chapter  24
40 Pages


Viruses are obligate genetic parasites that require the replication machinery of a cellular host in order to complete their own reproductive cycles. Outside of host cells, viruses exist as particles consisting of a nucleic acid genome surrounded by a protein coat, known as a capsid. Depending upon the specic virus, the genome may comprise DNA or RNA, which in turn may be double or single stranded. Viral capsids may be icosahedral, spherical, pleomorphic, lamentous, or rod shaped. Virus structure may also include additional features such as lipid envelopes, apical spikes, and tails (Figure 24.1). Soils provide an incredible range of niches housing a diverse

array of organisms, leading to a similarly diverse representation of viruses that parasitize these organisms. Soils have been shown to contain plant viruses (Fillhart et al., 1998; Delogu et al., 2003), insect viruses (Fuxa, 2004; Christian et  al., 2006), fungal viruses (Melzer and Bidochka, 1998), animal viruses (Duboise et al., 1979; Santamaria and Toranzos, 2003; Pourcher et al., 2007), and bacterial viruses (also known as bacteriophages or simply “phages”) (Yin et al., 1997; Ashelford et al., 1999a, 2000, 2003; Keel et al., 2002; Williamson et al., 2003, 2005, 2007).