Adaptive responses of outer membrane porin balance of Yersinia ruckeri under different incubation temperature, osmolarity, and oxygen availability

Abstract

The capability of Yersinia ruckeri to survive in the aquatic systems reflects its adaptation (most importantly through the alteration of membrane permeability) to the unfavorable environments. The nonspecific porins are a key factor contributing to the permeability. Here we studied the influence of the stimuli, such as temperature, osmolarity, and oxygen availability on regulation of Y. ruckeri porins. Using qRT-PCR and SDS-PAGE methods we found that major porins are tightly controlled by temperature. Hyperosmosis did not repress OmpF production. The limitation of oxygen availability led to decreased expression of both major porins and increased transcription of the minor porin OmpY. Regulation of the porin balance in Y. ruckeri, in spite of some similarities, diverges from that system in Escherichia coli. The changes in porin regulation can be adapted in Y. ruckeri in a species-specific manner determined by its aquatic habitats.

Keywords: Bacteria; environmental signal/stress responses; gene expression/regulation; outer membrane proteins; porins..

Figure 1

MALDI‐TOF mass spectrometry of proteins; 0.05 mg/mL BSA was used as a molecular weight marker.

Figure 2

Effect of cultivation temperature on porin expression. Histograms display relative expression levels, which are reported as fold change compared to average expression level of reference groups. Temperature of 26°C was used as a reference. Columns represent the mean of triplicate measurements in two independent experiments; error bars represent the standard deviations. Asterisks above bars indicate significant differences compared to the reference (P < 0.05). On the right side are located 12% SDS‐PAGE of porin samples. Gel was stained with Coomassie blue. Lines were rearranged according to conditions.

Figure 3

Effect of media osmolarity on porin expression. Histograms display relative expression levels, which are reported as fold change compared to average expression level of reference groups; 150 mmol/L NaCl condition was used as a reference. Columns represent the mean of triplicate measurements in two independent experiments; error bars represent the standard deviations. Asterisks above bars indicate significant differences compared to the reference (P < 0.05). On the right side are located 12% SDS‐PAGE of porin samples. Gel was stained with Coomassie blue. Lines were rearranged according to conditions.

Figure 4

Effect of oxygen availability on porin expression. Histograms display relative expression levels, which are reported as fold change compared to average expression level of reference groups. The aerobic condition was used as a reference. Columns represent the mean of triplicate measurements in two independent experiments; error bars represent the standard deviations. Asterisks above bars indicate significant differences compared to the reference (P < 0.05). On the right side are located 12% SDS‐PAGE of porin samples. Gel was stained with Coomassie blue. Lines were rearranged according to conditions.

Figure 5

OmpY relative expression under different environmental conditions. (A) Effect of media osmolarity, 150 mmol/L NaCl condition was used as a reference. (B) Effect of cultivation temperature, 26°C condition was used as a reference. (C) Effect of oxygen availability, aerobic condition was used as a reference. Expression levels are reported as fold change compared to average expression levels of reference groups. Columns represent the mean of triplicate measurements in two independent experiments; error bars represent the standard deviations. Asterisks above bars indicate significant differences compared to the reference (P < 0.05).