Fasciclin domain proteins (FDP) are found in all domains of life, but their biological role and regulation are not clearly understood. While studying the proteome of a mutant (Car1) of Azospirillum brasilense Sp7 with a Tn5 insertion in the gene encoding an anti-sigma factor (ChrR1), we found that FDP was maximally expressed. To study the biological role of this FDP, we inactivated fdp in A. brasilense Sp7 and in its Car1 mutant, which rendered them sensitive to methylene blue (MB) and toluidine blue (TB) in the presence of light. The transcription of fdp was also strongly upregulated by an ECF sigma factor (RpoE1) and photooxidative stress. The fdp null mutants of A. brasilense Sp7 and its Car1 mutant produced relatively fewer carotenoids and showed reduced flocculation. The reduced ability of fdp null mutants to flocculate was partly due to their reduced ability to produce carotenoids as inhibition of carotenoid synthesis by diphenylamine reduced their flocculation ability by 15–20%. Hence, FDP plays an important role in protecting A. brasilense Sp7 against photo-oxidative stress by supporting carotenoid accumulation and cell aggregation.

成束蛋白结构域蛋白 (FDP) 存在于生命的所有领域，但它们的生物学作用和调节尚不清楚。在研究在编码抗西格玛因子 (ChrR1) 的基因中插入 Tn5 的巴西固螺菌Sp7突变体 (Car1) 的蛋白质组时，我们发现 FDP 的表达量最大。为了研究这个FDP的生物学作用，我们灭活FDP在A. brasilense SP7，并在其分享帮助突变，这使得它们亚甲蓝（MB），并在光的存在甲苯胺蓝（TB）敏感。fdp的转录也受到 ECF 西格玛因子 (RpoE1) 和光氧化应激的强烈上调。A. brasilense的fdp无效突变体Sp7 及其 Car1 突变体产生的类胡萝卜素相对较少，絮凝减少。的能力降低FDP无效突变体中絮凝部分是由于它们的能力降低，以产生类胡萝卜素作为抑制类胡萝卜素合成由二苯胺的15-20％减少了他们的絮凝能力。因此，FDP通过支持类胡萝卜素积累和细胞聚集在保护A. brasilense Sp7 免受光氧化应激方面发挥重要作用。