Table of Contents Author Guidelines Submit a Manuscript
The Scientific World Journal
Volume 2014, Article ID 931793, 11 pages
http://dx.doi.org/10.1155/2014/931793
Research Article

Methylobacterium populi VP2: Plant Growth-Promoting Bacterium Isolated from a Highly Polluted Environment for Polycyclic Aromatic Hydrocarbon (PAH) Biodegradation

1DIA-Dipartimento di Agraria, Università degli Studi di Napoli Federico II, Via Università 100, 80055 Portici, Italy
2Dipartimento di Biologia, Università degli Studi di Napoli Federico II, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Napoli, Italy

Received 25 March 2014; Revised 28 May 2014; Accepted 10 July 2014; Published 3 August 2014

Academic Editor: Wen-Jun Li

Copyright © 2014 Valeria Ventorino et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Linked References

  1. S. K. Samanta, O. V. Singh, and R. K. Jain, “Polycyclic aromatic hydrocarbons: environmental pollution and bioremediation,” Trends in Biotechnology, vol. 20, no. 6, pp. 243–248, 2002. View at Publisher · View at Google Scholar · View at Scopus
  2. H. Sato and Y. Aoki, “Mutagenesis by environmental pollutants and bio-monitoring of environmental mutagens,” Current Drug Metabolism, vol. 3, no. 3, pp. 311–319, 2002. View at Publisher · View at Google Scholar · View at Scopus
  3. M. Alexander, Biodegradation and Bioremediation, Academic Press, San Diego, Calif, USA, 1999.
  4. W. Pimda and S. Bunnag, “Biodegradation of used motor oil by single and mixed cultures of cyanobacteria,” African Journal of Biotechnology, vol. 11, no. 37, pp. 9074–9078, 2012. View at Google Scholar
  5. R. Margesin and F. Schinner, “Efficiency of indigenous and inoculated cold-adapted soil microorganisms for biodegradation of diesel oil in alpine soils,” Applied and Environmental Microbiology, vol. 63, no. 7, pp. 2660–2664, 1997. View at Google Scholar · View at Scopus
  6. W. L. Straube, J. Jones-Meehan, P. H. Pritchard, and W. R. Jones, “Bench-scale optimization of bioaugmentation strategies for treatment of soils contaminated with high molecular weight polyaromatic hydrocarbons,” Resources, Conservation and Recycling, vol. 27, no. 1-2, pp. 27–37, 1999. View at Publisher · View at Google Scholar · View at Scopus
  7. D. L. Johnson, K. L. Maguire, D. R. Anderson, and S. P. McGrath, “Enhanced dissipation of chrysene in planted soil: the impact of a rhizobial inoculum,” Soil Biology and Biochemistry, vol. 36, no. 1, pp. 33–38, 2004. View at Publisher · View at Google Scholar · View at Scopus
  8. R. J. Grosser, M. Friedrich, D. M. Ward, and W. P. Inskeep, “Effect of model sorptive phases on phenanthrene biodegradation: different enrichment conditions influence bioavailability and selection of phenanthrene-degrading isolates,” Applied and Environmental Microbiology, vol. 66, no. 7, pp. 2695–2702, 2000. View at Publisher · View at Google Scholar · View at Scopus
  9. I. W. Sutherland, “Biofilm exopolysaccharides: a strong and sticky framework,” Microbiology, vol. 147, no. 1, pp. 3–9, 2001. View at Google Scholar · View at Scopus
  10. M. E. Davey and G. A. O'Toole, “Microbial biofilms: from ecology to molecular genetics,” Microbiology and Molecular Biology Reviews, vol. 64, no. 4, pp. 847–867, 2000. View at Publisher · View at Google Scholar · View at Scopus
  11. R. M. Donlan, “Biofilms: microbial life on surfaces,” Emerging Infectious Diseases, vol. 8, no. 9, pp. 881–890, 2002. View at Publisher · View at Google Scholar · View at Scopus
  12. J. W. Costerton, P. S. Stewart, and E. P. Greenberg, “Bacterial biofilms: a common cause of persistent infections,” Science, vol. 284, no. 5418, pp. 1318–1322, 1999. View at Publisher · View at Google Scholar · View at Scopus
