Magnetospirillum bellicus sp. nov., a Novel Dissimilatory Perchlorate-Reducing Alphaproteobacterium Isolated from a Bioelectrical Reactor

Abstract

Previously isolated dissimilatory perchlorate-reducing bacteria (DPRB) have been primarily affiliated with the Betaproteobacteria. Enrichments from the cathodic chamber of a bioelectrical reactor (BER) inoculated from creek water in Berkeley, CA, yielded a novel organism most closely related to a previously described strain, WD (99% 16S rRNA gene identity). Strain VDY T has 96% 16S rRNA gene identity to both Magnetospirillum gryphiswaldense and Magnetospirillum magnetotacticum, and along with strain WD, distinguishes a clade of perchlorate-reducing Magnetospirillum species in the Alphaproteobacteria. In spite of the phylogenetic location of VDY T , attempted PCR for the key magnetosome formation genes mamI and mamL was negative. Strain VDY T was motile, non-spore forming, and, in addition to perchlorate, could use oxygen, chlorate, nitrate, nitrite, and nitrous oxide as alternative electron acceptors with acetate as the electron donor. Transient chlorate accumulation occurred during respiration of perchlorate. The organism made use of fermentation end products, such as acetate and ethanol, as carbon sources and electron donors for heterotrophic growth, and in addition, strain VDY T could grow chemolithotrophically with hydrogen serving as the electron donor. VDY T contains a copy of the RuBisCo cbbM gene, which was expressed under autotrophic but not heterotrophic conditions. DNA-DNA hybridization with strain WD confirmed VDY T as a separate species (46.2% identity), and the name Magnetospirillum bellicus sp. nov. (DSM 21662, ATCC BAA-1730) is proposed.Dissimilatory perchlorate-reducing bacteria (DPRB) use perchlorate as a terminal electron acceptor during respiration, reducing it completely to chloride. As a consequence, bioremediation of perchlorate has been identified as the most effective means of treating this harmful contaminant (10), which, due to historically unregulated release into the environment, has become widespread (13,20,41). Fortunately, DPRB are ubiquitous and can be readily isolated from a variety of environments (1,10,11,39,44), and a key gene in the pathway, the chlorite dismutase (cld) gene, has been broadly detected (6). Much has been revealed about the biochemistry and genetics of microbial perchlorate reduction through the study of several model organisms, including Dechloromonas aromatica and Dechloromonas agitata, by a variety of groups (5,6,8,9,17,28,29,34,35,38, 47, 51, 56, 57).Less is known about the variation in physiology between these organisms or the evolution of the perchlorate reduction metabolism, highlighting a need for further isolation and characterization of pure cultures. The lack of congruence between phylogenetic trees of cld and the 16S rRNA gene among tested DPRB suggests that the metabolism may be the result of horizontal gene transfer (6). Given that various elements of the pathway may be mobile, it is not unreasonable to expect that organisms with a wide phylogenetic diversity could acquire the ability to reduce perchlorate. As more varied enrichment conditions ar...

A new cell morphotype among methane oxidizers: a spiral-shaped obligately microaerophilic methanotroph from northern low-oxygen environments

“…Despite 3 years of continuous purification work, the spiral-shaped microaerophilic methanotroph could not be obtained in an axenic culture. The recent discovery of glycolysis-based methane assimilation and production of acetate and hydrogen by methanotrophs under oxygen limitation (Kalyuzhnaya et al, 2013) could explain the occurrence of Magnetospirullum-like 'satellites', which use acetate as the electron donor for heterotrophic growth (Schleifer et al, 1991;Thrash et al, 2010). Some members of this genus, like Magnetospirullum bellicus, could also grow chemolithotrophically with hydrogen serving as the electron donor (Thrash et al, 2010).…”

Insight into the Evolution of Magnetotaxis in Magnetospirillum spp., Based on mam Gene Phylogeny

“…Three scenarios are possible. First, nonmagnetotactic Magnetospirillum species (e.g., M. bellicus [45]) may have been magnetotactic in their natural environment when sampled but lost the ability to produce magnetosomes during their isolation in culture due to the use of nonappropriate cultivation techniques for magnetosome formation. This is certainly plausible, as many cultivated MTB have been reported to lose this trait upon repeated subcultivation in the absence of selective pressure (9,31,36,39), from the loss or rearrangement of the MAI.…”

“…The genome of M. magneticum strain AMB-1 has been completed, and while most of the genomes of M. gryphiswaldense strain MSR-1 and M. magnetotacticum strain MS-1 have been sequenced, they have not yet been closed as a chromosome (8,29). Known magnetotactic Magnetospirillum species are facultatively anaerobic microaerophiles that biomineralize a chain of cuboctahedral crystals of magnetite, although some strains do not produce magnetosomes (e.g., M. bellicus [45]). Morphologically, all known Magnetospirillum species are helical and are bipolarly flagellated.…”

Cultivation-Independent Detection of Autotrophic Hydrogen-Oxidizing Bacteria by DNA Stable-Isotope Probing

“…Based on 16S rRNA gene similarity, the organism represented by band OPB2 is a member of the alphaproteobacteria and is closely related to Magnetospirillum bellicus strain VDY, a strain isolated for its ability to reduce perchlorate (52). The sequence of the band OPB1 shares 99% sequence identity with that of Spirochaeta caldaria strain DSMZ7334.…”

“…A clone matching band OPB1 was not obtained. The organisms represented by bands OPB1 and OPB2 are closely related to bacteria known to oxidize H 2 under anaerobic conditions (37,52), which suggests that anaerobic conditions developed in the mat during the SIP incubation even though the O 2 concentration in the headspace was never below 11%.…”