The Formol Titration of Bacteriological Media

How formaldehyde reacts with amino acids

Formaldehyde is a biological electrophile produced via processes including enzymatic demethylation. Despite its apparent simplicity, the reactions of formaldehyde with even basic biological components are incompletely defined. Here we report NMR-based studies on the reactions of formaldehyde with common proteinogenic and other nucleophilic amino acids. The results reveal formaldehyde reacts at different rates, forming hydroxymethylated, cyclised, cross-linked, or disproportionated products of varying stabilities. Of the tested common amino acids, cysteine reacts most efficiently, forming a stable thiazolidine. The reaction with lysine is less efficient; low levels of an Nε-methylated product are observed, raising the possibility of non-enzymatic lysine methylation by formaldehyde. Reactions with formaldehyde are faster than reactions with other tested biological carbonyl compounds, and the adducts are also more stable. The results reveal reactions of formaldehyde with amino acids, and by extension peptides and proteins, have potential roles in healthy and diseased biology, as well as in evolution.

The Relation of the Composition of the Culture Medium to the Formation of Endospores by Aerobic Bacilli

1. Spore formation in eight typical members of the genusBacillushas been studied.

2. Three of these strains, including one species ofB. anthracis, have been found to be practically asporogenous under the experimental conditions. In general the following statements hold good for the sporogenous races studied.

3. Spore formation is almost, or entirely, inhibited by cultivation on media rich in amino acids, such as tryptic digests of casein or meat. Similar inhibition results following cultivation on a medium containing reasonably high concentrations of a mixture of amino acids and asparagine.

4. When such media are suitably diluted with standard inorganic salt solutions the percentage of spores formed is greatly increased, and frequently at least 99 per cent. of spores are formed if the dilution is sufficiently high.

5. When simple nitrogenous compounds such as amino acids are added to a dilute casein digest medium in which sporulation is almost complete, a definite decrease in the percentage of spores present is observed. Asparagine, which is probably readily assimilated, apparently completely hinders spore formation in most cases. Other amino acids do not exert so pronounced an effect, and ammonium phosphate does not appreciably inhibit the formation of spores.

6. The fact that the addition of glycine suppresses growth markedly when it is added to a dilute casein digest medium, but does not appreciably hinder sporulation, suggests that the formation of spores is not due to any toxic effect of added compounds, or compounds already present in the medium.

7. Sporulation is almost complete in a “synthetic” medium in which low concentrations of ammonium phosphate and sucrose represent the sources of nitrogen and carbon, respectively. However, frequent transfers in such a medium may inhibit spore formation partially or entirely in certain instances. This effect probably depends upon the enhanced ability of the culture in question to utilise sucrose as a source of carbon when cultivated constantly in its presence.

8. It is concluded, from the above data, that endospore formation in aerobic bacilli bears an inverse relationship to the amount of available nutrient material present in the culture medium.

I am indebted to Prof. Sir F. G. Hopkins and Miss M. Stephenson for their constant encouragement during the progress of this work. My thanks are due to Mr Pirie of this Department who kindly furnished me with several of the amino acids employed, and to Dr Miles of the Department of Pathology for his kindness in supplying me with certain of the cultures.

TISSUE-DIGESTING ENZYME (HISTASE) OF STREPTOCOCCI

1. An extracellular, proteolytic enzyme has been observed in more than 30 strains of beta type, aerobic and facultative hemolytic streptococci. 2. The enzyme is readily demonstrable in sterile filtrates of cooked meat cultures. 3. No gas or foul odor is produced. 4. It is partially inactivated by exposure to about 60°C. for 45 minutes or longer. 5. The enzyme manifests itself in cooked meat cultures after about 48 hours incubation at 37°C. The sterile filtrate from a 10 day old culture acts within 18 hours. 6. From 50 to 75 per cent of the meat in a tube of cooked meat medium may be digested in about 3 weeks at room temperature after 5 days initial growth at 37°C. 7. No correlation is found, in the cases studied, between hemolysis and proteolysis. 8. Streptococci not digesting beef tissue will not digest human tissue, and those which do digest beef tissue also digest human tissue. This conclusion applies only to the nine strains studied. 9. Ability to digest animal tissues does not necessarily imply ability to digest casein, coagulated beef serum or gelatin. 10. The disappearance of the meat from cooked meat cultures of hemolytic streptococci is quantitatively roughly paralleled by increase of formol-titrable substances in the fluid portion of the medium. 11. The enzyme resembles trypsin in its action. Streptococci from a variety of sources, bovine, human and otherwise have shown varying degrees of proteolytic activity. 12. The name histase is proposed for this enzyme.

STUDIES ON THE TWORT-D'HERELLE PHENOMENON

1. The experiments here reported were carried out with a lytic principle isolated from the feces of normal rabbits. 2. It seems that bacteriophage is constantly present in the feces of caged laboratory rabbits. 3. A lytic filtrate active for Strain Shiga 73 (in a dilution of 1:1,000,000) and for the typhoid bacillus (in a dilution of 1:1,000), after twenty successive passages with Shiga bacillus was active, for its homologous strain, in a dilution of about 1:10,000,000,000 but no longer possessed any lytic activity for the typhoid strain. The same filtrate, after twenty successive passages with typhoid bacillus, was similarly active in a dilution of 1:10,000,000,000 for the typhoid strain but was only feebly active for the Shiga strain. 4. The passage of the lytic principle through collodion membranes was never observed. 5. No appreciable diminution in the activity of the filtrates was observed after exposure to cholesterol or lecithin. Killed bacterial suspensions, however, were found to exert a considerable neutralizing effect on the active principle. 6. Formol titrations of lysed cultures lead to the conclusion that the bacteriolysis caused by the bacteriophage is not a true proteolysis but rather a simple plasmolysis of the bacterial cell and not a splitting effect of the protein molecule. 7. We have never obtained active filtrates with the leucocytes of immune animals by the method of Lisbonne, Boulet, and Carrère (14). 8. It would appear, from the experiments, that the immunization of rabbits with the lytic principle results in the disappearance of the bacteriophage from their intestines. 9. All the sera from rabbits immunized with antityphoid or antiShiga filtrates agglutinated respectively the typhoid or Shiga bacilli. 10. Similarly, these sera fixed complement strongly in the presence of the homologous antigen. Five or six times the amount of serum was required to fix complement in the presence of heterologous antigen. 11. All of the immune sera were found to be more or less antilytic. In no case was a strictly specific antilysin obtained.