A THEORETICAL CONSIDERATION OF THE ACTION OF X-RAYS ON THE PROTOZOAN COLPIDIUM COLPODA

1. The theory which Crowther has advanced to account for the variation of the lethal dose of roentgen rays among the individuals of a group of Colpidium colpoda is reviewed. 2. It is shown that the use of his small-body theory to explain the small value of λ_e leads to certain further assumptions about the nature of the destructive effect. 3. An alternative hypothesis is discussed.     

A STUDY OF THE BACTERIA ASSOCIATED WITH THE ROOTS OF SUBTERRANEAN CLOVER AND WIMMERA RYE-GRASS

SUMMARY: A study of the bacteria from the surfaces of roots of subterranean clover ( T. subterraneum L.) and Wimmera rye-grass ( L. rigidum Gaud.) revealed that 21 genera were represented among the isolates from clover and 16 genera among those from rye-grass. Bacteria showing branched forms predominated and accounted for 63% of the 151 clover isolates and 78% of the 167 grass isolates. Most of these were identified as Arthrobacter , but from clover a significant proportion were Nocardia -like types. Members of the genera Mycoplana, Micromonospora, Mycobacterium , and Mycococcus were also identified among the branching forms.
Although the soil had been inoculated with effective rhizobia and the clover plants were effectively nodulated only one of the 318 isolates was capable of nodulating subterranean clover. The majority of the isolates were chromogenic and Gram-negative, produced acid from glucose and ammonia from peptone, were catalase-positive and grew best aerobically. Approximately half the isolates liquefied gelatin and produced hydrogen sulphide from peptone.     

THE EVOLUTIONARY SIGNIFICANCE OF BACTERIA ASSOCIATED WITH RHAGOLETIS

All Rhagoletis reportedly establish associations with one or more bacterial species, but the bases for these interactions and their implications for host race formation and speciation are poorly understood. Here we present the results of four studies designed to increase our understanding of these relationships. In the first study, we identify the bacteria associated with seven Rhagoletis taxa by surveying the inhabitants of the esophageal bulb, an organ whose major function appears to be the housing of microorganisms. The results suggest that no bacterium has entered into an obligate symbiotic relationship with any of the Rhagoletis taxa surveyed, although one bacterium, Klebsiella oxytoca, is a very common associate of six of the seven. In the second study we use horizontal starch gel electrophoresis to determine the genetic similarity of K. oxytoca clones isolated from different Rhagoletis populations. This analysis provides a rare look into the genetic structure of natural populations of an enteric bacterium and permits the construction of a dendrogram for the clones—a dendrogram which indicates that there is no clear-cut pattern to the distribution of K. oxytoca genotypes among Rhagoletis. Taken together, the above studies provide indirect evidence that the bacteria associated with Rhagoletis are not important determinants of host plant specificity. The third and fourth studies assess two possible functions associated bacteria may perform for Rhagoletis: pectic substances degradation and nitrogen fixation. Our results do not lend support to either function.     

THE ACTION OF ALKALIES ON PEPTIDES AND ON KETOPIPERAZINES

1. The tripeptide glycyl-levo-alanyl-glycine in solution of either one or ten equivalents of alkali does not undergo racemization on standing. 2. The dipeptide levo-alanyl-glycine under the conditions given in (1) does not undergo racemization. 3. In ketopiperazines, levo-alanyl-glycine anhydride and in levo-prolyl-glycine anhydride under the influence of dilute alkalies, racemization takes place. 4. Racemization in the present experiments was never complete. The degree of racemization seems to depend, on the one hand, on the stability of the ketopiperazine ring; on the other, on the concentration of the alkali. 5. The significance of these observations will depend on the outcome of the work on a larger number of polypeptides and ketopiperazines. The work is now in progress in this laboratory.     

