For long-term use, the smartest financial move is renting or buying a used 15th edition (which covers 95% of the material) and supplementing with OpenStax for the newer topics (virology, microbiome).
Before hunting for a free copy, ask yourself: Many professors still use the 15th or even 14th edition. Here’s what changed: Brock Biology Of Microorganisms 16th Edition -FREE-
Evolution, Cell Structure & Function, Metabolic Pathways, Information Flow & Genetics, Microbial Systems, Impact of Microorganisms Foundation & Diversity: For long-term use, the smartest financial move is
If you are a student with zero budget right now, follow this safe protocol: For long-term use
Check your school's library portal for an "eText" or "Online Resource" link. Many libraries license the e-book version from providers like VitalSource or directly through the publisher.