Microbial adhption to extreme environments 65

monium sulfate fractionation of the cell-free extract showed that the PO, oxidation!, which is accompanied by the formation of NADH, requires at least three components: An ammo- nium sulfate fraction of the cell-free extract,

the residue fraction containing the respiratory chain, and NAD as cofactor. Most probably a second cofactor, as yet not characterized. is required to accomplish full activity.

6.D. VOGELS

One way in which microorganisms can op- pose extreme conditions consists of a positive or negative tactic respotlse to a changing envi- ronment. Such a respor.se can be triggered by changes in temperature (thermotaxis) or in the chemical composition of the medium (chemotaxis). Adler ( 1966) and Mesibov and

dler (1972) made excellent studies on the positive chemotaxis of E. co2i towards various nutrients, e.g. amino acids and sugars. rTt ap- peared that a tactic response is also observed towards certain chemicals which are not me- tabolized or even are not transported inward at all. Therefore, chemoreceptors, which re- cognize the compcunds, must be located in the ccl or cell membrane. These recep- tors, w re quite specific, transfer the ob- served signal in such a way to the flagella that

movement alters. oshland (1972) pointed out

that bacteria are too small to detect concen- tration differences over one body length in concentration gradients normally applied in studies on chemotaxis. They suggested that bacteria must be fitted with some kind of ru- dimentary memory. Such a memory com- bined with a ~dime~tary nerve system that is involved in the translation of chemoreception into alteration of the position of flagella en- ables the bacteria to fly away from extreme conditions to favourable ones.

eferences

Adler, J., 1966, Chemotaxis in bacteria, Science 153, 708-716.

Macnab, R.M. and D.E. Koshland, Jr., 1972, The gadient- sensing mechanism in bacterial chemozaxis. &or. Natl. Acad. Sci. US 69,2509--2512.

Mesibov, R. and J. Adler, 1972, Chemotaxis toward amino acids in E. coli, J. Racteriol. 112,315-326.

66 Microbial adaptian to extreme environments

grown cells in 0.1 M potassium phosphate buffer containing 0.5% glycerol and 0.1% Tween 80. Both additions were essential. Op- timum conditions for chemotaxis toward

aspartic acid and glumatic acid. No tactic re- sponse is observed toward D-amino acids.

amino acids are a temperature of 30-C, a pH between 6 and 7 and an assay time of 30 min. The tactic response is linear with bacterial concentration up to 6 X ‘196 bacteria/ml.

B. wbtilis is chemotactic toward all com- mon L-amino acids, except arginine, lysine,

Reference

Adler, J., 1973, A method for measuring chemotaxis and use of the method to determine optimum contions for chemotaxis by E. COB, J. Gen. Microbial. 74,77-91.

ffALOBACTER/A, EXTREMELY HALOP ILK MICROOR~AN~S

I. DUNDAS

Halobacteria are striking examples of how life can adapt to the extreme environment of saturated brine ponds. Instead of protecting a normal metabolic apparatus by excluding salts from its internal environment, these cells have evolved a metabolic apparatus able to func- tion normally in the presence of saturated brines.

The underlying mechanisms for the obli- gate halophilic nature of structural and cata- lytic proteins in Halobacteria are not fully un- derstood. A generally accepted hypothesis holds that halophilic proteins have an excess of acidic amino acids and that high concentra- tions of specific cations Bre necessary to pre- vent the internal repulsive forces between acidic groups from deranging the native pro- tein configurations. Considerable experimen- tal evidence seems to support this thesis. R. Reistad ( 1970) isolated bulk protein from a Halobacteritlm and found that there is an ex- cess acidic over basic amino acids of about 10.5 mole corrected for amide. The pro:eins of cell envelopes also s ow an excess of ac amir-io acids. W~ldo~btedly os may play some role when ~~aZQb~eteri~m cells

lyse on dilution of their medium with distilled water, but the fact that lysis occurs at about the same sslt concentration when the medi*,$nl is diluted with isoosmolar solutions of mti,;A electrolytes and non- ct~Qlyte~ show tl?Gt

strated the specific requirement for sodium chloride for the active uptake of glutamate by N. salinarium. While many ionic species arc able to protect the apparent structural integri- ty of the cells, and several ionic species allow high activity of isolated enzymes, sodium chloride is specifically required for growth. ‘H seems that this specificity for NaCl is at least in part due to its requirement for transport mechanisms.

It was long thought that the inactivation of halophilic enzymes in t absence of salts was an irreversible process. olmes and Halvorson (1965) showed that activity could be retained

solution. It has

This correlates nicely with the fact that potas-