ON THE GROWTH AND RESPIRATION OF SULFUR-OXIDIZING BACTERIA

1. It is shown that Sulfomonas thiooxidans oxidizes elementary sulfur completely to sulfuric acid. Sodium thiosulfate is oxidized by this organism completely to sulfate. Sulfomonas thiooxidans differs, in this respect, from various other sulfur-oxidizing bacilli which either produce elementary sulfur, from the thiosulfate, or convert it into sulfates and persulfates. 2. The organism derives its carbon from the CO₂ of the atmosphere, but is incapable of deriving the carbon from carbonates or organic matter. 3. The S:C, or ratio between the amount of sulfur oxidized to sulfate and amount of carbon assimilated chemosynthetically from the CO₂ of the atmosphere, is, with elementary sulfur as a source of energy, 31.8, and with thiosulfate 64.2. The higher ratio in the case of the thiosulfate is due to the smaller amount of energy liberated in the oxidation of sulfur compound than in the elementary form. 4. Of the total energy made available in the oxidation of the sulfur to sulfuric acid, only 6.65 per cent is used by the organism for the reduction of atmospheric CO₂ and assimilation of carbon. 5. Sulfates do not exert any injurious effect upon sulfur oxidation by Sulfomonas thiooxidans. Any effect obtained is due to the cation rather than the sulfate radical. Nitrates exert a distinctly injurious action both on the growth and respiration of the organism. 6. There is a definite correlation between the amount of sulfur present and velocity of oxidation, very similar to that found in the growth of yeasts and nitrifying bacteria. Oxidation reaches a maximum with about 25 gm. of sulfur added to 100 cc. of medium. However, larger amounts of sulfur have no injurious effect. 7. Dextrose does not exert any appreciable injurious effect in concentrations less than 5 per cent. The injurious effect of peptone sets in at 0.1 per cent concentration and brings sulfur oxidation almost to a standstill in 1 per cent concentration. Dextrose does not exert any appreciable influence upon sulfur oxidation and carbon assimilation from the carbon dioxide of the atmosphere. 8. Sulfomonas thiooxidans can withstand large concentrations of sulfuric acid. The oxidation of sulfur is affected only to a small extent even by 0.25 molar initial concentration of the acid. In 0.5 molar solutions, the injurious effect becomes marked. The organism may produce as much as 1.5 molar acid, without being destroyed. 9. Growth is at an optimum at a hydrogen ion concentration equivalent to pH 2.0 to 5.5, dropping down rapidly on the alkaline side, but not to such an extent on the acid, particularly when a pure culture is employed. 10. Respiration of the sulfur-oxidizing bacteria can be studied by using the filtrate of a vigorously growing culture, to which a definite amount of sulfur is added, and incubating for 12 to 24 hours.     

THE DIFFERENTIAL ACTION OF CHEMICAL AGENTS,ESPECIALLY POLYMYXIN-B,ON CERTAIN ALGAE,BACTERIA AND FUNGI

Galloway , R. A., and R. W. Krauss (U. Maryland, College Park.) The differential action of chemical agents, especially polymyxin-B, on certain algae, bacteria and fungi. Amer. Jour. Bot. 46(1): 40-49. Illus. 1959.—Representatives from each of the major groups of compounds exhibiting toxicity toward microorganisms were screened to determine their relative effect on 2 green algae, Scenedesmus obliquas and Chlorella pyrenoidosa, 1 blue green alga, Anabaena variabilis, 4 species of bacteria in the genera Flavobacterium, Achromobacter, and Pseudomonas, and the fungus Aspergillus sydowii. The objective was the determination of the differential toxicity shown by chemical agents against these microorganisms. Polymyxin-B sulfate proved to have a high degree of selectivity which warranted detailed examination of its action. Manometric studies were made of the effects of this compound on rates of photosynthesis and respiration. The rate of photosynthesis in Scenedesmus was only slightly diminished by 640 p.p.m. polymyxin-B, but a rapid reduction in rate to a very low level was observed in Chlorella. The endogenous respiration rate in Scenedesmus was more than doubled. The rate of respiration on glucose, pyruvate, fumarate, and acetate remained unchanged except for a slight transient rise at a low pH or in the absence of magnesium. The effect of 640 p.p.m. of polymyxin-B on photosynthesis of Chlorella and on respiration, whether endogenous or on any of the substrates mentioned above, was a rapid, permanent reduction to a low level. Similar reduction in rate of respiration at 160 p.p.m. was observed in the bacteria and fungus, when these organisms were utilizing lactose, pyruvate, or fumarate as substrates. Two of the bacteria were exceptions in that no reduction occurred when they were respiring lactose. Inhibition of glucose phosphorylation was not found in the algae. Therefore some system other than an alternative phosphorylation must account for resistance to polymyxin-B.     

