Bacteriophages (phages) are ubiquitous and the most abundant biological entities on earth, while the genetic information on the environmental diversity and community composition of phages are limited, particularly in soils. Because of the study of genetic diversity of phages in natural environments has been proven to be difficult since no universal gene analogous to ribosomal RNA gene used to study microbial communities exists throughout all phage families. However, recent development in phage genomics showed that some family-specific genes are present and useful for evaluation phage diversity. Among them, g23, which encodes for the major capsid protein, is commonly used as a reliable biomarker for analysis of T4-type phages in natural environments.