Diversity and distribution of uncultured viruses.

摘要

Viruses, most of which are phages that infect bacteria, are the most abundant biological entities on the planet. Viruses play important roles in horizontal gene transfer, global carbon and nutrient cycles, and regulating the growth and structure of microbial communities. However, very little is known about the diversity or biogeography of environmental viruses. This is mainly due to characteristics of viruses that cause metholodogical limitations, such as their small size, the requirement of a host for growth, and the lack of a single genetic element conserved in all viral genomes. Culture-independent approaches such as amplification of conserved genes and metagenomics overcome these limitations, allowing insight into the composition, diversity, and structure of environmental viral communities. This thesis describes the first application of metagenomic sequencing to examine environmental viral communities, including the viruses present in seawater (Chapter 2), marine sediment (Chapter 3), human feces (Chapter 4), and human blood (Chapter 5). The data from these metagenomic approaches indicated that environmental viruses are mostly novel and extremely diverse. To obtain a more detailed understanding of global viral biogeography, amplification and sequencing of the DNA polymerase gene was used to study the diversity of T7-like Podophages in the environment (Chapter 6). This study demonstrated the presence of identical viral genes in different environments, suggesting that there is a common genomic pool for environmental viruses. Taken together, the studies of environmental viral diversity presented in this thesis suggest that viral diversity is extremely high on a local scale but relatively limited globally.