CENSUS – Diesel – Naphthalene and PAHs

Detect and quantify bacteria responsible for biodegradation of PAHs

Fuel oils including diesel are complex mixtures composed of varying fractions of n-alkanes, iso- and cycloalkanes, aromatic hydrocarbons, and sulfur, nitrogen, and oxygenated compounds.  As with gasoline, the aromatic hydrocarbon fraction typically raises concerns at diesel impacted sites.  Diesel fuel is usually described as an intermediate distillate of crude petroleum but is likely to contain both volatile monooaromatics (BTEX) and semi-volatile polycyclic aromatic hydrocarbons (PAHs).  Biodegradation of the monoaromatic compounds (BTEX) under both aerobic and anaerobic conditions is described in detail in the CENSUS Applications – Gasoline – BTEX.

As with BTEX, biodegradation of PAHs under aerobic conditions has been intensively studied over the past 30 years.  For most early studies aimed at elucidation of an aerobic catabolic pathway, naphthalene, the lowest molecular weight PAH, was used as the model compound.  Overall, the upper pathway for aerobic naphthalene biodegradation is analogous to that of monoaromatic hydrocarbons.  Biodegradation is initiated by a naphthalene dioxygenase enzyme producing a cis-dihydrodiol which is dehydrogenated to form dihydroxynaphthalene.  A second dioxygenase enzyme catalyzes cleavage of one of the aromatic rings eventually producing a monooaromatic compound salicylate which can be further metabolized.

CENSUS Targets for Aerobic PAHs

Target

MI Code 

  Relevance / Data Interpretation

Naphthalene Dioxygenase NAH Catalyzes aerobic biodegradationof naphthalene and other PAHs by incorporation of oxygen into the aromatic ring.
 Napthalene InducibleDioxygenase NIDA  Targets the naphthalene inducible dioxygenases found in Mycobacterium spp. and Rhodococcus spp. which are capable of mineralizing higher molecular weight PAHs including pyrene and benzo(a)pyrene.
Phenol Hydroxylase PHE Catalyzes further oxidation of BTEX compounds.  Presence indicates the potential for aerobic BTEX biodegradation.

Although originally viewed as recalcitrant under anaerobic conditions, naphthalene biodegradation under sulfate reducing conditions has been documented in recent years.  Currently however, biochemical pathways for anaerobic naphthalene biodegradation are not clear.  In fact, dehydrogenation, carboxylation, and methylation have all been proposed as the initial step suggesting multiple pathways may be used in the field.  A gene (naphthyl-2-methyl-succinate synthase) has been isolated from a marine environment that is believed to be responsible for the anaerobic biodegradation of 2-methylnapthalene by a marine isolate.

 

CENSUS Targets for Anaerobic PAHs

Target

MI Code 

  Relevance / Data Interpretation

Naphthyl-2-methyl-succinate synthase mnssA Gene encoding the enzyme believed to be responsible for anaerobic biodegradation of 2-methylnaphthalene by a marine isolate.
Naphthalene Carboxylase ANC Targets the only known gene encoding an enzyme responsible for the initial activation step in anaerobic naphthalene biodegradation.