To better be able to study the biological role of RoxP, we deleted roxP from P. acnes KPA171202 through mutagenesis according to a recently described protocol29. The deletion of roxP was verified by PCR amplification and sequencing (data not shown). The successful deletion of roxP was further verified by comparing the secreted protein fraction of P. acnes KPA171202 (wildtype) and the mutant strain KPA171202ΔroxP by 2D gel electrophoresis. The prominent protein spot of RoxP in the 2D gel pattern of the secreted proteins of the wildtype strain was absent in the pattern of the ΔroxP-mutant strain (Supplementary Fig. 4).
Next, we investigated the ability of sterile filtered culture supernatants from wildtype and ΔroxP-mutant P. acnes to protect molecules from oxidation. As a proof of principle to study the antioxidant effect of RoxP, we measured the degradation of oxy-hemoglobin incubated with wildtype or ΔroxP-mutant strain-derived supernatants, respectively. Oxidation of hemoglobin results in the degradation thereof, as detected by a decrease of Abs410 nm, while putative antioxidant effects of the supernatant will stabilize hemoglobin and limit degradation. The addition of wildtype supernatant resulted in no visible degradation of hemoglobin over a 5 h time period (Fig. 4c). However, addition of the ΔroxP-mutant supernatant resulted in complete degradation of hemoglobin within 5 h (Fig. 4d), indicating a reduced ability of the ΔroxP-mutant strain to protect the molecule (hemoglobin) from oxidative stress.
RoxP facilitates P. acnes survival in oxic environments in vitro
Other bacterial antioxidant proteins have been suggested to be of importance for oxygen tolerance30. To investigate the importance of RoxP for P. acnes survival in an oxic environment, cultures were grown under anaerobic and aerobic conditions. The ΔroxP-mutant strain had a slightly faster growth curve as compared to the wildtype during anaerobic conditions (Fig. 5a, solid lines), but had a much slower growth during aerobic conditions (Fig. 5a, dashed lines). Likewise, wildtype P. acnes was able to survive in a normal air oxygen environment for an extended period of time, while the ΔroxP-mutant was sensitive to oxygen, with no live bacteria present after six days of incubation (Fig. 5b, solid lines). Addition of free RoxP (0.02 mg/ml) enhanced the initial survival of both the wildtype and the ΔroxP-mutant strains (27 ± 16%, and 20 ± 22%, respectively), but had no lasting effect (Fig. 5b, dashed lines). Though a trend, the increased initial survival upon RoxP supplementation was not statistically significant.
To better be able to study the biological role of RoxP, we deleted roxP from P. acnes KPA171202 through mutagenesis according to a recently described protocol29. The deletion of roxP was verified by PCR amplification and sequencing (data not shown). The successful deletion of roxP was further verified by comparing the secreted protein fraction of P. acnes KPA171202 (wildtype) and the mutant strain KPA171202ΔroxP by 2D gel electrophoresis. The prominent protein spot of RoxP in the 2D gel pattern of the secreted proteins of the wildtype strain was absent in the pattern of the ΔroxP-mutant strain (Supplementary Fig. 4).Next, we investigated the ability of sterile filtered culture supernatants from wildtype and ΔroxP-mutant P. acnes to protect molecules from oxidation. As a proof of principle to study the antioxidant effect of RoxP, we measured the degradation of oxy-hemoglobin incubated with wildtype or ΔroxP-mutant strain-derived supernatants, respectively. Oxidation of hemoglobin results in the degradation thereof, as detected by a decrease of Abs410 nm, while putative antioxidant effects of the supernatant will stabilize hemoglobin and limit degradation. The addition of wildtype supernatant resulted in no visible degradation of hemoglobin over a 5 h time period (Fig. 4c). However, addition of the ΔroxP-mutant supernatant resulted in complete degradation of hemoglobin within 5 h (Fig. 4d), indicating a reduced ability of the ΔroxP-mutant strain to protect the molecule (hemoglobin) from oxidative stress.
RoxP facilitates P. acnes survival in oxic environments in vitro
Other bacterial antioxidant proteins have been suggested to be of importance for oxygen tolerance30. To investigate the importance of RoxP for P. acnes survival in an oxic environment, cultures were grown under anaerobic and aerobic conditions. The ΔroxP-mutant strain had a slightly faster growth curve as compared to the wildtype during anaerobic conditions (Fig. 5a, solid lines), but had a much slower growth during aerobic conditions (Fig. 5a, dashed lines). Likewise, wildtype P. acnes was able to survive in a normal air oxygen environment for an extended period of time, while the ΔroxP-mutant was sensitive to oxygen, with no live bacteria present after six days of incubation (Fig. 5b, solid lines). Addition of free RoxP (0.02 mg/ml) enhanced the initial survival of both the wildtype and the ΔroxP-mutant strains (27 ± 16%, and 20 ± 22%, respectively), but had no lasting effect (Fig. 5b, dashed lines). Though a trend, the increased initial survival upon RoxP supplementation was not statistically significant.
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