Measurement of growth and iron deposition in Sphaerotilus discophorus

Aspects of the physiology of iron deposition of an iron-precipitating strain of Sphaerotilus were investigated in laboratory culture to characterize the process. Measurement of growth (incorporated L-[3H]alanine) and iron deposition (incorporated 59Fe) demonstrated that Sphaerotilus exhibit a characteristic temporal pattern of iron deposition, which is delayed until the latter portion of the exponential or the onset of the stationary growth phase. The growth rate (mu=0.17 h-1) was apparently independent of the iron concentration in the medium. There was, furthermore, no direct correlation between the iron concentration and final cell protein yield. It was concluded from experiments involving growth on artificial substrata (glass cover slips) that sessile populations derived no phsiological advantage (manifested as differences in growth rates) over free-living cells. There was no difference in the rate or onset of iron deposition of attached compared to suspended cells. Blocking of protein synthesis by the addition of chloramphenicol suggested that, once iron deposition was initiated, continued protein synthesis was not required for full expression of this capability. The results suggested that iron deposition may be possibly mediated by certain of the constituents of the organism's sheath.