Planetary-scale heterotrophic microbial community modeling assesses metabolic synergy and viral impacts

Reviewer #1 (Public review):

The authors use metabolic reconstruction to build genome-scale models from TARA metagenomes.

This is not the first paper that attempts a reconstruction of metabolism on this scale. And like those that came before, its weakness is in the analysis of the resulting model.

I was initially quite excited about this manuscript as the reconstruction itself seems well done. However, the analysis does not deliver major or minor results.

It could be said that the modelling cuts some corners, for example in the identification of the flux modes. I was not quite able to follow why this is necessary, as numerical linear algebra methods seem to be able to handle problems of this size. But then again, I am quite confident that the sampling approach that the authors use produces a good enough approximation.

The weak point of the manuscript is the analysis that follows. The conclusions contain very few hard results, and the results that are presented talk mostly about concepts that are somewhat arbitrarily introduced and hard to relate back to nature. The authors construct a mix of their own concepts and others borrowed from cancer research, and neither of the metrics that are used is very convincing.

For example, the authors say they contribute to the complexity-stability debate, but that debate focuses on a particular notion of stability. What the authors call stability here is an entirely different concept that is completely unrelated to the stability of the complexity-stability debate; I would rather describe it as a resilience metric rather than stability.

The problem is that the metrics that are used lack an underlying firm grounding. Ecology was for a long time struggling with the same problem (and to some extent still is), but eventually much progress has been made by rigorously deriving metrics that are easy to relate back. The same would be possible here. Using Steuer's structural kinetic method, the reconstructed metabolism could be described dynamically, which would allow genuine stability analysis as well as other crucial metrics such as the observability and controllability, impact and sensitivity, which would make it far easier to relate results back.

Reviewer #2 (Public review):

This study used publicly available Tara Oceans and Tara Oceans Polar Circle metagenomic and metatranscriptomic datasets, including viromes, to construct sample-specific, gene-scale metabolic models. This reviewer understood that, for each sample, genes or transcripts associated with metabolic pathways were integrated into a single virtual "superorganism" or "community cell." These sample-level models were then compared across global ocean regions to investigate spatial patterns in heterotrophic prokaryotic metabolism, metabolic synergy, and the potential effects of virus-encoded auxiliary metabolic genes. However, it was not clear whether archaeal genes were also included in the heterotrophic prokaryotic fraction.

The study represents an ambitious and potentially valuable attempt to connect large-scale environmental omics data with constraint-based metabolic modeling. The authors handled a very large dataset and introduced quantitative approaches based on flux sampling, Reaction Cumulative Correlation, and synergy scores to describe community-level metabolic phenotypes using several mathematical formulations. The recovery of previously defined oceanic ecological zones from reaction-based models may provide preliminary support for the ecological relevance of the framework, although only approximately 26% of prokaryotic genes and 7% of viral genes were mapped to known metabolic reactions.

However, the framework should be understood as gene- or reaction-resolved, sample-level metabolic modeling rather than genome-resolved community modeling. By combining all detected genes within a sample into a single superorganism, the approach likely loses taxon-specific metabolic information and cannot directly distinguish intracellular metabolism from interspecies metabolic exchange. Consequently, several ecological interpretations, including cooperation, stability, reaction essentiality, and viral impacts, remain strongly dependent on the underlying model assumptions.

Overall, the manuscript presents a novel and scalable framework with considerable potential. However, greater methodological clarification and more cautious interpretation are needed before the ecological and biogeochemical conclusions can be fully supported.