Differential nucleoside recognition during Bacillus cereus 569 (ATCC 10876) spore germinationw

We have tested a series of inosine analogs for their effect on germinating B. cereus 569 spores. Our results showed that although inosine (hypoxanthine nucleoside) causes spore germination by itself, the kinetic pathway exhibited complex and strongly cooperative character. Contrary to inosine’s germinating effect, the purine pathway degradation products xanthine, xanthosine, uric acid, hypoxanthine, ribose, or ribose plus hypoxanthine failed to activate spore germination. Furthermore, even small modifications of inosine’s nucleobase or sugar moieties have deleterious effects on germination efficiency. In contrast to previous work with the B. cereus 3711 strain, incubation of B. cereus 569 spores with adenosine (6-aminopurine riboside) did not trigger germination, but prevented inosine-mediated germination. The inhibitory effect was lost if adenosine was substituted with adenine alone, or ribose plus adenine. Although adenosine is able to block inosine-mediated germination, it acts as a co-germinant in the presence of alanine. Nucleosides that have substitutions in the purine base are not able to trigger germination by themselves, but can act as co-germinants in the presence of sub-germinant concentrations of alanine. In contrast, modifications of the sugar moiety precluded germination activity under all conditions tested. The data suggests that only inosine can activate germination by itself. However, when alanine is present as a co-germinant, different germination receptors are activated that recognize a larger subset of nucleoside structures.