Growth, elemental composition, and formation of polyphosphate bodies in Vibrio natriegens cultures shifted from phosphate-limited to phosphate-pulsed media

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Abstract
Vibrio natriegens cultivated in a phosphate-limited chemostat at dilution rates of 0.32, 0.20, and 0.13 h−1 was given pulses of phosphate in an otherwise complete medium. Under the conditions used, complete depletion of phosphate occurred within 2–3 h and was followed by uptake of glucose and by cell division. For the most severely phosphate-limited cells (cultivated in the chemostat at dilution rate of 0.13 h−1), the elemental composition was determined by X-ray analysis at different times after adding phosphate. The amount of phosphorus per cell increased rapidly after the phosphate pulse but decreased when the cells started to divide after 2 h. An initial increase followed by a decrease was also found for chlorine, while the amount of sulphur remained constant before decreasing. Chlorine and calcium showed more complicated patterns. The pattern for magnesium, with a maximum after 45 min, may indicate a correlation between magnesium content and cell division. Multivariate analysis showed that cells differed significantly between sampling times. Addition of phosphate to the phosphate-starved culture also induced synthesis of polyphosphate bodies in the cells. Within 15 min an average of 3.8% of the cell volume consisted of polyphosphate bodies as shown by transmission electron microscopy. These bodies disappeared after an additional 30–60 min, indicating that polyphosphate is synthesized to facilitate phosphate uptake by minimizing the concentration gradient across the cell membrane.