Thermophilic Viruses and Their Association with Thermophiles
Wakao Fukuda and Tadayuki Imanaka
from: Thermophilic Microorganisms (Edited by: Fu-Li Li). Caister Academic Press, U.K. (2015) Pages: 237-250.
Viruses are small infectious particles containing own genome which consists of either DNA or RNA. Until now, a lot of viruses, which can infect organisms in the three domains, Eukaryote, Bacteria and Archaea, have been found from all over the world. Among them, a few percent of these known viruses can infect thermophilic archaea and bacteria. Viruses of thermophiles are classified into over ten families and virus particles (virions) of them show wide variety of shapes and size. Some viruses are lytic, but the other nonlytic. The wide diversity of virions from thermophiles is interesting to get new insights of the viral world. Viruses are commonly known as the cause of serious disease. In response, adaptive immune systems, named CRISPR (clustered regularly interspaced short palindromic repeat sequences) system, protect most of archaea from infections of extrachromosomal elements (ECEs). On the other hand, viruses can contribute to the evolutions of lives. The ECEs can transfer beneficial genes for adaptation to environment from one organism to another. Intriguingly, the regions formed by integration of viruses (provirus regions) also have been observed in some genomes of extremophiles, but some of these provirus regions lost the ability for virion-formation. The archaeal strains lacking virus-like region have shown growth defects, indicating that virus-like regions help cell growth in the certain conditions. Although virus infected to ancestor in ancient days might include virulence, virus-like regions seem to contribute to adaptation in certain environment at the present day read more ...