Potatoes are cultivated in Southwest Greenland without the use of pesticides and with limited crop rotation. However, despite the fact that plant-pathogenic fungi are present in the Greenlandic potato soils, no severe disease outbreaks, such as late blight, have been observed. In this PhD project, a number of beneficial fungal-inhibiting bacteria were isolated from a Rhizoctonia solani suppressive potato soil in Inneruulalik, South Greenland. Especially one bacterium, Pseudomonas fluorescens In5, showed high antifungal activity against ascomycetes, basidiomycetes, and oomycetes, and it was able to protect tomato seedlings against R. solani infection. Various molecular and biochemical methods, such as PCR and sequence analysis, genome mining, gene knock-out, heterologous recombination, TLC and HPLC analyses were used in order to assess the antifungal mechanisms of P. fluorescens In5. In addition, the fairly new technology, Matrix Assisted Laser Desorption/Ionization-Time Of Flight Imaging Mass Spectrometry (MALDI-TOF IMS) combined with genome mining were conducted to detect, identify and characterize antifungal compounds produced by P. fluorescens In5. Novel bioactive compounds from P. fluorescens In5 were identified and their antifungal as well as anticancer potentials were elucidated. Furthermore, the effect of biotic and abiotic factors on bacterial communities in the Greenlandic potato soils was studied in addition to beneficial rhizobacteria and their production of bioactive compounds.