Isolation and characterisation of bacteria degrading polycyclic aromatic hydrocarbons: Phenanthrene and anthracene

The aim was to isolate and characterise bacteria that can be used to degrade phenanthrene and anthracene. Bacteria were isolated by enrichment of contaminated soil in mineral medium. Growth profiles were assessed by colony forming units (CFU). Electron microscopy and 16S rRNA gene sequencing were employed to characterise these bacteria. Growth profiles were quantified by analysing the culture doubling time, and both the quantification of utilisation of aromatic compounds and the detection of phenanthrane metabolites were carried out by gas chromatography and mass-spectrometry. Two co-cultures of phenanthrene- and anthracene-biodegrading bacteria (PHEN-Cult and ANT-Cult, respectively) were isolated and characterised. The two co-cultures grew rapidly, reaching maximum counts of 1010 CFU/mL, within 2–10 days. The doubling time (dt) fell between 0.5–1.5 day (at PHEN and ANT concentrations of 1–100 ppm), making them among the most active PAH degrading microorganisms described so far. PHEN-Cult consists of two strains, Pseudomonas citronellolis, PHC3Z1A, and Stenotrophomonas maltophilia, JPHC3Z2B, while ANT-Cult is made of Ralstonia pickettii, JANC1A and Thermomonas haemolytica, JANC2B. Both co-cultures were more active at pH 7, 0–4% NaCl, and 37–40°C. They were also able to utilise naphthalene, salicylic acid and catechol. Starting with 100 ppm, within 15 days, 50–75% of PHEN and ANT were degraded, and the following were the PHEN metabolites that were identified: 3-naphthyl-allyl alcohol, phthalic acid ethyl diester, 2-hydroxybenzalpyruvic acid-methyl ester. These bacteria are appropriate for the removal of PHEN and ANT in contaminated environments, thus further studies are warranted to establish their ability to remove these PAHs in pilot and large scale.