Characterization of New Viruses from Hypersaline Environments

Abstract

Viruses of Archaea are the least studied group of viruses. Fewer than 50 archaeal viruses have been reported which constitutes less than one percent of all the isolated prokaryotic viruses. Only about one third of the isolated archaeal viruses infect halophiles. The diversity of haloviruses, virus ecology in highly saline environments and the interactions of haloviruses with their hosts have been little studied. The exiguous knowledge available on halophilic systems is not only due to inadequate sampling but also reflects the extra challenge highly saline systems set on biochemical studies.

In this study six new haloviruses were isolated and characterized. Viruses included four archaeal viruses and two bacteriophages. All of the other isolates exhibited head-tail morphology, except SH1 which was the first tailless icosahedral virus isolated from a high salt environment. Production and purification procedures were set up for all of these viruses and they were subjected to stability determinations.

Archaeal virus SH1 was studied in more detail. Biochemical studies revealed an internal membrane underneath the protein capsid and a linear dsDNA genome. The overall structure of SH1 resembles phages PRD1, PM2 and Bam35 as well as an archaeal virus STIV. SH1 possesses about 15 structural proteins that form complexes under non-reducing conditions. Quantitative dissociation provided information about the positions of these proteins in the virion. The life cycle of SH1 was also studied. This lytic virus infects Haloarcula hispanica. Adsorption to the host cells is fairly inefficient and the life cycle rather long.

Finally, virus responses in a variety of ionic conditions were studied. It was discovered that all of the studied viruses from low salt, marine and high salt environments tolerated larger range of salinities than their bacterial or archaeal hosts. The adsorption efficiency was not determined by the natural environment of a virus. Even though viruses with the slowest binding kinetics were among the haloviruses, fast binders were observed in viruses from all environments. When the salinity was altered, the virus adsorption responses were diverse. Four different behavioral patterns were observed: virus binding increased or decreased in increasing salinity, adsorption maximum was at a particular salt concentration or the salinity did not affect the binding. The way the virus binding was affected did not correlate with the environment, virus morphology or the organism the virus infects.

Solulliset eliöt jaetaan kolmeen domeeniin: eukaryootit, bakteerit ja arkit. Virukset infektoivat eliöitä näistä kaikista ryhmistä. Vähiten tutkittu virusryhmä on arkkeja infektoivat virukset. Alle 50 arkkivirusta on eristetty ja karakterisoitu, mikä on vähemmän kuin yksi prosentti tunnetuista bakteereita infektoivista viruksista. Korkean suolapitoisuuden virukset, halovirukset, ovat suurelta osin arkkiviruksia, ja eristetyistä arkkiviruksista näitä on noin kolmannes.

Väitöskirjatyössä eristettiin ja karakterisoittin kuusi halovirusta. Neljä näistä viruksista infektoi arkkeja ja kaksi bakteereita. Morfologialtaan ne olivat viruksia, joilla oli pää ja häntä, paitsi yksi joka oli ikosahdraalinen hännätön virus ja morfologialtaan uusi halovirusten joukossa. Tästä ikosahdraalisesta viruksesta tehtiin muita tarkempi karakterisaatio. Lisäksi väitöskirjatyössä tutkittiin myös laajemmin eristettyjen halovirusten ja muiden, sekä korkean että matalan suolan, virusten sopeutumista vaihtelevaan suolapitoisuuteen. Tämä tehtiin seuraamalla viruksen tarttumista isäntäsoluihin erilaisissa ioniolosuhteissa sekä tutkimalla viruksen suolankestävyyttä.