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

BELEN BORDIGNON; COMERCI, D; LETICIA LAROTONDA; LEILA BARTROLÍ; SOLER BISTUE, ALFONSO

Glasgow

Congreso; The FEMS meeting; 2019

Federation of European Microbiology Societies

Background: The genetic basis of bacterial growthrate (GR) is still unclear. Several features link bacterialgenome structure to GR. Thenumber of ribosomal RNA operons (rrn)correlate to GR. In fast-growing bacteria, the genes encoding for the flow ofgenetic information-the transcription and translation machineries-are close tothe origin of replication (oriC). Duringexponential growth, fast growers perform multi-fork replication. Thus, genes nearto oriC benefit of higher dosage.Therefore, such positional bias can be a strategy to maximize the expression oftranscription and translation machineries.  Objectives:  We aim at experimentally testingthese correlations in slow and fast-growing bacteria.Methods:  We used Bradyrhizobia as a model forslow-growing bacteria. Vibriocholerae is a fast GR whose genome can be widely modified by natural transformationcoupled to recombineering techniques based on lambdoid phage recombinationsites. This allowed altering the genomic location of S10-spc-α (S10) and the rpoBClocus which harbor most of ribosomal proteins and RNA polymerase genesrespectively.  Results: Growth curves testing differentisolates showed that Bradyrhizobia bearing 2 rrn grew faster than those bearinga 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 phenotypeindicating that relocation process per se was not detrimental. The relocationof S10 caused a stronger effect. These physiological alterations are probablydue to differences in gene dosage that occurs during the exponential phase dueto overlapping replication rounds.