Grupo de Microbiología del Suelo y Agrícola

Investigador Responsable Jesus Caballero-Mellado, Ph.D.

Main lines of Research: Taxonomy, diverstity and ecology of nitrogen-fixing bacteria associated with crop plants and their use in agriculture.

The research group

This Group was created in September 1995 in the Nitrogen Fixation Research Center (CIFN) with the objective of contributing to the improvement of sustainable agriculture through the basic and applied research in biological nitrogen fixation (BNF). Our studies have been directed at looking for well-known N 2 -fixing species (for instance, Azospirillum and Gluconacetobacter ), and for new rhizospheric and endophytic diazotrophs associated with plants of agricultural importance (e.g. corn and sugarcane) as well as "neglected" plants [e.g., coffee and teocintle (maize ancestor)], because it may provide a better picture not only of the distribution of N 2 -fixation ability among bacterial taxa, but also of the distribution and diversity of N 2 -fixing bacterial populations. For this, we have searched culture conditions for the selective isolation and definition of the taxonomic status of novel diazotrophs, using classic and molecular criteria, with the final objective of evaluating their potential to promote plant growth and increase yield of cereals, especially of maize.


The research Group alone or along with Mexican and International research teams has contributed with the knowledge on the microbial biodiversity describing novel nitrogen-fixing bacterial species associated with agricultural important plants such as Gluconacetobacter johannae , G. azotocaptans as well as Burkholderia unamae , B. xenovorans and B. tropica .

The research group has selected Azospirillum strains efficient in promoting plant growth and for increasing crop yields. Also, it has developed formulations for the biomass production of Azospirillum brasilense , and its stability in storage. On this basis, a large field-inoculation program was carried out in Mexico through the Ministry of Agriculture Research Institute (INIFAP), and Azospirillum inoculants were applied to around 600,000 ha of crop fields (mainly maize, but wheat, sorghum and barley as well) in Mexico during 1999, and on about 1.5 million ha during 2000. Inoculation showed consistent average yield increases of 26% in cereal crops under different levels of nitrogen fertilizer and climatic conditions during the summer of 1999 and 2000. Presently, by using our formulations and a mixture of A. brasilense strains selected by our research group, in Mexico a company sells an inoculant for maize and sorghum, and another for wheat and barley.

Present and Future perspectives

Our research team is interested in the production of efficient biofertilizers, searching for increasing the use of natural resources and as alternatives for decreasing the mineral fertilizers and other agrochemical inputs, all of this for looking to diminish the environmental pollution as well as its economic and social cost. In this direction, our studies on novel nitrogen-fixing plant-associated species have been extended to know bacterial mechanisms involved in the rhizospheric and endophytic colonization of plants as well as mechanisms related with the plant growth promotion such as phytohormones and enzyme synthesis, solubilization of minerals, suppression of plant pathogens, and degradation of xenobiotics applied commonly in agriculture. Concomitantly, we try to know the bacterial
genes that encode such mechanisms. In addition, we are analizing the genomic structure of novel diazotrophic Burkholderia species, and to further compare their genomic variability.

Técnico(s) Académico(s): QFB. Lourdes Martínez Aguilar