Abstract
For a long time, our understanding of metabolism has been dominated by the idea of biochemical unity, i.e.,that the central reaction sequences in metabolism are universally conserved between all forms of life. However, biochemical research in the last decades has revealed a surprising diversity in the central carbon metabolism of different microorganisms. Here, we will embrace this biochemical diversity and explain how genetic redundancy and functional degeneracy cause the diversity observed in central metabolic pathways, such as glycolysis, autotrophic CO2 fixation, and acetyl-CoA assimilation. We conclude that this diversity is not the exception, but rather the standard in microbiology.
Highlights
For a long time, our understanding of metabolism has been dominated by the idea of biochemical unity, i.e., that the central reaction sequences in metabolism are universally conserved between all forms of life
We will embrace this biochemical diversity and explain how genetic redundancy and functional degeneracy cause the diversity observed in central metabolic pathways, such as glycolysis, autotrophic CO2 fixation, and acetyl-CoA assimilation
In the case of methylamine, a simple organic amine that can serve as both a carbon and a nitrogen source, an interesting dichotomy of metabolic routes was described in methylotrophic bacteria
Summary
The same organism encodes the enzymes of the glyoxylate cycle, a canonical pathway for acetyl-CoA assimilation This functional degeneracy in respect to acetate and glycolate/ glyoxylate assimilation might infer additional metabolic flexibility of C. aurantiacus under certain conditions. (c) The trade-off between specialization and flexibility of metabolic pathways, illustrated on the microbial autotrophy as an example Microorganisms can expand their ecological flexibility by expressing enzyme isoforms with different physical or kinetic properties (e.g., RubisCO isoforms with different CO2 specificity or oxoglutarate:ferredoxin oxidoreductase isoforms with different oxygen sensitivity) or by operating two or more functionally degenerate pathways (e.g., a Riftia pachyptila endosymbionts that operate the CBB or rTCA cycle for autotrophic CO2 fixation). The studies summarized here indicate a much higher ecological relevance of the EDP than previously assumed, considering that it is used both by abundant phototrophs under mixotrophic and diurnal conditions, and by about 90% of marine bacteria
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