[Current status of life support systems for cosmonauts and ways of their enhancement in near future].

The paper reviews the results of efforts undertaken so far to develop three types of life support systems: fill-and-draw and physicochemical reclamation systems for space flights of up to one year in duration, and systems for more extended missions. The authors point to the engineering and logistical issues that should be given the highest priority in the next decades.

Uncommon properties of pLD105 conjugative plasmid.

Plasmid pLD105 isolated from a clinical strain of E. coli determines nitrofuran resistance due to inactivation of low-molecular-weight nitrofuran reductase subunit. pLD105 plasmid belongs to IncF. It is a conjugative plasmid and mobilizes chromosome markers, but is not transmitted to strains containing other plasmids. However, the presence of pLD105 plasmid in the recipient strain does not prevent incorporation of other plasmids, including nonconjugative ones. Transfer of nonconjugative plasmids from the donor to a recipient strain carrying pLD105 was denoted as "reverse donation".

[Biochemical bases for the effect of combining kanamycin and nitrofuran resistance genes in Escherichia coli cells]. / Biokhimicheskie osnovy éffekta sovmeshcheniia genov ustoichivosti k kanamitsinu i nitrofuranam v kletkakh Escherichia coli.

The fact of a significant increase in resistance to aminoglycosides when nfr genes with chromosomal or plasmid localization are combined with the plasmid genes coding for kanamycin-transferase in E. coli cells is confirmed. Gel-filtration of homogenates of the cells with and without pLD105 plasmid carrying nfr gene and of the cells with a chromosomal nfr gene revealed a 10 kD polypeptide when the plasmid is present. Relying on these results, it is concluded that the discovered polypeptide fulfils two roles: inhibiting of specific nitrofuran-reductase, which leads to nitrofurans resistance and a drop of transmembrane electric potential contributing to the increase of resistance to aminoglycosides (kanamycin) in strains with the plasmid nfr gene. Absence of the 10 kD polypeptide in the cells with a chromosomal nfr gene and other data are indicative of a possible existence of a different mechanism of resistance to nitrofurans and an increase of resistance to aminoglycosides in the strains with a chromosomal nfr mutation.

[Riboflavin operon in Bacillus subtilis contains additional promoters]. / Operon biosinteza riboflavina Bacillus subtilis soderzhit dopolnitel'nye promotory.

Using the methods of molecular cloning permitted to show that riboflavin operon of Bacillus subtilis contains four promoters. Three of them are functionally active in the Bacillus subtilis system. The main promoter of the operon with regulatory region was cloned in plasmid pPL603. Cells containing the constructed plasmid pGM32 are resistant to chloramphenicol. The level of resistance is regulated by concentration of riboflavin (the effector of operon). The following model of rib-operon has been proposed: (Formula: see text).