Isolation and Characterization of a Novel Single-Stranded RNA Virus Infectious to a Marine Fungoid Protist, Schizochytrium sp. (Thraustochytriaceae, Labyrinthulea)

Abstract

Thraustochytrids are cosmopolitan osmoheterotrophic microorganisms that play important roles as decomposers, producers of polyunsaturated fatty acids, and pathogens of mollusks, especially in coastal ecosystems. SssRNAV, a novel single-stranded RNA (ssRNA) virus infecting the marine fungoid protist Schizochytrium sp. (Labyrinthulea, Thraustochytriaceae) was isolated from the coastal water of Kobe Harbor, Japan, in July 2000, and its basic characteristics were examined. The virus particle is icosahedral, lacks a tail, and is ca. 25 nm in diameter. SssRNAV formed crystalline arrays and random assemblies within the cytoplasm of host cells, and it was also concentrated along the intracellular membrane structures. By means of one-step growth experiments, the lytic cycle and the burst size were estimated to be <8 h and 5.8 ؋ 10 3 to 6.4 ؋ 10 4 infectious units per host cell, respectively. SssRNAV had a single molecule of ssRNA that was approximately 10.2 kb long, three major proteins (37, 34, and 32 kDa), and two minor proteins (80 and 18 kDa). Although SssRNAV was considered to have some similarities with invertebrate viruses belonging to the family Dicistroviridae based on its partial nucleotide sequence, further genomic analysis is required to determine the detailed classification and nomenclature of SssRNAV. Our results indicate that viral infection is one of the significant factors controlling the dynamics of thraustochytrids and provide new insights into understanding the ecology of these organisms.

Endogenously Synthesized (−)-proto-Quercitol and Glycine Betaine Are Principal Compatible Solutes ofSchizochytriumsp. Strain S8 (ATCC 20889) and Three New Isolates of Phylogenetically Related Thraustochytrids

“…Based on their 18S rRNA gene sequences, they belonged to thraustochytrid group 1, and they formed a tight cluster together with Schizochytrium sp. strain N1-27 (28,55) and Thraustochytriidae sp. strain FJN-10 (accession number AY773276) (Fig.…”

Isolation and Characterization of a Single-Stranded RNA Virus Infecting the Marine Planktonic Diatom Chaetoceros tenuissimus Meunier

“…The tree also suggests lower relatedness of the diatom-infecting ssRNA viruses with those infectious to the other marine stramenopile organisms: Schizochytrium single-stranded RNA virus, infecting a fungoid protist, Sicyoidochytrium minutum (previously reported as Schizochytrium sp.) (23), and HaRNAV, infecting a bloom-forming raphidophyte, H. akashiwo (7).…”

Isolation and Characterization of a Single-Stranded RNA Virus Infecting the Bloom-Forming Diatom Chaetoceros socialis

“…(formerly Schizochytrium sp.) (19) and Heterosigma akashiwo RNA virus (HaRNAV; Marnaviridae) infecting the bloom-forming raphidophyte H. akashiwo (7,8). The ssRNA diatom viruses are unlike other known viruses at the family level.…”