Transcriptional Response of Pasteurella multocida to Defined Iron Sources

Pasteurella multocida was grown in iron-free chemically defined medium supplemented with hemoglobin, transferrin, ferritin, and ferric citrate as iron sources. Whole-genome DNA microarrays were used to monitor global gene expression over seven time points after the addition of the defined iron source to the medium. This resulted in a set of data containing over 338,000 gene expression observations. On average, 12% of P. multocida genes were differentially expressed under any single condition. A majority of these genes encoded P. multocida proteins that were involved in either transport and binding or were annotated as hypothetical proteins. Several trends are evident when the data from different iron sources are compared. In general, only two genes (ptsN and sapD) were expressed at elevated levels under all of the conditions tested. The results also show that genes with increased expression in the presence of hemoglobin did not respond to transferrin or ferritin as an iron source. Correspondingly, genes with increased expression in the transferrin and ferritin experiments were expressed at reduced levels when hemoglobin was supplied as the sole iron source. Finally, the data show that genes that were most responsive to the presence of ferric citrate did not follow a trend similar to that of the other iron sources, suggesting that different pathways respond to inorganic or organic sources of iron in P. multocida. Taken together, our results demonstrate that unique subsets of P. multocida genes are expressed in response to different iron sources and that many of these genes have yet to be functionally characterized.

多杀性巴氏杆菌（Pasteurella multocida）于以血红蛋白、转铁蛋白、铁蛋白及柠檬酸铁作为铁源补充的无铁化学成分限定培养基中培养。本研究采用全基因组DNA微阵列（whole-genome DNA microarray）监测向培养基中添加限定铁源后七个时间点的全局基因表达情况，最终得到包含33.8万余个基因表达观测值的数据集。平均而言，任意单一培养条件下，有多杀性巴氏杆菌12%的基因呈现差异表达。其中多数基因编码的蛋白要么参与转运与结合过程，要么被注释为假想蛋白（hypothetical protein）。对比不同铁源对应的实验数据，可观察到若干显著趋势：总体而言，所有受试培养条件下仅ptsN与sapD两个基因呈现高表达水平。实验结果同时显示，在以血红蛋白为铁源时表达上调的基因，并不会对作为铁源的转铁蛋白或铁蛋白产生响应；相应地，在转铁蛋白与铁蛋白实验中表达上调的基因，在以血红蛋白作为唯一铁源时则呈现低表达状态。最后，数据表明，对柠檬酸铁响应最为显著的基因，并未呈现与其他铁源相关基因相似的表达趋势，这提示多杀性巴氏杆菌应对无机铁源与有机铁源的通路存在差异。综合来看，本研究结果证实，多杀性巴氏杆菌存在响应不同铁源的特异性基因子集，且其中多数基因尚未完成功能鉴定。