Right answer is (c) Increased levels of proteases
To explain: A primary concern has been that B. subtilis produces a large amount and variety of proteases. These proteases can degrade the product very rapidly. Mutants with greatly reduced protease activity have become available, but even these mutants may have sufficient amounts of minor proteases to be troublesome. B. subtilis is also much more difficult to manipulate genetically than E. coli because of a limited range of vectors and promoters.