Role of the capsule produced by Bacillus megaterium ATCC 19213 in the accumulation of metallic cations.

A study was undertaken to determine if the capsule produced by Bacillus megaterium ATCC 19213 was capable of binding metallic ions. For non-toxic metallic ions, this was accomplished by determining the relative concentrations of Fe2+, Ca2+, Zn2+, Mg2+, and Mn2+ removed from a chemically defined medium by the normally capsulated parent strain and two mutants with much smaller capsules. For toxic metals, the rates of respiration of the parent strain and a small capsule mutant in the presence of Cu2+, Hg2+, and Ag1+ were compared. It was found that the parent strain accumulated more Ca2+, Mg2+, and Mn2+. Accumulation of Fe2+ and Zn2+ was similar for the parent strain and the small capsule mutants. Respiration of the parent strain was less inhibited by Cu2+, Hg2+, and Ag1+, indicating that these metals are also bound to the capsule.

Ultrastructure of the capsule of Bacillus megaterium ATCC 19213.

The ultrastructure of the firmly adherent capsule produced by Bacillus megaterium cultured on fructose mineral salts medium was examined using thin sectioning, freeze-etching, and critical point drying by transmission and scanning electron microscopy. The capsule material was shown to be fibrillar, with most fibrils containing bulbous protrusions. Two types of fibres were resolved. These were termed primary and cross-linking fibres. Primary fibres originated at the cell wall and had a diameter of 34-50 nm. They also contained bulbous protrusions and enlarged areas where branching occurred. Cross-linking fibres connected the primary fibres. The cross-linking fibres were much smaller, usually 15 micro m in diameter, and contained few enlarged areas. The primary fibres originated at sites on the cell wall approximately equidistant and 0.26 micro m apart.

Partial characterization of the mode of action of benzoic acid on aflatoxin biosynthesis.

Aflatoxin production by a toxigenic strain of Aspergillus flavus was greatly reduced by benzoic acid and sodium benzoate in synthetic media. The reduction was accompanied by the appearance of a yellow pigment. Spectral analyses partially characterized this pigment as closely related to an acetyl derivative of a versiconal-type compound. A cell-free extract prepared from A. flavus grown in synthetic media was active in converting this yellow compound into aflatoxin B1 in the presence of reduced nicotinamide adenine dinucleotide phosphate at 25 degrees C (pH 7.4). In the presence of benzoic acid and its salt or autoclaved cell-free extract, conversion of yellow compound to aflatoxin B1 was prevented. These results suggest that the yellow compound is an intermediate in the secondary metabolic cycle involved in aflatoxin B1 production. Benzoic acid, sodium benzoate, or autoclaving the cell-free extract appear to have respectively blocked or denatured an enzymatic step late in the biosynthetic pathway of aflatoxin B1.