  13. R. M. Donlan and J. W. Costerton, “Biofilms: survival mechanisms of clinically relevant microorganisms,” Clinical Microbiology Reviews, vol. 15, no. 2, pp. 167–193, 2002. View at Publisher · View at Google Scholar · View at Scopus
  14. R. Patel, “Biofilms and antimicrobial resistance,” Clinical Orthopaedics and Related Research, no. 437, pp. 41–47, 2005. View at Publisher · View at Google Scholar · View at Scopus
  15. L. Chen and Y. Wen, “The role of bacterial biofilm in persistent infections and control strategies,” International Journal of Oral Science, vol. 3, no. 2, pp. 66–73, 2011. View at Publisher · View at Google Scholar · View at Scopus
  16. M. Megharaj, B. Ramakrishnan, K. Venkateswarlu, N. Sethunathan, and R. Naidu, “Bioremediation approaches for organic pollutants: a critical perspective,” Environment International, vol. 37, no. 8, pp. 1362–1375, 2011. View at Publisher · View at Google Scholar · View at Scopus
  17. V. Andreoni, L. Cavalca, M. A. Rao et al., “Bacterial communities and enzyme activities of PAHs polluted soils,” Chemosphere, vol. 57, no. 5, pp. 401–412, 2004. View at Publisher · View at Google Scholar · View at Scopus
  18. X. Zhuang, J. Chen, H. Shim, and Z. Bai, “New advances in plant growth-promoting rhizobacteria for bioremediation,” Environment International, vol. 33, no. 3, pp. 406–413, 2007. View at Publisher · View at Google Scholar · View at Scopus
  19. M. A. Amezcua-Allieri, A. Rodríguez-Dorantes, and J. Meléndez-Estrada, “The use of biostimulation and bioaugmentation to remove phenanthrene from soil,” International Journal of Oil, Gas and Coal Technology, vol. 3, no. 1, pp. 39–59, 2010. View at Publisher · View at Google Scholar · View at Scopus
  20. S. Cherian and M. M. Oliveira, “Transgenic plants in phytoremediation: Recent advances and new possibilities,” Environmental Science and Technology, vol. 39, no. 24, pp. 9377–9390, 2005. View at Publisher · View at Google Scholar · View at Scopus
  21. W. Liu, J. Sun, L. Ding, Y. Luo, M. Chen, and C. Tang, “Rhizobacteria (Pseudomonas sp. SB) assist phytoremediation of oily-sludge-contaminated soil by tall fescue (Testuca arundinacea L.),” Plant and Soil, vol. 371, no. 1-2, pp. 533–542, 2013. View at Publisher · View at Google Scholar · View at Scopus
  22. M. Macková, B. Vrchotová, K. Francová et al., “Biotransformation of PCBs by plants and bacteria e consequences of plant-microbe interactions,” European Journal of Soil Biology, vol. 43, no. 4, pp. 233–241, 2007. View at Publisher · View at Google Scholar
  23. X. Huang, Y. El-Alawi, D. M. Penrose, B. R. Glick, and B. M. Greenberg, “A multi-process phytoremediation system for removal of polycyclic aromatic hydrocarbons from contaminated soils,” Environmental Pollution, vol. 130, no. 3, pp. 465–476, 2004. View at Publisher · View at Google Scholar · View at Scopus
  24. L. Liu, C. Jiang, X. Liu, J. Wu, J. Han, and S. Liu, “Plant-microbe association for rhizoremediation of chloronitroaromatic pollutants with Comamonas sp. strain CNB-1,” Environmental Microbiology, vol. 9, no. 2, pp. 465–473, 2007. View at Publisher · View at Google Scholar · View at Scopus
  25. P. Conte, A. Agretto, R. Spaccini, and A. Piccolo, “Soil remediation: humic acids as natural surfactants in the washings of highly contaminated soils,” Environmental Pollution, vol. 135, no. 3, pp. 515–522, 2005. View at Publisher · View at Google Scholar · View at Scopus
  26. F. Sannino, R. Spaccini, D. Savy, and A. Piccolo, “Remediation of highly contaminated soils from an industrial site by employing a combined treatment with exogeneous humic substances and oxidative biomimetic catalysis,” Journal of Hazardous Materials, vol. 261, pp. 55–62, 2013. View at Publisher · View at Google Scholar · View at Scopus
