RESUMO
Free-living, dinitrogen-fixing bacteria associated with roots of grasses were isolated from several locations in Israel. Bacteria with characteristics similar to those of Azospirillum were isolated from Cynodon dactylon roots and were compared with Azospirillum brasilense from Brasil (Sp-7) and from California (Cd). Colonies of the Israeli isolates were yellow and consisted of curved rods, 0.5-0.6 micron in diameter with polar flagella, whereas colonies of A. brasilense were pink (Sp-7) and red (Cd) and the cells were 1.0-1.1 micron in diameter with polar flagella. Ultraviolet absorption spectra of soluble c and membrane-bound c and b cytochromes were similar in all isolates. When grown in semisolid agar medium with or without ammonium chloride all isolates formed a growth zone below the surface. However, they grew best under aerobic conditions in liquid medium containing NH4Cl. All isolates could use salts of malate and lactate, arabinose, and galactose, but not mannitol, as sole carbon sources; they did not need biotin to shorten their lag phase. One Israeli isolate was capable of growing and fixing nitrogen with glucose as a sole carbon source. The Israeli isolates formed aggregates above pH 7.6 in liquid or semisolid medium and were capable of reducing nitrate to nitrogen gas under anaerobic conditions.
Assuntos
Bactérias/metabolismo , Fixação de Nitrogênio , Plantas/microbiologia , Spirillum/metabolismo , Bactérias/citologia , Bactérias/crescimento & desenvolvimento , Meios de Cultura , Pigmentação , Spirillum/citologia , Spirillum/crescimento & desenvolvimentoRESUMO
Sixty-one strains of the root-associated nitrogen fixer Spirillum lipoferum exhibited a similar morphology in peptone--succinate salts medium: vibrioid cells having a diameter of 1.0 micrometer. When grown in broth the cells had a single polar flagellum, but when grown on agar at 30 degrees C lateral flagella of shorter wavelength were also formed. The DNA base composition was 69--71 mol% guanine + cytosine when determined by thermal denaturation. DNA homology experiments indicated the occurrence of two distinct but related homology groups: 46 strains were in group I and 15 strains were in group II. Group II strains were distinguished by their ability to use glucose as a sole carbon source for growth in nitrogen-free medium, by their production of an acidic reaction in a peptone-based glucose medium, by their requirement for biotin, and by their formation of wider, longer, S-shaped or helical cells in semisolid nitrogen-free malate medium. The results indicate that two species exist, and on the basis of their characteristics it is proposed that they be assigned to a new genus, Azospirillum. Strians belonging to group II are named A. lipoferum (Beijerinck) comb. nov., while those belonging to group I are named A. brasilense sp. nov. Strain Sp 59b (ATCC29707) is proposed as the neotype strain for A. lipoferum, and strain Sp 7 (ATCC 29145) is proposed as the type strain for A. brasilense.