* E. coli bacteria: This is its natural host, and it's where it replicates and infects.

* Environmental samples: You can find bacteriophage lambda in various environments, such as soil, water, and sewage.

* Laboratory settings: Researchers often use E. coli and bacteriophage lambda in their labs to study phage biology, gene expression, and genetic manipulation.

Essentially, bacteriophage lambda is a virus that lives in the environment and specifically infects E. coli.