Lowrey Lillian C, Mote Katlyn B, Cotter Peggy A
Department of Microbiology and Immunology, The University of North Carolina at Chapel Hill, School of Medicine, Chapel Hill, North Carolina, United States of America.
PLoS Genet. 2025 May 20;21(5):e1011528. doi: 10.1371/journal.pgen.1011528. eCollection 2025 May.
Burkholderia thailandensis strain E264 (BtE264) and close relatives stochastically duplicate a 208.6 kb region of chromosome I via RecA-dependent recombination between two nearly identical insertion sequence elements. Because homologous recombination occurs at a constant, low level, populations of BtE264 are always heterogeneous, but cells containing two or more copies of the region (Dup+) have an advantage, and hence predominate, during biofilm growth, while those with a single copy (Dup-) are favored during planktonic growth. Moreover, only Dup+ bacteria form 'efficient' biofilms within 24 hours in liquid medium. We determined that duplicate copies of a subregion containing genes encoding an archaic chaperone-usher pathway pilus (csuFABCDE) and a two-component regulatory system (bfmSR) are necessary and sufficient for generating efficient biofilms and for conferring a selective advantage during biofilm growth. BfmSR functionality is required, as deletion of either bfmS or bfmR, or a mutation predicted to abrogate phosphorylation of BfmR, abrogates biofilm formation. However, duplicate copies of the csuFABCDE genes are not required. Instead, we found that BfmSR controls expression of csuFABCDE and bfmSR by activating a promoter upstream of csuF during biofilm growth or when the 208.6 kb region, or just bfmSR, are duplicated. Single cell analyses showed that duplication of the 208.6 kb region is sufficient to activate BfmSR in 75% of bacteria during planktonic (BfmSR 'OFF') growth conditions. Together, our data indicate that the combination of deterministic two-component signal transduction and stochastic, duplication-mediated activation of that TCS form a bet-hedging strategy that allows BtE264 to survive when conditions shift rapidly from those favoring planktonic growth to those requiring biofilm formation, such as may be encountered in the soils of Southeast Asia and Northern Australia. Our data highlight the positive impact that transposable elements can have on the evolution of bacterial populations.
泰国伯克霍尔德菌E264菌株（BtE264）及其近缘菌通过两个几乎相同的插入序列元件之间的RecA依赖性重组，随机复制1号染色体上一个208.6 kb的区域。由于同源重组以恒定的低水平发生，BtE264群体总是异质的，但含有该区域两个或更多拷贝的细胞（Dup+）具有优势，因此在生物膜生长过程中占主导地位，而单拷贝的细胞（Dup-）在浮游生长过程中更受青睐。此外，只有Dup+细菌能在液体培养基中24小时内形成“高效”生物膜。我们确定，包含编码古老伴侣-usher途径菌毛（csuFABCDE）和双组分调节系统（bfmSR）的基因的一个亚区域的重复拷贝对于形成高效生物膜以及在生物膜生长过程中赋予选择性优势是必要且充分的。需要BfmSR发挥功能，因为删除bfmS或bfmR，或一个预测会消除BfmR磷酸化的突变，都会消除生物膜形成。然而，csuFABCDE基因的重复拷贝并非必需。相反，我们发现BfmSR在生物膜生长期间或当208.6 kb区域或仅bfmSR被复制时，通过激活csuF上游的一个启动子来控制csuFABCDE和bfmSR的表达。单细胞分析表明，在浮游（BfmSR“关闭”）生长条件下，208.6 kb区域的复制足以在75%的细菌中激活BfmSR。总之，我们的数据表明，确定性的双组分信号转导与随机的、复制介导的该双组分系统激活相结合，形成了一种风险对冲策略，使BtE264能够在条件从有利于浮游生长迅速转变为需要形成生物膜的情况下存活，比如在东南亚和澳大利亚北部的土壤中可能遇到的情况。我们的数据突出了转座元件对细菌群体进化可能产生的积极影响。
