Viscardi, Sharon (2016) PRO-TECHNOLOGICAL BACTERIAL STRAINS FROM RENEWABLE RESOURCES FOR ECO-SUSTAINABLE APPLICATIONS. [Tesi di dottorato]

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In recent years the development of emerging countries, the rise in global demand, the growth of environmental consciousness, have destined research from one side to find alternative and renewable sources to produce biochemicals, and by the another side to reduce the use of fertilizers and synthetic pesticides. In this context, the following research project aims to isolate, characterize and select pro-technological bacterial strains, such as PGPB (Plant Growth Promoting Bacteria) used as biofertilizers and biocontrol agents in sustainable agriculture systems, and Succinic Acid Producing Bacteria, being succinic acid a very important intermediate for the production of polymers, and currently obtained by chemical hydrogenation of maleic anhydride derived from petroleum processes. The first part of this doctoral thesis shows the potential use of the isolated strain Azotobacter chroococcum 76A as biofertilizer in order to reduce mineral fertilization and to alleviate plant stress caused by salinity, a critical condition that could affect the 50% of arable European soils. One hundred six strains, previously isolated from soil, compost, lignocellulosic biomasses and food matrices were tested for their putative plant growth promotion activities. Between these strains, two strains of Azotobacter chroococcum were selected for their best PGP activities. They were found to be salt-tolerant since they were able to grow in liquid medium at increasing sodium chloride concentrations. Moreover they were evaluated for their ability to help plant development in abiotic stress conditions, and it was found that the selected strains tolerate aluminum, drought and salt stress in sterile conditions in vitro, and help plants to resist. In conclusion the selected strain 76A could be an interesting candidate to employ as bio-effector in sustainable agricultural systems also in stressful conditions leading to great economic and environmental benefits. The second part of this doctoral research project is about the isolation of Al-tolerant bacteria from rhizosphere and endosphere of ryegrass plants grown in Andisol soil as a potential inoculum to promote plant growth and alleviate the Al toxicity in pastures from southern Chile. A total of 5 strains belonging to Klebsiella sp. EC3, Stenotrophomona sp.EC5 from roots (endophytic) and Klebsiella sp., Serratia sp. and Enterobacter sp. were selected according their capacity to tolerate high Al concentration (10mM) and to present plant growth promoting traits as P solubilization, indol acetic acid (IAA), 1-aminocyclopropane-1-carboxylate deaminase (ACCd) and siderophore production. Our results showed that our inocula siderophore producers were able to bind Al+3 in Fe+3 deficient conditions. The efficiency of the consortia was confirmed in ryegrass plants, where bacteria were able to promote the growth and enhance the phosphatase activity in rhizospheric soils enriched with cattle dung. This major phosphatase activity was directly related with the P content in shoot of ryegrass. Our results permit suggest the bacteria strains in mixture with dung manure as a potential inocula to tolerate elevated Al concentration and promote the plant growth of pastures from acidic soils of Chile. The last part of the present doctoral thesis illustrates the isolation of succinic acid producing bacterial strains from samples of rumen and ruminal contents. The use of selective ad hoc substrates allowed to isolate 364 bacterial isolates. Identified by a polyphasic approach. We found some strains belonging to microbial species reported in the recent literature as producing considerable amounts of succinic acid but, also new species never tested for their specific biosynthetic capacity as in the case of Cosenzaea myxofaciens. Both have been tested and selected by the succinic acid production in different growth conditions. The optimization of the synthesis process of succinic acid was also conducted using pretreated and hydrolyzed lignocellulosic biomass. The strain Basfia succiniciproducens P-7P8 was the best producer reaching a concentration of succinic acid equal to 7.29 g / L with yields equal to 0.55, in line with the performance of the best biotechnological microbial strains used today for the synthesis of succinic acid to be used for the production of bioplastics.

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