Sixty strains of the bacterium Pseudomonas aeruginosa (Schroeter) Migula were proved to synthesis 2-n-alkyl-4-hydroxyquinolines (pseudans). The compounds were detexted in most of the strains, but only few of them showed high alkaloid production. The pseudans are located in the cells. Excretion into the medium after long cultivation seems to be due to autolytic processes.Thin-layer chromatography of the purified alkaloid fraction and gas chromatography of the acids producd by oxydative degradation of the alkaloids hve shown that all strains form pseudan VII (2-n-heptyl-4-hydroxyquinoline) and pseudan IX (2-n-nonyl-4-hydroxyquinoline) only.
Experiments on the physiology and biosynthese of the pseudans were carried out using strain 2977, which produces these compounds in good yields. The formation takes place during the idiophase (Fig. 1). After feeding anthranilic acid and acetate the production rate was considerably increased (Table 1). Strain 2977 degrades tryptophan by the “aromatic pathway” forming anthranilic acid as an interrmediate (Fig. 2). The production of higher amounts of this compound seems to be essential for a good rate of pseudan formation.
To study the biosynthesis, isotope labelled preparations of anthranilic acid, tryptophan, acetate, malonate and β-ketodecanoic acid methyl ester were fed (Table 2). For localization of the incoroprated radioactivity, procedures for the chemical degradation of the pseudan molecule were developed. They permit the serate estimation of the C-atoms 4–8a and the nitrogen as anthranilic acid, C-atoms 2 and 3 each as CO2, the two terminal C-atoms of the side chain as CO2 and methylamine respectively and the side chain as a whole. The results obtained have shown that the pseudan molecule is formed from anthranilic acid and acetate. Feeding malonic acid, it was demonstrated that the side chain is built starting from the terminal C-atoms (Fig. 4). The high sepcific incorporation of β-keto[3H]decanoic acid methyl ester indicates that a 3-keto acid is an intermidate. Thus the pathway shown in Fig.5 for the biosynthesis of the pseudans may be assumed to be valid. The incorporation of [2-14C]acetate into the pseudans was twice that of [1-14C]acetate. This effect may be due to an equilibrium between malonyl CoA and free malonic acid, which enables the formation of [1,3-14C2]malonyl-CoA from [1-14C]malonyl-CoA. During the formation of the β-keto acid half of the radioactivity is lost from this compound.