  27. O. Pepe, V. Ventorino, and G. Blaiotta, “Dynamic of functional microbial groups during mesophilic composting of agro-industrial wastes and free-living (N2)-fixing bacteria application,” Waste Management, vol. 33, no. 7, pp. 1616–1625, 2013. View at Publisher · View at Google Scholar · View at Scopus
  28. S. Halebian, B. Harris, S. M. Finegold, and R. D. Rolfe, “Rapid method that aids in distinguishing gram-positive from gram-negative anaerobic bacteria,” Journal of Clinical Microbiology, vol. 13, no. 3, pp. 444–448, 1981. View at Google Scholar · View at Scopus
  29. P. N. Green and I. J. Bousfield, “A taxonomic study of some Gram-negative facultatively methylotrophic bacteria,” Microbiology, vol. 128, no. 3, pp. 623–638, 1982. View at Google Scholar · View at Scopus
  30. W. G. Weisburg, S. M. Barns, D. A. Pelletier, and D. J. Lane, “16S ribosomal DNA amplification for phylogenetic study,” Journal of Bacteriology, vol. 173, no. 2, pp. 697–703, 1991. View at Google Scholar · View at Scopus
  31. A. Alfonzo, S. Lo Piccolo, G. Conigliaro, V. Ventorino, S. Burruano, and G. Moschetti, “Antifungal peptides produced by Bacillus amyloliquefaciens AG1 active against grapevine fungal pathogens,” Annals of Microbiology, vol. 62, no. 4, pp. 1593–1599, 2012. View at Publisher · View at Google Scholar · View at Scopus
  32. S. Palomba, G. Blaiotta, V. Ventorino, A. Saccone, and O. Pepe, “Microbial characterization of sourdough for sweet baked products in the Campania region (southern Italy) by a polyphasic approach,” Annals of Microbiology, vol. 61, no. 2, pp. 307–314, 2011. View at Publisher · View at Google Scholar · View at Scopus
  33. O. Pepe, S. Palomba, L. Sannino et al., “Characterization in the archaeological excavation site of heterotrophic bacteria and fungi of deteriorated wall painting of Herculaneum in Italy,” Journal of Environmental Biology, vol. 32, no. 2, pp. 241–250, 2011. View at Google Scholar · View at Scopus
  34. S. F. Altschul, T. L. Madden, A. A. Schäffer et al., “Gapped BLAST and PSI-BLAST: a new generation of protein database search programs,” Nucleic Acids Research, vol. 25, no. 17, pp. 3389–3402, 1997. View at Publisher · View at Google Scholar · View at Scopus
  35. J. D. Thompson, D. G. Higgins, and T. J. Gibson, “CLUSTAL W: improving the sensitivity of progressive multiple sequence alignment through sequence weighting, position-specific gap penalties and weight matrix choice,” Nucleic Acids Research, vol. 22, no. 22, pp. 4673–4680, 1994. View at Publisher · View at Google Scholar · View at Scopus
  36. K. Tamura, J. Dudley, M. Nei, and S. Kumar, “MEGA4: molecular evolutionary genetics analysis (MEGA) software version 4.0,” Molecular Biology and Evolution, vol. 24, no. 8, pp. 1596–1599, 2007. View at Publisher · View at Google Scholar · View at Scopus
  37. E. Notomista, F. Pennacchio, V. Cafaro et al., “The Marine Isolate Novosphingobium sp. PP1Y Shows Specific Adaptation to Use the Aromatic Fraction of Fuels as the Sole Carbon and Energy Source,” Microbial Ecology, vol. 61, no. 3, pp. 582–594, 2011. View at Publisher · View at Google Scholar · View at Scopus
  38. A. L. Mattos-Guaraldi, L. C. D. Formiga, and A. F. B. Andrade, “Cell surface hydrophobicity of sucrose fermenting and nonfermenting Corynebacterium diphtheriae strains evaluated by different methods,” Current Microbiology, vol. 38, no. 1, pp. 37–42, 1999. View at Publisher · View at Google Scholar · View at Scopus
