, 2010), it provides a broader view of fixed samples, aiding in comparative fluorescent channel intensity calculations. As would be expected, the guinea-pig antibody against whole C. burnetii produced a strong fluorescent signal. Changes in the IcmT levels were measured against this standard. Fluorescence was observed in both channels for each time point sampled (data not shown). Figure 4c shows a graphical representation of these data relative to 0 hpi. Analysis
revealed that from 0 to 24 hpi, a significant increase (P<0.05) in the amount of IcmT relative to whole C. burnetii occurred between each time point measured. From 24 to 168 hpi, a statistically significant change was not detected. Although subtle, Selleck PD 332991 these data demonstrate Target Selective Inhibitor Library cell assay that IcmT expression increases early during infection, and then remains relatively unchanged for the duration of the infectious cycle. Whether these changes during this crucial time in PV development are required for C. burnetii survival is yet to be determined. However, the need for secreted effector proteins to control the development and trafficking of the PV early during the infectious cycle would likely be central to C. burnetii’s survival. Whether the IcmT detected at 0 hpi is part of a functional T4BSS
structure poised to secrete effector proteins upon host cell contact or whether a functional T4BSS structure is assembled once the bacteria enter the host cell
remains to be elucidated. Combined with our RT-qPCR analysis, these data suggest that C. burnetii T4BSS IcmT expression closely follows the increase in icmT transcript early during infection (0–24 hpi) and becomes relatively uniform for the duration of the infection (24–168 hpi). A comparison of Fig. 3 (icmT) and Fig. 4c indicates that an increase in RNA expression early during infection is followed by an increase in IcmT protein levels from a low at 0 hpi. Although the increase in RNA is modest, the relationship between the RNA and the corresponding IcmT protein expression indicates that temporal regulation of IcmT expression exists during the C. burnetii infectious cycle. In summary, we have shown that the C. burnetii T4BSS RI is expressed as a set of three operons and that de novo transcription and translation of C. burnetii T4BSS else genes is present as early as 8 hpi. In addition, we have shown that an increase in transcription is accompanied by an increase in at least one protein, IcmT, in the first 24 hpi. Protein levels for the C. burnetii T4BSS RI IcmT homolog appear to be relatively constant at later stages of an infection (48–168 hpi). These data provide an increase in our understanding of the temporal regulation of the C. burnetii T4BSS early during infection and indicate that this bacterial virulence mechanism is maintained throughout infection.
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