title: Living in an Extremely Polluted Environment: Clues from the Genome of Melanin-Producing Aeromonas salmonicida subsp. pectinolytica 34melT.
abstract: Aeromonas salmonicida subsp. pectinolytica 34mel(T) can be considered an extremophile due to the characteristics of the heavily polluted river from which it was isolated. While four subspecies of A. salmonicida are known fish pathogens, 34mel(T) belongs to the only subspecies isolated solely from the environment. Genome analysis revealed a high metabolic versatility, the capability to cope with diverse stress agents, and the lack of several virulence factors found in pathogenic Aeromonas. The most relevant phenotypic characteristics of 34mel(T) are pectin degradation, a distinctive trait of A. salmonicida subsp. pectinolytica, and melanin production. Genes coding for three pectate lyases were detected in a cluster, unique to this microorganism, that contains all genes needed for pectin degradation. Melanin synthesis in 34mel(T) is hypothesized to occur through the homogentisate pathway, as no tyrosinases or laccases were detected and the homogentisate 1,2-dioxygenase gene is inactivated by a transposon insertion, leading to the accumulation of the melanin precursor homogentisate. Comparative genome analysis of other melanogenic Aeromonas strains revealed that this gene was inactivated by transposon insertions or point mutations, indicating that melanin biosynthesis in Aeromonas occurs through the homogentisate pathway. Horizontal gene transfer could have contributed to the adaptation of 34mel(T) to a highly polluted environment, as 13 genomic islands were identified in its genome, some of them containing genes coding for fitness-related traits. Heavy metal resistance genes were also found, along with others associated with oxidative and nitrosative stresses. These characteristics, together with melanin production and the ability to use different substrates, may explain the ability of this microorganism to live in an extremely polluted environment.
authors.affiliation: Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: María Elisa
authors.initials: ME
authors.lastname: Pavan
authors.affiliation: Biomedical Technologies Laboratory, Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy.
authors.forename: Esteban E
authors.initials: EE
authors.lastname: Pavan
authors.affiliation: Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina IQUIBICEN-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Nancy I
authors.initials: NI
authors.lastname: López
authors.affiliation: Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Laura
authors.initials: L
authors.lastname: Levin
authors.affiliation: Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina IQUIBICEN-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina jul@qb.fcen.uba.ar.
authors.forename: M Julia
authors.identifier: http://orcid.org/0000-0002-6130-4740
authors.initials: MJ
authors.lastname: Pettinari
mesh_terms: D000220:Adaptation, Biological; D048409:Aeromonas salmonicida / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D001711:Biotransformation; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics*; D024881:Drug Resistance, Bacterial; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D008543:Melanins / Q000378:metabolism; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D019216:Metals, Heavy / Q000633:toxicity; D008969:Molecular Sequence Data; D010368:Pectins / Q000378:metabolism; D045483:Rivers / Q000382:microbiology; D017422:Sequence Analysis, DNA; D014877:Water Pollution, Chemical
chemical_list: D004269:DNA, Bacterial; D008543:Melanins; D019216:Metals, Heavy; D010368:Pectins