title: Why orange Guaymas Basin Beggiatoa spp. are orange: single-filament-genome-enabled identification of an abundant octaheme cytochrome with hydroxylamine oxidase, hydrazine oxidase, and nitrite reductase activities.
abstract: Orange, white, and yellow vacuolated Beggiatoaceae filaments are visually dominant members of microbial mats found near sea floor hydrothermal vents and cold seeps, with orange filaments typically concentrated toward the mat centers. No marine vacuolate Beggiatoaceae are yet in pure culture, but evidence to date suggests they are nitrate-reducing, sulfide-oxidizing bacteria. The nearly complete genome sequence of a single orange Beggiatoa ("Candidatus Maribeggiatoa") filament from a microbial mat sample collected in 2008 at a hydrothermal site in Guaymas Basin (Gulf of California, Mexico) was recently obtained. From this sequence, the gene encoding an abundant soluble orange-pigmented protein in Guaymas Basin mat samples (collected in 2009) was identified by microcapillary reverse-phase high-performance liquid chromatography (HPLC) nano-electrospray tandem mass spectrometry (μLC-MS-MS) of a pigmented band excised from a denaturing polyacrylamide gel. The predicted protein sequence is related to a large group of octaheme cytochromes whose few characterized representatives are hydroxylamine or hydrazine oxidases. The protein was partially purified and shown by in vitro assays to have hydroxylamine oxidase, hydrazine oxidase, and nitrite reductase activities. From what is known of Beggiatoaceae physiology, nitrite reduction is the most likely in vivo role of the octaheme protein, but future experiments are required to confirm this tentative conclusion. Thus, while present-day genomic and proteomic techniques have allowed precise identification of an abundant mat protein, and its potential activities could be assayed, proof of its physiological role remains elusive in the absence of a pure culture that can be genetically manipulated.
authors.affiliation: Department of Marine Sciences, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA. bmacgreg@unc.edu
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: MacGregor
authors.forename: Jennifer F
authors.initials: JF
authors.lastname: Biddle
authors.forename: Jason R
authors.initials: JR
authors.lastname: Siebert
authors.forename: Eric
authors.initials: E
authors.lastname: Staunton
authors.forename: Eric L
authors.initials: EL
authors.lastname: Hegg
authors.forename: Ann G
authors.initials: AG
authors.lastname: Matthysse
authors.forename: Andreas
authors.initials: A
authors.lastname: Teske
mesh_terms: D053524:Beggiatoa / Q000201:enzymology* / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003580:Cytochromes / Q000302:isolation & purification / Q000378:metabolism*; D019015:Geologic Sediments / Q000382:microbiology; D008800:Mexico; D009572:Nitrite Reductases / Q000302:isolation & purification / Q000378:metabolism; D010088:Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism; D010860:Pigments, Biological / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D053719:Tandem Mass Spectrometry
chemical_list: D003580:Cytochromes; D010860:Pigments, Biological; D010088:Oxidoreductases; D009572:Nitrite Reductases; C021401:hydroxylamine dehydrogenase