Hoeflea anabaenae sp. nov., an epiphytic symbiont that attaches to the heterocysts of a strain of Anabaena

Abstract

The heterotrophic, epiphytic, symbiotic bacterial strain WH2KTwas previously isolated from a two-member culture in which it was attached to the heterocysts of a strain ofAnabaena(SSM-00). Analysis of its 16S rRNA gene sequence demonstrated that the symbiont was most closely related to the type strain ofHoeflea marina(96.9 % similarity), which belongs to the familyPhyllobacteriaceaewithin the orderRhizobialesof the classAlphaproteobacteria. A polyphasic taxonomic study was performed on strain WH2KT, which consisted of irregular rods (2–5 µm long, 0.2 µm wide) that appeared to be narrower at one pole. Optimal growth was obtained in complex media with 15 g sea salts l−1, at 18–34 °C (30 °C optimum) and at pH 6.0–8.0 (optimum pH 6.5). Unknown growth requirements were provided by small amounts of yeast extract but not by standard vitamin and trace metal solutions. Of the substrates tested, WH2KTwas able to utilize only acetate, pyruvate, malate and fumarate. Growth was observed only under aerobic and microaerobic conditions, and nitrate was not reduced. No photosynthetic pigments were detected under any of the growth conditions tested. The predominant fatty acids were a summed feature that comprises C18 : 1ω7c, C18 : 1ω9t, C18 : 1ω12tor any combination of these (64.0 %) and an unidentified fatty acid of equivalent chain length 17.603 (13.5 %). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine, phosphoglycolipid, unknown lipids and an unidentified aminolipid. The only respiratory ubiquinone detected was Q-10. The DNA G+C content of the strain was 58.1 mol%. The organism can form a site-specific attached symbiotic relationship with a species ofAnabaena. Based on phylogenetic and phenotypic evidence, it is proposed that strain WH2KTbe classified within a novel species of the genusHoeflea, for which the nameHoeflea anabaenaesp. nov. is proposed. The type strain is WH2KT( = CCUG 56626T = NRRL B-59520T).