A Feldmannia Algal Virus Has Two Genome Size-Classes

Abstract

Persistent viruses occur intracellularly in brown algae, specifically the Ectocarpales, and as reported here in the genus Feldmannia. Feldmannia species are small (1 mm-several cm), filamentous forms with single-celled meiotic sporangia that normally produce haploid zoospores. In the isolate reported here, spores were not observed in the sporangia but rather numerous (approximately 10(6) per cell) polyhedral viruses are formed in their place. Two dsDNA genome classes of 158 and 178 kbp, with two restriction site variants of each, are described. The individual abundance of each genome in viral preparations is affected by culture temperature. A cosmid library was used to generate circular restriction enzyme (BamHi, Noti, and Psti) site maps.

Identification of Two Virus Integration Sites in the Brown Alga Feldmannia Chromosome

“…Cosmid DNA was isolated by alkaline lysis DNA minipreps (17). Restriction fragment order was determined by analysis of overlapping clones and by comparison to previously mapped virus clones (8).…”

“…Over 50 cosmids that hybridized with these viral probes were selected. Restriction fragment patterns for each clone were compared with virus DNA patterns on gels, and each viral insert was mapped against previously published maps prepared for FsV-158 and FsV-178 (8). Most of the inserts produced maps identical to those already known for purified virus.…”

“…In laboratory-grown algal isolates, viruses with two genome size-classes of 158 and 178 kbp are produced (designated FsV-158 and FsV-178), whose ratio is dependent on the temperature used to grow the host (8).…”

“…The two viral genomes with circular restriction maps are very similar but differ in the number of small, ϳ170-bp repeats (8,11). Both virus genomes are stable in the host after 7 years of monthly serial passage (8).…”

“…Both virus genomes are stable in the host after 7 years of monthly serial passage (8). Genes encoding DNA polymerase, protein kinases, integrases, transposases, and other enzymes have been identified in the FsV genome (9,12,13,15).…”