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Two myxobacterial strains (KH5-1 T and NO1) were isolated from the activated sludge tanks treating municipal sewage wastewater in Japan. These strains were recognised as myxobacteria based on their phenotypic characteristics of swarming colonies and fruiting bodies. Phylogenetic analyses using the 16S rRNA gene revealed that strains KH5-1 T and NO1 were affiliated with the genus Corallococcus, with the closest neighbours being Corallococcus exercitus AB043A T (99.77% and 99.84%, respectively). Genome comparisons using orthologous average nucleotide identity (orthoANI) and digital DNA-DNA hybridisation similarity (dDDH) with strains KH5-1 T and NO1 and their phylogenetically close relatives in Corallococcus spp. were below the thresholds. The major cellular fatty acids of strains KH5-1 T and NO1 were iso-C 15:0 (31.9%, 30.0%), summed feature 3 (comprising C 16:1 ω7c and/or C 1 6:1 ω6c) (20.2%, 17.7%), and iso-C 17:0 (12.1%, 14.8%), and the major respiratory quinone was found to be menaquinone (MK)-8. Based on the phenotypic, chemotaxonomic, and phylogenetic evidence, strains KH5-1 T and NO1 represent a new species in the genus Corallococcus, for which the proposed name is Corallococcus caeni sp. nov. The type strain is KH5-1 T (= NCIMB 15510 T  = JCM 36609 T )., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In this study, Sorangium cellulosum So ce56 was phenotypically and genotypically analysed in order to evaluate whether this strain can be used in a comprehensive genome project as a representative of the secondary metabolite-producing myxobacteria. In contrast to many other strains of S. cellulosum, strain So ce56 was found to have various advantageous features, including fast and homogeneous growth in submerged cultures and the ability to complete its morphological differentiation cycle on agar, even when the inoculant originates from a liquid culture. Two groups of secondary metabolites isolated from the culture broth were identified, the polyketides etnangien and chivosazole. The presence of polyketide synthase-encoding genes in the genome of strain So ce56 was demonstrated via PCR. The phenotypic classification was confirmed by comparison of 16S rDNA sequences which showed that S. cellulosum So ce56 clusters within a separate lineage together with S. cellulosum ATCC 25531 and the epothilone producer S. cellulosum So ce90. The genome of S. cellulosum So ce56 belongs to the largest bacterial genomes described so far. It is estimated to be 12.2 Mb in size, by pulsed-field gel electrophoresis. In order to demonstrate that S. cellulosum So ce56 is a convenient strain for molecular biological studies, a genetic manipulation system was developed. Using triparental mating, polyketide synthase-encoding genes were inactivated, leading to chivosazole-negative mutants.

The molar percentages of guanine plus cytosine in the DNA of 51 strains of Simonsiellaceae were determined by buoyant density ultracentrifugation of cell lysates in CsCl. The DNA base ratios ranged from 41-55 mole-% guanine plus cytosine. These values fall within the range known for the Order Cytophagales, the non-fruiting gliding bacteria, and are outside the range of the Order Myxobacterales, the fruiting myxobacteria. Among the strains of the genus Simonsiella, four distinct group can be delineated on the basis of source of origin (sheep, dog, cat, human) and GC content. The neotype of Alysiella filiformis has a GC content of 45.4 mole-%.