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A Gram-negative, strictly aerobic, short rod-shaped, non-motile bacterial strain designated 4M24 T was isolated from cotton-waste compost. Analysis of the 16S rRNA gene sequence of strain 4M24 T revealed that it is a member of the genus Sphingobacterium, sharing 88.5-94.5 % sequence similarity with type strains of the genus Sphingobacterium and being most closely related to Sphingobacterium daejeonense TR6-04 T (94.5 % sequence similarity) and Sphingobacterium mizutaii ATCC 33299 T (92.2 % similarity). The major fatty acids of strain 4M24 T grown on trypticase soy agar medium were summed feature 3 (iso-C 15 : 0 2-OH and/or C 16 : 1 v7c; 37.5 %), iso-C 15 : 0 (29.5 %) and iso-C 17 : 0 3-OH (19.7 %). The G+C content of the genomic DNA was 42.3 mol%. On the basis of phenotypic and genotypic characteristics, strain 4M24 T represents a novel species of the genus Sphingobacterium, for which the name Sphingobacterium composti sp. nov. is proposed. The type strain is 4M24 T (=KACC 11313 T =DSM 18850 T ).

The existence of microgauss magnetic fields in galaxy clusters have been established through observations of synchrotron radiation and Faraday rotation. They are conjectured to be generated via small-scale dynamo by turbulent flow motions in the intracluster medium (ICM). Some of giant radio relics, on the other hand, show the structures of synchrotron polarization vectors, organized over the scales of ∼ Mpc, challenging the turbulence origin of cluster magnetic fields. Unlike turbulence in the interstellar medium, turbulence in the ICM is subsonic. And it is driven sporadically in highly stratified backgrounds, when major mergers occur during the hierarchical formation of clusters. To investigate quantitatively the characteristics of turbulence dynamo in such ICM environment, we performed a set of turbulence simulations using a high-order-accurate, magnetohydrodynamic (MHD) code. We find that turbulence dynamo could generate the cluster magnetic fields up to the observed level from the primordial seed fields of 10 −15 G or so within the age of the universe, if the MHD description of the ICM could be extended down to ∼ kpc scales. However, highly organized structures of polarization vectors, such as those observed in the Sausage relic, are difficult to be reproduced by the shock compression of turbulence-generated magnetic fields. This implies that the modeling of giant radio relics may require the pre-existing magnetic fields organized over ∼ Mpc scales.

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