This sounds familiar - I think I recall someone reporting Dicty blebbing off small membrane bound vesicles. It may be that what you are seeing isn't so much contamination but some kind of physiological peculiarity of sick Dicty cells. That is, instead of them killing Dicty, it's actually a symptom of the Dicty cells dying. 

> On Nov 8, 2013, at 9:32 AM, "Damer, Cynthia Kay" <[log in to unmask]> wrote:
> 
> Dear Colleagues,
> 
> My lab is currently experiencing a culture contamination problem that I have not experienced previously.  We are culturing Dicty in HL-5 supplemented with penicillin and streptomycin on plastic sterile culture dishes.  The contaminant appears to be very small (less than a micron) and spherical and is not able to move.  In addition, it is very slow growing.  However, as the contaminant becomes more numerous, the Dicty cells become rounded and eventually die.  Unfortunately, even when we thaw out strains in new media, the contaminate appears again.  We've also tried centrifuging and washing many times and greatly diluting the cultures.  This seems to get rid of most of it, but it eventually grows up again.
> 
> Any advice would be appreciated.
> 
> Thanks,
> 
> Cynthia
> 
> Cynthia K. Damer
> Professor
> Biology Department
> Brooks Hall Room 229
> Central Michigan University
> Mount Pleasant, MI 48859
> (989) 774-3455