革蘭氏陰性菌具有多樣性的分泌系統，能將蛋白質通過複雜雙層膜構造，輸送到胞外。最近發現許多病原細菌帶有能將作用蛋白質經由一種新穎、命名為第六型分泌系統的裝置、直接注入標的細胞。綠膿桿菌為人類伺機性病原菌，具有鞭毛，且能導致嚴重感染，包括急性敗血症和肺纖維化囊腫。綠膿桿菌帶有三套第六型分泌系統的基因群組，極可能與該菌感染能力有很大關係。雖然已經有許多文獻探討第六型分泌系統的組裝方式，但對其調控的了解仍然相當欠缺。在綠膿桿菌第二套的第六型分泌系統的基因群組中，我們發現一個σ54 依賴性的轉錄活化子基因，命名為sfa2 (pa1663)。本研究建構了Sfa2的剔除突變株，結果發現生長曲線、聚集能力、生物膜生成，綠膿素產量，剛果紅結合力，泳動與群泳能力、溶血性、酯解酶，彈性蛋白酶與蛋白酶活性，捕鐵能力，以及鼠李醣酯產量分析等皆與野生株無顯著的差異。在VB培養液所培養的PAO1和Sfa2的突變株在AHL產量，細胞表面的型態以及胞外分泌蛋白體有較明顯的影響。但是細菌間的競爭能力，對哺乳細胞毒性和入侵能力，以及對大白菜葉子的感染能力，在Sfa2的突變株則顯著的下降。利用生物資訊學分析可知Sfa2蛋白含有細菌轉錄增強性結合蛋白的重要保留區域，包括AAA+專一性區域以及螺旋-轉-螺旋區域。進一步利用即時定量聚合酶連鎖反應分析可知，第二套第六型分泌系統的基因群組在基礎養分的培養環境下才會被誘導出來，而剃除Sfa2基因會使得第二套基因群組的表現量下降。使用凝膠電泳遷移分析確認Sfa2會與pa1656上游地方約372-672 bp 的區域結合。我們也利用雙分子螢光互補實驗分析證實Saf2與σ54 有交互作用。這些結果證實σ54 依賴性轉錄活化子Sfa2在綠膿桿菌PAO1第二套第六型分泌系統擔負著重要的轉錄調控作用。

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