The carbamido diacetyl reaction: a test for citrulline

Dialysis culture of T-strain mycoplasmas

Using dialyzing cultures of T-strain mycoplasmas, it was possible to make some observations relevant to the growth and metabolism of these organisms which would not be possible in nondialyzing cultures due to growth inhibition of the organisms by elevated pH and increased ammonium ion concentration in media containing urea. The rate of ammonia accumulation was found to be related to the initial urea concentration in the medium and could not be accounted for by any change in the multiplication rate of the organisms. More ammonia was generated than could be accounted for by the added urea alone, suggesting that an ammonia-producing activity other than urease may be present in T-strain mycoplasmas. Titers above 10(7) color change units per ml were achieved in dialysis cultures of a T-strain mycoplasma in the presence of urea, and such titers were maintained for approximately 60 h during dialysis culture in the absence of added urea.

Potamotrygon spp.: elasmobranchs with low urea content

All previously reported species of Chondrichthyes, from both marine and fresh water, have contained urea at concentrations ranging from about 300 to 1300 milligrams of urea nitrogen per 100 milliliters of fluid. Body fluids from two species of Potamotrygon, permanent residents of the Amazon basin, contained only 2 to 3 milligrams of urea nitrogen per 100 milliliters. Although they have abandoned the retention of urea exhibited by other chondrichthyans, the extent to which they have lost the mechanisms of retaining and tolerating urea in a hypertonic medium has not been determined.