A microorganism that is a mutant bacterial strain of the species Actinosynnema pretiosum , designated PF4-4, (ATCC PTA-3921), being capable of producing maytansinoid ansamitocins such as ansamitocin P-3 in improved yield compared to previous known strains, and capable of growth under varied culture conditions, and methods of producing maytansinoid ansamitocins by culturing PF4-4 in a suitable growth medium.
1. A method of producing an enhanced Actinosynnema strain that produces an ansamitocin in an amount of between about 1.2-fold and about 10-fold more than the amount produced by a parental Actinosynnema strain from which the enhanced strain is derived, said method comprising:
(a) treating a bacterial culture of an Actinosynnema strain with a mutagen,
(b) growing the treated bacteria of (a) under selective pressure,
(c) selecting an isolate from the product of (b) that exhibits increased production of an ansamitocin compared with the culture used in (a), and
(d) optionally repeating (a), (b) and (c) until an isolate that produces between about 1.2-fold and about 10-fold more of an ansamitocin than the culture used in (a) is obtained.
2. The method of claim 1 , wherein said Actinosynnema strain is a strain of an Actinosynnema pretiosum.
3. The method of claim 1 , wherein the mutagen is UV light or 1-methyl-3-nitro-1-nitroso-guanidine.
4. The method of claim 1 , wherein the enhanced Actinosynnema strain produces an ansamitocin in an amount of between 1.2-fold and 10-fold more than the amount produced by the parental Actinosynnema strain.
5. The method of claim 1 , wherein the enhanced Actinosynnema strain produces an ansamitocin in an amount of between 1.8-fold and 10-fold more than the amount produced by the parental Actinosynnema strain.
6. The method of claim 1 , wherein the enhanced Actinosynnema strain produces an ansamitocin in an amount of between 5-fold and 10-fold more than the amount produced by the parental Actinosynnema strain.
7. The method of claim 1 , wherein the selective pressure comprises growth of the treated bacteria on CM4-1 media.