THE INFLUENCE OF X-RAYS ON THE PROPERTIES OF BLOOD

When rabbits are exposed to x-radiation as described, there results a definite change in the See PDF for Equation ratio of their plasma. This change is evidently one which defines a state of uncompensated alkali excess. The time required for a maximum change in the chemical reaction is the same as that required for a maximum change in the decrease of leucocytes. Sodium bicarbonate injected into the peritoneal cavity is followed by results identical with those observed following exposure to x-rays. The maximum changes occur in a shorter time following bicarbonate injection, but the relation between chemical and morphological changes are the same. We consider this analogy to be an important one in that it is suggestive of a relationship between the effect of salt and the effect of x-rays.     

THE ACTION OF SULFONAMIDES ON THE RESPIRATION OF BACTERIA AND YEAST : INHIBITION OF BACTERIAL AND YEAST CARBOXYLASES BY SULFONAMIDE DRUGS STRUCTURALLY RELATED TO COCARBOXYLASE

The inhibiting effects of sulfonamide drugs and their derivatives on the anaerobic decarboxylation of pyruvic acid by Staphylococcus aureus, Escherichia coli, baker''s and brewer''s yeast, and a carboxylase preparation from brewer''s yeast have been investigated. These drugs are: sulfanilamide, sulfapyridine, sulfadiazine, sulfamethyldiazine, sulfathiazole, sulfamethylthiazole, sulfanilamido-5-ethyl-4-thiazolone, 2-aminopyrimidine, 2-aminothiazole, and 2-aminopyridine. The sulfathiazole ring appears to exercise decidedly greater specific inhibiting effect on the carboxylases of Staph. aureus and E. coli. The inhibiting effect on yeast carboxylase is non-differentiable among all the substances tried, except sulfamethyldiazine which is completely ineffective on the carboxylases of the organisms studied. The specific inhibitory effect of sulfathiazole on the carboxylases of Staph. aureus and E. coli in comparison to sulfanilamide, sulfapyridine, and sulfadiazine is in harmony with in vivo and in vitro experimental results of other investigators. The results of the present investigation appear to support the hypothesis (1) that sulfonamides exert their bacteriostatic action through chemical affinity for the carrier proteins of certain respiratory enzymes of the bacterial cell, and that this affinity may in part be related to structural similarity between components of the drugs and the corresponding respiratory coenzymes.     

海洋游仆虫细胞核染色质组分和组蛋白的初步研究

收集海洋游仆虫(Euplotes vannus)的细胞,制备其染色质。稀酸抽提染色质得到的组蛋白经聚丙烯酰胺凝胶电泳、SDS-聚丙烯酰胺梯度凝胶电泳、等电点聚焦和氨基酸分析等方法测定,其核染色质中组蛋白占核总蛋白的69.6％;DNA:RNA:组蛋白:非组蛋白为1∶0.022∶1.1∶0.047。染色质的全组蛋白由16种氨基酸组成,碱性氨基酸与酸性氨基酸之比为1.06∶1,是一种弱碱性蛋白质。等电点为pH8.1—9.15,分子量为10,500—22,000道尔顿。