Project description:Cyanophages infecting the marine cyanobacteria Prochlorococcus and Synechococcus encode and express genes for the photosynthetic light reactions. Sequenced cyanophage genomes lack Calvin cycle genes, however, suggesting that photosynthetic energy harvested via phage proteins is not used for carbon fixation. We report here that cyanophages carry and express a Calvin cycle inhibitor, CP12, whose host homologue directs carbon flux from the Calvin cycle to the pentose phosphate pathway (PPP). Phage CP12 was coexpressed with phage genes involved in the light reactions, deoxynucleotide biosynthesis, and the PPP, including a transaldolase gene that is the most prevalent PPP gene in cyanophages. Phage transaldolase was purified to homogeneity from several strains and shown to be functional in vitro, suggesting that it might facilitate increased flux through this key reaction in the host PPP, augmenting production of NADPH and ribose 5-phosphate. Kinetic measurements of phage and host transaldolases revealed that the phage enzymes have k(cat)/K(m) values only approximately one third of the corresponding host enzymes. The lower efficiency of phage transaldolase may be a tradeoff for other selective advantages such as reduced gene size: we show that more than half of host-like cyanophage genes are significantly shorter than their host homologues. Consistent with decreased Calvin cycle activity and increased PPP and light reaction activity under infection, the host NADPH/NADP ratio increased two-fold in infected cells. We propose that phage-augmented NADPH production fuels deoxynucleotide biosynthesis for phage replication, and that the selection pressures molding phage genomes involve fitness advantages conferred through mobilization of host energy stores.
Project description:As significant drivers of cyanobacteria mortality, cyanophages have been known to regulate the population dynamics, metabolic activities, and community structure of this most important marine autotrophic picoplankton and, therefore, influence the global primary production and biogeochemical cycle in aquatic ecosystems. In the present study, a lytic Synechococcus phage, namely S-SZBM1, was isolated and identified. Cyanophage S-SZBM1 has a double-stranded DNA genome of 177,834 bp with a G+C content of 43.31% and contains a total of 218 predicted ORFs and six tRNA genes. Phylogenetic analysis and nucleotide-based intergenomic similarity suggested that cyanophage S-SZBM1 belongs to a new genus under the family Kyanoviridae. A variety of auxiliary metabolic genes (AMGs) that have been proved or speculated to relate to photosynthesis, carbon metabolism, nucleotide synthesis and metabolism, cell protection, and other cell metabolism were identified in cyanophage S-SZBM1 genome and may affect host processes during infection. In addition, 24 of 32 predicted structural proteins were identified by a high-throughput proteome analysis which were potentially involved in the assembly processes of virion. The genomic and proteomic analysis features of cyanophage S-SZBM1 offer a valuable insight into the interactions between cyanophages and their hosts during infection.
Project description:In the recent years, RNA silencing has been studied extensively to be a conserved regulatory process in plants. In the antiviral silencing, the intermediate double-stranded RNA form during the replication of RNA viruses were recognized and processed into abundant of overlapping viral siRNA (viRNAs). Accordingly, the cloned viRNAs could be conversely assembled into some contigs of viruses, which is recently exploited for identifying new viruses and their genome sequences.To obtain rapidly the complete genome sequence of BYSMV, we carried out deep sequencing of small RNAs from healthy and BYSMV infected wheat, respectively. Thirteen contigs were assembled from the overlapping viRNAs only present in the infected wheat but not in the healthy wheat. The results of BLAST showed that ten contigs shared about 96% identity with the reported L gene of BYSMV isolate Zanjan-1. Viral assembly from the BYSMV infected wheat plants to obtain the full lengh genome and characterise the viral siRNAs
Project description:Auxiliary metabolic genes (AMG) are commonly found in the genomes of phages that infect cyanobacteria and increase the fitness of the cyanophage. AMGs are often homologs of host genes, and also typically related to photosynthesis. For example, the ΦcpeT gene in the cyanophage P-HM1 encodes a putative phycobiliprotein lyase related to cyanobacterial T-type lyases, which facilitate attachment of linear tetrapyrrole chromophores to Cys-155 of phycobiliprotein β-subunits, suggesting that ΦCpeT may also help assemble light-harvesting phycobiliproteins during infection. To investigate this possibility, we structurally and biochemically characterized recombinant ΦCpeT. The solved crystal structure of ΦCpeT at 1.8-Å resolution revealed that the protein adopts a similar fold as the cyanobacterial T-type lyase CpcT from Nostoc sp. PCC7120 but overall is more compact and smaller. ΦCpeT specifically binds phycoerythrobilin (PEB) in vitro leading to a tight complex that can also be formed in Escherichia coli when it is co-expressed with genes encoding PEB biosynthesis (i.e. ho1 and pebS). The formed ΦCpeT·PEB complex was very stable as the chromophore was not lost during chromatography and displayed a strong red fluorescence with a fluorescence quantum yield of ΦF = 0.3. This complex was not directly able to transfer PEB to the host phycobiliprotein β-subunit. However, it could assist the host lyase CpeS in its function by providing a pool of readily available PEB, a feature that might be important for fast phycobiliprotein assembly during phage infection.
Project description:In the recent years, RNA silencing has been studied extensively to be a conserved regulatory process in plants. In the antiviral silencing, the intermediate double-stranded RNA form during the replication of RNA viruses were recognized and processed into abundant of overlapping viral siRNA (viRNAs). Accordingly, the cloned viRNAs could be conversely assembled into some contigs of viruses, which is recently exploited for identifying new viruses and their genome sequences.To obtain rapidly the complete genome sequence of BYSMV, we carried out deep sequencing of small RNAs from healthy and BYSMV infected wheat, respectively. Thirteen contigs were assembled from the overlapping viRNAs only present in the infected wheat but not in the healthy wheat. The results of BLAST showed that ten contigs shared about 96% identity with the reported L gene of BYSMV isolate Zanjan-1.