MICROBIAL DIVERSITY IN EXTREME ENVIRONMENTS: A RESOURCE FOR A SUSTAINABLE AGRICULTURE MANAGEMENT
Tesi di Dottorato
Data di Pubblicazione:
2012
Citazione:
MICROBIAL DIVERSITY IN EXTREME ENVIRONMENTS: A RESOURCE FOR A SUSTAINABLE AGRICULTURE MANAGEMENT / F. Mapelli ; tutor: S. Borin ; coordinatore: G. Zocchi. Universita' degli Studi di Milano, 2012 Feb 10. 24. ciclo, Anno Accademico 2011.
Abstract:
During the last decades many studies have been undertaken to investigate life in extreme environments, leading to the discovery of novel organisms and novel habitats previously though to be unapproachable for life. Microbes are key players in a number of ecological processes such as mineral dissolution, soil genesis, plant growth promotion (PGP) and bioremediation of polluted sites and they are the main responsibles for element cycles both in conventional and extreme ecosystems. The biotechnological potential of extremophiles is well recognized, and the aim of this PhD project was to give further insight on the possible exploitation of the microbiome naturally adapted to cope with extreme values of one or more environmental parameters to develop sustainable strategies in agriculture and ecosystem management with a particular focus on arid and saline lands.
Mineral-microbe interactions have been studied in detail, particularly regarding the importance of bioweathering bacteria in the ambit of soil fertility promotion in arid lands. Specific sites within the Midtre Lovénbreen glacier moraine (Svalbard, Norway), where pyritic rocks were present, hosted an active acidophilic iron-oxidizing bacterial community involved in the bioweathering of pyrite supplied by the rock disaggregation due to winter freezing. A decreased iron concentration and acidification were observed along the wheathered area departing form the pyrite-rich rock, where the oxidation of ferrous iron led to the accumulation of ferric oxy-hydroxides in the above soil. These ferric compounds were linked to the increase of soil physico-chemical properties that in turn determined a higher water holding capacity (WHC) and nutrient content in the surrounding vegetated area, densely colonized by mosses and small vascular plants. At the outer border of the vegetated area, the rest of the moraine hosted typical first colonizer bacteria, mainly belonging to the class Cyanobacteria, that are capable of nitrogen and carbon fixation. Thus, compared to the rest of the moraine, the enhancement of soil formation processes and plant colonization in the vegetated area was driven by the synergy between acidification and leaching activity of a chemolitotrophic community and the cyanobacteria-mediated primary productivity. A detailed description of the bacterial communities colonizing the weathered area, the vegetated area, and the barren moraine was obtained through the construction of 16S rRNA gene libraries. The statistical ∫-Libshuff analysis indicated these areas as three different ecological niches. The microbiome of the weathered area was dominated by few bacterial taxa due to the low pH value of the biological soil crust (BSC) whereas the vegetated area and the moraine displayed higher biodiversity. The most abundant phylogenetic groups in these BSCs were nevertheless different and in the case of the vegetated area they corresponded to those typical of mature and rhizospheric soils.
The ability of microorganisms to interact with minerals is an essential factor that influence plant nutrition by providing nutrients, such as phosphorous, that are generally present in the soils as insoluble forms. The capability to solubilize poorly bioavailable nutrients is one of the PGP activities that have been investigated in the microbiome associated to different plant species living in arid hypersaline soils in Central and South Tunisia (Olea europea and Salicornia spp.) or acid soils located in a volcanic area in Mexico. A large collection of bacterial isolates has been constituted, identified and characterized for the in vitro PGP potential.
Halophilic bacteria were isolated from the rhizosphere of Salicornia plants on oligotrophic media enriched with NaCl. The isolates obtained from 1
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
F. Mapelli
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