Signatures of genomic nucleotide metabolism and diel partitioning in an algal virocell

Viruses in marine systems are often a contributor to mortality and the reintroduction of particulate and dissolved organic matter into the microbial loop via the viral shunt. Viral activity can contribute on a large ecological scale, as population-wide viral infection has frequently been associated with the collapse of harmful algal blooms. Frequently the physiological and intracellular mechanisms driving full populations to collapse are not completely understood. The harmful algal bloom causing Aureococcus anophagefferens is a eukaryote that can detrimentally affect ecosystems through both light attenuation and the production of a hypothesized shellfish toxin. At the peak of bloom activity, it has been shown that many (~37%) cells are visibly infected with an icosahedral virus, now isolated and known as Kratosvirus quantuckense, or AaV. This work has continued the characterization of AaV in the context of infection in A. anophagefferens primarily through a focus on the virocell (i.e. infected host cell) and the metabolic shifts that occur during infection. To examine infection in the context of a diel cycle that may be observed in situ, physiological measurements were taken throughout the growth cycle of infected and uninfected A. anophagefferens. It was noted that A. anophagefferens swells in size through carbon fixation and reduces in size after dividing overnight. Likewise, it was noted that AaV infected cells continue to increase in size throughout the light cycle, but do not shrink again. To characterize the epigenetic modification on AaV and what function it may play in infection, the AaV genome was sequenced using Nanopore technology to establish a viral methylome. Nine unique motifs were identified as being targeted for methylation. To understand the shift in GC-usage between A. anophagefferens and AaV, open reading frames were analyzed for codon biases. Here it was found that AaV utilized a similar codon bias to that which was found in host organelle genes. Likewise, inhibition of deaminase activity with zebularine revealed a connection between deaminase activity and proper production of viral particles. Overall, this work has provided entry to novel avenues in research surrounding the metabolism of the AaV virocell.

Viruses in marine systems are often a contributor to mortality and the reintroduction of particulate and dissolved organic matter into the microbial loop via the viral shunt. Viral activity can contribute on a large ecological scale, as population-wide viral infection has frequently been associated with the collapse of harmful algal blooms. Frequently the physiological and intracellular mechanisms driving full populations to collapse are not completely understood. The harmful algal bloom causing Aureococcus anophagefferens is a eukaryote that can detrimentally affect ecosystems through both light attenuation and the production of a hypothesized shellfish toxin. At the peak of bloom activity, it has been shown that many (~37%) cells are visibly infected with an icosahedral virus, now isolated and known as Kratosvirus quantuckense, or AaV. This work has continued the characterization of AaV in the context of infection in A. anophagefferens primarily through a focus on the virocell (i.e. infected host cell) and the metabolic shifts that occur during infection. To examine infection in the context of a diel cycle that may be observed in situ, physiological measurements were taken throughout the growth cycle of infected and uninfected A. anophagefferens. It was noted that A. anophagefferens swells in size through carbon fixation and reduces in size after dividing overnight. Likewise, it was noted that AaV infected cells continue to increase in size throughout the light cycle, but do not shrink again. To characterize the epigenetic modification on AaV and what function it may play in infection, the AaV genome was sequenced using Nanopore technology to establish a viral methylome. Nine unique motifs were identified as being targeted for methylation. To understand the shift in GC-usage between A. anophagefferens and AaV, open reading frames were analyzed for codon biases. Here it was found that AaV utilized a similar codon bias to that which was found in host organelle genes. Likewise, inhibition of deaminase activity with zebularine revealed a connection between deaminase activity and proper production of viral particles. Overall, this work has provided entry to novel avenues in research surrounding the metabolism of the AaV virocell.