  39. M. E. Silva-Stenico, F. T. H. Pacheco, J. L. M. Rodrigues, E. Carrilho, and M. T. Siu, “Growth and siderophore production of Xylella fastidiosa under iron-limited conditions,” Microbiological Research, vol. 160, no. 4, pp. 429–436, 2005. View at Publisher · View at Google Scholar · View at Scopus
  40. M. Anastasio, O. Pepe, T. Cirillo, S. Palomba, G. Blaiotta, and F. Villani, “Selection and use of phytate -degrading LAB to improve cereal-based products by mineral solubilization during dough fermentation,” Journal of Food Science, vol. 75, no. 1, pp. M28–M35, 2010. View at Publisher · View at Google Scholar · View at Scopus
  41. B. Van Aken, C. M. Peres, S. L. Doty, J. M. Yoon, and J. L. Schnoor, “Methylobacterium populi sp. nov., a novel aerobic, pink-pigmented, facultatively methylotrophic, methane-utilizing bacterium isolated from poplar trees (Populus deltoides x nigra DN34),” International Journal of Systematic and Evolutionary Microbiology, vol. 54, no. 4, pp. 1191–1196, 2004. View at Publisher · View at Google Scholar · View at Scopus
  42. A. P. Wood, D. P. Kelly, I. R. McDonald et al., “A novel pink-pigmented facultative methylotroph, Methylobacterium thiocyanatum sp. nov., capable of growth on thiocyanate or cyanate as sole nitrogen sources,” Archives of Microbiology, vol. 169, no. 2, pp. 148–158, 1998. View at Publisher · View at Google Scholar · View at Scopus
  43. A. A. Bodour, J. Wang, M. L. Brusseau, and R. M. Maier, “Temporal change in culturable phenanthrene degraders in response to long-term exposure to phenanthrene in a soil column system,” Environmental Microbiology, vol. 5, no. 10, pp. 888–895, 2003. View at Publisher · View at Google Scholar · View at Scopus
  44. B. Van Aken, J. M. Yoon, and J. L. Schnoor, “Biodegradation of nitro-substituted explosives 2,4,6-trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, and octahydro-13,5,7-tet-ranitro-1,3,5-tetrazocine by a phytosymbiotic Methylobacterium sp. associated with poplar tissues (Populus deltoides × nigra DN34),” Applied and Environmental Microbiology, vol. 70, no. 1, pp. 508–517, 2004. View at Publisher · View at Google Scholar · View at Scopus
  45. J. Li and J. Gu, “Complete degradation of dimethyl isophthalate requires the biochemical cooperation between Klebsiella oxytoca Sc and Methylobacterium mesophilicum Sr Isolated from Wetland sediment,” Science of the Total Environment, vol. 380, no. 1–3, pp. 181–187, 2007. View at Publisher · View at Google Scholar · View at Scopus
  46. B. Lalevic, V. Raicevic, D. Kikovic et al., “Biodegradation of MTBE by bacteria isolated from oil hydrocarbons—contaminated environments,” International Journal of Environmental Research, vol. 6, no. 1, pp. 81–86, 2012. View at Google Scholar · View at Scopus
  47. M. Rosenberg and S. Kjelleberg, “Hydrophobic interactions in bacterial adhesion,” Advances in Microbial Ecology, vol. 9, pp. 353–393, 1986. View at Google Scholar
  48. V. Anesti, J. Vohra, S. Goonetilleka et al., “Molecular detection and isolation of facultatively methylotrophic bacteria, including Methylobacterium podarium sp. nov., from the human foot microflora,” Environmental Microbiology, vol. 6, no. 8, pp. 820–830, 2004. View at Publisher · View at Google Scholar · View at Scopus
  49. V. Anesti, I. R. McDonald, M. Ramaswamy, W. G. Wade, D. P. Kelly, and A. P. Wood, “Isolation and molecular detection of methylotrophic bacteria occurring in the human mouth,” Environmental Microbiology, vol. 7, no. 8, pp. 1227–1238, 2005. View at Publisher · View at Google Scholar · View at Scopus
  50. L. C. Simões, M. Simões, and M. J. Vieira, “Adhesion and biofilm formation on polystyrene by drinking water-isolated bacteria,” Antonie van Leeuwenhoek, vol. 98, no. 3, pp. 317–329, 2010. View at Publisher · View at Google Scholar · View at Scopus
