Tropentag, October 6 - 8, 2009 in Hamburg "Biophysical and Socio-economic Frame Conditions for the Sustainable Management of Natural Resources"

Morphological Characterisation and Genetic Identification of Rhizobacteria in Cuban Agricultural Soils

¹Central University of Las Villas, Faculty of Agricultural Sciences, Cuba
²Catholic University of Leuven, Centre for Microbial and Plant Genetics, Belgium
³Ghent University, Laboratory of Microbiology, Belgium
⁴University of Rostock, Faculty of Agricultural and Environmental Sciences, Germany
⁵Council of Higher Scientific Investigation, Spain

Abstract

The microbial activity in soil is one of the most important factors for maintaining sustainability in crop production. The ecology and diversity of microbes is the base to unravel the different process that take place in several ecosystems. This report aims the isolation and characterisation of microorganisms in cereal-legume intercropping system. Samples from common bean (Phaseolus vulgaris L.) nodules, soil and sorghum roots (Sorghum bicolor (L.) Moench) were analysed to determine the biodiversity of diazotrophic and rhizosphere bacteria in an agricultural Cuban system. The morphological analysis demonstrated several groups of isolates with differences in growth type, colour, polysaccharide production and border of the colonies. Genetic characterisation using 16S rDNA revealed 8 groups of bacteria belonging to the genera: Agrobacterium, Rhizobium, Ochrobactrum, Sphingomonas, Stenotrophomonas, Bacillus, Brevibacillus and Paenibacillus. 47% of the sequences matched for 100% sequences in the EMBL database, while 53% of the sequences scored above 99% of identity. In nodule samples 37.5% of the isolates were 100% similar to Agrobacterium tumefaciens or Rhizobium species. Two species of Rhizobium isolated (R. etli and R. tropici) were detected in nodule samples. In nodulation tests, Agrobacterium isolates were unable to nodulate the original host. No statistical difference was observed for nodulation between the Rhizobium isolates and the R. etli reference strain. The results presented in this study are of importance to determine the interspecies microbial relationships in the rhizosphere, possibly increasing our understanding on biotic factors interfering with the Rhizobium-legume symbiosis and as a source of inoculant strains for local environmental conditions.

Keywords: 16S rDNA, bacteria, diazotrophic, rhizosphere

Contact Address: Bettina Eichler-Loebermann, University of Rostock, Faculty of Agricultural and Environmental Sciences, J. von Liebig Weg 6, 18059 Rostock, Germany, e-mail: bettina.eichleruni-rostock.de