^-AMINOBENZOIC ACID 



suboxydans and Lactobacillus arabinosus, which also fail to grow in the 

 absence of ^-aminobenzoic acid.^' ^ Other Clostridia for which p-sunino- 

 benzoic acid is essential are : CI. butylicum,^ CI. felsineum,^ and CI. 

 kluyveri.^ It was also essential for Lactobacillus helveticus and L. 

 Pentosus,"^ and an X-ray mutant of Escherichia coli.^ 



Bacterial Synthesis of p-Aminobenzoic Acid 



^-Aminobenzoic acid is synthesised by many bacteria.^ Sulpha- 

 thiazole-resistant strains of Staph, aureus produced more than suscept- 

 ible strains,^' ^^ and the additional _^-aminobenzoic acid was sufficient 

 to account for the fastness of these strains to sulphathiazole.^^ H. 

 Mcllwain ^^ showed that some of the _^-aminobenzoic acid present in 

 the cells of haemolytic streptococci could readily be removed by 

 washing with saline and that only the tightly bound portion was 

 responsible for sulphonamide-fastness. Sulphonamide-resistant strains 

 of D. pneumoniae and Shigella paradysenteriae showed no increase in 

 the ability to synthesise ^-aminobenzoic acid. 



The amounts of ^-aminobenzoic acid in Aerobacter aerogenes, 

 Serratia marcescens, Pseudomonas aeruginosa, Streptococcus haemo- 

 lyticus and Escherichia coli were calculated by H. Mcllwain ^^ to be 

 7700, 3100, 4700, 3800 and 17,000 molecules per cell respectively. The 

 corresponding rates of synthesis were 4-0, 1-2, 5-5, i-i and 3-9 mole- 

 cules per cell per second. 



Three X-ray mutants of E. coli, however, required ;/)-aminobenzoic 

 acid for growth, but this could be replaced by a combination of amino 

 acids, a purine and thymine ; the presence of methionine in the 

 amino acid. mixture was essential. ^^^^ In a medium containing these 

 supplements, the mutants were resistant to the action of sulphon- 

 amides. The evidence suggests that _^-aminobenzoic acid plays 

 a part in the synthesis of purines and thymine, methionine and 

 possibly other amino acids, thus resembling vitamin B12 and folic 

 acid (pages 515, 539, 543). Pteroylglutamic acid did not replace 

 ^-aminobenzoic acid, however, as a gi-owth factor for the mutants. 



A soil bacillus belonging to the Pseudomoneaceae was isolated which 

 developed an enzyme specific for the oxidation of ^-aminobenzoic acid 

 to carbon dioxide, water and ammonia. ^^ The growth of this organism 

 was inhibited by sulphapyridine, and ^-aminobenzoic acid counter- 

 acted the inhibition. The organism could be used to identify _/)-amino- 

 benzoic acid in amounts as small as 10 /xg. It was used by Spink 

 et al.^^ to demonstrate that a sulphonamide-resistant strain of Staph, 

 aureus produced more _/)-aminobenzoic acid than a non-resistant strain, 

 confirming the result obtained by Landy et al.^^ 



556 



