Biology subjects

Williams, T. A.

Publications and source records attributed to Williams, T. A..

At least 19 recordsLinked to original sources

bioRxiv2026

A bacterial nucleolus for cold adaptation

Compartmentalisation enables cells to spatially organise essential biochemical processes. This is exemplified by the eukaryotic nucleolus, which concentrates the machinery for ribosome biogenesis. Bacteria are generally thought to lack an equivalent compartment. Here we discover a nucleolus-like condensate in Escherichia coli that emerges at rDNA loci during cold adaptation to spatially organise and promote ribosome biogenesis. Low temperatures, which stabilise RNA secondary structures, induce accumulation of the RNA-remodelling enzyme CsdA. This raises the cellular CsdA concentration above its condensation threshold, driving condensate formation at rDNA loci when rRNA transcription is active. CsdA compartments enrich the rRNA transcription machinery and ribosome-biogenesis factors, spatially linking rRNA synthesis to downstream processing and assembly. Disrupting CsdA condensation impairs ribosome maturation and reduces bacterial adaptation to cold temperature, demonstrating functional importance of condensate formation. Comparative genomics suggests that analogous condensate-forming RNA remodelling enzymes have evolved repeatedly across diverse bacterial lineages. Our findings establish biomolecular condensates as a unifying organisational principle of ribosome biogenesis across the tree of life and suggest that adaptive compartmentalisation can emerge when environmental conditions challenge the efficiency of essential biochemical processes.

cell biology↗

bioRxiv2026

Improved ancestral genome reconstruction using a learned gene-content grammar

Ancestral gene content inferences allow inferring the set of genes - and by extension, the cellular features and metabolic capabilities - of ancestral organisms, based on data from modern genomes. Current methods differ in their approach to ancestral inferences and the kinds of errors they make: reconciliation methods map gene trees onto species trees, and tend to under-estimate ancestral contents due to phylogenetic noise; profile methods model the evolution of phylogenetic profiles (presence-absence or count data) on the species tree, and tend to return inflated ancestors because they ignore gene trees and as a result can only account for horizontal gene transfer (HGT) in a limited manner. For reasons of tractability, both approaches also share a core limitation: neither uses the fact that genes do not act alone but belong to operons, protein complexes, and metabolic pathways that may be gained and lost together or experience shared selective constraints. Here, we show that this context - the grammar of gene content - provides a rich source of information that can be used to greatly improve ancestral gene content inference and metabolic reconstruction under both the reconciliation- and profile-based approaches. We model this structure as an Ising model and infer its parameters from 113,104 bacterial and archaeal genomes (one per species representative in GTDB). We validate the model on extant taxa using phylum-level holdout (i.e. using test data from different prokaryotic phyla than training data), showing that it can accurately "denoise", i.e., reconstruct gene repertoires from highly fragmented and noisy input data, learning about protein-protein interactions and gene essentiality during the training process. When applied to ancestral reconstructions, the denoiser fills gaps in conservative reconstructions and removes excess genes from overly-generous ones, such that different reconstruction methods converge to broadly concordant conclusions. By using this gene content grammar, patchy method-dependent ancestral reconstructions can be turned into organism-like ones, and yield agreement on the gene families, cell-biological features, and metabolic capabilities of the deepest nodes in the tree of life.

evolutionary biology↗

bioRxiv2026

Models trained with noisy genomes extend bacterial phenotype prediction into deep time

Predicting phenotype from genotype in extant organisms is increasingly tractable through the accumulation of genome sequences and the development of machine-learning algorithms. Here we show that machine learning can be applied to reconstructed ancestral gene content, extending these predictions into the past. We trained models on a diverse set of bacterial phenotypes and found that introducing noise into gene content profiles allows predictions to generalize over larger evolutionary distances. For phenotypes with signal spread across many genes - such as metabolic oxygen use, cell envelope architecture and optimal growth temperature - noise augmentation extends resolution back to the root of the bacterial domain, while for other phenotypes - including GC content and sporulation - the range remains more limited. We therefore conclude that the last bacterial common ancestor (LBCA) was likely an anaerobic, double-membraned, and moderately thermophilic bacterium (46-75{degrees}C). Moreover, this work provides a general approach for learning about the genomic basis of phenotypes and drawing inferences about their early evolution.

evolutionary biology↗

bioRxiv2025

Correlated dynamics, reactive conformations and non-Arrhenius behaviour in the temperature-dependence of enzyme activity: triosephosphate isomerase

