PhD defence by Amaru Miranda Djurhuus

Producing food efficiently is a global issue. Ultimately, lack of food at a global  level, results in millions going hungry every year. One reason for this, is that a large proportion of crops and produce is lost due to plant diseases. A significant proportion of these diseases are caused by bacteria, which can both destroy crops and rot produce after harvesting. While this has always been the case, we are still struggling to keep down diseases, often requiring us to fall back to simple solutions such as cultural practices in order to remove infected material or hinder the spread of disease, while chemical solutions which are more effective for large scale agriculture, such as antibiotics or heavy metals are unwanted due to their negative effects on human health and the environment. 

This lack of good treatments for bacterial diseases has brought back focus on a century-old technology, which in recent years has garnered the attention of researchers in the fight against antibiotic resistance (paper 9), bacteriophages. Bacteriophages (or phages) are viruses, which are obligate parasites of bacteria, infecting them to replicate their DNA and produce new viral particles. While phages are immensely ubiquitous, we have still not isolated many phages targeting important bacterial plant pathogens, and if we have, we often do not have a lot of information about their interactions. For this reason, phages were isolated, sequenced and characterized for some of the most prominent bacterial plant pathogens, such as bacteria belonging to the Pectobacteriaceae, Pseudomonas syringae and Erwinia amylovora (papers 1-5). The isolated phages were assessed both through bioinformatic characterization to classify them and understand their properties, as well as biological assays such as interactions with biofilm and effective host ranges or their ability to reduce disease. As phages might be important in a broader agricultural context, viral-bacterial interactions were also investigated in the phyllosphere (paper 6) and potential plant epiphytes (paper 7-8). 

Together, these studies have enriched our knowledge regarding phages of plant associated bacteria, which can contribute to current efforts to implement phages in a more sensible manner. Furthermore, this work has used cutting edge approaches such as the use of 3rd generation sequencing, which have simultaneously highlighted intriguing interactions between phages and bacteria, as well as identifying possible pitfalls when investigating viral samples.