Project description:Background. Bacteria of the Candidate Phyla Radiation (CPR), constituting about 25% of the bacterial biodiversity, are characterized by small cell size and patchy genomes without complete key metabolic pathways suggesting symbiotic life styles. Gracilibacteria (BD1-5) are part of the CPR branch, they possess alternate coded genomes and have two cultivated members that were shown to be microbial predators. However, besides genomic sampling, little is known about the lifestyle of Gracilibacteria, their temporal dynamics, and activity in natural ecosystems, and particularly groundwater where they have initially been genomically resolved. The current study was set out with the aim of investigating the metaproteogenome of Gracilibacteria as a function of time in the cold-water geyser Wallender Born in the Volcanic Eifel region in Germany, to estimate their activity in situ and discern expressed genes involved in their lifestyle. Results. We coupled genome-resolved metagenomics and metaproteomics to investigate a microbial community enriched in Gracilibacteria across a 12-day time-series. Groundwater was collected and sequentially filtered onto 0.2-μm and 0.1-μm filters to fraction CPR and other bacteria. Based on 670 Gbps of metagenomic data, 1129 different ribosomal protein S3 marker genes and 751 high-quality genomes (123 population genomes after dereplication), we identified dominant bacteria belonging to Galionellales and Gracilibacteria along with keystone microbes, low in genomic abundance but substantially contributing to proteomic abundance. Seven high-quality Gracilibacteria genomes showed typical limitations in their central metabolism but no co-occurrence to potential hosts. Their genomes encoded for a high number of proteins related to a predatory lifestyle, whose expression was detected in the proteome and included subunits related to type IV and type II secretion systems, as well as features related to cell-cell interactions and cell motility. Conclusion. We present a highly resolved analysis coupling metagenomics to metaproteomics for elucidating microbial dynamics of Gracilibacteria in groundwater. We posit that Gracilibacteria are successful microbial predators in this ecosystem potentially aiding in population control of this highly disturbed microbial community from the deep biosphere.
2024-08-08 | PXD042980 | Pride
Project description:Genetic manipulation of candidate phyla radiation bacteria
Project description:Project description: In this study, we have characterized with distinct biochemical assays the activity of a predicted glutamate racemase from an uncultivated bacterium (Candidatus Saccharimonas aalborgenesis), classified taxonomically within the Candidate Phyla Radiation (CPR). This racemase was produced in a Salmonella auxotrophic mutant defective in its endogenous glutamate racemase. Despite the low identity of the predicated racemase from this uncultivated bacterium compared to that of Salmonella (MurI), ~32.0%, it exhibited high specificity for glutamate as substrate in in vitro racemization assays among the rest of canonical amino acids. Moreover, the expression of this novel racemase complemented the D-Glu auxotrophy of the host bacterium used as chassis (Salmonella). Besides these physiological analyses, the study also characterized the composition and structure of the peptidoglycan produced by bacteria expressing each of the two glutamate racemases, exogenous and endogenous.
Data processing protocol: Three biological replicates of two Salmonella strains expressing either the predicted glutamate racemase from the uncultivated bacterium Candidatus Saccharimonas aalborgenesis (Delta-murI-CPR, R1-R3) or the endogenous glutamate racemase (MurI) (Delta-murI-SAL, R1-R3) were grown in the nutrient rich medium LB to reach the exponential phase. At this time, bacteria were collected by centrifugation, washed and lysed by boiling in a 4% SDS-containing buffer. From this material, peptidoglycan was purified by standard protocol. Briefly, after high-speed centrifugation, the pellet containing peptidoglycan as the only SDS-insoluble material was subjected to successive enzymatic treatments with alpha-amylase, pronase (as protease) and, muramidase to cleave the glycan chains and to yield individual uncross-linked and cross-linked muropeptides. The muropeptide mixtures were analysed by LC-MS/MS to obtain a list of parental masses representing the complexity of the sample, i.e. the diversity of co-existing muropeptide classes. The parental masses were assigned as "muropeptides" when a mass of 204.3, corresponding to the N-acetyl-glucosamine molecule, was detected in the fragmentation spectra. The complete lists of parental masses were examined using FreeStyle (Thermo) software and compared among samples (biological replicas and control-problem pairs) by statistical parameters using XCMS software.