Since the discovery of D20 (heavy water) and its use as a moderator in nuclear reactors, its biological effects have been extensively, although seldom deeply, studied. This article reviews these effects on whole animals, animal cells, and microorganisms. Both "solvent isotope effects," those due to the special properties of D20 as a solvent, and "deuterium isotope effects" (DIE), which result when D replaces H in many biological molecules, are considered. The low toxicity of D20 toward mammals is reflected in its widespread use for measuring water spaces in humans and other animals. Higher concentrations (usually >20% of body weight) can be toxic to animals and animal cells. Effects on the nervous system and the liver and on formation of different blood cells have been noted. At the cellular level, D20 may affect mitosis and membrane function. Protozoa are able to withstand up to 70% D20. Algae and bacteria can adapt to grow in 100% D2O and can serve as sources of a large number of deuterated molecules. D2O increases heat stability of macromolecules but may decrease cellular heat stability, possibly as a result of inhibition of chaperonin formation. High D2O concentrations can reduce salt- and ethanol-induced hypertension in rats and protect mice from gamma irradation. Such concentrations are also used in boron neutron capture therapy to increase neutron penetration to boron compounds bound to malignant cells. D2O is more toxic to malignant than normal animal cells, but at concentrations too high for regular therapeutic use. D2O and deuterated drugs are widely used in studies of metabolism of drugs and toxic substances in humans and other animals. The deuterated forms of drugs often have different actions than the protonated forms. Some deuterated drugs show different transport processes. Most are more resistant to metabolic changes, especially those changes mediated by cytochrome P450 systems. Deuteration may also change the pathway of drug metabolism (metabolic switching). Changed metabolism may lead to increased duration of action and lower toxicity. It may also lead to lower activity, if the drug is normally changed to the active form in vivo. Deuteration can also lower the genotoxicity of the anticancer drug tamoxifen and other compounds. Deuteration increases effectiveness of long-chain fatty acids and fluoro-D-phenylalanine by preventing their breakdown by target microorganisms. A few deuterated antibiotics have been prepared, and their antimicrobial activity was found to be little changed. Their action on resistant bacteria has not been studied, but there is no reason to believe that they would be more effective against such bacteria. Insect resistance to insecticides is very often due to insecticide destruction through the cytochrome P450 system. Deuterated insecticides might well be more effective against resistant insects, but this potentially valuable possibility has not yet been studied.

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Strains of halophilic rods, presumably halobacteria, produce substances that inhibit the growth of other halobacteria but not halococci or moderate halophiles. The spectrum of action of these substances, called "halocins," was determined on 39 halobacteria or presumed halobacteria. The properties of halocin H4, produced by strain R-4, were studied using Halobacterium halobium as an indicator organism. Halocin H4 is adsorbed by the indicator organism and causes both death and lysis. It is a high molecular weight substance(s), destroyed by heat or exposure to low salt concentrations or treatment with a protease. Experiments are presented to show that it is not a virus.

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Wood chips from Eucalyptus viminalis were steam treated over a ränge of tempcratures and rcsidence times in the abscnce or presence of SO 2 . When the Substrate was steam treated without explosion, the initial moisture content of the chips had a significant influence on the recovery yield and the degrce of enzymatic hydrolysis. Prctreatment by steam explosion showed no Variation resulting from differences in the initial moisture content of the chips. SO 2 catalysis was shown to be particulary beneficial for the steam treatment of green chips. More than 95% of the original cellulose could be hydrolyscd to glucose with more than 80% of the original pentosan recovered äs xylose in the water soluble fraction.This indicated a need for chips with a high enough moisture content necessary to generate enough sulphurous acid from SO 2 to act äs an effective catalyst.

An actinomycete, isolated as a contaminant of a culture medium containing 25% NaCl, has been classified as Actinopolyspora halophila gen. et sp. nov. in the family Nocardiaceae. The morphology and biochemical characteristics of this organism distinguish it from other members of the family Nocardiaceae and other genera possessing a type IV cell wall. It requires high NaCl concentrations for growth and can grow in saturated NaCl. The lowest concentration permitting growth in liquid medium is 12%, and on solid medium, 10%. Colonies developing at lower salt concentrations contain holes resembling viral plaques. No growth occurred in a medium containing 30% KCl instead of NaCl. This organism can grow in simple media with NH4+ salts as nitrogen source and different sugars and other compounds as carbon source. Though it has a salt requirement almost as great as the extremely halophilic rods and cocci, it differs from these in containing diaminopimelic acid and in sensitivity to lysozyme; both properties suggest that it has a mucopeptide cell wall. It also contains some phospholipids common to other actinomycetes, but does not contain any phytanyl ether linked lipids characteristic of other extremely halophilic bacteria.