Browsing by Subject "bacterial communities"

The above-ground surfaces of plants (the phyllosphere) are inhabited by a diverse variety of microbes that interact with the host plant affecting its health and growth. One of the predominant factors influencing the composition and formation of the phyllosphere microbial community is the species and genotype of the plant. In my thesis, I investigated whether three different Rubus species (R. arcticus, R. saxatilis, and R. chamaemorus) form similar phyllosphere microbial communities, and whether the genotype of the host plant has more impact on the community composition than the microbiota that the plants are exposed to. I also tested how different microbiota treatments would affect Rubus plant growth. The experiment was conducted with micropropagated plants of the three aforementioned Rubus species. The plants were treated with different microbiota collected from the leaves of wild plants of the three Rubus species and the growth of the plants was observed. The phyllosphere fungal and bacterial communities of the plants were sequenced from leaf samples and analyzed to inspect the overall diversity and difference of the communities (using Kruskal-Wallis test and PERMANOVA) and to identify possible core microbes within the Rubus species’ phyllosphere communities. I found that Rubus phyllosphere microbiota was dominated by bacteria classes Alphaproteobacteria and Gammaproteobacteria, and fungal classes Eurotiomycetes, Sordariomycetes, Agaricomycetes, and Dothideomycetes. The host plant genotype had more significance on the composition of phyllosphere microbiota than the origin of the microbiota. The different microbiota treatments had no significant effect on the plant leaf growth. My thesis shows how host plant genotype influences the shaping of the phyllosphere communities as well as how transferable the microbial communities are between species from the same genus. Understanding of the phyllosphere microbiota can have potential applications in the promotion of plant health and fitness.

The interactions between sediment chemistry and bacterial communities are multidirectional and complex. A hypoxia-driven decrease in dissolved oxygen (O2) leads to changes in sediment chemistry, bacterial community and ultimately alters their interactions. The sediment components very sensitive to changes in O2 are iron (Fe) and manganese (Mn) oxides. When O2 content decreases, they will be reduced by bacteria in order to obtain energy. This study was carried out with sediment samples collected from sites of different oxygen status in the Gulf of Finland. The focus was to unravel the interactions between sediment chemistry and bacterial communities by means of chemical extractions distinguishing between Fe and Mn pools of different solubility and, thus, bioavailability. For this purpose, a two-step chemical extraction was carried out in order to selectively quantify the easily reducible and more crystalline fractions of Fe and Mn oxides. The chemistry of phosphorus (P) is intrinsically linked to Fe and aluminum (Al) oxides but not to Mn oxides which are not able to retain P. Unlike Fe and Mn, Al is not a redox-sensitive element but its oxides are of importance in controlling the release of P from sediments by resorption of P. The extracts were analyzed for Fe, Mn, Al and P. Furthermore, a next generation high-input method was used to extract the DNA from the sediments. The results of the chemical extractions and taxonomical classification of the bacteria were statistically analyzed. Subsequently, the interactions between the easily-reducible fractions of Fe and Mn oxides and bacterial communities were established using correlations (correlation coefficient ≥ 0.7). The extractability of Fe and Mn increased in poorly-oxygenated and hypoxic conditions. Iron seemed to originate in the easily-reducible fraction, while Mn was in a less reactive form than Fe. As expected, the extractability of Al did not vary with changing oxygen status. In addition, the rather low extractability of P suggests a strong initial adsorption of P on Al oxides. In environment low in oxygen, P released from the Fe oxides was resorbed by Al oxides. We conclude that the major bacterial processes in the sediments are related to the reduction of sulfate and sulfur and decomposition of organic matter. The bacterial communities varied both vertically and horizontally. The vertical variation was mainly explained by the redox potential, while the horizontal variation was more complex and essentially related to easily-reducible Fe and total carbon and nitrogen in sediment. The correlations between the easily-reducible Fe and Mn and the bacterial communities revealed taxa that reduce Fe and/or Mn, some that oxidize metals, and others that could benefit from organic rich environments created by Fe, Mn and S-reducing bacteria. The correlations indicate causative relationships and indirect associations, which can provide leads for future research.