Isolation and characterization of Cycloclasticus strains from Yellow Sea sediments and biodegradation of pyrene and fluoranthene by their syntrophic association with Marinobacter strains

• The Cycloclasticus strains of Yellow Sea were isolates with novel characteristics.
• The Cycloclasticus strains of Yellow Sea could degrade pyrene and fluoranthene.
• The defined co-culture enhanced Cycloclasticus strains' pyrene and fluoranthene degradation rates.

Three Cycloclasticus strains, NY93E, PY97M, and PY97N, isolated from the sediments of Yellow Sea, were characterized. Interaction between Cycloclasticus strains and Marinobacter strains in the biodegradation of high-molecular weight polycyclic aromatic hydrocarbons (HMW PAHs) was also studied. The three strains exhibited novel characteristics compared with their counterparts within the genus Cycloclasticus. When used as sole sources of carbon and energy, pyrene and fluoranthene can be degraded by each of the three strains, and the degradation rates of 0.02 g L−1 pyrene and fluoranthene determined by GC–MS were in the range 52%–63% and 49%–65% after 21 d, respectively. The gene clusters encoding the iron–sulfur protein of the PAH dioxygenase were PCR amplified from these strains and their nucleotide sequences exhibited more than 98% nucleotide similarity with their counterpart in Cycloclasticus sp. A5. In addition, the denaturing gradient gel electrophoresis (DGGE) profile revealed that Cycloclasticus spp. and Sphingomonas spp. were the dominant members in the phenanthrene-degrading consortium enriched from the Yellow Sea sediments. Furthermore, the defined consortium of Cycloclasticus sp. PY97M and Marinobacter sp. D15-8W exhibited obvious synergic effects in HMW PAH biodegradation. The degradation rates of 0.02 g L−1 pyrene and fluoranthene by the consortium increased from 63% − 76% and 65% − 83% compared with that of the pure culture of strain PY97M, respectively. In conclusion, the three Cycloclasticus strains can degrade HMW PAHs pyrene and fluoranthene, and their syntrophic association with Marinobacter strains is promising in the bioremediation of HMW PAH-contaminated marine environment.