Marine Viruses 2016

The research effort, publication rate and scientific community within the field of marine viruses have been growing rapidly over the past decade and viruses are now known to play key roles in microbial population dynamics, diversity and evolution as well as biogeochemical cycling. The compilation of papers included in the current Special Issue highlights the exploration of eukaryotic and prokaryotic viruses, from discovery to complex interplays between virus and host and virus–host interactions with ecologically relevant environmental variables. The discovery of novel viruses and new mechanisms underlying virus distribution and diversity exemplify the fascinating world of marine viruses. The oceans greatly shape Earth’s climate, hold 1.37 billion km3 of seawater, produce half of the oxygen in the atmosphere, and are integral to all known life. In a time where life in the oceans is under increasing threat (global warming, pollution, economic use) it is pressing to understand how viruses affect host population dynamics, biodiversity, biogeochemical cycling and ecosystem efficiency

Isolation and characterisation of novel viruses infecting marine phytoplankton

Viruses are the most abundant biological agents in the global marine environment. Through cellular lysis viruses influence many biogeochemical and ecological processes, including energy and nutrient cycling, host distribution and abundance, algal bloom control and genetic transfer. Nano- and picophytoplankton are ubiquitous in the world’s oceans and are responsible for a high proportion of the annual global carbon fixation. However, relatively few viruses have been isolated and described that infect these key primary producers and little is known of their diversity, dynamics or propagation strategies. The aims of this study were to detect, isolate and characterise novel marine viruses that infect these important members of the phytoplankton assemblage. Screening of seawater samples for viruses that infect a broad representation of nano and picophytoplankton species was undertaken here. To enable this, a large culture collection of 106 phytoplankton species was established and used to screen seawater samples for viruses on a weekly basis over a two year period. A total of 12 novel viruses infecting the prasinophyte species’ Ostreococcus tauri and Micromonas pusilla were isolated from seawater sampled in coastal waters of the Western English Channel. Viruses were purified by plaque purification or liquid serial dilution techniques. Characterisation of novel virus isolates included growth kinetics, visualisation using transmission electron microscopy, host range analysis and estimates of viral genome sizes using pulsed field gel electrophoresis. Phylogenetic analysis of these viruses was conducted based on the sequence of the conserved DNA polymerase gene. Genome sequencing of two of the viruses infecting O. tauri was completed and revealed many exciting features, including a suite of genes hitherto unreported, or with rare occurrence, in viruses. Evidence is presented for horizontal gene transfer between viruses isolated in this study and their hosts, as well as between other eukaryotic and bacterial sources. Functional characterisation of the viral genomes sequenced and described in this study will provide clearer insights into viral dynamics and evolutionary history

Isolation and characterisation of novel viruses infecting marine phytoplankton

Viruses are the most abundant biological agents in the global marine environment. Through cellular lysis viruses influence many biogeochemical and ecological processes, including energy and nutrient cycling, host distribution and abundance, algal bloom control and genetic transfer. Nano- and picophytoplankton are ubiquitous in the world’s oceans and are responsible for a high proportion of the annual global carbon fixation. However, relatively few viruses have been isolated and described that infect these key primary producers and little is known of their diversity, dynamics or propagation strategies. The aims of this study were to detect, isolate and characterise novel marine viruses that infect these important members of the phytoplankton assemblage. Screening of seawater samples for viruses that infect a broad representation of nano and picophytoplankton species was undertaken here. To enable this, a large culture collection of 106 phytoplankton species was established and used to screen seawater samples for viruses on a weekly basis over a two year period. A total of 12 novel viruses infecting the prasinophyte species’ Ostreococcus tauri and Micromonas pusilla were isolated from seawater sampled in coastal waters of the Western English Channel. Viruses were purified by plaque purification or liquid serial dilution techniques. Characterisation of novel virus isolates included growth kinetics, visualisation using transmission electron microscopy, host range analysis and estimates of viral genome sizes using pulsed field gel electrophoresis. Phylogenetic analysis of these viruses was conducted based on the sequence of the conserved DNA polymerase gene. Genome sequencing of two of the viruses infecting O. tauri was completed and revealed many exciting features, including a suite of genes hitherto unreported, or with rare occurrence, in viruses. Evidence is presented for horizontal gene transfer between viruses isolated in this study and their hosts, as well as between other eukaryotic and bacterial sources. Functional characterisation of the viral genomes sequenced and described in this study will provide clearer insights into viral dynamics and evolutionary history.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Molecular genetic analysis of the zwf region of cyanobacterial genomes

The oxidative pentose phosphate (OPP) cycle is the main route of carbohydrate dissimilation in cyanobacteria in the dark. In heterocysts, the OPP is a supplier of reductant to nitrogenase, thus playing an important role in nitrogen fixation. Molecular genetic analysis of glucose-6-phosphate dehydrogenase (G6PDH) and the other components of the opp cycle have been focused on recently in an effort to understand the function and regulation of the cycle in vegetative cells and in heterocysts of cyanobacteria. This study presents data on nucleotide and amino acid sequences of three enzymes of the OPP cycle (glucose-6-phosphate dehydrogenase, transaldolase and fructose-l ,6-bisphosphatase) of the filamentous, heterocystous strain Anabaena sp. PCC7120. Mutagenesis studies on the transaldolase gene (tal) of Anabaena sp. PCC7120 and the opcA gene of the unicellular strain Synechococcus sp. PCC7942 are also reported. A 4,169 bp region around the zwf gene of Anabaena sp. PCC7120 was sequenced. Three genes are located in the region: fop, tal and zwf, which encode fructose-l,6-bisphosphatase (FBPase), transaldolase and glucose-6-phosphate dehydrogenase (G6PDH), respectively. The fop gene encodes a polypeptide of 349 amino acids. The product of the tal gene consists of 381 amino acids. The zwJ gene encodes a protein of 509 amino acids. Four cysteine residues are present in the enzyme. Two of these cysteines (Cys-187 and Cys-445) are absolutely conserved in cyanobacterial G6PDH. This result reinforces the likelihood of their role in the regulation of enzyme activity. Subclones carrying a range of zwf fragments of Anabaena sp. PCC7120 did not complement the zwJmutant Escherichia coli strain DF214. Western blot analysis showed that Anabaena sp. PCC7120 G6PDH did not express in E. coli DF214. Attempts aimed at production of a deletion/insertion zwf mutant of Anabaena sp. PCC7120 were not successful. The tal gene of Anabaena sp. PCC7120 was mutated to investigate growth and survival of the mutant cells in the presence and absence of combined nitrogen. Transaldolase activity in the tal mutant cells was similar to that in the wild-type cells. The growth rates of the tal mutant cells were not significantly different from that of the wild-type cells. These results imply that more than one copy of the tal gene is present in the Anabaena sp. PCC7120 genome. A gene, designated opcA, downstream from the zwf gene of Synechococcus sp. PCC7942 was mutated to investigate the possible effect of the gene on G6PDH activity. G6PDH activity in the mutant cells was reduced by 98.6%. Western blot analysis showed that the zwf was expressed in the opcA mutant cells, but the active form of the enzyme was a considerable reduced. All the results suggest that the opcA gene affects the assembly of G6PDH or enzyme activity, but possibly not expression of the zwf gene