1. Viruses The Interface Between Living and Nonliving

2. Viruses: Acellular Infectious Agents All viruses are obligate intracellular parasites: specific hosts Carry out no metabolic functions Replication inside a host cell only Very small colloidal particles: 25-350 nm

3. Virus Structure Nucleic acid –May be either DNA or RNA –May be either single or double stranded Capsid –Outer protein coat surrounding nucleic acid –Composed of individual capsomeres Envelope –Only in some animal viruses (budding viruses) –Derived from host cell

4. Examples of Virus Structure

5. Tobacco Mosaic Virus

6. Pox Virus

7. Polio Virus

8. Phi X174

9. Structure of Bacteriophages

10. Viral Replication Lytic –Viral nucleic acid enters host –Takes over host cell metabolic machinery –Synthesis of new viral components –Assembly –Release of new viral particles Lysogenic –Viral nucleic acid enters host –Viral NA incorporates into host genome –Induction causes viral replication and initiates lytic replication

12. Viruses in Water and Wastewater

13. Detection/Enumeration Methods Plaque/Pock Assay –Inoculate viral suspension into susceptible host and count areas of cell death Direct counts via EM Detection of viral nucleic acid: PCR

14. Plaque Assay

15. PCR Polymerase chain reaction Amplification of a specific sequence of DNA Taq polymerase

16. Viruses in Water and Wastewater Over 140 types of enteric viruses may be found in fecally contaminated water –Hepatitis –Rotavirus –Norwalk type agent –Poliovirus –Coxsackievirus –Echovirus –Adenoviruses –Astroviruses –Caliciviruses

17. Transport of Viruses in the Subsurface

18. Treatment: Viruses