Ecology, Evolution, Behavior and Systematics

Abstract Thaumarchaeota have been detected in several industrial and municipal wastewater treatment plants (WWTPs), despite the fact that ammonia-oxidizing archaea (AOA) are thought to be adapted to low ammonia environments. However, the activity, physiology and metabolism of WWTP-associated AOA remain poorly understood. We report the cultivation and complete genome sequence of Candidatus Nitrosocosmicus exaquare, a novel AOA representative from a municipal WWTP in Guelph, Ontario (Canada). In enrichment culture, Ca. N. exaquare oxidizes ammonia to nitrite stoichiometrically, is mesophilic, and tolerates at least 15 mm of ammonium chloride or sodium nitrite. Microautoradiography (MAR) for enrichment cultures demonstrates that Ca. N. exaquare assimilates bicarbonate in association with ammonia oxidation. However, despite using inorganic carbon, the ammonia-oxidizing activity of Ca. N. exaquare is greatly stimulated in enrichment culture by the addition of organic compounds, especially malate and succinate. Ca. N. exaquare cells are coccoid with a diameter of ~1–2 μm. Phylogenetically, Ca. N. exaquare belongs to the Nitrososphaera sister cluster within the Group I.1b Thaumarchaeota, a lineage which includes most other reported AOA sequences from municipal and industrial WWTPs. The 2.99 Mbp genome of Ca. N. exaquare encodes pathways for ammonia oxidation, bicarbonate fixation, and urea transport and breakdown. In addition, this genome encodes several key genes for dealing with oxidative stress, including peroxidase and catalase. Incubations of WWTP biofilm demonstrate partial inhibition of ammonia-oxidizing activity by 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), suggesting that Ca. N. exaquare-like AOA may contribute to nitrification in situ. However, CARD-FISH-MAR showed no incorporation of bicarbonate by detected Thaumarchaeaota, suggesting that detected AOA may incorporate non-bicarbonate carbon sources or rely on an alternative and yet unknown metabolism.

Bacteria that directly use electrodes as metabolic electron donors (biocathodes) have been proposed for applications ranging from microbial electrosynthesis to advanced bioelectronics for cellular communication with machines. However, just as we understand very little about oxidation of analogous natural insoluble electron donors, such as iron oxide, the organisms and extracellular electron transfer (EET) pathways underlying the electrode-cell direct electron transfer processes are almost completely unknown. Biocathodes are a stable biofilm cultivation platform to interrogate both the rate and mechanism of EET using electrochemistry and to study the electroautotrophic organisms that catalyze these reactions. Here we provide new evidence supporting the hypothesis that the uncultured bacterium “CandidatusTenderia electrophaga” directly couples extracellular electron transfer to CO2fixation. Our results provide insight into developing biocathode technology, such as microbial electrosynthesis, as well as advancing our understanding of chemolithoautotrophy.

Recently, a novel species of the genusBorreliawas identified inBothriocroton concolorandIxodes holocyclusticks from echidnas. Analyses of 16S rRNA andflaBgenes identified three closely related genotypes of this bacterium (Borreliasp. Aus A-C) that were unique and distinct from previously described borreliae. Phylogenetic analyses offlaB(763 bp),groEL(1537 bp),gyrB(1702 bp) andglpQ(874 bp) gene sequences and concatenated sequences (3585 bp) of three gene loci (16S rRNA,flaBandgyrB) were consistent with previous findings and confirm that this novel species of the genusBorreliais more closely related to, yet distinct from, the Reptile-associated (REP) and Relapsing Fever (RF) groups. At theflaBlocus, genotypes A, B and C shared the highest percentage sequence similarities (87.9, 88 and 87.9 %, respectively) withB.orrelia turcica(REP), whereas at thegroELandgyrBloci, these genotypes were most similar (88.2–89.4 %) toB.orrelia hermsii(RF). At theglpQlocus, genotypes A and B were most similar (85.7 and 85.4 % respectively) toBorreliasp. Tortoise14H1 (REP). The presence of theglpQgene, which is absent in the Lyme Borreliosis group spirochaetes, further emphasises that the novel species of the genusBorreliacharacterized in the present study does not belong to this group. Phylogenetic analyses at multiple loci produced consistent topographies revealing the monophyletic grouping of this bacterium, therefore providing strong support for its species status. We propose the name ‘CandidatusBorreliatachyglossi’, and hypothesize that this species of the genusBorreliamay be endemic to Australia. The pathogenic potential of this bacterium is not yet known.

Abstract. Endolithic microbial communities are prominent features of intertidal marine habitats, where they colonize a variety of substrates, contributing to their erosion. Almost 2 centuries worth of naturalistic studies focused on a few true-boring (euendolithic) phototrophs, but substrate preference has received little attention. The Isla de Mona (Puerto Rico) intertidal zone offers a unique setting to investigate substrate specificity of endolithic communities since various phosphate rock, limestone and dolostone outcrops occur there. High-throughput 16S rDNA genetic sampling, enhanced by targeted cultivation, revealed that, while euendolithic cyanobacteria were dominant operational taxonomic units (OTUs), the communities were invariably of high diversity, well beyond that reported in traditional studies and implying an unexpected metabolic complexity potentially contributed by secondary colonizers. While the overall community composition did not show differences traceable to the nature of the mineral substrate, we detected specialization among particular euendolithic cyanobacterial clades towards the type of substrate they excavate but only at the OTU phylogenetic level, implying that close relatives have specialized recurrently into particular substrates. The cationic mineral component was determinant in this preference, suggesting the existence in nature of alternatives to the boring mechanism described in culture that is based exclusively on transcellular calcium transport.