Research student profile: Mary Otieno

Project title

Proteomic changes related to desiccation tolerance in Rhizobia

Project overview

This study aims to evaluate the desiccation tolerance of rhizobia by characterizing physiological and metabolic changes in cells during growth in different sources of peat. It is widely acknowledged that inoculation of legumes with effective rhizobia can improve yields through biological nitrogen fixation providing a sustainable source of nitrogen as a substitute for inorganic fertilizers, through the adoption of rhizobial inoculants However, poor survival of rhizobia during delivery to broad-acre legume crops is still a major concern and limits the potential for maximum nodulation by elite strains, nitrogen fixation and yield. Legume inoculants are most commonly applied to seed prior to sowing; however, the seed surface presents a hostile environment for rhizobia, exposing cells to desiccation stress and potentially toxic chemicals, thus limiting survival and subsequent nitrogen fixation. Therefore, improving survival of rhizobia under conditions of physiological stress may promote biological nitrogen fixation and enhance plant growth and improved crop productivity.

Although desiccation is among the most significant environmental stresses encountered by bacterial cells, which face both fluctuating-periodical and long-term exposure to drought conditions, the mechanisms providing resistance to this stress are still poorly understood. The gap in knowledge remains, especially in relation to the physiological and morphological responses of rhizobia to desiccation. A better understanding of the physiological tolerance mechanisms of rhizobia in response to the various environmental stresses that compromise survival will assist in the selection of robust strains that are more compatible with seed coating applications.

Survival and desiccation tolerance of the strains will be measured after growth of rhizobial strains in peat extracts from different sources. Changes in protein expression will be measured using two-dimensional (2D) gel electrophoresis and mass spectrometry. After confirmation that selected gene expressions are modified after growth in peat extract, their role in desiccation tolerance will be measured using strains carrying relevant mutations by knocking out the genes coding for the desiccation tolerant proteins, and determining survival over time. Chemical analysis of peat extract responsible for modified protein expression will allow development and modification of new inoculant formulations designed for improved desiccation tolerance of rhizobia.

The main outcome of this research will be to understand the protein changes and growth media modifications that enhance desiccation tolerance. These findings can ultimately be employed in enhancing Biological Nitrogen Fixation through improved survival of rhizobia during inoculation, especially in pre-inoculated legume seeds.


I was born and brought up in Kenya, where I did my BSc in Biotechnology at Kenyatta University, graduated in 2009. I then got a scholarship from the Bill and Melinda Gates Foundation through CIAT-TSBF to do a master’s degree at Moi University, Eldoret. I graduated in 2012 with an MSc in Soil Science.

I have a PhD scholarship from the Australia Awards (formerly AusAID).

I received the best poster award, in the 17th International Congress on Nitrogen Fixation in Fremantle, Western Australia, 27th November - 1st December, 2011.


  • Atieno, M., Herrmann, L., Okalebo, R., & Lesueur, D. (2012). Efficiency of different formulations of Bradyrhizobium japonicum and effect of co-inoculation of Bacillus subtilis with two different strains of Bradyrhizobium japonicum. World Journal of Microbiology and Biotechnology, 28(7), 2541-2550.
  • Lesueur, D., Atieno, M., Mathu, S., & Herrmann, L. (2012). Importance of rhizobia in Agriculture: potential of the commercial inoculants and native strains for improving legume yields in different land-use systems. Paper presented at the EGU General Assembly Conference Abstracts.
  • Herrmann, L., Atieno, M., Brau, L., Lesueur, D. (2014). Microbial quality of commercial inoculants to increase BNF and nutrient use efficiency. In: de Bruijn, F.J. (ed) Molecular microbial ecology of the rhizosphere. (2014). Wiley-Blackwell, Hoboken.