Biology subjects

Penev, P.

Publications and source records attributed to Penev, P..

6 recordsLinked to original sources

bioRxiv2026

The origin and evolution of archaeal Borg extrachromosomal elements

Borgs are giant linear extrachromosomal elements (ECEs) of methane-oxidizing Methanoperedens archaea whose evolutionary origin and ecosystem distribution remain unknown. Here we detected 240 Borgs in diverse saline, soil, and freshwater ecosystems. 27 encode methyl-coenzyme M reductases central to methane metabolism, eight have full rRNA operons related to those of Methanoperedens, and some contain up to four ribosomal proteins. We also identified 323 mini-Borgs whose proteome content and gene phylogenies classify as a distinct ECE type. Based on 105 complete and near-complete genomes, Borgs and mini-Borgs share core genes in conserved order, indicating common ancestry. Phylogenetic and diversity analyses suggest that Borgs evolved via gene acquisition into a backbone inherited from mini-Borgs. This evolutionary trajectory mirrors those proposed for giant viruses of both eukaryotes and bacteria.

microbiology↗

bioRxiv2026

Microbial autotrophy is widespread across soils and most prevalent in deep and saturated environments

Genes for CO2 fixation occur in soil microorganisms, but little is known about the pathways that are most common across ecosystem types, the organisms with these genes, where different CO2 fixation pathways are most prevalent, and the energy sources that support autotrophy across ecosystems. Here, we investigated microbial capacity for autotrophy in soils using 853 metagenomes and 201 metatranscriptomes from a wide range of terrestrial ecosystems (agricultural soils, wetlands, weathering rock). Autotrophy-associated RuBisCO (Form I and II) is widely encoded across all soils and occurs in bacteria from numerous lineages (38 phyla). RuBisCO Form IE is consistently more phylogenetically diverse in soils than in marine ecosystems, suggesting that it may have evolved to function in soil-like environments. A newly discovered deeply branching Form I RuBisCO, Form I, supports the hypothesis that Form I RuBisCO originated in anaerobic environments. Further, saturated soils harbor more, and more distinct, autotrophic microbes, many of which may use the Calvin-Benson-Bassham cycle or Wood-Ljungdahl pathway for CO2 fixation. Overall, the results indicate that autotrophy is a particularly important metabolism in deep, saturated soils and weathering rock.

microbiology↗

bioRxiv2025

Spatial and depth structuring predominate over temporal variation in Mediterranean grassland soil viral communities

Viruses have the potential to influence microbial community structure and elemental cycling in soils, but it remains unclear how these communities are distributed across space and time, which can shape how they respond to environmental change and impact ecosystem processes. Mediterranean grasslands, with their pronounced seasonal moisture fluctuations, offer an ideal system to examine viral biogeography. While previous studies hint at spatial structuring and moisture controls on viral communities, temporal responses to seasonal moisture shifts have not been comprehensively investigated in situ. Here, we generated 59 viromes and leveraged 89 metagenomes from two Mediterranean grasslands to measure soil viral communities across horizontal space (sampling zone), depth, and key seasonal stages of the Mediterranean water year (e.g. plant productivity, dry down and wetup). Sampling zone was the dominant driver of viral community composition in viromes, with time secondarily explaining variation in viral communities. In contrast, viral richness and DNA yields varied primarily across time. Spatial structuring also emerged in viruses recovered from metagenomes, with depth having the strongest effect, followed by sampling zone. Environmental variables and predicted host distributions partially explained these patterns, but substantial variation remained unaccounted for, suggesting a role for dispersal limitation. Overall, soil viral communities were primarily structured by spatial factors, with temporal and environmental influences acting secondarily, highlighting the importance of fine-scale spatial dynamics in understanding viral ecology. Future studies should explicitly examine the role of dispersal limitation and fine-scale host-environment interactions to fully resolve drivers of soil viral biogeography.

