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The role of salicylic acid in iron metabolism was examined in two wild-type strains (mc(2)155 and NCIMB 8548) and three mutant strains (mc(2)1292 [lacking exochelin], SM3 [lacking iron-dependent repressor protein IdeR] and S99 [a salicylate-requiring auxotroph derived in this study]) of Mycobacterium smegmatis. Synthesis of salicylate in SM3 was derepressed even in the presence of iron, as was synthesis of the siderophores exochelin, mycobactin, and carboxymycobactin. S99 was dependent on salicylate for growth and failed to grow with the three ferrisiderophores, suggesting that salicylate fulfills an additional function(s) other than being a precursor of mycobactin and carboxymycobactin. Salicylic acid at 100 microgram/ml repressed the formation of a 29-kDa cell envelope protein (putative exochelin receptor protein) in S99 grown both iron deficiently and iron sufficiently. In contrast, synthesis of this protein was affected only under iron-limited conditions in the parent strain, mc(2)155, and remained unaltered in SM3, suggesting an interaction between the IdeR protein and salicylate. Thus, salicylate may also function as a signal molecule for recognition of cellular iron status. Growth of all strains and mutants with p-aminosalicylate (PAS) at 100 microgram/ml increased salicylate accumulation between three- and eightfold under both iron-limited and iron-sufficient growth conditions and decreased mycobactin accumulation by 40 to 80% but increased carboxymycobactin accumulation by 50 to 55%. Thus, although PAS inhibited salicylate conversion to mycobactin, presumptively by blocking salicylate AMP kinase, PAS also interferes with the additional functions of salicylate, as its effect was heightened in S99 when the salicylate concentration was minimal.

Lipid accumulation and fatty acid composition in Candida 107 have been studied using a two-stage continuous culture system in which the first vessel was run under carbon-limited conditions and then the entire output was passed into a second vessel, where lipid accumulation was stimulated by adding only glucose. Maximum lipid accumulation (28% of yeast [dry weight]) occurred for a volume ratio of vessel 1 to vessel 2 of 3:5, with 30 g of glucose per liter being added to vessel 2 operated at 25 degrees C with an aeration rate of between 0.1 and 1.0 volume of air/volume of medium per min. Although the maximum specific rate of lipid formation (0.05 g of lipid/g of yeast per h) was higher than in a nitrogen-limited, single-stage system, the efficiency of lipid formation was much less and never exceeded 14 g of lipid produced per 100 g of glucose consumed. The fatty acid composition was not significantly altered in either the two-stage or single-stage culture (nitrogen-limited) systems by changes in growth temperature (from 19 to 33 degrees C) or aeration rates (0.05 to 1.0 volume of air/volume of medium per min); or, in the two-stage system, by changes in the residence time of the yeast in the second vessel (from 3.2 to 24.4 h), or, in the single-stage system, by changes in pH (from 3.5 to 7.5). Only when the concentration of glucose entering vessel 2 of the two-stage system was less than 30 g/liter did significant changes in the fatty acids occur. Thus, although a two-stage continuous culture system allows lipid accumulation to be separated from the growth phase, it offers no practical advantages over a single-stage system as a means of producing microbial oils and fats.

Ratledge, Colin (Medical Research Council of Ireland, Trinity College, Dublin, Ireland), and Frank G. Winder. Effect of iron and zinc on growth patterns of Escherichia coli in an iron-deficient medium. J. Bacteriol. 87:823-827. 1964.-Escherichia coli grew poorly in a shaken glycerol-salts medium depleted of trace metals. Normal growth was restored by the addition of 2.0 mug of iron per ml. At lower levels of iron, the lag period was increased and the rate of growth and the yield were decreased. Unless the initial concentration of iron was reduced below 0.035 mug/ml, the effect on the yield was comparatively small. Below this concentration, growth was approximately linear and the yield was proportional to the amount of iron present; these cultures underwent a second phase of growth about 24 hr after the original cessation of growth, the growth being slower than before and accompanied by increase in length of the bacteria. Zinc (0.10 mug/ml) was usually inhibitory during the first growth phase, but induced an earlier and more rapid second growth phase; it greatly increased the degree of filament formation. With a small inoculum (about 560 cells per ml) in depleted medium, the lag period was 1 day with 0.5 mug of iron per ml, but was 8 days when no additions were made.