5 ± 4.5 mM for maltose and a KM value of 343.1 ± 13.8 mM for trehalose. The catalytic efficiency (Vmax/KM) for maltose and trehalose were 0.2 and 0.15 U mg−1 mM−1, respectively. In addition, a cooperative substrate binding was found displayed by the determined Hill coefficients (nH) of 2.8 for maltose and 2.1 for trehalose as a substrate, respectively. The final trehalose yield of various maltose concentrations (50–1000 mM) was constant between 58 and 59%, implying that substrate concentration had no inhibitory influence on ACTS activity.

A novel bacterial strain designated as NIO-1008ᵀ was isolated from marine sediments sample in Chorao Island India. Cells of the strains were gram positive and non-motile, displayed a rod–coccus life cycle and formed cream to light grey colonies on nutrient agar. Strain NIO-1008ᵀ had the chemotaxonomic markers that were consistent for classification in the genus Arthrobacter, i.e. MK-9(H₂) (50.3 %), as the major menaquinone, and the minor amount of MK-7 (H₂-27.5 %), MK-8 (H₄-11.6 %) and MK-8 (H₂-10.4 %). anteiso-C₁₅:₀, iso-C₁₅:₀, iso-C₁₆:₀ and C₁₅:₀ were the predominant fatty acids. Galactose, glucose and rhamnose are the cell-wall sugars, and DNA G+C content was 61.3 mol%. Phylogenetic analysis, based on 16S rRNA gene sequencing, showed that the strains were most similar to Arthrobacter equi IMMIB L-1606ᵀ, Arthrobacter chlorophenolicus DSM 12829ᵀ, Arthrobacter defluvii KCTC 19209ᵀ and Arthrobacter niigatensis CCTCC AB 206012ᵀ with 98.5, 98.4, 98.0 and 97.8 %, respectively, and formed a separate lineage. Combined phenotypic data and DNA–DNA hybridization data supported the conclusion that strains NIO-1008ᵀ represent a novel species within the genus Arthrobacter, for which the name Arthrobacter enclensis sp. nov., is proposed. The type strain is NIO-1008ᵀ = (NCIM 5488ᵀ = DSM 25279ᵀ).

The decomposition of various aromatic hydrocarbon intermediates was examined using a recombinant oxidative enzyme immobilized on single-walled carbon nanotubes (SWCNTs). Hydroxyquinol 1,2-dioxygenase (CphA-I), which catalyzes ring cleavage of catechol and its analogues, was obtained from Arthrobacter chlorophenolicus A6 via cloning, overexpression, and subsequent purification. This recombinant enzyme was immobilized on SWCNTs by physical adsorption and covalent coupling in the absence and presence of N-hydroxysuccinimide. The immobilization yield was as high as 52.1 %, and a high level of enzyme activity of up to 64.7 % was preserved after immobilization. Kinetic analysis showed that the substrate utilization rates (v ₘₐₓ) and catalytic efficiencies (k cₐₜ/K M) of the immobilized enzyme for all substrates evaluated were similar to those of the free enzyme, indicating minimal loss of enzyme activity during immobilization. The immobilized enzyme was more stable toward extreme pH, temperature, and ionic strength conditions than the free enzyme. Thus, the oxidative enzyme immobilized on SWCNTs can be used as an effective and stable biocatalyst for the biochemical remediation process if further investigations would be carried out under field conditions.

Chlorophenols (CP) are listed as priority pollutants both by US EPA as well European community. In the present study, biodegradation of 4-CP was investigated using a cells immobilized in calcium alginate beads system. The batch shake flask study of the cells entrapped in calcium alginate beads system followed substrate inhibition kinetics. The bio-kinetic constants that are necessary to design and simulation of the bioreactor system were estimated from the best fitted Edward model. Further, performance of the cells immobilized in calcium alginate beads system for the degradation of 4-CP was evaluated in an upflow packed bed reactor (PBR) by varying its influent concentration from 100 to 250 mg/L and hydraulic retention time (HRT) between 8 h and 2 h. Almost complete removal of 4-CP and 98.6% effluent toxicity removal were obtained in the reactor at a 4-CP loading rate of 1275 mg/L/d or lesser. However, at higher 4-CP loading rates, the performance of the packed bed reactor (PBR) was found to be deteriorated due to the temporary accumulation of 4-chlorocatehol. The study reveals the potential of cells entrapped in calcium alginate beads system for biodegradation of 4-CP from contaminated wastewater.

The focus of this study was the cloning, expression, and characterization of recombinant ginsenoside hydrolyzing β -glucosidase from Arthrobacter chlorophenolicus with an ultimate objective to more efficiently bio-transform ginsenosides. The gene bglAch , consisting of 1,260 bp (419 amino acid residues) was cloned and the recombinant enzyme, overexpressed in Escherichia coli BL21 (DE3), was characterized. The GST-fused BglAch was purified using GST·Bind agarose resin and characterized. Under optimal conditions (pH 6.0 and 37°C) BglAch hydrolyzed the outer glucose and arabinopyranose moieties of ginsenosides Rb1 and Rb2 at the C20 position of the aglycone into ginsenoside Rd. This was followed by hydrolysis into F 2 of the outer glucose moiety of ginsenoside Rd at the C3 position of the aglycone. Additionally, BglAch more slowly transformed Rc to F 2 via C-Mc 1 (compared to hydrolysis of Rb 1 or Rb 2 ). These results indicate that the recombinant BglAch could be useful for the production of ginsenoside F 2 for use in the pharmaceutical and cosmetic industries.