BACKGROUND

Adenosine 5'-triphosphate (ATP) plays both a central role as an intracellular energy source, and a crucial extracellular signaling role in diverse physiological processes of animals and plants. However, there are less reports concerning the signaling role of microbial extracellular ATP (eATP). Hypocrellins are effective anticancer photodynamic therapy (PDT) agents from bambusicolous Shiraia fungi. The co-culture of Shiraia sp. S9 and a bacterium Pseudomonas fulva SB1 isolated from Shiraia fruiting bodies was established for enhanced hypocrellin A (HA) production. The signaling roles of eATP to mediate hypocrellin biosynthesis were investigated in the co-culture.

RESULTS

The co-culture induced release of eATP at 378 nM to the medium around 4 h. The eATP release was interdependent on cytosolic Ca concentration and reactive oxygen species (ROS) production, respectively. The eATP production could be suppressed by the Ca chelator EGTA or abolished by the channel blocker La, ROS scavenger vitamin C and NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI). The bacterium-induced HO production was strongly inhibited by reactive blue (RB), a specific inhibitor of membrane purinoceptors, but dependent on the induced Ca influx in the co-culture. On the other hand, the application of exogenous ATP (exATP) at 10-300 µM to Shiraia cultures also promoted fungal conidiation and HA production, both of which were blocked effectively by the purinoceptor inhibitors pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid (PPADS) and RB, and ATP hydrolase apyrase. Both the induced expression of HA biosynthetic genes and HA accumulation were inhibited significantly under the blocking of the eATP or Ca signaling, and the scavenge of ROS in the co-culture.

CONCLUSIONS

Our results indicate that eATP release is an early event during the intimate bacterial-fungal interaction and eATP plays a signaling role in the bacterial elicitation on fungal metabolites. Ca and ROS are closely linked for activation of the induced ATP release and its signal transduction. This is the first report on eATP production in the fungal-bacterial co-culture and its involvement in the induced biosynthesis of fungal metabolites.