Über die Zahl der Kopien eines außerkaryotischen Gens bei Chlamydomonas reinhardii

The streptomycin sensitive (ss-) revertants of the streptomycin dependent mutant sd₃ segregate on streptomycin medium again sd-cells. This sd-segregation decreases continuously with increasing time of cultivation until zero-level is reached. The revertant R 20 differ from the other revertants mainly that the rate of segregation remaining almost at the same high level a long time. But the results of clonings showed that also in R 20 the number of cells able to segregate sd-cells decreases. After 6 months, only 20% of the cells still possessed this ability. Former investigations showed that the ss-revertants still had sd-informations. These informations segregate in the following cell-divisions and produce again sd-colonies on the streptomycin medium. The rate of segregation was changing with the different clones. This proves the non-oriented distribution of the sd- and ss-gene copies at the mitotic division. The clonings demonstrate also the existence of much more than 2 copies. According to Sager and Ramanis the genes of the chloroplast exist at the most in 2 copies. If the statement should be true in principle for all vegetative cells, then the sd-information cannot be in the chloroplast. It must be located in the mitochondria.     

Sodium Content of Community Water Supplies in California

The amount of sodium ion in water used for ingestion may be critical in effective use of a low sodium dietary regimen. Waters containing not over 20 mg of sodium per liter are provided for in the sodium restricted diets set forth by the American Heart Association. For diets containing more than 500 mg of sodium a day, waters of greater sodium content may be used if proper dietary adjustments are made.While assessment of the long-term average sodium content of a community water supply is difficult, the determined values for sodium lend to classification within range categories. The larger community water supplies in California are presented within several range categories of sodium content.The more commonly used water softeners add sodium to water. The sodium-restricted patient should be cautioned against their use. Similar consideration should probably be given to water supplies of retirement communities where the potential for disorders requiring sodium restriction is greater than in the general population.     

Dependence of Diaminopurine Utilization on the Mutational Site of Purine Auxotrophy in Bacillus subtilis II. Tracer Experiments

Tracer experiments were carried out in an attempt to explain why guanineless auxotrophs can use diaminopurine as a guanine replacement but nonexacting purine auxotrophs cannot do so. Cell suspensions of the nonexacting purineless Bacillus subtilis MB-1356 incorporated more radioactivity from diaminopurine-2-¹⁴C into nucleic acid than did guanineless B. subtilis MB-1517. The radioactivity in MB-1356 ribonucleic acid (RNA) was distributed in both adenine and guanine nucleotides, thus eliminating the possibility that the deamination of diaminopurine to guanine occurred predominantly on the level of nucleoside di- or triphosphates. Strain MB-1517 incorporated adenine-8-¹⁴C into nucleic acids extremely poorly. This correlated with results obtained with cell-free extracts; strain MB-1517 showed much less adenosine monophosphate (AMP) pyrophosphorylase activity than did MB-1356. Likewise, guanineless MB-1517 converted diaminopurine to its nucleotide much more slowly than did the nonexacting purine auxotroph. The results indicated that the lack of growth of nonexacting auxotrophs on diaminopurine alone is due not to an inability to convert the analogue to nucleic acid adenine but to the greater capacity of the nonexacting auxotrophs to convert diaminopurine to its 5′-ribonucleotide. Presumably, this compound, or a coenzyme analogue produced from it, inhibits growth of mutants which cannot make AMP de novo and only when the medium is devoid of adenine.     

BEHAVIORAL CHARACTERISTICS OF DANGEROUS DRIVERS—Importance of Correction

Studies of accident-prone drivers emphasize the frequency of unstable, aggressive or antisocial personalities expressing themselves through the automobile as a real and a symbolic weapon. Such expressions may be voluntary or unconscious and may also lead a driver to injure himself or seek injury from others.Because of the great public danger from such drivers, it is urgent that judges and enforcers of the law recognize the psychic motivation in habitual violation and withhold driving privileges from violators until a psychic adjustment has been made. Physicians can contribute in gaining acceptance for this attitude of enforcement, and in setting up adequate psychiatric procedures for correction of violators.     

Diversifications in the Tube Dilution Test for Antibiotic Sensitivity of Microorganisms

The tube dilution method of performing antibiotic sensitivity tests is commonly employed as an accurate method for defining the minimal inhibitory concentration in relation to pathogenic organisms. It is also used as a reference for comparing minimal inhibitory concentrations with the size of the zone of inhibition in the agar diffusion test. Although surveys have shown that there is no standardized method and technique of performing the tube dilution test, it is generally assumed that all of the diversified methods will yield the same results and interpretations. With the assistance of five experts, seven different tube dilution methods were compared; 16 antibiotics, and three organisms for each antibiotic, were used. The conclusions drawn are that, although the accuracy of a single method within its own confines is acknowledged, the minimal inhibitory concentrations and interpretations cannot be interpolated from one laboratory to another where a different technique is employed. The results are frequently discrepant. It is suggested that a uniform method be developed and promulgated for general use.     

A microtest system for the serial assay of phytotoxic compounds using photoautotrophic cell suspension cultures of Chenopodium rubrum

Chenopodium rubrum photoautotrophic cell suspensions were grown in plastic tissue culture dishes under photoautotrophic conditions. Growth was monitored by measuring cell number, packed cell volume, chlorophyll content and oxygen production. Such microtiter dishes are suitable systems for the serial assay of growth inhibition and various physiological effects (i.e. chlorophyll fluorescence, cell viability, oxygen production) of photoautotrophic cells as caused by herbicides and fungal phytotoxins. The applicability of the test system is discussed.Abbreviations pcv packed cell volume - fr.w. fresh weight - rpm revol. per minute - DMSO dimethyl sulfoxide - PMS phenazine methosulfate - NBT nitro-blue tetrazolium chloride