QS is delayed in the absence of Hfq
To elucidate the relationship between Hfq and QS, we performed QS signal-production assays with wild-type, ∆hfq mutant, and ∆hfq complementation strains. QS signals were extracted in the mid/late log phase (OD600 = 0.9, 1.5 and 1.8) and developed on C18 reversed-phase TLC plates. QS signalling in the ∆hfq mutant (−) decreased significantly but recovered to the level of the wild-type after transforming with pCOK335 (+; pLAFR3::hfq ) (Fig. 7A, B). These results suggest that Hfq positively regulates QS signal production. We also examined whether the reduction in QS signal in the ∆hfq mutant was due to bacterial growth; our results showed that growth in ∆hfq was not retarded compared with the wild-type strain (data not shown). Using β-galactosidase activity assays, we found that expression of eanIdecreased significantly in the absence of Hfq (−) but recovered by transformation with pCOK335 (+; pLAFR3::hfq ) (Fig. 7C). This is consistent with the finding that QS signal production in the ∆hfqmutant was significantly lower (Fig. 7A, B). These results indicate that Hfq positively regulates QS, which is delayed in the absence of Hfq inP . ananatis .