Abstract
The family Mimiviridae, comprised by giant DNA viruses, has been increasingly studied since the isolation of the Acanthamoeba polyphaga mimivirus (APMV), in 2003. In this work, we describe the genome analysis of two new mimiviruses, each isolated from a distinct Brazilian environment. Furthermore, for the first time, we are reporting the genomic characterization of mimiviruses of group C in Brazil (Br-mimiC), where a predominance of mimiviruses from group A has been previously reported. The genomes of the Br-mimiC isolates Mimivirus gilmour (MVGM) and Mimivirus golden (MVGD) are composed of double-stranded DNA molecules of ∼1.2 Mb, each encoding more than 1,100 open reading frames. Genome functional annotations highlighted the presence of mimivirus group C hallmark genes, such as the set of seven aminoacyl-tRNA synthetases. However, the set of tRNA encoded by the Br-mimiC was distinct from those of other group C mimiviruses. Differences could also be observed in a genome synteny analysis, which demonstrated the presence of inversions and loci translocations at both extremities of Br-mimiC genomes. Both phylogenetic and phyletic analyses corroborate previous results, undoubtedly grouping the new Brazilian isolates into mimivirus group C. Finally, an updated pan-genome analysis of genus Mimivirus was performed including all new genomes available until the present moment. This last analysis showed a slight increase in the number of clusters of orthologous groups of proteins among mimiviruses of group A, with a larger increase after addition of sequences from mimiviruses of groups B and C, as well as a plateau tendency after the inclusion of the last four mimiviruses of group C, including the Br-mimiC isolates. Future prospective studies will help us to understand the genetic diversity among mimiviruses.
Highlights
We report the molecular and phylogenetic analysis of two Brazilian mimiviruses from lineage C (Br-mimiC): (1) Mimivirus gilmour (MVGM) – isolated from water collected at Pampulha lagoon by Dornas et al (2015); (2) Mimivirus golden (MVGD) – isolated from golden mussels (Limnoperna fortunei) collected from Guaíba Lake, Rio Grande do Sul, Brazil, in July 2014
We identified 28 and 19 ORFans into MVGM and MVGD genomes, respectively
19 and 18 open reading frames (ORFs) without BLAST hit and smaller than 50 aa were not include in the subsequent analysis neither in the final annotation of MVGM and MVGD genomes, respectively
Summary
Researchers have been working on the biology and molecular characterization of other mimivirus relatives isolated from several human and environmental samples, the latter of which include cooling water tower, freshwater, saltwater, soil, leech, oyster, and other sources collected in many countries in Oceania, Europe, Asia, Africa, and South America (La Scola et al, 2008; Fischer et al, 2010; Arslan et al, 2011; Yoosuf et al, 2012; Boughalmi et al, 2013a,b,c; Pagnier et al, 2013; Saadi et al, 2013a,b; Campos et al, 2014; Bajrai et al, 2016; Takemura et al, 2016) During those studies, notable sets of genes seemingly encoded by the genome of these new viruses were observed. All these astonishing discoveries could be the “tip of the iceberg” regarding mimivirus features, as ∼50% of the sequences of these viruses encode proteins that are hypothetical, i.e., without a defined function (La Scola et al, 2003; Raoult et al, 2004)
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