In order to deal with various environmental conditions, most living organisms adapt and respond to environmental cues through nucleotide-based second-messenger signaling. Such signals regulate various endogenous factors required for environmental adaptation. In bacteria, there are five kinds of nucleotide-based second messengers, one of which is cyclic di-guanosine monophosphate (c-di-GMP). The molecule is known to regulate many cellular functions including growth, motility, biofilm formation, and virulence. Various environmental cues cause changes in the intracellular concentration of c-di-GMP, depending on the activity of specific c-di-GMP synthases and hydrolases in cells. In this review, we provide insights into nucleotide signaling in bacteria, emphasizing its impact on basic metabolism, its association with other signaling mechanisms, and its role in regulating the virulence of a wide range of bacteria. Moreover, we discuss recent studies suggesting a role for the implicated signaling molecules in bacterial persistence and antibiotic resistance.

Maturation of oocytes is maintained by complex procedures along with follicular genesis and is a critical step for embryonic development. Purine known as an oocyte maturation regulator is present in follicular fluid. In this study, the roles of guanosine as a strong inhibitor of GVBD and a modulator of cyclic GMP concentration in ooyctes were revealed. Denuded immature oocytes were treated with guanosine, and the maturation rates and cGMP concentration of oocytes were measured. GVBD was blocked in a concentration dependent manner by guanosine, but this effect was reversible. However, GVBD was lagged yet not significant by adenosine. Both guanosine and adenosine modified cGMP concentration in oocytes. The characteristic of the guanosine-treated oocyte was significantly higher cGMP compared with the adenosine-treated oocyes at initial time of the maturation. Based these results, guanosine may be a strong and reversible GVBD inhibitor. Although the precise mechanism of guanosine presently is unclear, the results suggest that guanosine may lead the accumulation of cGMP in oocyte cytoplasm, which in turn suppresses GVBD.