Biology subjects

Adam, Z. R.

Publications and source records attributed to Adam, Z. R..

6 recordsLinked to original sources

bioRxiv2025

Agnostic Tools for Life Detection: A Multiscale Approach to Biological and Chemical Reaction Networks

Life manifests itself across a variety of different operative scales, ranging from molecular networks up to ecologies. Deep conceptual difficulties arise when trying to define exactly what lifes distinguishing attributes are, and how they may be quantitatively distinguished from abiotic systems that are complicated but demonstrably not alive. Here we assembled different biotic and abiotic chemical reaction networks to test whether network-level (macroscale) and reaction-level (microscale) metrics can impartially distinguish biotic from abiotic category networks. Macroscale attributes such as statistical tests for a discrete networks heavy-tailed connectivity distribution generally distinguish bona fide biotic and protobiotic networks (E. coli heterotrophy, pruned protometabolism, KEGG) from abiotic networks but with two significant exceptions (radiolytic network and the Open Reaction Database). Microscale attributes such as an analysis of the frequency of a set of six primitive reaction motifs shows a depletion of some motifs in all chemical networks and the prevalence of others in specific networks; all networks were readily distinguishable from random network variants across all motifs. A comparison of the chemical spaces spanned by the different networks points to similarity and dissimilarity relationships between networks. Independent component analysis of an aggregate of all measured attributes, across all contexts, reliably distinguishes abiotic, prebiotic and biotic networks from one another. The combination of macro- and microscale attributes forms an agnostic toolset that may help to evaluate the prebiotic plausibility of different candidate settings for the origins of life, and may inform new ways of detecting and recognizing living systems (engineered or extraterrestrial) that differ from Terran biochemistry.

systems biology↗

bioRxiv2025

ChemOrigins: A community curated database for origins of life chemistry

The origin of life is one of the most compelling questions in science. While experimental prebiotic chemistry has produced a wide range of reactions and plausible pathways, the resulting data remain fragmented across numerous publications and disciplinary journals. Here, we introduce ChemOrigins, an open-access, community-curated knowledge graph that organizes experimentally supported prebiotic reactions. By representing molecules, reactions, conditions, and literature sources as interconnected nodes, ChemOrigins enables modular grouping of reactions and supports complex, query-driven exploration via a graph database architecture. We demonstrate the utility of this framework through text-based searches, reaction network expansions, and the interactive visualization of user-annotated chemical modules. Unlike generative models, ChemOrigins prioritizes curated, evidence-based content and fosters community contributions through expert annotations and a user-friendly interface. As a structured resource, ChemOrigins is designed to complement existing chemical databases and serve as a foundation for computational, educational, and theoretical research in the origins-of-life field.

bioinformatics↗

bioRxiv2025

Did Iron Suppress Eukaryote Emergence and Early Radiation?

The last eukaryotic common ancestor (LECA) is widely thought to have been an oxygen-respiring organism, arising through endosymbiosis when a free-living bacterium became the mitochondrion. Owing to the mitochondrions central metabolic task of oxidative phosphorylation, oxygen availability has long been a hypothesized driver of eukaryogenesis. However, this hypothesis is challenged by a temporal disconnect, spanning several hundred million years, between the earliest geochemical evidence for oxygen in the environment ([~]3.2-2.5 Ga) and the oldest widely accepted eukaryotic fossils ([~]1.7 Ga). Notably, the earliest candidate eukaryotes appear contemporaneous with the cessation of major iron deposits and rise of sulfide- and sulfate-rich marine sediments in coastal environments. Here, we integrate Proterozoic surface geochemical records with the microbial biochemistry of iron to examine potential environmental constraints on early eukaryotic evolution. Iron bioavailability exerts complex and often antagonistic effects on both aerobic and anaerobic microbial lineages that contributed to LECA. Elevated iron levels likely disrupted cellular homeostasis, particularly by destabilizing labile iron pools and promoting oxidative damage to bacterial lipids. The programmed cell death pathways known as ferroptosis, which is widespread among eukaryotic lineages, may trace its origins to iron-rich conditions in Archaean and Paleoproterozoic seawater and LECA. Our findings challenge oxygen-centered paradigms of eukaryogenesis and reframes the long-recognized temporal gap as a consequence of iron-mediated physiological constraints.

