Characterization of Penaeus vannamei mitogenome focusing on genetic diversity.

The diversity of the Penaeus vannamei mitochondrial genome has still been poorly characterized, there are no validated mitochondrial markers available for populational studies, and the heteroplasmy has not yet been investigated in this species. In this study, metagenomic reads extracted from the muscle of a single individual were used to assemble the mitochondrial genome (mtDNA). These data associated with mitochondrial genomes previously described allowed to evaluate the inter-individual variability and heteroplasmy. Comparison among 45 mtDNA control regions led to the detection of conserved and variable segments and the characterization of two hypervariable regions. The analysis of diversity revealed mostly low frequency polymorphisms, and heteroplasmy was found in practically all mitochondrial genes, with a high occurrence of indels. These results indicate that the design of mitochondrial markers for P. vannamei must be done with caution. The mapping of conserved and variable regions and the characterization of heteroplasmy presented here will contribute to increasing the efficiency of mitochondrial markers for population or individual studies.

Direct sequencing of the white spot syndrome virus from Brazil: Genome assembly and new insights on phylogeny.

White spot syndrome virus (WSSV) has been the cause of great economic losses in world shrimp farming. In this work the genome of a Brazilian WSSV isolate was determined from direct sequencing of total DNA extracted from an infected whiteleg shrimp, and assembled based on a chimera template approach. Comparisons between WSSV-BR and other isolates revealed that the Brazilian virus has a relatively small genome, and is very similar to isolates from Thailand and Mexico. A phylogenetic relationship using different approaches has demonstrated that these isolates share a common evolutionary history. An analysis of conflicting phylogenetic signals also considering genomes of other isolates revealed that the evolutionary history of WSSV may be related to recombination events. We observed that these events can also be traced at some level by analyzing the homologous regions in the WSSV genome. The existence of recombination events introduces a new point of view that must be considered in the evolutionary history of WSSV.