What are the advantages of Bacillus species as expression hosts?

Bacillus species offer unique advantages for recombinant protein production. Benefits: excellent secretion capacity (up to grams per liter directly to medium), GRAS status (B. subtilis), no endotoxin issues (unlike E. coli), well-developed genetics and molecular tools, ability to produce and secrete active enzymes, and established industrial fermentation processes. Common hosts: B. subtilis (model organism), B. megaterium (high secretion), B. licheniformis (industrial enzyme production). Applications: industrial enzymes (proteases, amylases), food-grade proteins, and pharmaceutical intermediates. Challenges: proteases degrading secreted proteins (protease-deficient strains available), plasmid instability (integrative vectors preferred), and lower yields than intracellular E. coli expression for some proteins. Secretory production eliminates cell lysis and simplifies downstream processing.