Biology subjects

Petersen, J. M.

Publications and source records attributed to Petersen, J. M..

6 recordsLinked to original sources

bioRxiv2026

Spinal Cord Microglia Exhibit Impaired Repair Responses to Myelin Damage

BackgroundMultiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) that affects both the brain and spinal cord, although the brain has historically received greater attention. In the inducible, oligodendrocyte-specific knockout model of Myrf, which results in white matter damage to both the brain and spinal cord, our laboratory previously demonstrated that the brain undergoes partial remyelination following white matter damage, whereas the spinal cord fails to do so. We also observed that brain microglia display a much stronger activation than spinal cord microglia in this model. Microglia regulate remyelination by clearing myelin debris, processing resulting lipids, and modulating an inflammation response. ResultsHere, to test our hypothesis, we characterized microglial phenotypes during demyelination in both tissues. The brain exhibited greater early microglial recruitment and higher baseline expression of activation and phagocytic markers, suggesting a primed state for responding to damage. In contrast, spinal cord microglia showed delayed phagocytic marker expression, sustained inflammation, and a predominately amoeboid morphology during demyelination. ConclusionsTogether, these findings indicate that brain microglia mount a timely and coordinated response to demyelination that supports remyelination, whereas spinal cord microglia adopt a dysfunctional phenotype that may contribute to impaired myelin repair.

neuroscience↗

bioRxiv2025

Organosulfur cycling in the multi-partner symbiosis between lucinid bivalves, sulphur-oxidizing symbionts, and Endozoicomonas

Organosulfur compounds play an important role in chemotaxis, stress protection, and nutrition in many marine symbioses. Lucinidae, an ancient and species-rich family of marine bivalves, host chemosynthetic sulphur-oxidising bacteria within gill epithelial cells, and is well-known for its contribution to inorganic sulphur cycling in marine sediments worldwide. Little is known about organosulfur transformations by lucinid-associated microbiota or the hosts potential contribution. Here, we integrated field measurements, genomics, transcriptomics, and experimental assays to investigate organosulfur cycling in three lucinid species from temperate and tropical environments. Concentrations of the osmolyte dimethylsulphoniopropionate (DMSP) in lucinids were typically much higher than in their surrounding environment, and varied with host species and season, but not with symbiont abundance. Indeed, candidate DMSP synthesis DSYB genes were expressed by the animal hosts implying that the host may be the source of DMSP. Furthermore, a newly identified and isolated Candidatus Endozoicomonas endolucinida symbiont was capable of DMSP catabolism to dimethylsulphide (DMS), which could be further syntrophically oxidised by the sulphur-oxidising symbionts that encode methanethiol oxidase genes in their genomes. Finally, incubation experiments supported a combined role of the host and its associated microbiome in organosulfur cycling during stress, with the highest DMSP concentrations measured when holobionts were incubated with antibiotics under anoxic conditions. This study identified a previously unrecognised microbial partner in lucinid symbioses and revealed its potential organosulphur-based metabolic interactions with both the host and the sulphur-oxidising symbionts, highlighting the capacity of these widespread associations to influence global organosulfur cycling.

ecology↗

bioRxiv2025

Symbiont diversity within Loripes orbiculatus and the case for multiple hosts

Seagrasses support immense biodiversity and are critical for maintaining coastal ecosystem health. These foundation species benefit from a three-way facultative relationship with one of the common inhabitants of seagrass meadows, lucinid bivalves, which host specific bacterial Ca. Thiodiazotropha symbionts. Relatives of the bivalve symbionts have been detected on seagrass roots raising the possibility that these symbionts may colonize both animals and plants; however, no study has yet compared bivalve- and seagrass-associated symbionts at the same site and time. Our combination of 16S rRNA amplicon and metagenome sequencing revealed a greater diversity than was previously observed within both lucinid bivalves and on seagrass roots from the Adriatic Sea. We show that two of the Ca. Thiodiazotropha ASVs found on seagrass roots are identical to those found in bivalve hosts at the same site. This suggests that symbiont sharing may occur in the seagrass habitat between these two species, which has important evolutionary and ecological implications for both hosts and symbionts, as well as thin response to climate change.

