New documentation to an existing part
relA not only causes stringent reactions but also accumulates polyphosphoric acid.
ppGpp generated by relA is a competitive inhibitor of the polyP.
Method to release polyphosphate from bacteria
In the article, “A Simple Method to Release Polyphosphate from Activated Sludge for Phosphorus Reuse and Recycling”, authors Akio Kuroda et al. propose a new, simple method for releasing polyphosphate (polyP) and recovering P in a reusable form from activated sludge. The principle of the proposed method relies on their finding that polyP could be released from activated sludge by heating it at 70℃ for about 1 hour and then precipitated by the addition of CaCl₂ at room temperature without pH adjustment.
They found such things by following methods. First, they created sludge samples that were taken from the enhanced biological phosphorus removal(EBPR). Second, they incubated it at 50, 60, 70, 80, or 90℃. After 20 to 120 min of incubation, the heated samples were centrifuged for 5 min at 8000g, and the supernatants were subjected to chemical analysis. As a result, they observed that the polyP was released into the liquid phase when the sludge was heated at 70℃ for approximately 1 hour. (Fig.1) In contrast, DNA, which was rendered visible at 470 nm by DAPI, mostly remained inside the sludge flocs.
Although the mechanism underlying polyP release remains to be clarified, one possible explanation may be that the cell membrane of sludge microorganisms was partially disrupted by heating so that polyP could diffuse out of the cytoplasm. Also, they found that the rate and extent of polyP release were clearly dependent on the heating temperature. Moreover, they also found that the chain length of polyP gradually decreased because of polyP hydrolysis.
Additionally, they mention that the released polyP could be easily precipitated by the addition of CaCl₂ at room temperature without adjusting pH. The authors think that, in combination with EBPR, the present method has potential for the development of a simple process for recovering P in a reusable form from wastewater.