Hopmans, E. | bioRxiv Science

bioRxiv2024

Unraveling an unknown diversity of archaeal and bacterial tetraether membrane lipid producers in a euxinic marine system

Bacterial membrane lipids have been traditionally defined as fatty acids (FAs) bilayers linked through ester bonds, while those of Archaea as ether-linked isoprenoids forming bilayers or monolayers of membrane spanning lipids (MSLs) known as isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs). This paradigm has been challenged with the discovery of branched GDGTs (brGDGTs), membrane spanning ether-bound branched alkyl FAs, that are of bacterial origin but whose specific producers in the environment are often unknown. The limited number of available microbial cultures restricts the knowledge of the biological sources of membrane lipids, which in turn limits their potential applicability as biomarkers. To address this limitation, we detected membrane lipids in the Black Sea using high resolution accurate mass/mass spectrometry and inferred their potential producers by targeting lipid biosynthetic pathways encoded on the metagenome, in metagenome-assembled genomes and unbinned scaffolds. We also detected brGDGTs and overly branched GDGTs in the suboxic and euxinic waters, which are potentially attributed, to members of the Planctomycetota, Cloacimonadota, Desulfobacterota, Chloroflexota, Actinobacteria and Myxococcota--all anaerobic microorganisms. These results open a new chapter in the use of specific brGDGTs as biomarkers of anoxic conditions in marine settings and of the role of these membrane lipids in microbial adaptation.

microbiology↗

bioRxiv2020

Profiling diverse sequence tandem repeats in colorectal cancer reveals co-occurrence of microsatellite and chromosomal instability involving Chromosome 8

Colorectal carcinomas (CRCs) which have lost DNA mismatch repair display hypermutability evident in a molecular phenotype called microsatellite instability (MSI). These mismatch repair deficient tumors are thought to lack widespread genomic instability features, such as copy number changes and rearrangements. To identify MSI for clinical diagnosis, current molecular testing looks for changes in mononucleotide or dinucleotide repeats. However, microsatellites have other types of sequence tandem repeats such as tri- and tetranucleotide motifs. These additional classes of microsatellites are generally not examined for MSI but are known to be unstable in a phenotype known as elevated microsatellite alterations at selected tetranucleotide repeats, or EMAST. We developed a sequencing approach that provides ultra-high coverage (>2500X) of microsatellite targets and cancer genes for profiling genomic instability. We assessed the diverse repeat motifs across 200 microsatellites. Our approach provides highly sensitive detection of MSI with high specificity, evaluates copy number alterations with high accuracy, delineates chromosomal instability (CIN) classification and deconvolutes subclonal architecture. By examining both MSI and CIN, we discovered mutations and copy number alterations that defined mixed genomic instability states of CIN and MSI, which are normally considered exclusive. An increase in copy number of chromosome arm 8q was prevalent among MSI tumors. Moreover, we identified an inter-chromosomal translocation event from a CRC with co-occurrence of MSI. Subclonal analysis demonstrated that mutations which are typically considered to be exclusive in MSI, shows mutual occurrence in MSI tumors with more sensitive characterization. Our approach revealed that MSH3 mutations are a potential source of mixed genomic instability features. Overall, our study demonstrates that some colorectal cancers have features of both microsatellite and chromosomal instability. This result may have implications for immunotherapy treatment.

genomics↗