microbiology↗

bioRxiv2025

Temporal dynamics of CNS cholesterol esters correlate with demyelination and remyelination

Elevated cholesterol ester levels have been observed in the CNS of patients with neurological diseases, yet the source of cholesterol ester accumulation and whether it is directly linked to demyelination remains undefined. This study investigates the temporal dynamics of cholesterol esters using the Plp1-iCKO-Myrf mouse model, which features distinct phases of demyelination and remyelination. Our findings reveal that cholesterol ester levels increased with demyelination in both the brain and the spinal cord. In the brain, cholesterol esters declined to normal levels during remyelination, whereas cholesterol esters remained elevated in the spinal cord, which had limited remyelination. Expression of both acetyl-CoA-acyltransferase 1 (ACAT1) and lecithin-cholesterol acyltransferase (LCAT) were elevated during demyelination, suggesting the potential involvement of both proteins in the formation of cholesterol esters. Co-localization studies revealed that ACAT1 is predominantly expressed by microglia and LCAT is predominantly expressed by astrocytes during demyelination highlighting the active roles of glia cells in cholesterol ester metabolism. In addition, we showed that administering the remyelinating drug, Sob-AM2, effectively reduced the level of cholesterol ester accumulation in the brain during demyelination underscoring the potential that manipulating cholesterol ester regulatory pathways may offer for restoring cholesterol homeostasis and promoting remyelination in demyelinating diseases.

neuroscience↗

bioRxiv2019

Horizontally transmitted symbiont populations in deep-sea mussels are genetically isolated

Eukaryotes are habitats for bacterial organisms where the host colonization and dispersal among individual hosts have consequences for the bacterial ecology and evolution. Vertical symbiont transmission leads to geographic isolation of the microbial population and consequently to genetic isolation of microbiotas from individual hosts. In contrast, the extent of geographic and genetic isolation of horizontally transmitted microbiota is poorly characterized. Here we show that chemosynthetic symbionts of individual Bathymodiolus brooksi mussels constitute genetically isolated populations. The reconstruction of core genome-wide strain sequences from high-resolution metagenomes revealed distinct phylogenetic clades. Nucleotide diversity and strain composition vary along the mussel lifespan and individual hosts show a high degree of genetic isolation. Our results suggest that the uptake of environmental bacteria is a restricted process in B. brooksi, where self-infection of the gill tissue results in serial founder effects during symbiont evolution. We conclude that bacterial colonization dynamics over the host life-cycle is thus an important determinant of population structure and genome evolution of horizontally transmitted symbionts.

microbiology↗

bioRxiv2018

Horizontal acquisition of a patchwork Calvin cycle by symbiotic and free-living Campylobacterota (formerly Epsilonproteobacteria)

Although the majority of known autotrophs use the Calvin-Benson-Bassham (CBB) cycle for carbon fixation, all currently described autotrophs from the Campylobacterota (previously Epsilonproteobacteria) use the reductive tricarboxylic acid cycle (rTCA) instead. We discovered campylobacterotal epibionts (\"Candidatus Thiobarba\") of deep-sea mussels that have acquired a complete CBB cycle and lost key genes of the rTCA cycle. Intriguingly, the phylogenies of campylobacterotal CBB genes suggest they were acquired in multiple transfers from Gammaproteobacteria closely related to sulfur-oxidizing endosymbionts associated with the mussels, as well as from Betaproteobacteria. We hypothesize that \"Ca. Thiobarba\" switched from the rTCA to a fully functional CBB cycle during its evolution, by acquiring genes from multiple sources, including co-occurring symbionts. We also found key CBB cycle genes in free-living Campylobacterota, suggesting that the CBB cycle may be more widespread in this phylum than previously known. Metatranscriptomics and metaproteomics confirmed high expression of CBB cycle genes in mussel-associated \"Ca. Thiobarba\". Direct stable isotope fingerprinting showed that \"Ca. Thiobarba\" has typical CBB signatures, additional evidence that it uses this cycle for carbon fixation. Our discovery calls into question current assumptions about the distribution of carbon fixation pathways across the tree of life, and the interpretation of stable isotope measurements in the environment.

microbiology↗