evolutionary biology↗

bioRxiv2023

The modular biochemical reaction network structure of cellular translation

Translation is an essential attribute of all living cells. At the heart of cellular operation, it is a chemical information decoding process that begins with an input string of nucleotides and ends with the synthesis of a specific output string of peptides. The translation process is interconnected with gene expression, physiological regulation, transcription, and responses to signaling molecules, among other cellular functions. Foundational efforts have uncovered a wealth of knowledge about the mechanistic functions of and many interactions between components of translation, but the broader biochemical connections between translation, metabolism and polymer biosynthesis that enable translation to occur have not been comprehensively mapped. Here we present a multilayer graph of biochemical reactions describing the translation, polymer biosynthesis and metabolism networks of an Escherichia coli cell. Intriguingly, the compounds that compose these three layers are distinctly aggregated into three modes regardless of their layer categorization. Multimodal mass distributions are well-known in ecosystems, but this is the first such distribution reported at the biochemical level. The degree distributions of the translation and metabolic networks are each likely to be heavy-tailed, but the polymer biosynthesis network is not. A multimodal mass-degree distribution indicates that the translation and metabolism networks are each distinct, adaptive biochemical modules, and that the gaps between the modes reflect evolved responses to the functional use of metabolite, polypeptide and polynucleotide compounds. The chemical reaction network of cellular translation opens new avenues for exploring complex adaptive phenomena such as percolation and phase changes in biochemical contexts.

molecular biology↗

bioRxiv2021

Functional divergence and spectral tuning of microbial rhodopsins from an ancestral proton pump

For billions of years, life has continuously adapted to dynamic physical conditions near the Earths surface. Fossils and other preserved biosignatures in the paleontological record are the most direct evidence for reconstructing the broad historical contours of this adaptive interplay. However, biosignatures dating to Earths earliest history are exceedingly rare. Here, we combine phylogenetic inference of primordial rhodopsin proteins with modeled spectral features of the Precambrian Earth environment to reconstruct the paleobiological history of this essential family of photoactive transmembrane proteins. Our results suggest that ancestral microbial rhodopsins likely acted as light-driven proton pumps and were spectrally tuned toward the absorption of green light, which would have enabled their hosts to occupy depths in a water column or biofilm where UV wavelengths were attenuated. Subsequent diversification of rhodopsin functions and peak absorption frequencies was enabled by the expansion of surface ecological niches induced by the accumulation of atmospheric oxygen. Inferred ancestors retain distinct associations between extant functions and peak absorption frequencies. Our findings suggest that novel information encoded by biomolecules can be used as "paleosensors" for conditions of ancient, inhabited niches of host organisms not represented elsewhere in the paleontological record. The coupling of functional diversification and spectral tuning of this taxonomically diverse protein family underscores the utility of rhodopsins as universal testbeds for inferring remotely detectable biosignatures on inhabited planetary bodies.

evolutionary biology↗

bioRxiv2021

Molecular foundations of Precambrian uniformitarianism

The earliest geochemical indicators of microbes--and the enzymes that powered them--extend back almost 3.8 billion years on our planet. Paleobiologists often attempt to understand these indicators by assuming that the behaviors of modern microbes and enzymes are consistent (uniform) with those of their predecessors. A uniformitarian assumption (i.e., the idea that fundamental geobiological processes have occurred in much the same manner over Earth history) seems at odds with our understanding of the inherent variability of living systems. Here, we examine whether a uniformitarian assumption for an enzyme thought to generate carbon isotope indicators of biological activity, RuBisCO, can be corroborated by independently studying the history of changes recorded within RuBisCOs genetic sequences. Specifically, we resurrected a Precambrian-age, ancient RuBisCO by engineering its ancient DNA inside a modern cyanobacterium genome and measured the engineered organisms fitness and carbon-isotope-discrimination profile. The envelope of ancestral RuBisCO isotopic fractionation observed here indicates that uniformitarian assumptions may be warranted, but with important caveats. Our results suggest that further inquiries that link molecule-level evolutionary changes with planet-level geochemical conditions are needed to discern whether enzyme-affected isotope fractionation trends extend deeper into the early Precambrian. Experimental studies illuminating lifes early molecular innovations are crucial to explore the foundations of Precambrian uniformitarian assumptions.

evolutionary biology↗