International Biodeterioration & Biodegradation 56 (2005) 143–150 Anthracene biodegradation by Pseudomonas sp. isolated from a petrochemical sludge landfarming site Rodrigo J.S. Jacques a , Eder C. Santos a , Fa´tima M. Bento a , Maria C.R. Peralba b , Pedro A. Selbach a , Enilson L.S. Sa´ a , Fla´vio A.O. Camargo a,Ã a Department of Soil Science, Faculty of Agronomy, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil 7712 Bento Gonc - alves Ave 91540-000, Brazil b Department of Organic Chemistry, Institute of Chemistry, Federal University of Rio Grande do Sul. Porto Alegre, RS, Brazil 9500 Bento Gonc - alves Ave 91540-000, Brazil Received 1 April 2005; received in revised form 1 June 2005; accepted 20 June 2005 Available online 2 September 2005 Abstract Anthracene is a polycyclic aromatic hydrocarbon (PAH) that presents a high pollution potential and health risk and has been used as a model for degradation studies on PAHs because of its relative toxicity. This study aimed to evaluate anthracene degradation by Pseudomonas sp. isolated from a 14-year-old petrochemical sludge landfarming site. Three isolates were selected from 26 by the best growth in anthracene and two of them were identified by 16S rRNA gene sequencing as Ps. aeruginosa and Ps. citronellolis. They showed better growth at pH 7.0 and 30 1C in medium containing up to 2 g anthracene L 1 . They were also able to grow in medium containing phenanthrene, pyrene, gasoline and diesel oil. Analysis of anthracene degradation estimated by gas chromatography showed that Ps. aeruginosa isolate 312A had the highest rate of degradation (3.90 mg L 1 day 1 ), degrading 71% of the anthracene added to the medium (250 mg L 1 ) after 48 days. Ps. citronellolis 222A showed an intermediate level of degradation (51%), but Ps. aeruginosa 332C degraded only 24.4%. Isolate 312A was also responsible for the highest phenanthrene and pyrene degradation after 48 days. In order to establish the mechanisms involved in the PAH degradation, surfactant production by the isolates was assessed by an emulsification index and reduction of the surface tension in the mineral medium free of cells. Emulsification was not detected, indicating that the isolates did not produce high molecular weight surfactant, although reduction in surface tension indicated production of low molecular weight surfactant compounds. The medium containing Ps. citronellolis 222A showed the highest reduction in surface tension, which could increase anthracene bioavailability for biodegradation. To our knowledge, this is the first report concerning increase of anthracene degradation by surfactants produced by Ps. citronellolis. However, the highest degradation rate shown by Ps. aeruginosa 312A was not related to surfactant production, indicating that some other mechanism could be involved in anthracene degradation. The Pseudomonas isolates may be useful for the study of PAH degradation and for bioremediation purposes. r 2005 Published by Elsevier Ltd. Keywords: Ps. aeruginosa; Ps. citronellolis; Biosurfactant; Phenanthrene; Pyrene 1. Introduction Anthracene is one among more than 100 polycyclic aromatic hydrocarbons (PAHs) and was chosen for the study of PAH degradation because of its relative toxicity. These chemical compounds show a skeleton of carbon and hydrogen atoms arranged in two or more aromatic rings of low solubility that makes them resistant to nucleophilic attack (Johnsen et al., 2005). PAH exposure occurs by inhalation, ingestion and dermal contact and PAHs are highly lipid-soluble and quickly absorbed by the gastro-intestinal tract of ARTICLE IN PRESS www.elsevier.com/locate/ibiod 0964-8305/$ - see front matter r 2005 Published by Elsevier Ltd. doi:10.1016/j.ibiod.2005.06.005 Ã Corresponding author. Tel.: +5551 3316 6035; fax: +5551 3316 6040. E-mail address: fcamargo@ufrgs.br (F.A.O. Camargo).