ecology↗

bioRxiv2025

Circular 23S rRNA within archaeal ribosomes

The ribosomal RNAs (rRNAs) that form the core of ribosomes are believed to occur as linear molecules. Here, we investigated rRNAs from diverse and mostly uncultivated archaea and found evidence that, in at least eight phylum-level archaeal lineages, the 23S rRNAs within mature ribosomes are circular. Sequencing of total cellular RNA indicates that the transcriptional abundances of archaeal circular 23S rRNAs vastly exceed those of linear counterparts, and linear versions are often undetectable. As the majority of rRNAs derive from mature ribosomes, the data suggested that the circular molecules are within the ribosomes. Thus, we directly sequenced RNA extracted from isolated ribosomes of a model archaeon, Methanosarcina acetivorans, and confirmed that the assembled 23S rRNAs are circular. Structural modeling places the 5 and 3 ends of the linear precursors of archaeal 23S rRNAs in close proximity to form a GNRA tetraloop (in which N is A, C, G, or U and R is A or G), consistent with their further circularization within ribosomes. We confirm the existence of circular 16S rRNA intermediates in transcriptomes of most archaea, yet a circular form is not evident in some distinct archaeal groups. Overall, the results uncover unexpected variations in the processing required to generate mature rRNAs and the conformation of functional molecules in archaeal ribosomes.

microbiology↗

bioRxiv2022

A widespread group of large plasmids in methanotrophic Methanoperedens archaea

Anaerobic methanotrophic (ANME) archaea conserve energy from the breakdown of methane, an important driver of global warming, yet the extrachromosomal genetic elements that impact the activities of ANME archaea are little understood. Here we describe large plasmids associated with ANME archaea of the Methanoperedens genus. These have been maintained in two bioreactors that contain enrichment cultures dominated by different Methanoperedens species and co-occur with Methanoperedens species in other anoxic environments. By manual curation we show that two of the plasmids are large (155,607 bp and 191,912 bp), circular, and replicate bidirectionally. The group of Methanoperedens species that carry these plasmids is related to "Ca. Methanoperedens nitroreducens", "Ca. Methanoperedens ferrireducens", "Ca. Methanoperedens manganicus" and the plasmids occur in the same copy number as the main chromosome. The larger plasmid encodes transporters that potentially enhance access to Ni, which is required for the methyl-CoM reductase (Mcr), Co required for the cobalamin cofactor needed for methyltransferases, and amino acid uptake. We show that many plasmid genes are actively transcribed, including genes involved in plasmid chromosome maintenance and segregation, a Co2+/Ni2+ transporter and cell protective proteins. Notably, one plasmid carries three tRNAs and two colocalized genes encoding ribosomal protein uL16 and elongation factor eEF2. These are not encoded in the host Methanoperedens genome and uL16 and eEF2 were highly expressed, indicating an obligate interdependence between this plasmid and its host. The finding of plasmids of Methanoperedens opens the way for the development of genetic vectors that could be used to probe little understood aspects of Methanoperedens physiology. Ultimately, this may provide a route to introduce or alter genes that may enhance growth and overall metabolism to accelerate methane oxidation rates.

microbiology↗

bioRxiv2021

Phage-encoded ribosomal protein S21 expression is linked to late stage phage replication

The ribosomal protein S21 (bS21) gene has been detected in diverse viruses with a large range of genome sizes, yet its in situ expression and potential significance have not been investigated. Here, we report five closely related clades of bacteriophages (phages) represented by 47 genomes (8 curated to completion and up to 331 kbp in length) that encode a bS21 gene. The bS21 gene is on the reverse strand within a conserved region that encodes the large terminase, major capsid protein, prohead protease, portal vertex proteins and some hypothetical proteins. These phages are predicted to infect Bacteroidetes species that inhabit a range of depths in freshwater lakes. Transcriptionally active bS21-encoding phages were sampled in the late-stage of replication, when core structural genes, bS21 and a neighboring gene of unknown function were highly expressed. Thus, our analyses suggest that bS21, which is involved in translation initiation, substitutes into the Bacteroidetes ribosomes and selects for phage transcripts during the late-stage replication when large-scale phage protein production is required for assembly of phage particles.

microbiology↗