Effect of cell density and mutation on the expression of Rhi genes in Rhizobium leguminosarum biovar viciae

B Boboye,A Downie

doi:10.12944/cwe.2.2.05

Abstract

Effects of cell density, symbiotic plasmid and mutation (by transposon mutagenesis) on the expression of rhi genes in Rhizobium leguminosarum biovar viciae were studied. Strains of the bacterium bearing and lacking regulatory gene rhiR were grown to late exponential phase and assayed for the production of rhi genes inducer. R. leguminosarum biovar viciae was specific for the synthesis of the rhi genes inducer. Expression of rhi genes advanced with increased cell population without any difference between Sym minus and Sym plus plasmid strains of the bacterium. Highest amount of the inducer was produced in the exponential phase. The growth of the microbe with and without Sym plasmid showed that symbiotic plasmid enhanced the optimal formation of rhi genes inducer. Iniducer formation in the absence of Sym plasmid was less than 20 Miller units of b-galactosidase activity in contrast to 2375 Miller units for plasmid-containing strain. Tn-5 mutagenesis generated four groups of mutants. Classes I, II, III and IV mutants were low, moderate-, high- and super-producers of the inducer. These groups showed 145-250, 625-896, 1031-1375 and 1563 Miller units of phosphatase activity respectively.

Highlights

Rhizobium leguminosarum biovar viciae is a rod-shaped, motile, gram-negative, nitrogen-fixing bacterium which fixes nitrogen on legumes such as lentils, peas and vetches[1,2]
In order to do this, we studied the effects of cell density and mutation on the expression of rhi genes in the bacterium
The colony forming units increased with incubation time in R. leguminosarum in the presence and absence of symbiotic plasmid.The two bacterial

Summary

Introduction

Rhizobium leguminosarum biovar viciae is a rod-shaped, motile, gram-negative, nitrogen-fixing bacterium which fixes nitrogen on legumes such as lentils, peas and vetches[1,2]. These legumes like others are important in the provision of bodybuilding minerals, calcium, vitamins A and B, thiamine, niacin and oil[3,4,5,6,7]. RhiR has a homology with LuxR which belongs to LuxR-LuxI family This class of transcriptional activators is common to a diverse group of gram-negative bacteria[10,11] including the quorum-sensing signal molecules and the LuxRI homologs that were identified in fish pathogen Edwardsiella tarda[12].

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Conclusion