Testing organizational features linking the genome structure to growth rate in very fast and a very slow growing bacteria.

BELÉN BURDIGNON; LEILA BARTROLI; LETICIA INÉS LAROTONDA; DIEGO COMERCI; ALFONSO SOLER BISTUE

Glasgow

Congreso; 8th Congress of European Microbiology (FEMS 2019); 2019

(FEMS)

Background: The genetic basis of bacterial growth rate (GR) is still unclear. Several features link bacterial genome structure to GR. The number of ribosomal RNA operons (rrn) correlate to GR. In fast-growing bacteria, the genes encoding for the flow of genetic information-the transcription and translation machineries-are close to the origin of replication (oriC). During exponential growth, fast growers perform multi-fork replication. Thus, genes near to oriC benefit of higher dosage. Therefore, such positional bias can be a strategy to maximize the expression of transcription and translation machineries. Objectives: We aim at experimentally testing these correlations in slow and fast-growing bacteria.Methods: We used Bradyrhizobia as a model for slow-growing bacteria. Vibrio cholerae is a fast GR whose genome can be widely modified by natural transformation coupled to recombineering techniques based on lambdoid phage recombination sites. This allowed altering the genomic location of S10-spc-α (S10) and the rpoBC locus which harbor most of ribosomal proteins and RNA polymerase genes respectively. Results: Growth curves testing different isolates showed that Bradyrhizobia bearing 2 rrn grew faster than those bearing a single operon, independently of the culture media tested. In V. cholerae, the relocation of S10 or rpoBC loci far form oriC led to lower GR. Close relocation displayed no phenotype indicating that relocation process per se was not detrimental. The relocation of S10 caused a stronger effect. These physiological alterations are probably due to differences in gene dosage that occurs during the exponential phase due to overlapping replication rounds.