ABSTRACT
The actinobacterium Arthrobacter sp. UMCV2 promotes plant growth through the emission of N,N-dimethylhexadecilamine (DMHDA). The Medicago-Sinorhizobium nodulation has been employed to study symbiotic nitrogen fixation by rhizobia in nodulating Fabaceae. Herein, we isolated three Sinorhizobium medicae strains that were used to induce nodules in Medicago truncatula. The co-inoculation of M. truncatula with Arthrobacter sp. strain UMCV2 produced a higher number of effective nodules than inoculation with only Sinorhizobium strains. Similarly, the exposure of inoculated M. truncatula to DMHDA produced a greater number of effective nodules compared to non-exposed plants. Thus, we conclude that Arthrobacter sp. UMCV2 promotes nodulation, and propose that this effect is produced, at least partly, via DMHDA emission.
Subject(s)
Arthrobacter , Medicago truncatula , Medicago truncatula/microbiology , Arthrobacter/drug effects , Arthrobacter/physiology , Sinorhizobium/physiology , Sinorhizobium/drug effects , Plant Root Nodulation/drug effects , Symbiosis , Nitrogen Fixation/drug effectsABSTRACT
In this paper the influence of the exopolysaccharides produced by Sinorhizobium meliloti strains on the nodulation rates in alfalfa plants has been considered. The experiments were performed in a rotary shaker and in an air-lift type fermentor. Different Sinorhizobium meliloti strains were used. Bacterial growth rates were determined by viable cell counts. Exopolysaccharide concentration was determined by precipitation with ethanol. It was observed that maximum cell concentration was in the order of 1 x 10(10) cell/ml and exopolysaccharide content was approximately 11 g/l. The experiments performed with alfalfa plants in a controlled environment chamber showed that, when inoculation was carried out with diluted suspensions (1/10), nodulation time was reduced from 10 to 4 days, while the strains retained their symbiotic properties.
Subject(s)
Bacteriological Techniques/instrumentation , Medicago sativa/microbiology , Polysaccharides, Bacterial/biosynthesis , Sinorhizobium/growth & development , Aerobiosis , Culture Media/metabolism , Fermentation , Oxygen/pharmacology , Sinorhizobium/drug effects , Sinorhizobium/metabolism , Time FactorsABSTRACT
Sinorhizobium morelense sp. nov. is described to designate a group of bacteria isolated from root nodules of Leucaena leucocephala. S. morelense shows 98% 16S rRNA gene sequence similarity to some Sinorhizobium species and to Ensifer adhaerens. This novel species is distinguished from other Sinorhizobium species and from E. adhaerens by DNA-DNA hybridization, 165 rRNA gene restriction fragments and sequence and some distinctive phenotypic features. Strains of this species are highly resistant to some antibiotics, such as carbenicillin (1 mg ml(-1)), kanamycin (500 microg ml(-1)) and erythromycin (300 microg ml(-1)). They do not form nodules, but a nodulating strain, Lc57, is closely related to the novel species. Strain Lc04T (= LMG 21331T = CFN E1007T) is designated as the type strain of this novel species.