  51. P. B. Rossetto, M. N. Dourado, M. C. Quecine et al., “Specific plant induced biofilm formation in Methylobacterium species,” Brazilian Journal of Microbiology, vol. 42, no. 3, pp. 878–883, 2011. View at Google Scholar · View at Scopus
  52. T. Yano, H. Kubota, J. Hanai, J. Hitomi, and H. Tokuda, “Stress tolerance of Methylobacteriumbiofilms in bathrooms,” Microbes and Environments, vol. 28, no. 1, pp. 87–95, 2013. View at Publisher · View at Google Scholar · View at Scopus
  53. N. Cerca, G. B. Pier, M. Vilanova, R. Oliveira, and J. Azeredo, “Quantitative analysis of adhesion and biofilm formation on hydrophilic and hydrophobic surfaces of clinical isolates of Staphylococcus epidermidis,” Research in Microbiology, vol. 156, no. 4, pp. 506–514, 2005. View at Publisher · View at Google Scholar · View at Scopus
  54. L. J. Douglas, “Candida biofilms and their role in infection,” Trends in Microbiology, vol. 11, no. 1, pp. 30–36, 2003. View at Publisher · View at Google Scholar · View at Scopus
  55. A. Pompilio, R. Piccolomini, C. Picciani, D. D'Antonio, V. Savini, and G. Di Bonaventura, “Factors associated with adherence to and biofilm formation on polystyrene by Stenotrophomonas maltophilia: The role of cell surface hydrophobicity and motility,” FEMS Microbiology Letters, vol. 287, no. 1, pp. 41–47, 2008. View at Publisher · View at Google Scholar · View at Scopus
  56. A. K. Kwaszewska, A. Brewczyńska, and E. M. Szewczyk, “Hydrophobicity and biofilm formation of lipophilic skin corynebacteria,” Polish Journal of Microbiology, vol. 55, no. 3, pp. 189–193, 2006. View at Google Scholar · View at Scopus
  57. M. Madhaiyan, S. Poonguzhali, S. P. Sundaram, and T. Sa, “A new insight into foliar applied methanol influencing phylloplane methylotrophic dynamics and growth promotion of cotton (Gossypium hirsutum L.) and sugarcane (Saccharum officinarum L.),” Environmental and Experimental Botany, vol. 57, no. 1-2, pp. 168–176, 2006. View at Publisher · View at Google Scholar · View at Scopus
  58. D. N. Fedorov, N. V. Doronina, and Y. A. Trotsenko, “Cloning and characterization of indolepyruvate decarboxylase from Methylobacterium extorquens AM1,” Biochemistry, vol. 75, no. 12, pp. 1435–1443, 2010. View at Publisher · View at Google Scholar · View at Scopus
  59. Z. S. Omer, R. Tombolini, A. Broberg, and B. Gerhardson, “Indole-3-acetic acid production by pink-pigmented facultative methylotrophic bacteria,” Plant Growth Regulation, vol. 43, no. 1, pp. 93–96, 2004. View at Publisher · View at Google Scholar · View at Scopus
  60. E. G. Ivanova, N. V. Doronina, and Y. A. Trotsenko, “Aerobic methylobacteria are capable of synthesizing auxins,” Microbiology, vol. 70, no. 4, pp. 392–397, 2001. View at Publisher · View at Google Scholar · View at Scopus
  61. C. M. Ribeiro and E. J. B. N. Cardoso, “Isolation, selection and characterization of root-associated growth promoting bacteria in Brazil Pine (Araucaria angustifolia),” Microbiological Research, vol. 167, no. 2, pp. 69–78, 2012. View at Publisher · View at Google Scholar · View at Scopus
  62. S. Jayashree, P. Vadivukkarasi, K. Anand, Y. Kato, and S. Seshadri, “Evaluation of pink-pigmented facultative methylotrophic bacteria for phosphate solubilization,” Archives of Microbiology, vol. 193, no. 8, pp. 543–552, 2011. View at Publisher · View at Google Scholar · View at Scopus
  63. Z. A. Siddiqui, “PGPR: prospective biocontrol agents of plant phatogens,” in PGPR: Biocontrol and Biofertilization, Z. A. Siddiqui, Ed., pp. 111–142, Springer, Dordrecht, The Netherlands, 2006. View at Google Scholar
