Eco-evolution and cellular functionality of the heterozygous bacterial genus Achromatium

• Applicant: Dr. Danny Ionescu
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms ; Microbial Ecology and Applied Microbiology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465407921

Achromatium is a large bacterium found globally across very different environments. It has periplasmic CaCO3 crystals that invaginate the cytoplasmic membrane and seem to compartmentalize the cell. Achromatium is heterozygous, harboring across ca. 300 chromosomes per cell, a genomic diversity comparable to that of entire microbial communities. This, contrasts with current dogmas that assume all multiple chromosomes of polyploid prokaryotes are identical. Fluorescent labelling of rRNA shows different alleles are expressed in different parts of the cell. If this functional compartmentalization exists, Achromatium is a bacterial equivalent of multicellular organisms. Achromatium has an identical functional potential regardless of its habitat, yet gene expression patterns form clusters encompassing mostly similar environments. Achromatium is a perfect model for studying mechanisms and eco-evolutionary consequences of microbial heterozygosity and intracellular genetic diversity. Therefore, I will investigate 1) The mechanisms by which this large intracellular diversity is generated, regulated, and propagated as well as 2) The ecological advantages driving Achromatium to harbor a high-maintenance, genetic system. In two recent publications I suggested that: i) Genetic diversity is generated via chromosome shuffling during cell division; ii) Achromatium expresses different alleles under different environmental conditions; iii) Achromatium accumulates functions over time. The 3 hypotheses will be tested using fresh cells available year-round in Lake Stechlin. The large cell size (<100x40 um) allows for easier use of imaging techniques typically limited by the size of bacteria. Cell structure will be resolved by electron microscopy. Imaging of the cell’s metabolome and DNA/protein synthesis will be used to test functional compartmentalization. Heterozygosity will be confirmed by sequencing individual chromosomes. Chromosome shuffling will be tested by imaging and by separately sequencing dividing cells. Differential expression of multiple alleles under different experimental conditions will be tested by single cell transcriptomes using a new, successfully tested, method to overcome the genomic diversity between cells. To tests for environment-specific gene enrichment, marine, estuary and freshwater metagenomes and metatranscriptomes will be sequenced. If the above hypotheses prove to be correct, Achromatium may represent a unicellular evolutionary basis of sexual reproduction and multicellularity and it uses an alternative evolutionary path for adaptation where multiple alleles are accumulated to offer a tailored response for different environmental conditions. This will likely change our perception about the evolution and function of polyploid bacteria

• DFG Programme: Research Grants
• International Connection: Romania
• Cooperation Partner: Professor Dr. Lucian Barbu-Tudoran