| dc.description.abstract | Selenium (Se) is an essential micronutrient for humans with antioxidant properties.
Selenium deficiency in the human diet affected around 15% of world population
increasing the probability of ocurrence of diverse disease such as cancer, thyroid
dysfunction and the reduction of immune functions among others. In Chile, cereal crops
production (wheat, oat and barley) is one of the most important sources of nutrition for
the population. This crop frequently has suboptimal levels of Se due to diverse factors
associated with plant species, soil type, fertilization and the nature of selenium
compounds available. In this context, the rhizosphere harbors a wide variety of bacterial
species which play important role in the biogeochemical cycle of nutrients and
micronutrients such as Se. Microbiological transformations of Se (methylation,
oxidation, and reduction) have been suggested as biotechnological tools for
bioremediation of Se-contaminated soils. However, there are not studies focused to the
potential application of Se-utilizing bacteria in agriculture to increase the content of Se
available in the rhizosphere. For this reason, the general aim of this Doctoral thesis was
to study the bioaccumulation of Se by native bacteria present in the rhizosphere of
cereals grown in Chilean acid soils (Andisols), in order to develop a biotechnological
tool for Se-biofortification of wheat. Firstly, we present a general vision of the
problematic of Se in human health and plant by a critical review of worldwide research
in Chapter II . From a biofortification perspective, we described that Se-accumulating
rhizobacteria can be used for Se enrich plants. In this context, the Chapter III shown
the occurrence of Se tolerant bacteria in the rhizosphere and its contributions to enhance
Se content in plants. The results described that selenobacteria selected; belong to the
genera Stenotrophomonas, Bacillus, Enterobacter and Pseudomonas, similar genera to
the ones previously reported in seleniferous soils. The Selenobacteria have a great
ability to tolerate and accumulate Se intra- and extracellular in micro- and nanospherical
Se0
deposits. Furthermore, effectively the inoculation of wheat plantlets with
selenobacteria inocula showed increased Se content in plant tissues. In addition, the
results here obtained suggest that selenobacteria inocula can be used as a biotechnological tool for Se biofortification in plant. In fact, the effectiveness to
enhance Se content in grain by the co-inoculation of selenobacteria strains and
mycorrhizal arbuscular fungus (Glomus claroideum) demonstrated a great potential of
these rhizosphere microorganisms for biofortification of wheat and derivates foods (i.e.
Se enriched flour). This microbial association enhanced the Se content of grains in
23.5% compared with non-mycorrizal plants, associated with a higher biodiversity on
the rhizosphere (Chapter IV). Thus, our results showed that Se biosynthesized by
selenobacteria can be translocated inside the plants toward the grain. This results
support the hypothesis that selenobacteria have a great potential for Se-biofortification
of cereals (Chapter V).
In summary, Se-biofertilizer based on selenobacteria isolated from volcanic soils
are more effective than Se inorganic source for uptake and translocation in wheat plants
and representing a promising strategy for Se biofortification to be used at large-scale for
intensive cereal crops. | |