Heat capacity changes are increasingly recognised as crucial for understanding the temperature dependence of enzyme-catalysed reaction rates. Here, we combine experiments and molecular dynamics simulations to investigate triosephosphate isomerase (TIM, TPI) from psychrophilic, mesophilic and thermophilic organisms. Kinetic data show clear curvature in rate-temperature plots, particularly for the cold-adapted enzyme, independent of unfolding. This non-Arrhenius behaviour is accounted for by Macromolecular Rate Theory (MMRT), implying an activation heat capacity, largest for the psychrophile. Simulations reveal the molecular origins of these differences, showing significant conformational and dynamical changes between reactant and transition states in the cold-adapted enzyme, with a smaller activation heat capacity in the mesophilic enzyme, and near-zero for the thermophile. Transition-state-like conformations and reorganized correlated dynamics underlie these adaptations. These results demonstrate that dynamical differences between crucial states along the reaction pathway play a key role in determining the optimum temperature of activity for this archetypal enzyme.

biochemistry↗

bioRxiv2025

Phylogenetic reconciliation supports a methanogenic ancestor of the Archaea and a derived origin for host-associated lineages

The phylogeny of the Archaea continues to be revisited and revised as new groups are discovered and phylogenetic methods improve, but key questions about their early evolution remain. It has been suggested that the root of the Archaea may lie on, or potentially within, any of three major groups - the Euryarchaeota, TACK+Asgard clade, and DPANN, the last of which includes many host-associated and genome-reduced lineages. These root hypotheses make starkly different predictions about the nature of early archaeal evolution: for example, a root on or within DPANN might suggest a small-genome and host-associated ancestor, with methanogenesis, the hallmark metabolism of the Archaea, evolving later. Here, we investigate the position of the archaeal root and the nature of the last archaeal common ancestor using a range of phylogenetic approaches, including the best available site- and branch-heterogeneous substitution models, and new gene tree-species tree reconciliation models that capture changes in rates of gene duplication, loss and transfer across the phylogeny. Our analyses converge on a narrow archaeal root region at/near the base of the Euryarchaeota, supporting hypotheses in which the Last Archaeal Common Ancestor (LACA) was a complex, free-living (hyper-)thermophilic methanogen. We recover DPANN as the sister group to TACK and Asgard archaea, and suggest that their genome evolution has been characterised by episodes of genome streamlining and expansion, driven by gene loss and transfer.

evolutionary biology↗

bioRxiv2025

The prokaryotic origins of the COMMD protein family involved in eukaryotic membrane trafficking

The ten eukaryotic COMMD proteins are core components of the Commander complex, with central roles in endosomal membrane trafficking and signalling. Each protein has an -helical N-terminal (HN) domain with a C-terminal copper metabolism gene MURR1 (COMM) domain. These ten family members assemble into a heterodecameric ring composed of five specific heterodimers. In this work we have combined structural homology searches with genome-wide predicted structures to identify ancestral COMMD-like proteins that exist as single genes in Bacteria and Archaea. Although there is limited sequence similarity to the eukaryotic proteins the bacterial and archaeal COMMD-like proteins are predicted to form homomeric ring-shaped assemblies like their eukaryotic counterparts. Our biophysical studies, crystal and cryo-EM structures confirm COMMD-like proteins readily form homooligomeric rings composed of eight or ten subunits assembled from core dimeric building blocks and inter-dimer interactions that are analogous to the heterodecameric core structure of the eukaryotic Commander complex. Phylogenetic analyses using amino acid sequences and FoldSeek structural alphabet (3Di) infer that the closest identified relatives to the eukaryotic COMMD proteins are found in Myxococcota bacteria. These findings indicate that COMMD genes emerged early in eukaryotic evolution through multiple rounds of duplication from a single ancestral gene likely acquired from bacteria.

biochemistry↗

bioRxiv2025

Caliditerrarchaeota, a new sister to Nanohaloarchaeota, provides insights into the evolution of DPANN halophily

