Advisor

Kenneth Stedman

Date of Award

Winter 2-27-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Biology

Department

Biology

Physical Description

1 online resource (vii, 139 pages)

Subjects

Silica, Viruses -- Dispersal, Bacteriophage T4 -- Dispersal, Paleoecology

DOI

10.15760/etd.2191

Abstract

Silicification of organisms in silica-depositing environments can impact both their ecology and their presence in the fossil record. Although microbes have been silicified under laboratory and environmental conditions, viruses had not been, prior to this work. Bacteriophage T4 was successfully silicified under laboratory conditions that closely simulated those found in silica-depositing hot springs. Virus morphology was maintained during the short period of silicification (48 hours), and a clear elemental signature of silicon and phosphorus was detected by energy-dispersive X-ray spectrophotometry (EDX). However, the EDX signature of silicified virus was not sufficiently distinct from that of cell membrane or phosphate minerals for that technique to be used to discover viral remains in hot spring mineral deposits.

Having shown that bacteriophage T4 can be silicified, it was then determined that the impact of silica exposure on infectivity varied widely between different viruses. The effect on infectivity did not appear to be related to virus size or morphology. In addition, the impact on infectivity was at least partially reversible, indicating that it was caused, at least in part, by occluding infection-related structures on the virus, rather than destruction or denaturation of the virus.

Those viruses which showed a decline in infectivity with silica exposure also showed increased resistance to desiccation after being exposed to silica, which has implication for long-range virus dispersal. The desiccation resistance was proportional to the degree that silicification reduced infectivity in that virus. Desiccation resistance also declined with prolonged exposure to drying, suggesting that the mechanism was due to the silica coating helping to retain water rather than replacing the hydrogen bonding of water.

Virus dispersal is critical for both the spread of disease and the diverse roles that viruses play in Earth ecology. However, the mechanisms of host-independent virus dispersal are poorly understood and hotly debated. These experiments showed that, under mild conditions, diverse viruses can be coated in silica and that silica coating provides some, if not most, viruses with remarkable desiccation tolerance. Virus silicification thus provides a potential mechanism for global dispersal of viruses that could not otherwise tolerate the desiccation of wind-borne transportation.

Persistent Identifier

http://archives.pdx.edu/ds/psu/14571

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