I have found an easy way of getting rid of fungal infections in cultures of
Chlamydomonas reinhardtii. It takes advantage of the fact that C.r. can grow
in the presence of methionine sulfoximine (MSX, a well known inhibitor of
glutamine synthase), provided arginine is added to the medium, while most
of our unwanted visitors cannot.
If a fungal infection appears on a plate and it seems difficult to pick a
clean Chlamy inoculum, streak on a TAP plate supplemented with MSX (100
microM) and arginine (100 mg/l). If possible, place in bright light for 3-4
days, streak back on your usual medium (or a fresh TARG/MSX plate if you
want to be extremely careful). This works fine even with heavily infected
cultures. It seems to work also with bacterial infections.
I have no definite explanation why arginine allows resistance to MSX. In its
absence, 50 microM MSX are enough to kill C.r. I suspect C.r. has a high
ability to use arginine as exclusive ammonium source, bypassing NH3 and the
need for glutamine synthase.
Good luck. Let me know of problems you may encounter, or improvements, or
explanations.
Olivier VALLON
