An early insight into the biology and virulence traits of the algal genus Prototheca

Shave, Christopher David (2024). An early insight into the biology and virulence traits of the algal genus Prototheca. University of Birmingham. Ph.D.

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Abstract

The aim of this thesis is to provide a deeper understanding of the basis of pathology in the genus Prototheca, an enigmatic group of pathogenic algae known to infect humans, cattle, and other mammalian hosts. These infections represent burdens on public health, as a result of chronic infection and inefficient treatment, and economic output, as a result of reduced milk production. The mechanisms that allow algae to infect mammalian hosts, and their interactions with mammalian immunity, are currently unknown.

Prototheca is also taxonomically complex, and pathogenic species are distantly related within the genus. Additionally, Prototheca is paraphyletic. The monophyletic clade containing all Prototheca species must also include at least the genera Auxenochlorella and Helicosporidium, forming the AHP lineage.

Much of the existing work on Prototheca is taxonomically restricted, covering a handful of species and largely ignoring the larger AHP lineage. This makes it difficult to meaningfully identify features important for the pathology of Prototheca species, or whether pathogenic AHP species share a common basis for pathology. Thus, this thesis takes a broader view, looking at the wider AHP lineage rather than one or two species. This thesis also considers multiple aspects of pathology, considering that pathology in Prototheca species may be accidental rather than as a result of specific adaptation to infection.

The methods and results of this thesis are varied. A method based on phenol DNA extraction was developed to detect Prototheca in milk, and was used to detect the first reported cases of bovine protothecosis from the UK. A method based on growth curves identified that ability to grow at 37°C separates known pathogenic AHP species from non- pathogenic AHP species. Exposure of AHP species to macrophages revealed that capacity for phagocytosis varies between the AHP species, without an obvious link to pathology. Genome sequencing produced complete organelle genomes for members of the AHP lineage and revealed that Prototheca have lost genes core to the Chlorophyta lineage. Finally, phylogenetics have clarified several relationships within the AHP lineage, revealing two major sub-lineages of the AHP lineage and up to seven boundaries for new genera.

This thesis provides a theoretical and experimental basis for future investigation, allowing for specific questions to be asked of the AHP lineage and more valid comparisons to be made within more closely related members of the lineage.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):