Different dilutions of stationary-phase JR32 and LpΔclpP cells were also spotted on the plates. In the presence

of sodium, exponential-phase cells exhibited indistinguishable AP26113 sodium sensitivity, irrespective of the genotype (Figure 5A). However, the LpΔclpP mutant displayed an approximately 300-fold higher resistance than JR32 in stationary phase (Figure 5A). The loss of sodium sensitivity as a result of clpP deletion was again reversed in LpΔclpP-pclpP (Figure 5A). The relationship between sodium resistance and clpP deletion was Doramapimod further confirmed by the plate-spotting assay (Figure 5B). Notably, while more resitant to sodium in both assays, LpΔclpP required two more days to form colonies on NaCl plates compared to JR32 (Figure 5; data not shown). Taken together, these results demonstrate that the deletion of clpP enhances the sodium resistance of L. pneumophila in stationary phase with a slower growth rate, implying a possible role of ClpP in virulence. MK-8931 Figure 5 Sodium tolerance of L. pneumophila Lp ΔclpP mutant was enhanced. (A). Overnight bacterial cultures in mid-exponential phase were inoculated into fresh medium and grew to exponential phase (OD600 from 1.0 to 1.5) or stationary phase (OD600 from 3.5 to 4.5), then the CFU was determined by plating duplicate samples of JR32

(black bars), LpΔclpP mutant (white bars), and complemented strain (gray bars) on BCYE and BCYE containing 100 mM NaCl. The experiment was carried out in triplicate.

* p < 0.01. (B). For direct visualization, different dilutions of stationary-phase JR32 and LpΔclpP cells were also spotted onto plates in triplicate. Loss of clpP impaires L. pneumophila growth and its cytotoxicity against A. castellanii To determine whether ClpP homologue may function in the virulence of L. pneumophila, we performed the amoebae plate test (APT) previously used to determine virulence [45]. The amoebae (A. castellanii) host cells were spread onto BCYE plates before stationary-phase L. pneumophila cells were spotted in 10-fold serial dilutions, and the plates were subsequently incubated at 37°C for 5 days. As shown in Figure 6A, WT JR32 and the complemented strain LpΔclpP-pclpP exhibited robust growth even at 10-8 dilution when co-incubated with amoebae. However, LpΔclpP showed a growth defect resembling ZD1839 research buy the phenotype observed in the negative control ΔdotA strain which was rendered completely avirulent by an in-frame deletion in the dotA gene [46]. As an additional control, cells were spotted onto the plates in the absence of amoebae, and no difference in growth was observed among the four strains (data not shown). Figure 6 The L. pneumophila clpP mutant was impaired in both cytotoxicity against amoebae A. castellanii and growth on amoebae plates. (A) Growth of L. pneumophila LpΔclpP mutant in the amoebae plate test was impaired. L.