Utilization of energy stored in the form of Na+ and K+ ion gradients by bacterial cells

The hypothesis that Na+ and K+ gradients have an energy storing function [V. P. Skulachev (1978) FEBS Lett. 87, 171-176] has been tested in experiments with Escherichia coli, the marine bacterium Vibrio harveyi, an extremely halophilic Halobacterium halobium and a fresh-water cyanobacterium Phormidium uncinatum from Lake Baikal living at an extremely low salt concentration. The capability of these microorganisms to maintain delta microH was compared using motility as a delta microH-supported function. It was found that in all cases the gradient of monovalent cations is competent to prolong the period of active motility after other energy sources are exhausted. Maximal prolongation was found in H. halobium, which in a Na+ medium was still motile when light was switched off for 9 h under anaerobic conditions. In V. harveyi the motility was maintained for 1 h, in E. coli for about 10 min and in Ph. uncinatum for about 2 min. Thus the delta microH buffer capacity of the monovalent cation gradient is proportional to the content of these cations in the habitat. It was also found that in Ph. uncinatum only delta pK is effective, whereas in E. coli and V. harveyi both delta pK and delta pNa are. In E. coli when the K+ release is completed and the cells become motionless, motility can be temporarily restored by adding NaCl which initiates an H+ efflux. Under conditions of exhaustion of energy sources, the Na+ and K+ gradient was shown to stabilize potential in H. halobium cells, measured with a tetraphenylphosphonium probe. In H. halobium and E. coli, the anaerobic ATP level was found to stabilize when the Na+ and K+ gradients were present. Addition of N,N'-dicyclohexylcarbodiimide destabilized this level, which indicated that Na+ and K+ gradients could support de novo ATP synthesis. It is concluded that the data obtained are in agreement with the concept of the energy storing by the Na+ and K+ gradients. Other functions of these gradients and the mechanisms of their formation are discussed.     

Physical conditions of propagation media and their influence on the rooting of cuttings

Summary The formation and subsequent growth of roots by cuttings of poinsettia, hydrangea, rose and azalea in various propagation media, Jiffy-7, Jiffy-9 and Grodan under different conditions of aeration was investigated. The interrelationships of the effects of air content of the media, temperature and light intensity on the rooting of poinsettia cuttings was also studied.With low air contents (0 cm moisture tension) in the propagation media the formation and growth of roots was strongly inhibited. The rooting performance of rose appeared to be less affected by the poor aeration. Increasing air content improved rooting but best results were obtained at moisture tensions of 4 to 8 cm. Rooting seems to be better correlated with oxygen diffusion rate (ODR) than with air content.For poinsettia cuttings the optimum temperature for rooting was 24 to 28°C. At low temperatures rooting was delayed while at higher temperatures it was almost completely inhibited. Callus formation increased with temperature but decreased with increasing moisture tension. Conditions which induced large callus formation inhibited root formation.High light intensity during rooting reduced overall rooting performance and the inhibition was most pronounced in conjunction with high moisture tensions.Report No. 255.     

Electronmicroscopic Observations on the Degradation of Cellulose Fibres by Cellvibrio fulvus and Sporocytophaga myxococcoides

S ummary : Cellvibrio fulvus and Sporocytophaga myxococcoides were grown on different types of cellulose fibres and the degradation was followed by means of light and electron microscopy. The very compact fibres prepared from cotton were degraded slowly by C. fulvus. The bacteria penetrated into the lumen of the fibres, accumulated there in large numbers, and degraded the fibres from within. Sporocytophaga myxococcoides attacked fibres both from the outside and from within by making close contact with the cellulose. Lignin free pulp fibres, which have a very open structure, were rapidly degraded by both kinds of bacteria. Cellvibrio fulvus also degraded these fibres from within. It is concluded that structure of the fibre greatly influences the rate at which different kinds of cellulolytio bacteria decompose cellulose.