Microbiology

Abstract Magnetotactic bacteria (MTB) of the genus ‘Candidatus Magnetobacterium’ in phylum Nitrospirae are of great interest because of the formation of hundreds of bullet-shaped magnetite magnetosomes in multiple bundles of chains per cell. These bacteria are worldwide distributed in aquatic environments and have important roles in the biogeochemical cycles of iron and sulfur. However, except for a few short genomic fragments, no genome data are available for this ecologically important genus, and little is known about their metabolic capacity owing to the lack of pure cultures. Here we report the first draft genome sequence of 3.42 Mb from an uncultivated strain tentatively named ‘Ca. Magnetobacterium casensis’ isolated from Lake Miyun, China. The genome sequence indicates an autotrophic lifestyle using the Wood–Ljungdahl pathway for CO2 fixation, which has not been described in any previously known MTB or Nitrospirae organisms. Pathways involved in the denitrification, sulfur oxidation and sulfate reduction have been predicted, indicating its considerable capacity for adaptation to variable geochemical conditions and roles in local biogeochemical cycles. Moreover, we have identified a complete magnetosome gene island containing mam, mad and a set of novel genes (named as man genes) putatively responsible for the formation of bullet-shaped magnetite magnetosomes and the arrangement of multiple magnetosome chains. This first comprehensive genomic analysis sheds light on the physiology, ecology and biomineralization of the poorly understood ‘Ca. Magnetobacterium’ genus.

Summary In an acetate‐fed anaerobic–aerobic membrane bioreactor with deteriorated enhanced biological phosphorus removal ( EBPR ), D efluviicoccus ‐related tetrad‐forming organisms ( DTFO ) were observed to predominate in the microbial community. Using metagenomics, a partial genome of the predominant DTFO , ‘ C andidatus   D efluviicoccus tetraformis strain TFO 71’, was successfully constructed and characterized. Examining the genome confirmed the presence of genes related to the synthesis and degradation of glycogen and polyhydroxyalkanoate ( PHA ), which function as energy and carbon storage compounds. TFO 71 and ‘ C andidatus   A ccumulibacter phosphatis’ ( CAP ) UW ‐1 and CAP UW ‐2, representative polyphosphate‐accumulating organisms ( PAO ), have PHA metabolism‐related genes with high homology, but TFO 71 has unique genes for PHA synthesis, gene regulation and granule management. We further discovered genes encoding DTFO polyphosphate ( polyP ) synthesis, suggesting that TFO 71 may synthesize polyP under untested conditions. However, TFO 71 may not activate these genes under EBPR conditions because the retrieved genome does not contain all inorganic phosphate transporters that are characteristic of PAOs ( CAP UW ‐1, CAP UW ‐2, M icrolunatus phosphovorus   NM ‐1 and T etrasphaera species). As a first step in characterizing EBPR ‐associated DTFO metabolism, this study identifies important differences between DTFO and PAO that may contribute to EBPR community competition and deterioration.

A thermotolerant, Gram-strain-negative, non-spore-forming and strictly aerobic bacterium, designated GU51T, was isolated from Guhai hot spring in Jimsar county, Xinjiang province, north-west China. Each cell of strain GU51Tconsisted of an oval body and two symmetrical long (3–6 µm) prosthecae. The strain moved by polar flagellum. Oxidase and catalase were produced. Strain GU51Tgrew within the ranges of 37–65 °C (optimum 48–50 °C), 0.5–7.5 % (w/v) NaCl (optimum 2–3 %) and pH 6.0–9.0 (optimum pH 7.5). The major respiratory quinone detected was ubiquinone 10 (U-10) and the genomic DNA G+C content was 66.7±0.4 mol%. Major fatty acids (>5 %) were C16 : 0, C18 : 1ω7cand 11-methyl C18 : 1ω7c. The polar lipids consisted of diphosphatidylglycerol, five glycolipids, phosphatidylglycerol and an unknown phospholipid. Phylogenetic analysis showed the closest relatives of strain GU51Twere members of the genusParvularculawith 92.3 % 16S rRNA gene sequence similarity. On the basis of this polyphasic taxonomic characterization, it is suggested that strain GU51Trepresents a novel species of a new genus in the family ‘Parvularculaceae’, for which the nameAmphiplicatus metriothermophilusgen. nov., sp. nov. is proposed. The type strain of the type species is GU51T( = CGMCC 1.12710T = JCM 19779T).

Abstract Amoebae serve as hosts for various intracellular bacteria, including human pathogens. These microbes are able to overcome amoebal defense mechanisms and successfully establish a niche for replication, which is usually the cytoplasm. Here, we report on the discovery of a bacterial symbiont that is located inside the nucleus of its Hartmannella sp. host. This symbiont, tentatively named ‘Candidatus Nucleicultrix amoebiphila’, is only moderately related to known bacteria (∼90% 16S and 23S rRNA sequence similarity) and member of a novel clade of protist symbionts affiliated with the Rickettsiales and Rhodospirillales. Screening of 16S rRNA amplicon data sets revealed a broad distribution of these bacteria in freshwater and soil habitats. ‘Candidatus Nucleicultrix amoebiphila’ traffics within 6 h post infection to the host nucleus. Maximum infection levels are reached after 96–120 h, at which time point the nucleus is pronouncedly enlarged and filled with bacteria. Transmission of the symbionts occurs vertically upon host cell division but may also occur horizontally through host cell lysis. Although we observed no impact on the fitness of the original Hartmannella sp. host, the bacteria are rather lytic for Acanthamoeba castellanii. Intranuclear symbiosis is an exceptional phenomenon, and amoebae represent an ideal model system to further investigate evolution and underlying molecular mechanisms of these unique microbial associations.