From: Microbial diversity
![Cover of Coffee Break](/corehtml/pmc/pmcgifs/bookshelf/thumbs/th-coffeebrk-lrg.png)
Coffee Break: Tutorials for NCBI Tools [Internet].
Dean L, McEntyre J, editors.
Bethesda (MD): National Center for Biotechnology Information (US); 1999-.
NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.