There is a need for easy, practical, reliable and robust techniques for the identification and classification of bacterial isolates to the species level as alternatives to 16S rRNA gene sequence analysis and DNA-DNA hybridization. Here, we demonstrate that multilocus sequence analysis (MLSA) of housekeeping genes is a valuable alternative technique. An MLSA study of 10 housekeeping genes (atpD, dnaK, gap, glnA, gltA, gyrB, pnp, recA, rpoB and thrC) was performed on 34 representatives of the genus Ensifer. Genetic analysis and comparison with 16S and 23S rRNA gene sequences demonstrated clear species boundaries and a higher discrimination potential for all housekeeping genes. Comparison of housekeeping gene sequence data with DNA-DNA reassociation data revealed good correlation at the intraspecies level, but indicated that housekeeping gene sequencing is superior to DNA-DNA hybridization for the assessment of genetic relatedness between Ensifer species. Our MLSA data, confirmed by DNA-DNA hybridizations, support the suggestion that Ensifer xinjiangensis is a later heterotypic synonym of Ensifer fredii.

Many eukaryotes are closely associated with bacteria which enable them to expand their physiological capacities. Associations between algae (photosynthetic eukaryotes) and bacteria have been described for over a hundred years. A wide range of beneficial and detrimental interactions exists between macroalgae (seaweeds) and epi‐ and endosymbiotic bacteria that reside either on the surface or within the algal cells. While it has been shown that these chemically mediated interactions are based on the exchange of nutrients, minerals, and secondary metabolites, the diversity and specificity of macroalgal–bacterial relationships have not been thoroughly investigated. Some of these alliances have been found to be algal or bacterial species‐specific, whereas others are widespread among different symbiotic partners. Reviewing 161 macroalgal–bacterial studies from the last 55 years, a definite bacterial core community, consisting of Gammaproteobacteria, CFB group, Alphaproteobacteria, Firmicutes, and Actinobacteria species, seems to exist which is specifically (functionally) adapted to an algal host–associated lifestyle. Because seaweed–bacterial associations are appealing from evolutionary and applied perspectives, future studies should integrate the aspects of diverse biological fields.

Bradyrhizobium canariense sp. nov., an acidtolerant endosymbiont that nodulates endemic genistoid legumes (Papilionoideae: Genisteae) from the Canary Islands, along with Bradyrhizobium japonicum bv. genistearum, Bradyrhizobium genospecies alpha and Bradyrhizobium genospecies beta

Rhizobia are the common bacterial symbionts that form nitrogen-fixing root nodules in legumes. However, recently other bacteria have been shown to nodulate and fix nitrogen symbiotically with these plants. Neptunia natans is an aquatic legume indigenous to tropical and subtropical regions and in African soils is nodulated by Allorhizobium undicola. This legume develops an unusual root-nodule symbiosis on floating stems in aquatic environments through a unique infection process. Here, we analyzed the low-molecular-weight RNA and 16S ribosomal DNA (rDNA) sequence of the same fast-growing isolates from India that were previously used to define the developmental morphology of the unique infection process in this symbiosis with N. natans and found that they are phylogenetically located in the genus Devosia, not Allorhizobium or Rhizobium. The 16S rDNA sequences of these two Neptunia-nodulating Devosia strains differ from the only species currently described in that genus, Devosia riboflavina. From the same isolated colonies, we also located their nodD and nifH genes involved in nodulation and nitrogen fixation on a plasmid of approximately 170 kb. Sequence analysis showed that their nodD and nifH genes are most closely related to nodD and nifH of Rhizobium tropici, suggesting that this newly described Neptunia-nodulating Devosia species may have acquired these symbiotic genes by horizontal transfer.Neptunia natans (L.f.) Druce is an aquatic legume native to several continents of the humid tropics and is used for both human consumption and as green manure for rice cultivation in Asiatic countries. This legume is unusual in that it normally develops buoyant floating stems that grow profusely on the surface of freshwater ponds, and in this aquatic environment it develops many stem-associated nitrogen-fixing nodules.The developmental morphology of the infection process leading to formation of nitrogen-fixing nodules in N. natans has been examined under strict gnotobiotically controlled conditions, and several unique aspects of this specialized, aquatic plant-bacterium symbiosis distinguish it from other legume root-nodule symbioses (22). After colonizing the root and floating stem surfaces, the aquatic bacterium symbiont enters the primary root cortex and stem interior through natural wounds caused by splitting of the epidermis and emergence of young lateral and adventitious roots, respectively, and then stimulates early development of nodules in the cortex at the base of these roots primordia, but not in the stem itself (22). Following crack entry through the nodule periphery, the bacteria penetrate internal nodule host cells; induce formation of bona fide tubular infection threads that disseminate them further intracellularly; and then release the bacteria into infection droplets, where they multiply. The endosymbiotic bacteria transform into nitrogen-fixing bacteroids within symbiosomes that eventually become filled with an unusual fibrillar matrix towards the end of their active nitrogen-fixing cycle in the aquatic e...

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