Initial reactions in the biodegradation of 1-chloro-4-nitrobenzene by a newly isolated bacterium, strain LW1

Isolation and characterization of a new poly(3-hydroxybutyrate)-degrading, denitrifying bacterium from activated sludge

A new denitrifying chemoorganotrophic bacterium capable of aerobic and anaerobic degradation of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) was isolated from activated sludge. A phylogenetic analysis based on 16S rDNA sequences indicated that the new isolate is a member of the beta subclass of the Proteobacteria and represents a distinct line of descent within the family Comamonadaceae. During denitrifying growth with 3-hydroxybutyrate, PHB, or PHBV as the sole carbon source, the isolate reduced nitrate to N2 without appreciable accumulation of nitrite and nitrous oxide as intermediate products. Kinetic analyses of the denitrification with different grades of PHBV indicated that approximately 0.7 g of PHBV was required to reduce 1 g of NO3-. A high denitrification rate (19 mg N-NO3- removed h(-1) x g(-1) dry wt of cells) was found with PHBV as the electron donor.

Evaluation of the denitrifying microbiota of anoxic reactors

Removal of inorganic nitrogen compounds from wastewaters can be accomplished by a combination of the biological processes of nitrification and denitrification. The information on the microbiota present in denitrifying reactors is still scarce. In the present work the evaluation of the denitrifying microbiota of different reactor sludges was performed by specific activity measurements and MPN count of denitrifiers. We also present the isolation and physiological and phylogenetic characterisation of denitrifying bacteria from the anoxic reactor of a combined system treating landfill leachate. Specific denitrifying activity measurements were faster to perform and more reliable than MPN enumerations. 16S rDNA characterisation of the isolates showed that they belonged to the genera Thauera, Acidovorax and Alcaligenes and were closely related to microorganisms retrieved from ecosystems rich in recalcitrant compounds. Two of the isolates could grow on aromatic compounds as sole carbon source.

Biodegradation of nitroaromatic pollutants: from pathways to remediation

Nitroaromatic compounds are important contaminants of the environment, mainly of anthropogenic origin. They are produced as intermediates and products in the industrial manufacturing of dyes, explosives, pesticides, etc. Their toxicity has been extensively demonstrated in a whole range of living organisms, and nitroaromatic contamination dating from World War II is the proof of the recalcitrance of such compounds to microbial recycling. In spite of this, bacteria have evolved diverse pathways that allow them to mineralize specific nitroaromatic compounds. Degradation sequences initiated by an oxidation, an attack by a hydride ion, or a partial reduction have been documented. Some of these reactions have been exploited in bioreactors. Although pathways and enzymes involved are rather well understood, the molecular basis of these pathways is still currently under investigation. However, productive metabolism is an exception. As a rule, most bacteria are only able to reduce the nitro group into an amino function. This reduction is cometabolic: the metabolism of exogenous carbon sources is required to provide reducing equivalents. Composting and processes in bioreactors have exploited the easy reduction of the nitroaromatic compounds. In the case an amino-aromatic compound is produced, it is important to incorporate it in the remediation scheme. Some processes dealing with both nitro- and amino-aromatic compounds have been described, the amino derivative being either mineralized by the same or, more often, another microorganism, or immobilized on soil particles. Depending on the nitroaromatic compound and the environment it is contaminating, a whole range of reactions and reactor studies are now available to help devise a successful remediation strategy.

Cloning and characterization of the pnb genes, encoding enzymes for 4-nitrobenzoate catabolism in Pseudomonas putida TW3

Pseudomonas putida strain TW3 is able to metabolize 4-nitrotoluene via 4-nitrobenzoate (4NBen) and 3, 4-dihydroxybenzoic acid (protocatechuate [PCA]) to central metabolites. We have cloned, sequenced, and characterized a 6-kbp fragment of TW3 DNA which contains five genes, two of which encode the enzymes involved in the catabolism of 4NBen to PCA. In order, they encode a 4NBen reductase (PnbA) which is responsible for catalyzing the direct reduction of 4NBen to 4-hydroxylaminobenzoate with the oxidation of 2 mol of NADH per mol of 4NBen, a reductase-like enzyme (Orf1) which appears to have no function in the pathway, a regulator protein (PnbR) of the LysR family, a 4-hydroxylaminobenzoate lyase (PnbB) which catalyzes the conversion of 4-hydroxylaminobenzoate to PCA and ammonium, and a second lyase-like enzyme (Orf2) which is closely associated with pnbB but appears to have no function in the pathway. The central pnbR gene is transcribed in the opposite direction to the other four genes. These genes complete the characterization of the whole pathway of 4-nitrotoluene catabolism to the ring cleavage substrate PCA in P. putida strain TW3.

Reactions involved in the lower pathway for degradation of 4-nitrotoluene by Mycobacterium strain HL 4-NT-1

In spite of the variety of initial reactions, the aerobic biodegradation of aromatic compounds generally yields dihydroxy intermediates for ring cleavage. Recent investigation of the degradation of nitroaromatic compounds revealed that some nitroaromatic compounds are initially converted to 2-aminophenol rather than dihydroxy intermediates by a number of microorganisms. The complete pathway for the metabolism of 2-aminophenol during the degradation of nitrobenzene by Pseudomonas pseudoalcaligenes JS45 has been elucidated previously. The pathway is parallel to the catechol extradiol ring cleavage pathway, except that 2-aminophenol is the ring cleavage substrate. Here we report the elucidation of the pathway of 2-amino-4-methylphenol (6-amino-m-cresol) metabolism during the degradation of 4-nitrotoluene by Mycobacterium strain HL 4-NT-1 and the comparison of the substrate specificities of the relevant enzymes in strains JS45 and HL 4-NT-1. The results indicate that the 2-aminophenol ring cleavage pathway in strain JS45 is not unique but is representative of the pathways of metabolism of other o-aminophenolic compounds.