Studies Relating the Fluorescence of CaDPA and DPA to the Fluorescence of Bacillus Spores

摘要

Dipicolinic acid (DPA), mostly in the form of Calcium-DPA is a major constituent of bacterial endospores, a non-metabolizing long-term survival form of Bacillus and Clostridium bacterial species. The contribution of this chemical to the autofluorescence or luminescence of these spore is examined primarily by comparing excitation-emission (Ex-Em) graphs taken from a normal strain (DPA+) of Bacillus subtilis spores and from spores of a mutant strain (DPA-) derived from the same DPA + strain. Ex-Em graphs of the pure chemicals CaDPA, DPA and tryptophan are shown to correspond to particular features of these graphs for the spores. When the spores are wet or are in a water suspension, much less influence of the DPA is evident than when they are dry. By comparing the Ex-Em graphs for luminescence from the DPA+spores when they are dry, with these graphs for chemical DPA or CaDPA, regions of the tow dimensional graph are found which corresponds to the fluorescence spectrum of dry CaDPA and also of DPA suggesting that not all the DPA is complexed with Calcium. The same regions become more prominent when the spores are UV irradiated when dry and much more prominent when the spores are UV irradiated in solution. Another experiment shows much more influence of CaDPA when spores are grown in rich medium as compared with spores grown in minimal sporulating medium.