Proteomic profiling of Rhizobium tropici PRF 81: identification of conserved and specific responses to heat stress.
BACKGROUND
Rhizobium tropici strain PRF 81 (= SEMIA 4080) has been used in commercial inoculants for application to common-bean crops in Brazil since 1998, due to its high efficiency in fixing nitrogen, competitiveness against indigenous rhizobial populations and capacity to adapt to stressful tropical conditions, representing a key alternative to application of N-fertilizers. The objective of our study was to obtain an overview of adaptive responses to heat stress of strain PRF 81, by analyzing differentially expressed proteins when the bacterium is grown at 28°C and 35°C.


RESULTS
Two-dimensional gel electrophoresis (2DE) revealed up-regulation of fifty-nine spots that were identified by MALDI-TOF/TOF-TOF. Differentially expressed proteins were associated with the functional COG categories of metabolism, cellular processes and signaling, information storage and processing. Among the up-regulated proteins, we found some related to conserved heat responses, such as molecular chaperones DnaK and GroEL, and other related proteins, such as translation factors EF-Tu, EF-G, EF-Ts and IF2. Interestingly, several oxidative stress-responsive proteins were also up-regulated, and these results reveal the diversity of adaptation mechanisms presented by this thermotolerant strain, suggesting a cross-talk between heat and oxidative stresses.


CONCLUSIONS
Our data provide valuable protein-expression information relevant to the ongoing genome sequencing of strain PRF 81, and contributes to our still-poor knowledge of the molecular determinants of the thermotolerance exhibited by R. tropici species.
Embrapa Soja, C.P. 231, 86001-970 Londrina, PR, Brazil.
Douglas Fabiano
DF
Gomes
Jesiane Stefânia da Silva
JS
Batista
Aline Luiza
AL
Schiavon
Diva Souza
DS
Andrade
Mariangela
M
Hungria
D001426:Bacterial Proteins / Q000032:analysis*; D015180:Electrophoresis, Gel, Two-Dimensional; D020543:Proteome / Q000032:analysis*; D040901:Proteomics; D042162:Rhizobium tropici / Q000737:chemistry* / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013312:Stress, Physiological; D013696:Temperature
D001426:Bacterial Proteins; D020543:Proteome