  64. G. K. Sahu and S. S. Sindhu, “Disease control and plant growth promotion of green gram by siderophore producing Pseudomonas sp,” Research Journal of Microbiology, vol. 6, no. 10, pp. 735–749, 2011. View at Publisher · View at Google Scholar · View at Scopus
  65. P. T. Lacava, M. E. Silva-Stenico, W. L. Araújo et al., “Detection of siderophores in endophytic bacteria Methylobacterium spp. associated with Xylella fastidiosa subsp. pauca,” Pesquisa Agropecuaria Brasileira, vol. 43, no. 4, pp. 521–528, 2008. View at Publisher · View at Google Scholar · View at Scopus
  66. A. V. C. Simionato, C. Simó, A. Cifuentes et al., “Capillary electrophoresis-mass spectrometry of citrus endophytic bacteria siderophores,” Electrophoresis, vol. 27, no. 13, pp. 2567–2574, 2006. View at Google Scholar
  67. A. Gholizadeh and B. B. Kohnehrouz, “A molecular evidence for the presence of methylobacterial-type Fe siderophore receptor in Celosia cristata,” Plant, Soil and Environment, vol. 56, no. 3, pp. 133–138, 2010. View at Publisher · View at Google Scholar · View at Scopus
  68. M. Madhaiyan, S. Poonguzhali, M. Senthilkumar et al., “Growth promotion and induction of systemic resistance in rice cultivar Co-47 (Oryza sativa L.) by Methylobacterium spp.,” Botanical Bulletin of Academia Sinica, vol. 45, no. 4, pp. 315–324, 2004. View at Google Scholar · View at Scopus
  69. M. Kummerová and E. Kmentová, “Photoinduced toxicity of fluoranthene on germination and early development of plant seedling,” Chemosphere, vol. 56, no. 4, pp. 387–393, 2004. View at Publisher · View at Google Scholar · View at Scopus
  70. Y. Song, P. Gong, Q. Zhou, and T. Sun, “Phytotoxicity assessment of phenanthrene, pyrene and their mixtures by a soil-based seedling emergence test,” Journal of Environmental Sciences, vol. 17, no. 4, pp. 580–583, 2005. View at Google Scholar · View at Scopus
  71. M. J. Smith, T. H. Flowers, H. J. Duncan, and J. Alder, “Effects of polycyclic aromatic hydrocarbons on germination and subsequent growth of grasses and legumes in freshly contaminated soil and soil with aged PAHs residues,” Environmental Pollution, vol. 141, no. 3, pp. 519–525, 2006. View at Publisher · View at Google Scholar · View at Scopus
  72. H. Wei, S. Song, H. Tian, and T. Liu, “Effects of phenanthrene on seed germination and some physiological activities of wheat seedling,” Compets Rendus Biologies, vol. 337, no. 2, pp. 95–100, 2014. View at Google Scholar
  73. X. Mei, D. Lin, Y. Xu, Y. Wu, and Y. Tu, “Effects of phenanthrene on chemical composition and enzyme activity in fresh tea leaves,” Food Chemistry, vol. 115, no. 2, pp. 569–573, 2009. View at Publisher · View at Google Scholar · View at Scopus
  74. I. Oguntimehin, F. Eissa, and H. Sakugawa, “Negative effects of fluoranthene on the ecophysiology of tomato plants (Lycopersicon esculentum Mill) fluoranthene mists negatively affected tomato plants,” Chemosphere, vol. 78, no. 7, pp. 877–884, 2010. View at Publisher · View at Google Scholar · View at Scopus
  75. G. J. Ahammed, H.-L. Yuan, J. O. Ogweno et al., “Brassinosteroid alleviates phenanthrene and pyrene phytotoxicity by increasing detoxification activity and photosynthesis in tomato,” Chemosphere, vol. 86, no. 5, pp. 546–555, 2012. View at Publisher · View at Google Scholar · View at Scopus
  76. G. J. Ahammed, C. Gao, J. O. Ogweno et al., “Brassinosteroids induce plant tolerance against phenanthrene by enhancing degradation and detoxification in Solanum lycopersicum L.,” Ecotoxicology and Environmental Safety, vol. 80, pp. 28–36, 2012. View at Publisher · View at Google Scholar · View at Scopus