The Nanohaloarchaeota are a clade of halophilic symbionts with small cells and genomes. Originally placed within the Euryarchaeota, they are now widely thought to belong to the DPANN archaea. However, the evolution of this clade and its phylogenetic placement within DPANN remain poorly understood. We applied phylogenetic and comparative genomic analyses to assess the evolutionary relationship and genome evolution of the Nanohaloarchaeota and related DPANN lineages. Our phylogenetic analyses resolve Nanohaloarchaeota as a sister group to a phylum-level lineage referred to as EX4484-52, together forming a clade with Aenigmatarchaeota. Representatives of EX4484-52, for which we propose the name Caliditerrarchaeota, have an anaerobic, thermophilic lifestyle but do not appear to be adapted to high salt concentrations. Using gene tree-species tree reconciliations, we investigated the origin of halophily across these archaeal lineages revealing that adaptations to high-salt appear to have evolved on the branch to Nanohaloarchaeota after their divergence from Aenigmatarchaeota and Caliditerrarchaeota. In agreement with recent work, we also identify hallmarks of halophily in another order-level lineage within the Aenigmatarchaeota (Haloaenigmatarchaeaceae) which appears to represent a second independent adaptation of a DPANN clade to halophily. The two halophilic DPANN lineages are inferred to have distinct sets of proteins that enable them to live in environments with high salt levels. Notably, phylogenetic analyses reveal a dominant signal of gene transfers between Haloaenigmatarchaeaceae and Halarchaeoplasmatales, indicating a potential host-symbiont relationship. This work provides the first detailed investigation of the enigmatic Caliditerrarchaeota, and new insights into the evolution of halophilic lifestyles within DPANN.

evolutionary biology↗

bioRxiv2025

Phylogenomic analyses reveal that Panguiarchaeum is a clade of genome-reduced Asgard archaea

The Asgard archaea are a diverse archaeal phylum important for our understanding of cellular evolution because they include the lineage that gave rise to eukaryotes. Recent phylogenomic work has focused on characterising the diversity of Asgard archaea in an effort to identify the closest extant relatives of eukaryotes. However, resolving archaeal phylogeny is challenging, and the positions of two recently-described lineages - Njordarchaeales and Panguiarchaeales - are uncertain, in ways that directly bear on hypotheses of early evolution. In initial phylogenetic analyses, these lineages branched either with Asgards or with the distantly-related Korarchaeota, and it has been suggested that their genomes may be affected by metagenomic contamination. Resolving this debate is important because these clades include genome-reduced lineages that may help inform our understanding of the evolution of symbiosis within Asgard archaea. Here, we performed phylogenetic analyses revealing that the Njordarchaeales and Pangiuarchaeales constitute the new class Njordarchaeia within Asgard archaea. We found no evidence of metagenomic contamination affecting phylogenetic analyses. Njordarchaeia exhibit hallmarks of adaptations to (hyper-)thermophilic lifestyles, including biased sequence compositions that can induce phylogenetic artifacts unless adequately modelled. Panguiarchaeum is metabolically distinct from its relatives, with reduced metabolic potential and various auxotrophies. Phylogenetic reconciliation recovers a complex common ancestor of Asgard archaea that encoded the Wood-Ljungdahl pathway. The subsequent loss of this pathway during the reductive evolution of Panguiarchaeum may have been associated with the switch to a symbiotic lifestyle based on H2-syntrophy. Thus, Panguiarchaeum may contain the first obligate symbionts within Asgard archaea.

evolutionary biology↗

bioRxiv2025

Identification of a VPS29 isoform with restricted association to Retriever and Retromer accessory proteins through auto-inhibition.

The endosomal-lysosomal network is a hub of organelles that orchestrate the dynamic sorting of hundreds of integral membrane proteins to maintain cellular homeostasis. VPS29 is a central conductor of this network through its assembly into Retromer, Retriever and Commander endosomal sorting complexes, and its role in regulating RAB GTPase activity. Two VPS29 isoforms have been described, VPS29A and VPS29B, that differ solely in their amino-terminal sequences. Here we identify a third VPS29 isoform, which we term VPS29C, that harbours an extended amino-terminal sequence compared to VPS29A and VPS29B. Through a combination of AlphaFold predictive modelling, in vitro complex reconstitution, mass spectrometry and molecular cell biology, we find that the amino-terminal VPS29C extension constitutes an autoinhibitory sequence that limits access to a hydrophobic groove necessary for effector protein recruitment to Retromer, and association with Retriever and Commander. VPS29C is therefore unique in its ability to uncouple Retromer-dependent cargo sorting from the broader roles of VPS29A and VPS29B in regulating the endosomal-lysosomal network through accessory protein recruitment. Our identification and characterisation of VPS29C points to additional complexity in the differential subunit assembly of Retromer, an important consideration given the increasing interest in Retromer as a potential therapeutic target in neurodegenerative diseases. SIGNIFICANCE STATEMENTThe endosomal-lysosomal network is essential for normal cellular function with network defects being associated with numerous neurodegenerative diseases. Two heterotrimeric complexes, Retromer and Retriever, control transmembrane protein recycling through the network. Of these, reduced Retromer expression is observed in Alzheimers disease and Retromer mutations lead to familial Parkinsons disease. Here, we identify and characterise a new isoform of VPS29, a subunit shared between Retromer and Retriever. We reveal how this isoform, VPS29C, adopts an auto-inhibitory conformation to limit its association into Retriever and restrict the binding of VPS29C-containing Retromer to accessory proteins vital for regulating network function. By revealing added complexity in Retromer assembly and function, we provide new insight into Retromers potential as a therapeutic target in neurodegenerative diseases.

