Metabolic Pathways for Degradation of Aromatic Hydrocarbons by Bacteria

Abstract

The aim of this review was to build an updated collection of information focused on the mechanisms and elements involved in metabolic pathways of aromatic hydrocarbons by bacteria. Enzymes as an expression of the genetic load and the type of electron acceptor available, as an environmental factor, were highlighted. In general, the review showed that both aerobic routes and anaerobic routes for the degradation of aromatic hydrocarbons are divided into two pathways. The first, named the upper pathways, entails the route from the original compound to central intermediate compounds still containing the aromatic ring but with the benzene nucleus chemically destabilized. The second, named the lower pathway, begins with ring de-aromatization and subsequent cleavage, resulting in metabolites that can be used by bacteria in the production of biomass. Under anaerobic conditions the five mechanisms of activation of the benzene ring described show the diversity of chemical reactions that can take place. Obtaining carbon and energy from an aromatic hydrocarbon molecule is a process that exhibits the high complexity level of the metabolic apparatus of anaerobic microorganisms. The ability of these bacteria to express enzymes that catalyze reactions, known only in non-biological conditions, using final electron acceptors with a low redox potential, is a most interesting topic. The discovery of phylogenetic and functional characteristics of cultivable and noncultivable hydrocarbon degrading bacteria has been made possible by improvements in molecular research techniques such as SIP (stable isotope probing) tracing the incorporation of (13)C, (15)N and (18)O into nucleic acids and proteins. Since many metabolic pathways in which enzyme and metabolite participants are still unknown, much new research is required. Therefore, it will surely allow enhancing the known and future applications in practice.

The Interaction between Plants and Bacteria in the Remediation of Petroleum Hydrocarbons: An Environmental Perspective

“…The principle behind biostimulation as a method to increase PHC degradation relies on the establishment of a propitious environment for hydrocarbonclastic bacterial communities through the addition of nutrients (e.g., nitrogen and phosphorus, horse manure, poultry litter, domestic sewage, rice straw biochar, crop residues), and other supplementary components such as biosurfactants and electron acceptors [e.g., O 2 , chelated Fe (III), nitrates, sulfate] (Gallego et al, 2001; Molina-Barahona et al, 2004; Coles et al, 2009; Lai et al, 2009; Qin et al, 2013; Zhao et al, 2015; Ladino-Orjuela et al, 2016). The adjuvant role of these factors is related either to the metabolic activity of the naturally occurring degrading bacteria or to the bioavailability of PHCs.…”

Responses of Microbial Communities to Hydrocarbon Exposures

“…Heterotrophic microorganisms (microbes that obtain their metabolic energy and cellular carbon from organic carbon compounds) use a plethora of metabolic pathways for consuming hydrocarbons in the largely nutrientlimited marine environment. The majority of research to date has emphasized the pathways for degradation and/or transformation of aliphatic and aromatic hydrocarbons, since these dominate crude oils and are gas chromatography (GC) amenable and thus easier to study (Fuchs et al, 2011;Abbasian et al, 2015;Ladino-Orjuela et al, 2016).…”

“…A diverse set of peripheral pathways transform aromatic compounds into one of a few key central intermediates (Fuchs et al, 2011;Ladino-Orjuela et al, 2016;Figure 2b). Under aerobic conditions, these are typically monooxygenases or dioxygenases that hydroxylate the aromatic compound to produce catechol, primarily protocatechuate, gentistate, or homogentistate (Fuchs et al, 2011).…”

From Functional Potential of Soil Bacterial Communities Towards Petroleum Hydrocarbons Bioremediation

“…Evidence for biodegradation of high-molecular-weight PAHs, containing more than four aromatic rings such as chrysene, benzo[a]pyrene and benz[a]anthracene is still limited. This is in contrast to the bacterial degradation of monoaromatic compounds and low-molecular-weight PAHs (containing two or three aromatic rings) such as naphthalene, acenaphthene, fluorene, phenanthrene and anthracene, since the biochemical pathways for their breakdown have been well studied and reviewed (Fuentes et al 2014;Jones et al 2011;Ladino-Orjuela et al 2016;Lu et al 2011;Peng et al 2008;Seo et al 2009;Wick et al 2003). The biodegradation process of these relatively simpler compounds is commonly separated into peripheral and central pathways.…”