Proteomic Analysis of Rhizobium favelukesii LPU83 in Response to Acid Stress

Acid soils constitute a severe problem
for leguminous crops mainly
through a disturbance in rhizobium–legume interactions. Rhizobium favelukesiian acid-tolerant rhizobium
able to nodulate alfalfais highly competitive for nodule occupation
under acid conditions but inefficient for biologic nitrogen fixation.
In this work, we obtained a general description of the acid-stress
response of R. favelukesii LPU83 by
means of proteomics by comparing the total proteome profiles in the
presence or absence of acid stress by nanoflow ultrahigh-performance
liquid chromatography coupled to mass spectrometry. Thus, a total
of 336 proteins were identified with a significant differential expression,
136 of which species were significantly overexpressed and 200 underexpressed
in acidity. An in silico functional characterization with those respective
proteins revealed a complex and pleiotropic response by these rhizobia
involving components of oxidative phosphorylation, glutamate metabolism,
and peptidoglycan biosynthesis, among other pathways. Furthermore,
a lower permeability was evidenced in the acid-stressed cells along
with several overexpressed proteins related to γ-aminobutyric
acid metabolism, such as the gene product of livK, which gene was mutated. This mutant exhibited an acid-sensitive
phenotype in agreement with the proteomics results. We conclude that
both the γ-aminobutyric acid metabolism and a modified cellular
envelope could be relevant to acid tolerance in R.
favelukesii.