cell biology↗

bioRxiv2024

Natural variation of the drug-binding residues in eukaryotic ribosomes

Drugs that target eukaryotic ribosomes are becoming increasingly important as research tools and potential therapies against cancer and pathogenic eukaryotes. However, in the absence of comparative studies, we currently do not know how many eukaryotes possess ribosomal drug-binding sites identical to those in humans, and how many significantly differ from humans. To address this, we traced the evolutionary history of individual ribosomal drug-binding residues from the emergence of eukaryotes to the present day. We found that ribosomal drug-binding sites are divergent across eukaryotic clades, with some of the clades exhibiting more substitutions in their ribosomal drug-binding sites compared to humans than humans do compared to bacteria. Overall, our work provides a resource for understanding the evolutionary divergence of drug-binding sites in eukaryotic ribosomes, which may inform the use of ribosome inhibitors as research tools and lineage-specific drugs against eukaryotic parasites.

microbiology↗

bioRxiv2024

Transcriptome and evolutionary analysis of Pseudotrichomonas keilini, a free-living anaerobic eukaryote

The early evolution of eukaryotes and their adaptations to low-oxygen environments are fascinating open questions in biology. Genome-scale data from novel eukaryotes, and particularly from free-living lineages, are key to answering these questions. The Parabasalia are an ancient lineage of anaerobes, and the most speciose lineage of Metamonada, a major lineage of eukaryotes. The most well-studied metamonads are parasitic parabasalids including Trichomonas vaginalis, Tritrichomonas foetus, and Giardia intestinalis, but very little genome-scale data is available for free-living members of the group. Here, we sequenced the transcriptome of Pseudotrichomonas keilini, a free-living parabasalian. Comparative genomic analysis indicated that P. keilini possesses a metabolism and gene complement that are in many respects similar to its parasitic relative Trichomonas vaginalis, and that in the time since their most recent common ancestor, it is the Trichomonas vaginalis lineage that has experienced more genomic change, likely due to the transition to a parasitic lifestyle. Features shared between P. keilini and Trichomonas vaginalis include a hydrogenosome (anaerobic mitochondrial homologue) that we predict to function much as in Trichomonas vaginalis, and a complete glycolytic pathway that is likely to represent one of the primary means by which P. keilini obtains ATP. Phylogenomic analysis indicates that P. keilini branches within a clade of endobiotic parabasalids, consistent with the hypothesis that different parabasalid lineages evolved towards parasitic or free-living lifestyles from an endobiotic, anaerobic or microaerophilic common ancestor.

evolutionary biology↗

bioRxiv2024

Evolutionarily conserved principles of ESCRT-III-mediated membrane remodelling revealed by a two-subunit Asgard archaeal system

ESCRT-III proteins assemble into composite polymers that undergo stepwise changes in composition and structure to deform membranes across the tree of life. Here, using a phylogenetic analysis we demonstrate that the two ESCRT-III proteins present in our closest archaeal relatives are evolutionarily related to B-type and A-type eukaryotic paralogues, which initiate and execute membrane remodelling, respectively. This deep homology is reflected in ESCRT-III structure and function as demonstrated by the fact that ESCRT-IIIB assembles into parallel arrays on planar membranes to initiate membrane deformation, and is required to recruit ESCRT-IIIA to generate composite polymers. ESCRT-IIIA homopolymers can then remodel membranes into tubes, as a likely prelude to scission. Taken together, this analysis reveals a set of conserved principles governing ESCRT-III-dependent membrane remodelling that first emerged with the evolution of a two-component ESCRT-III system in the Asgard archaea, and which continue to underlie complex multi-component, ESCRT-III-dependent membrane remodelling in eukaryotes.

