GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

12. METABOLIC ACTIVITY OF AEROBIC HETEROTROPHS

12.6. INCOMPLETE OXIDATION

During Respiration, the majority of aerobic microorganisms oxidize organic nutrients to CO₂ and Water. Since carbon reaches its highest oxidation state within the CO₂ molecule, this constitutes complete oxidation. This type of respiration is distinct from Incomplete Oxidations, in which partially oxidized Organic compounds are released as metabolic byproducts.

The End products of incomplete oxidations can include acetic, gluconic, fumaric, citric, and lactic acids, among Other Compounds. Because these products closely resemble those formed during Fermentation, incomplete oxidation is often referred to as «oxidative fermentation».

In biotechnology, important processes involving incomplete oxidation include the Production of organic acids by Bacteria and Fungi, Amino acid synthesis by bacteria, microbial biotransformation of substances, and The Biosynthesis of secondary metabolites (such as Antibiotics, Polysaccharides, Vitamins, Lectins, etc.).

Class="center">

Fig. 12.9. Three types of aromatic ring Cleavage

METABOLIC ACTIVITY OF aerobic heterotrophs

			Energy	Anabolic METABOLISM
Substrate	Catabolic pathway	Key Enzymes	metabolism (NADH generation for the Respiratory Chain)	Anaplerotic reactions for C₁-dicarboxylic acid synthesis	Gluconeogenesis
	Glycolysis	Phosphofructokinase	TCA cycle	Carboxylation of Pyruvate and phosphoenolpyruvate	None
CARBOHYDRATES (hexoses)	ED pathway	6-phosphogluconate dehydratase; 2-keto-3-deoxy- 6-phosphogluconate aldolase	TCA cycle	Same	None
	Gluconate degradation pathway	NAD(P)- or PQQ-dependent glucose dehydrogenases	TCA cycle, glucose oxidation	Same	None
Ethanol	Oxidation via acetaldehyde (AA) and acetate to acetyl-CoA	NAD(P)- or PQQ-dependent Alcohol dehydrogenases	Oxidation of ethanol, AA, TCA cycle, Glyoxylate cycle	Glyoxylate cycle	Present
Acetate	Acetyl-CoA formation	Acetate kinase; acetyl-CoA synthetase	TCA cycle, glyoxylate cycle	Same	Present
Oxalate, glyoxylate	Glycerate pathway	Glyoxylate carboligase	TCA cycle	Malate formation from glyoxylate and acetyl-CoA (malate synthase)	Present
Methane, methanol	Oxidation to HCHO (followed by the Serine pathway)	Serine transhydroxymethylase; hydroxypyruvate reductase	Oxidation of methane and methanol to CO₂	Reaction catalyzed by isocitrate lyase	Present
Methane, methanol	Oxidation to HCHO (followed by the hexulose phosphate pathway)	Hexulose phosphate synthase	Oxidation of methane and methanol to CO₂	Phosphoenolpyruvate carboxylation	Present
n-Alkanes and Fatty acids	Oxidation of n-alkanes to fatty acids; β-Oxidation of Fatty acids	Monooxygenases; acyl-CoA synthetases	TCA cycle, β-oxidation of fatty acids	Glyoxylate cycle	Present
Aromatic Compounds	Transformation into pyrocatechol and protocatechuic acid followed by dioxygenation (ortho and meta ring cleavage)	Pyrocatechase; protocatechuate 3,4-dioxygenase Metapyrocatechase; protocatechuate 4,5-dioxygenase	TCA cycle	Pyruvate carboxylation; glyoxylate cycle	Present
Aromatic Compounds	Transformation into gentisic acid	Gentisate 1,2-dioxygenase	TCA cycle	Pyruvate carboxylation; glyoxylate cycle

Last update: 12/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
editorial organization of content;
standardization of terminology in accordance with academic sources;
verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.