N-Acylhomoserine lactones (AHLs) are important bacterial messengers, mediating different bacterial traits by quorum sensing in a cell-density dependent manner. AHLs are also produced by many bacteria of the marine Roseobacter group, which constitutes a large group within the marine microbiome. Often, specific mixtures of AHLs differing in chain length and oxidation status are produced by bacteria, but how the biosynthetic enzymes, LuxI homologs, are selecting the correct acyl precursors is largely unknown. We have analyzed the AHL production in Dinoroseobacter shibae and three Phaeobacter inhibens strains, revealing strain-specific mixtures. Although large differences were present between the species, the fatty acid profiles, the pool for the acyl precursors for AHL biosynthesis, were very similar. To test the acyl-chain selectivity, the three enzymes LuxI1 and LuxI2 from D. shibae DFL-12 as well as PgaI2 from P. inhibens DSM 17395 were heterologously expressed in E. coli and the enzymes isolated for in vitro incubation experiments. The enzymes readily accepted shortened acyl coenzyme A analogs, N-pantothenoylcysteamine thioesters of fatty acids (PCEs). Fifteen PCEs were synthesized, varying in chain length from C4 to C20, the degree of unsaturation and also including unusual acid esters, e.g., 2E,11Z-C18:2-PCE. The latter served as a precursor of the major AHL of D. shibae DFL-12 LuxI1, 2E,11Z-C18:2-homoserine lactone (HSL). Incubation experiments revealed that PgaI2 accepts all substrates except C4 and C20-PCE. Competition experiments demonstrated a preference of this enzyme for C10 and C12 PCEs. In contrast, the LuxI enzymes of D. shibae are more selective. While 2E,11Z-C18:2-PCE is preferentially accepted by LuxI1, all other PCEs were not, except for the shorter, saturated C10–C14-PCEs. The AHL synthase LuxI2 accepted only C14 PCE and 3-hydroxydecanoyl-PCE. In summary, chain-length selectivity in AHLs can vary between different AHL enzymes. Both, a broad substrate acceptance and tuned specificity occur in the investigated enzymes.
N-酰基脱氨核糖乳酸(AHLs)是重要的细菌信使,在细胞密度依赖的方式中介导不同的细菌特征。AHLs也被许多海洋玫瑰细菌组的细菌产生,这在海洋微生物组中占据着一个大的群体。通常,细菌会产生具有不同链长和氧化状态的AHLs的特定混合物,但是生物合成酶LuxI同源物如何选择正确的酰前体大部分是未知的。我们分析了Dinoroseobacter shibae和三株Phaeobacter inhibens菌株中的AHL产生,揭示了菌株特异性混合物。尽管这些物种之间存在很大差异,但脂肪酸谱,即AHL生物合成的酰前体池,非常相似。为了测试酰链选择性,从D. shibae DFL-12的三种酶LuxI1和LuxI2以及从P. inhibens DSM 17395的PgaI2在大肠杆菌中异源表达,并将酶分离用于体外孵育实验。这些酶容易接受缩短的酰辅酶A类似物,即脂肪酸的泛酸半胱氨基乙酰硫酯(PCEs)。合成了15种PCEs,链长从C4到C20不等,不饱和度不同,还包括不寻常的酸酯,例如2E,11Z-C18:2-PCE。后者作为D. shibae DFL-12 LuxI1的主要AHL的前体,2E,11Z-C18:2-脱氨核糖乳酸(HSL)。孵育实验表明,PgaI2接受除C4和C20-PCE之外的所有底物。竞争实验表明,这种酶对C10和C12 PCE有偏好。相比之下,D. shibae的LuxI酶更具选择性。虽然2E,11Z-C18:2-PCE优先被LuxI1接受,但除了较短的饱和C10-C14-PCE之外,所有其他PCE都不被接受。AHL合酶LuxI2仅接受C14 PCE和3-羟基癸酰-PCE。总之,AHL中的链长选择性在不同的AHL酶之间可能有所不同。在研究的酶中既有广泛的底物接受性,也有调节的特异性。