evolutionary biology↗

bioRxiv2024

Chimeric Origins and Dynamic Evolution of Central Carbon Metabolism in Eukaryotes

The origin of eukaryotes was a key event in the history of life. Current leading hypotheses propose that a symbiosis between an asgardarchaeal host cell and an alphaproteobacterial endosymbiont represented a crucial step in eukaryotic origins and invoke a central role for syntrophic interactions - that is, metabolic cross-feeding between the partners as the basis for their subsequent evolutionary integration. A major unanswered question is whether the metabolism of modern eukaryotes bears any vestige of this ancestral interaction. To investigate this question in detail, we systematically analyze the evolutionary origins of the eukaryotic gene repertoires mediating central carbon metabolism. Our phylogenetic and sequence analyses reveal that this gene repertoire is chimeric, with ancestral contributions from Asgardarchaeota and Alphaproteobacteria operating predominantly in glycolysis and TCA, respectively. Furthermore, our analyses reveal diverse additional contributions from other prokaryotic sources as well as the extent to which this ancestral metabolic interplay has been remodeled via gene loss, transfer, and subcellular retargeting in the >2Ga since the origin of eukaryotic cells. Together, our work demonstrates that in contrast to previous assumptions, the eukaryotic metabolism preserves information about the nature of the original asgardarchaeal-alphaproteobacterial interactions, and supports syntrophy scenarios on the origin of the eukaryotic cell.

evolutionary biology↗

bioRxiv2023

Genome of the glacier alga Ancylonema and its insights into the evolution of streptophyte life on ice and land

Contemporary glaciers and ice sheets are home to communities of streptophyte glacier algae that must balance their requirements for photosynthesis and growth with tolerance of extremes in temperature, desiccation and UV radiation. These same environmental challenges have been hypothesized as the driving force behind the evolution of land plants from streptophyte algal ancestors in the Cryogenian (720-635 million years ago). Here, we sequence, assemble and analyze the metagenome-assembled genome (MAG) of the glacier alga Ancylonema nordenskioldii to investigate its adaptations to life in ice, and whether this represents a vestige of Cryogenian anydrophyte exaptations. Phylogenetic analysis confirms the placement of glacier algae within the sister lineage to land plants, Zygnematophyceae. The MAG is characterized by an expansion of genes involved in high irradiance and UV light tolerance, whilst lineage-specific diversification led to the novel screening pigmentation of glacier algae. We found no support for the hypothesis of a common genomic basis for adaptations to ice and to land in streptophytes. Comparative genomic analysis revealed that reductive genome evolution in the ancestor of Zygnematophyceae correlates with their reductive morphological evolution. This first genome-scale data for glacier algae supports an Ancylonema-specific adaptation to the cryosphere, as well as shedding light on the genome evolution of land plants and Zygnematophyceae.

evolutionary biology↗

bioRxiv2023

An evolutionary timescale for Bacteria calibrated using the Great Oxidation Event

Most of lifes diversity and history is microbial but it has left a meagre fossil record, greatly hindering understanding of evolution in deep time. However, the co-evolution of life and the Earth system has left signatures of bacterial metabolism in the geochemical record, most conspicuously the Great Oxidation Event (GOE) [~]2.33 billion years ago (Ga, (Poulton et al. 2021)), in which oxygenic photosynthesis and tectonism (Eguchi, Seales, and Dasgupta 2019) transformed Earths biosphere from dominantly anaerobic to aerobic. Here, we combine machine learning and phylogenetic reconciliation to infer ancestral transitions to aerobic lifestyles during bacterial evolution. Linking these transitions to the GOE provides new constraints to infer the timetree of Bacteria. We find that extant bacterial phyla are truly ancient, having radiated in the Archaean and the Proterozoic: the oldest include Bacillota (Firmicutes), which radiated 3.1-3.7 Ga, Cyanobacteria (3.3-3.5 Ga) and Patescibacteria (3-3.5 Ga). We show that most bacterial phyla were ancestrally anaerobic and that most transitions to an aerobic lifestyle post-dated the GOE. Our analyses trace oxygen production and consumption back to Cyanobacteria. From that starting point, horizontal transfer seeded aerobic lifestyles across bacterial diversity over hundreds of millions of years. Our analyses demonstrate that the diversification of aerobes proceeded in two waves corresponding to the GOE and to a second sustained rise in atmospheric O2 at the dawn of the Palezoic (Krause et al. 2022).

