Publications

4372

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.

AbstractThe Candidate Phyla Radiation (CPR) is a large group of bacteria, the scale of which approaches that of all other bacteria. CPR organisms are inferred to depend on other community members for many basic cellular building blocks and all appear to be obligate anaerobes. To date, there has been no evidence for any significant respiratory capacity in an organism from this radiation. Here we report a curated draft genome for ‘Candidatus Parcunitrobacter nitroensis’ a member of the Parcubacteria (OD1) superphylum of the CPR. The genome encodes versatile energy pathways, including fermentative and respiratory capacities, nitrogen and fatty acid metabolism, as well as the first complete electron transport chain described for a member of the CPR. The sequences of all of these enzymes are highly divergent from sequences found in other organisms, suggesting that these capacities were not recently acquired from non-CPR organisms. Although the wide respiration-based repertoire points to a different lifestyle compared to other CPR bacteria, we predict similar obligate dependence on other organisms or the microbial community. The results substantially expand the known metabolic potential of CPR bacteria, although sequence comparisons indicate that these capacities are very rare in members of this radiation.

Candidatus Midichloria mitochondrii is the sheep tick Ixodes ricinus endosymbiont. This unique bacteria can occupy and persist within the mitochondria of animals. I. ricinus is an important vector of human pathogens in natural focal of infections. Candidatus M. mitochondrii found in the intermembrane space of mitochondria and in the cytoplasm of ovarian cells in 100% females of I. ricinus. The bacteria contain flagella in the salivary glands of ticks. Candidatus M. mitochondrii has two groups of unique genes for the members of the order Rickettsiales (cbb3 cytochrome oxidase and flagellin), which allows it to play an important role in embryogenesis of the I. ricinus ticks and cause seroconversion in 58% of patients after ticks bloodsucking. This bacterium formed MALOs group (midichloria and like organisms) with genetically closely related organisms which demonstrated a association with a wide range of host from arthropods to ciliates, amoebae, sponges, fish and various animals and humans. Now there is no data about replication the Candidatus M. mitochondrii in humans and pathogenicity of this microorganism. Although a high percentage of seropositive samples obtained from patients after bloodsucking of I. ricinus in anamnesis, this bacterium cannot yet be regarded as responsible for the pathology as known human pathogenic from order Rickettsi-ales (Rickettsia, Anaplasma and Ehrlichia spp.). Needed to reconsider the attitude to an immune response to the saliva of I. ricinus, taking into account the potential impact of Candidatus M. mitochondrii. It is considered highly possible role of this bacterium in the immune response and immunomodulation in humans with bloodsucking of I. ricinus in anamnesis. DNA of Candidatus M. mitochondrii was the first time detected in I. ricinus ticks from European part of Russia.

Abstract Marine oxygen minimum zones (OMZs) are expanding regions of intense nitrogen cycling. Up to half of the nitrogen available for marine organisms is removed from the ocean in these regions. Metagenomic studies have identified an abundant group of sulfur-oxidizing bacteria (SUP05) with the genetic potential for nitrogen cycling and loss in OMZs. However, SUP05 have defied cultivation and their physiology remains untested. We cultured, sequenced and tested the physiology of an isolate from the SUP05 clade. We describe a facultatively anaerobic sulfur-oxidizing chemolithoautotroph that produces nitrite and consumes ammonium under anaerobic conditions. Genetic evidence that closely related strains are abundant at nitrite maxima in OMZs suggests that sulfur-oxidizing chemoautotrophs from the SUP05 clade are a potential source of nitrite, fueling competing nitrogen removal processes in the ocean.