Comprehensive phenotypic characterization of newly isolated cold-adapted bacteria from Antarctic temporary meltwater ponds
Doctoral thesis
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https://hdl.handle.net/11250/3121689Utgivelsesdato
2024Metadata
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Sammendrag
Antarctic meltwater ponds are unique unexplored biotopes characterized by a high complexity of microbiota and affected by ever-changing ecological factors. Cold-adapted bacteria isolated from Antarctic meltwater ponds represent excellent model organisms to study climate change induced stress adaptation. Moreover, these bacteria may possess biotechnologically relevant properties and can be used for production of valuable chemicals.
The main aim of this PhD work was to perform comprehensive phenotypic characterization of newly isolated cold-adapted bacteria from unexplored sea-affected meltwater ponds in the Thala Hills Oasis (Enderby Land, East Antarctica). As a first step of the PhD work, physicochemical and biological analysis of water from the studied meltwater ponds as well as isolation and identification of bacteria, their physiological characterization and evaluation of their antibiotic susceptibility was performed in Paper I. It has been shown that the meltwater ponds have water with alkaline pH and can be characterized by a relatively high bacterial activity. In total of twenty-nine bacterial isolates were retrieved from the meltwater samples. By using 16S rRNA gene sequencing, the isolated bacteria were classified as Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes, belonging to 12 genera where Pseudomonas was the predominant genus. Many isolates were psychrotrophic, capable of producing pigments and extracellular enzymes, where lipases and proteases were prevalent. Antibiotic susceptibility testing revealed a presence of resistance to at least one antibiotic for most of the isolates and seven isolates showed multi-resistance.
Alterations in cellular lipids are considered as one of the adaptation strategies to harsh environmental conditions. Temperature is one of the most important factors inducing tremendous biochemical changes in bacterial cells. Temperature-induced changes of cellular lipids and other biomolecules in the isolated Antarctic meltwater bacteria were studied in Paper II. A distinct change in fatty acid profile for different Gram-groups, phyla, genera, and species was observed. Notably, most bacteria increased their lipid content when grown at lower temperatures. Fourier-transform infrared spectroscopy (FTIR) analysis highlighted temperature-triggered alterations in lipids, proteins and polysaccharides, where the most significant changes were observed in the polysaccharide region at 1200-900 cm-1, particularly for the peak at 1083 cm−1, related to phosphodiester groups mainly from phospholipids (for Gram-negative bacteria) and teichoic /lipoteichoic acids (for Gram-positive bacteria).
In order to further understand temperature-induced cellular biochemical responses in Antarctic meltwater bacteria, profiling of the total cellular biochemical profile of bacteria grown at different temperatures and in various forms of culture medium was performed in Paper III. The obtained results showed that overall variability of cell chemistry was lower when bacteria were cultivated on agar. The effect of temperature appeared to be specie-specific with the biggest alterations detected for the bacteria with a wide growth temperature range. Lipids were least affected while polysaccharides were the most affected by the temperature.
In Paper I it was observed that several of the newly isolated cold-adapted bacteria were pigmented. Therefore, in Paper IV pigment production was studied using FT-Raman spectroscopy and reference analytical techniques. High-throughput screening performed by FT-Raman indicated that from twenty-nine tested bacteria seven Antarctic meltwater bacteria were characterized by pigments production. Among pigments identified in the meltwater bacteria, several have industrial importance – such as β-carotene, canthaxanthin, lycopene, and zeaxanthin. A subset of the pigment producing meltwater bacteria was further studied to evaluate pigment production and biomass productivity under blue-light exposition. Due to that bacterial pigments have been suggested to be used in solar cells dyeing or dye-synthesized solar cells, a photostability of intact pigment bacterial biomass was investigated.
Overall, this PhD work provided comprehensive knowledge on the biochemical characterization and biotechnological potential of the Antarctic meltwater pound bacteria. It was shown that isolates from Antarctic MPs may have biotechnological potential and could be used as bioindicators to track antibiotic resistance spreading and the impact of human or animal presence in polar regions. This PhD work showed that Antarctic meltwater bacteria change their total biochemical profile in response to different temperatures and this change is species-specific. Several meltwater bacterial isolates showed to be promising producers of industrially relevant pigments. Finally, this PhD work showed remarkable effectiveness of high-throughput FTIR and FT-Raman spectroscopy for screenings, bioprospecting, and biochemical characterization of newly isolated bacteria. Antarktiske smeltevannsdammer er unike og uutforskede biotoper kjennetegnet av høy kompleksitet av mikrobiota og påvirket av stadig skiftende økologiske faktorer. Kaldtilpassede bakterier isolert fra Antarktis' smeltevannsdammer representerer utmerkede modellorganismer for å studere tilpasning til klimaendringer. Videre kan disse bakteriene inneha bioteknologisk relevante egenskaper og brukes til produksjon av verdifulle kjemikalier.