Department of Biological Sciences, Duquesne Universitygrid.255272.5, Pittsburgh, Pennsylvania, USA.
J Bacteriol. 2022 Oct 18;204(10):e0028522. doi: 10.1128/jb.00285-22. Epub 2022 Sep 27.
Cells in microbial communities on surfaces live and divide in close proximity, which greatly enhances the potential for social interactions. Spatiogenetic structures are manifested through competitive and cooperative interactions among the same and different genotypes within a shared space, and extracellular secretions appear to function dynamically at the forefront. A previous experimental evolution study utilizing Pseudomonas fluorescens Pf0-1 colonies demonstrated that diverse mutations in the gene were repeatedly and exclusively selected through the formation of a dominant spatial structure. RsmE's primary molecular function is translation repression, and its homologs regulate various social and virulence phenotypes. Pseudomonas spp. possess multiple paralogs of Rsm proteins, and RsmA, RsmE, and RsmI are the most prevalent. Here, we demonstrate that the production of a mucoid polymer and a biosurfactant are exclusively regulated through RsmE, contradicting the generalized notion of functional redundancy among the Rsm paralogs. Furthermore, we identified the biosurfactant as the cyclic lipopeptide gacamide A. Competition and microscopy analyses showed that the mucoid polymer is solely responsible for creating a space of low cellular density, which is shared exclusively by the same genotype. Gacamide A and other RsmE-regulated products appear to establish a physical boundary that prevents the encroachment of the competing genotype into the newly created space. Although cyclic lipopeptides and other biosurfactants are best known for their antimicrobial properties and reducing surface tension to promote the spreading of cells on various surfaces, they also appear to help define spatial structure formation within a dense community. In densely populated colonies of the bacterium Pseudomonas fluorescens Pf0-1, diverse mutations in the gene are naturally selected by solving the problem of overcrowding. Here, we show that RsmE-regulated secretions function together to create and protect space of low cell density. A biosurfactant generally promotes the spreading of bacterial cells on abiotic surfaces; however, it appears to function atypically within a crowded population by physically defining genotypic boundaries. Another significant finding is that these secretions are not regulated by RsmE's paralogs that share high sequence similarity. The experimental pipeline described in this study is highly tractable and should facilitate future studies to explore additional RsmE-regulated products and address why RsmE is functionally unique from its paralogs.
表面微生物群落中的细胞生活和分裂非常接近,这极大地增强了社交互动的潜力。通过在共享空间中同一和不同基因型之间的竞争和合作相互作用表现出遗传结构,并且细胞外分泌物似乎在前沿动态发挥作用。先前利用荧光假单胞菌 Pf0-1 菌落进行的实验进化研究表明,基因中的多种突变通过形成占主导地位的空间结构而被反复且专门选择。RsmE 的主要分子功能是翻译抑制,其同源物调节各种社交和毒力表型。假单胞菌属拥有多种 Rsm 蛋白的同源物,其中 RsmA、RsmE 和 RsmI 最为普遍。在这里,我们证明了粘液聚合物和生物表面活性剂的产生仅受 RsmE 调节,这与 Rsm 同源物之间功能冗余的普遍概念相矛盾。此外,我们确定生物表面活性剂为环脂肽 gacamide A。竞争和显微镜分析表明,粘液聚合物仅负责创建细胞密度低的空间,该空间仅由相同基因型共享。gacamide A 和其他 RsmE 调节产物似乎建立了物理边界,防止竞争基因型侵入新创建的空间。虽然环状脂肽和其他生物表面活性剂以其抗菌特性和降低表面张力以促进细胞在各种表面上扩散而闻名,但它们似乎还有助于在密集群落中定义空间结构形成。在荧光假单胞菌 Pf0-1 的密集菌落在解决过度拥挤的问题时,基因中的多种突变自然被选择。在这里,我们表明 RsmE 调节的分泌物共同作用以创建和保护低细胞密度的空间。生物表面活性剂通常促进细菌细胞在非生物表面上的扩散;然而,它似乎通过物理定义基因型边界在拥挤的种群中表现异常。另一个重要发现是,这些分泌物不受具有高度序列相似性的 RsmE 同源物调节。本研究中描述的实验管道非常易于处理,应该有助于未来的研究探索其他 RsmE 调节产物,并解决为什么 RsmE 与其同源物在功能上是独特的。
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