evolutionary biology↗

bioRxiv2023

ATP synthase evolution on a cross-braced dated tree of life

The timing of early cellular evolution from the divergence of Archaea and Bacteria to the origin of eukaryotes remains poorly constrained. The ATP synthase complex is thought to have originated prior to the Last Universal Common Ancestor (LUCA) and analyses of ATP synthase genes, together with ribosomes, have played a key role in inferring and rooting the tree of life. Here we reconstruct the evolutionary history of ATP synthases using an expanded sampling of Archaea, Bacteria, and eukaryotes. We developed a phylogenetic cross-bracing approach making use of endosymbioses and ancient gene duplications of the major ATP synthase subunits to infer a highly resolved, dated species tree and establish an absolute timeline for ATP synthase evolution. Our analyses show that the divergence of the ATP synthase into F- and A/V-type lineages, was a very early event in cellular evolution dating back to more than 4Ga potentially predating the diversification of Archaea and Bacteria. Our cross-braced, dated tree of life also provides insight into more recent evolutionary transitions including eukaryogenesis, showing that the eukaryotic nuclear and mitochondrial lineages diverged from their closest archaeal (2.67-2.19Ga) and bacterial (2.58-2.12Ga) relatives at roughly the same time, with the nuclear stem being moderately longer.

evolutionary biology↗

bioRxiv2023

The power and limitations of species tree-aware phylogenetics

Species tree-aware phylogenetic methods model how gene trees are generated along the species tree by a series of evolutionary events, including the duplication, transfer and loss of genes. Over the past ten years these methods have emerged as a powerful tool for inferring and rooting gene and species trees, inferring ancestral gene repertoires, and studying the processes of gene and genome evolution. However, these methods are complex and can be more difficult to use than traditional phylogenetic approaches. Method development is rapid, and it can be difficult to decide between approaches and interpret results. Here, we review ALE and GeneRax, two popular packages for reconciling gene and species trees, explaining how they work, how results can be interpreted, and providing a tutorial for practical analysis. It was recently suggested that reconciliation-based estimates of duplication and transfer frequencies are unreliable. We evaluate this criticism and find that, provided parameters are estimated from the data rather than being fixed based on prior assumptions, reconciliation-based inferences are in good agreement with the literature, recovering variation in gene duplication and transfer frequencies across lineages consistent with the known biology of studied clades. For example, published datasets support the view that transfers greatly outnumber duplications in most prokaryotic lineages. We conclude by discussing some limitations of current models and prospects for future progress. Significance statementEvolutionary trees provide a framework for understanding the history of life and organising biodiversity. In this review, we discuss some recent progress on statistical methods that allow us to combine information from many different genes within the framework of an overarching phylogenetic species tree. We review the advantages and uses of these methods and discuss case studies where they have been used to resolve deep branches within the tree of life. We conclude with the limitations of current methods and suggest how they might be overcome in the future.

evolutionary biology↗

bioRxiv2023

Salactin, a dynamically unstable actin homolog in Haloarchaea

Across the domains of life, actin homologs are integral components of many essential processes such as DNA segregation, cell division, and cell shape determination. Archaea genomes, like those of bacteria and eukaryotes, also encode actin homologs, but much less is known about these proteins in vivo dynamics and cellular functions. We identified and characterized the function and dynamics of Salactin, an actin homolog in the hypersaline archaeon Halobacterium salinarum. Despite Salactins homology to bacterial MreB proteins, we find it does not function as a MreB ortholog in H. salinarum. Rather, live-cell imaging revealed that Salactin forms dynamically unstable filaments that grow and shrink out of the cell poles. Like other dynamically unstable polymers, Salactin monomers add at the growing filament end and its ATP-bound critical concentration is substantially lower than the ADP-bound form. When H. salinarums chromosomal copy number becomes limiting under low phosphate growth conditions, cells lacking Salactin show perturbed DNA distributions. Taken together, we propose that Salactin is part of a previously unknown chromosomal segregation apparatus required during low-ploidy conditions.

microbiology↗