Hoffmann Tamara, Schütz Alexandra, Brosius Margot, Völker Andrea, Völker Uwe, Bremer Erhard
Department of Biology, Philipps University Marburg, Karl-von-Frisch Strasse, D-35032 Marburg, Federal Republic of Germany.
J Bacteriol. 2002 Feb;184(3):718-27. doi: 10.1128/JB.184.3.718-727.2002.
Proteome analysis of Bacillus subtilis cells grown at low and high salinity revealed the induction of 16 protein spots and the repression of 2 protein spots, respectively. Most of these protein spots were identified by mass spectrometry. Four of the 16 high-salinity-induced proteins corresponded to DhbA, DhbB, DhbC, and DhbE, enzymes that are involved in the synthesis of 2,3-dihydroxybenzoate (DHB) and its modification and esterification to the iron siderophore bacillibactin. These proteins are encoded by the dhbACEBF operon, which is negatively controlled by the central iron regulatory protein Fur and is derepressed upon iron limitation. We found that iron limitation and high salinity derepressed dhb expression to a similar extent and that both led to the accumulation of comparable amounts of DHB in the culture supernatant. DHB production increased linearly with the degree of salinity of the growth medium but could still be reduced by an excess of iron. Such an excess of iron also partially reversed the growth defect exhibited by salt-stressed B. subtilis cultures. Taken together, these findings strongly suggest that B. subtilis cells grown at high salinity experience iron limitation. In support of this notion, we found that the expression of several genes and operons encoding putative iron uptake systems was increased upon salt stress. The unexpected finding that high-salinity stress has an iron limitation component might be of special ecophysiological importance for the growth of B. subtilis in natural settings, in which bioavailable iron is usually scarce.
对在低盐度和高盐度条件下生长的枯草芽孢杆菌细胞进行蛋白质组分析，结果分别显示有16个蛋白点被诱导表达，2个蛋白点的表达受到抑制。这些蛋白点大多通过质谱鉴定。16个高盐诱导蛋白中有4个与DhbA、DhbB、DhbC和DhbE相对应，这些酶参与2,3 -二羟基苯甲酸（DHB）的合成及其修饰和酯化形成铁载体杆菌肽。这些蛋白由dhbACEBF操纵子编码，该操纵子受中心铁调节蛋白Fur的负调控，在铁限制时去阻遏。我们发现铁限制和高盐度在相似程度上去阻遏dhb的表达，并且两者都导致培养上清液中积累相当量的DHB。DHB的产生随生长培养基盐度的增加呈线性增加，但过量的铁仍可使其减少。这种过量的铁也部分逆转了盐胁迫的枯草芽孢杆菌培养物所表现出的生长缺陷。综上所述，这些发现有力地表明，在高盐度条件下生长的枯草芽孢杆菌细胞经历了铁限制。支持这一观点的是，我们发现盐胁迫时，几个编码假定铁摄取系统的基因和操纵子的表达增加。高盐度胁迫具有铁限制成分这一意外发现，对于枯草芽孢杆菌在自然环境中的生长可能具有特殊的生态生理重要性，因为在自然环境中可生物利用的铁通常很稀缺。
