General Microbiology - Schlegel H. 1987

Incomplete oxidations
Transformation of substances by microorganisms

The high Specificity of oxidations carried out by acetic acid Bacteria, combined with an exceptionally high product yield and the major economic significance of these processes (such as sorbose production), prompted microbiologists in the 1930s to intensively investigate the catalytic properties of microorganisms and their ability to metabolize both natural and xenobiotic compounds.

Microorganisms mediate highly specific processes of oxidation, hydrogenation, Hydrolysis, Esterification, Condensation, methylation, decarboxylation, dehydration, deamination, amination, and many other reactions. Furthermore, these biological transformations are stereospecific. They can be performed by actinomycetes and other bacteria, as well as by lower and higher Fungi.

Particularly remarkable success has been achieved through The Use of microbes in steroid synthesis. The Chemical synthesis of cortisone and hydrocortisone involves over 30 steps and yields a low product output. Utilizing microorganisms, this process has been reduced to 13 steps. One of the most challenging steps in this synthesis is the Introduction of a hydroxyl group into position 11 of the steroid Skeleton. This step is carried out by lower fungi (Rhizopus arrhizus, Curvularia lunata, Cunninghamella blakesleeana) and Streptomyces fradiae. A classic example of specific oxidation is The conversion of Reichstein's substance S into hydrocortisone:

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Alongside such oxidations, many fungi possessing stereospecific oxygenases effect hydroxylation at nearly all positions of the steroid molecule. Other microbial enzymatic activities include the dehydrogenation of alcohol hydroxyl groups, the introduction of double bonds, the reduction of keto and oxo groups, etc.

An example of an addition reaction is The formation of phenylacetylcarbinol, a crucial intermediate in the synthesis of ephedrine. Benzaldehyde added to a fermenting Yeast culture is apparently acetylated by them, much like acetoin formation, wherein "active acetaldehyde" (see Fig. 7.6

[2]) is transferred to benzaldehyde. The processes following the formation of phenylacetylcarbinol are purely Chemical Reactions.

An example of directed Enzymatic Cleavage of a substance using microorganisms is The production of 6-aminopenicillanic acid. Certain bacteria and fungi containing specific acylases cleave natural Penicillins to yield 6-aminopenicillanic acid, which can subsequently serve as a Starting Material for the production of Semisynthetic penicillins.