A new comparative genomic analysis published in Science Advances reports that the enzymatic toolkit present in the proposed last universal common ancestor (LUCA) was more limited than previously assumed, and that numerous essential enzymes in modern Bacteria and Archaea appear to have arisen independently after LUCA.
Key findings from the genomic survey
The authors report that 166 enzymes of core metabolism can be traced to LUCA. However, the study also finds that significant numbers of enzymes required for basic biosynthetic tasks are not shared homologically between the two primary prokaryotic domains. Specifically:
- 89 enzymes in Bacteria that perform fundamental biosynthetic functions have no homologues in Archaea;
- 38 enzymes in Archaea that carry out similar essential roles are not homologous to any found in Bacteria.
Those enzymes, the paper notes, are involved in core processes and are "required for the synthesis of amino acids, cofactors, and nucleobases."
"Plotting the phylogenetic distributions of core biosynthetic enzymes across bacteria and archaea reveals that enzymatic metabolism in LUCA was incomplete. It expanded via origins of novel enzymes in the lineages leading to LACA [last archaeal common ancestor] and LBCA [last bacterial common ancestor], closely mirroring lineage-specific assembly of the ribosome."
Why the result matters
The apparent lack of homology for dozens of crucial enzymes challenges the straightforward expectation that the same enzymatic activities in Bacteria and Archaea were inherited directly from a single common ancestral enzyme in LUCA. If two unrelated proteins catalyse the same reaction in the two domains and show no detectable homology, it suggests either independent invention or extensive replacement after divergence.
Those possibilities carry different implications. Independent origins would indicate convergent solutions to biochemical problems early in life’s history, while post‑LUCA replacement would imply substantial innovation and turnover of metabolic machinery in each lineage since their split. The authors favour a view in which LUCA carried an incomplete enzymatic metabolism that later expanded by the origin of novel enzymes on the branches leading to the last archaeal and bacterial common ancestors.
Context and caution
The study’s breadth of genomic sampling is cited as impressive by commentators. However, detecting homology — especially for ancient proteins — is technically difficult. Proteins can diverge beyond recognition, horizontal gene transfer can shuffle functions between lineages, and different methods for identifying ancestral relationships can yield different reconstructions. The authors’ interpretation is one plausible reading of the genomic patterns; it underscores the complexity of reconstructing deep evolutionary history from modern genomes.
| Category | Reported count |
|---|---|
| Enzymes tracing to LUCA | 166 |
| Non-homologous enzymes unique to Bacteria | 89 |
| Non-homologous enzymes unique to Archaea | 38 |
Taken together, the numbers indicate that a substantial fraction of essential biosynthetic functions in modern prokaryotes either arose independently after LUCA or were replaced independently in each lineage.
Broader consequences for evolutionary biology
The paper reopens questions about how strictly we should expect universal common ancestry to predict homologous molecular machinery across all life. It does not deny common descent in a general sense, but it highlights that certain predictions of a simple, unbroken inheritance of individual enzymes may not hold at deep evolutionary timescales.
For researchers, this will push further study into several areas: improved methods for detecting ancient homology, experimental work to test whether structurally unrelated enzymes use convergent catalytic strategies, and more comprehensive sampling of microbial diversity to refine reconstructions of early metabolism. Each path will help clarify whether these non‑homologous enzymes are genuine examples of independent invention or the product of more complex evolutionary dynamics.
The study offers a reminder that the oldest chapters of life’s story remain partly obscured, and that genomes continue to reveal surprises about how the fundamental processes of life were assembled.
