Culture‐independent characterization of novel psychrophilic magnetotactic cocci from Antarctic marine sediments

Abstract

Magnetotactic bacteria (MTB) are a heterogeneous group of ubiquitous aquatic microorganisms capable of biomineralizing nano-sized, membrane-bound, magnetic iron-rich mineral particles called magnetosomes. MTB are found in chemically-stratified aquatic sediments and/or water columns with a wide range of salinities, moderate to high temperatures, and pH varying from neutral to strongly alkaline. MTB from very cold environments have not been investigated to any great degree and here we characterize MTB from the low temperature Antarctic maritime region. Sediment samples were collected at nine sampling sites within Admiralty Bay, King George Island (62°23'S 58°27'W) from 2009 to 2013. Samples from five sites contained MTB and those from two of these sites contained large number of magnetotactic cocci that were studied using electron microscopy and molecular techniques. The magnetotactic cocci contained magnetosomes either arranged as two or four chains or as a disorganized cluster. The crystalline habit and composition of all magnetosomes analyzed with high-resolution transmission electron microscopy and energy dispersive X-ray microanalysis were consistent with elongated prismatic crystals of magnetite (Fe O ). The retrieved 16S rRNA gene sequences from magnetically-enriched magnetotactic cocci clustered into three distinct groups affiliated with the Alphaproteobacteria class of the Proteobacteria. Novel sequences of each phylogenetic cluster were confirmed using fluorescent in situ hybridization. Metagenomic data analysis of magnetically-enriched magnetotactic cocci revealed the presence of mam genes and MTB-specific hypothetical protein coding genes. Sequence homology and phylogenetic analysis indicated that predicted proteins are related to those of cultivated alphaproteobacterial MTB. The consistent and continuous low temperature of the sediment where the magnetotactic cocci are present (always below 1°C) suggests that these MTB from maritime Antarctica are psychrophiles. Moreover, similar morphotypes and 16S gene sequences were retrieved from samples collected from different sites from maritime Antarctica for several years suggesting that these new strains of MTB are indigenous members of Antarctic microbiota.

Genome-Based Metabolic Reconstruction of a Novel Uncultivated Freshwater Magnetotactic coccus “Ca. Magnetaquicoccus inordinatus” UR-1, and Proposal of a Candidate Family “Ca. Magnetaquicoccaceae”

“…Magnetotactic cocci are one type of magnetotactic bacteria (MTB). Since the first description of MTB (Blakemore, 1975), many studies have shown that magnetotactic cocci are the most frequent morphotype among other MTB, both in freshwater (Moench and Konetzka, 1978; Spring et al, 1995; Flies et al, 2005a,b; Lin and Pan, 2009, 2010) and marine habitats (Spring et al, 1998; Abreu et al, 2012; Zhang et al, 2012; Du et al, 2017). However, only five representatives— Magnetococcus marinus MC-1 T (Frankel et al, 1997), Magnetofaba australis IT-1 (Morillo et al, 2014), “ Ca .…”

Magnetotactic Coccus Strain SHHC-1 Affiliated to Alphaproteobacteria Forms Octahedral Magnetite Magnetosomes

“…These known cultured and uncultured MTB have been assigned to the Alpha -, Gamma -, and Delta-proteobacteria classes of the Proteobacteria phylum (Lefèvre and Bazylinski, 2013), the Nitrospirae phylum (Spring et al, 1993), and even the “ Candidatus Omnitrophica” phylum (Kolinko et al, 2012). Despite the morphological and phylogenetic diversity of MTB, the most commonly observed types present in natural environments are coccoid-to-ovoid cells, the so-called magnetococci (Moench and Konetzka, 1978; Spring et al, 1992, 1995; Thornhill et al, 1995; Cox et al, 2002; Flies et al, 2005; Pan et al, 2008, 2009; Lin and Pan, 2009; Zhang et al, 2012; Chen et al, 2015; Abreu et al, 2016). Previous 16S rDNA phylogenetic analyses have shown that magnetococci are also highly diverse.…”

Bacterial community structure and novel species of magnetotactic bacteria in sediments from a seamount in the Mariana volcanic arc

“…In this study, we performed a systematic investigation of the bacterial diversity and community structure in sediments collected from 14 stations on a seamount located in the tropical western Pacific Ocean; additionally, this cruise marks the first time this seamount has been surveyed. We focused on the occurrence of seamount magnetotactic bacteria (MTB) that are widely distributed in freshwater and marine ecosystems 12 – 16 . MTB are a morphologically, phylogenetically, and physiologically diverse group of bacteria that produce single-domain magnetite (Fe 3 O 4 ) or greigite (Fe 3 S 4 ) crystals in intracellular organelles called magnetosomes.…”