You are given a set of culture plates: some show bacteria growing up to the edge of a mold colony, while others show a distinct inhibition zone around the mold. Which conclusion is best supported, and what follow-up would test whether the inhibitory effect is due to a secreted antibiotic?

• A. No conclusion can be drawn because only genetic differences between bacteria would explain variable growth; sequence the bacterial genomes on each plate first
• B. Plates with inhibition indicate bacterial competition for oxygen is preventing growth near mold; test by incubating plates in an oxygen-enriched chamber to determine if inhibition ceases
• C. Plates with inhibition suggest the mold secretes a substance that diffuses and inhibits bacteria; test by filtering mold broth to remove cells and apply sterile filtrate to bacterial lawns to see if inhibition persists
• D. Inhibition zones mean bacteria are being consumed by mold hyphae directly; test with electron microscopy to show fungal ingestion of bacterial cells in the zone

Answer: (C)