[Factors inducing transition from growth to dormancy in rhizobacteria Azospirillum brasilense].

The factors suppressing division of the cells of the rhizobacterium Azospirillum brasilense and inducing their transition to a dormant state were analyzed. These included the presence of hexylresorcinol or heavy metals (Cu and Co) in the medium, oxygen stress, and transfer of the cells into the physiological saline or phosphate buffer solution. The results were used to develop a protocol for obtaining of uncultured cells of A. brasilense Sp245, a natural symbiont of wheat. The cells lost their ability to grow on synthetic agar medium, but could revert to growth when incubated in freshly prepared liquid medium. Needle-shaped crystals differing from struvite, which has been previously reported for this strain, were found in the dormant culture of A. brasilense Sp245.

[Formation of TRA-dependent surface structures in Agrobacterium tumefaciens and their absence in R1 (deltatraR) mutant]. / Obrazovanie TRA-zavisimykh poverkhnostnykh struktur u Agrobacterium tumefaciens i ikh otsutstvie u mutanta R1 (deltatraR).

Agrobacteria have Ti plasmid DNA delivering systems for the transfer to recipient cells by the conjugation mechanism. This transfer is absolutely dependent on induction tra genes. It is not clear which tra-dependent surface (extracellular) proteins (structures) are involved in the transport mechanism and whether these proteins also play a role in the contact formation. SDS-PAGE electrophoresis of proteins released from the cell showed disappearance of 63 and 67 kD proteins in R1(delta traR) strain, which were found in the growth medium and triton extract from the outer membrane of Ti plasmid-harboring A. tumefaciens R10 strains. The traR defective mutant did not express these proteins and had a higher hemagglutination and flocculation capacity than the wild strain. On the other hand, the wild strain showed D-galactose and N-acetyl-galactosamine specific hemagglutination which was not shown by traR mutant. Motility and chemotactic behavior of traR mutant in semisolid medium were defective. As a rule, one (or rarely two) thread-like connections in vir(-) and tra(+) conditions were observed on the agrobacterial cell surface. SDS pretreatment of agrobacterial cells had a significant effect on the expression of tra-dependent surface structures.