Abstract
A novel Alcaligenes sp. strain P156, which can utilize nicotinamide as its sole source of carbon, nitrogen and energy, was enriched and isolated from soil in a solid waste treatment plant. Aerobic growth and degradation with nicotinamide were characterized. Seven nicotinamide degradation-related genes were obtained by sequence alignment from the genome sequence of strain P156. Four genes, designated naaA, naaD, naaE and naaF, were cloned and heterologously expressed. Nicotinamide degradation is initiated by deamination to form nicotinic acid catalyzed by the nicotinamidase NaaA, which shares highest amino acid sequence identity (27.2%) with nicotinamidase from Arabidopsis thaliana. Nicotinic acid is converted to 6-hydroxynicotinic acid, which is further oxidized to 2,5-dihydroxypyridine (2,5-DHP). 2,5-DHP is then transformed to a ring-cleavage product, N-formylmaleamic acid, by an Fe2+ dependent dioxygenase NaaD. N-formylmaleamic acid is transformed to fumaric acid through maleamic acid and maleic acid by NaaE and NaaF, respectively. To our knowledge, this is the first report of the complete microbial degradation of nicotinamide in bacteria. Nicotinamide is considered as a model compound for the study of microbial degradation of pyridinic compounds, and the nicotinamide degrading related genes in strain P156 were distributed differently from the reported similar gene clusters. Therefore, this study contribute to the knowledge on the degradation of pyridinic compounds.
Highlights
Nicotinamide, known as a form of vitamin B3, is a part of the coenzyme nicotinamide adenine dinucleotide (NADH/NAD+) and is crucial to life
The strain, which could use picolinic acid (PIA) and nicotinamide as the sole source of carbon, nitrogen, and energy, was obtained by plate streaking with enrichment cultivation and designated as P156 (Table 1)
Strain P156 was identified as a Gram-negative, aerobic strain and classified as Alcaligenes sp
Summary
Nicotinamide, known as a form of vitamin B3, is a part of the coenzyme nicotinamide adenine dinucleotide (NADH/NAD+) and is crucial to life. The study of microbial transformation of nicotinamide mainly focus on the first deamination step[12,13]. Nicotinamide was transformed to nicotinic acid by nicotinamidase releasing NH4+ 13. This reaction is involved in NAD+ biosynthesis, but in many other important physiological processes. Nicotinamide is ubiquitous in all living organisms, degradation of nicotinamide could be considered as model systems for the degradation of pyridinic compounds. Degradable ND ND ND + + ND + + ND + ND nicotinamide will help us to understand the degradation processes of other pyridinic pollutants, such as picloram and diquat[7,15]. We have isolated a nicotinamide degrading bacterium, Alcaligenes sp. The objective of this work is to demonstrate the nicotinamide catabolism in bacteria
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