Cologgi Dena L, Otwell Anne E, Speers Allison M, Rotondo John A, Reguera Gemma
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, 48824, USA.
Present address: Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, 98195, USA.
Int Microbiol. 2021 Nov;24(4):631-648. doi: 10.1007/s10123-021-00176-y. Epub 2021 Apr 27.
Geobacter biofilms synthesize an electroactive exopolysaccharide matrix with conductive pili and c-cytochromes that spatially organizes cells optimally for growth and electron transport to iron oxide substrates, soluble metal contaminants, and current-harvesting electrodes. Despite its relevance to bioremediation and bioenergy applications, little is known about the developmental stages leading to the formation of mature (>20 μm thick) electroactive biofilms. Thus, we developed a transposon mutagenesis method and a high-throughput screening assay and identified mutants of Geobacter sulfurreducens PCA interrupted in the initial stages of surface colonization (attachment and monolayer formation) and the vertical growth and maturation of multilayered biofilms. The molecular dissection of biofilm formation demonstrated that cells undergo a regulated developmental program to first colonize the surface to saturation and then synthesize an electroactive matrix to support optimal cell growth within structured communities. Transitioning from a monolayer to a multilayered, mature biofilm required the expression of conductive pili, consistent with the essential role of these extracellular protein appendages as electronic conduits across all layers of the biofilms. The genetic screening also identified cell envelope processes, regulatory pathways, and electron transport components not previously linked to biofilm formation. These genes provide much-needed understanding of the cellular reprogramming needed to build electroactive biofilms. Importantly, they serve as predictive markers of the physiology and reductive capacity of Geobacter biofilms during the bioremediation of toxic metals and radionuclides and current harvesting in bioelectrochemical systems.
地杆菌生物膜合成一种具有导电菌毛和c型细胞色素的电活性胞外多糖基质，这种基质能在空间上最佳地组织细胞，以促进其生长以及向氧化铁底物、可溶性金属污染物和电流收集电极进行电子传递。尽管其与生物修复和生物能源应用相关，但对于导致成熟（>20μm厚）电活性生物膜形成的发育阶段却知之甚少。因此，我们开发了一种转座子诱变方法和一种高通量筛选测定法，并鉴定出了在表面定殖（附着和单层形成）初始阶段以及多层生物膜的垂直生长和成熟过程中被中断的嗜硫还原地杆菌PCA突变体。对生物膜形成的分子剖析表明，细胞经历一个受调控的发育程序，首先在表面定殖至饱和，然后合成一种电活性基质，以支持结构化群落内的最佳细胞生长。从单层向多层成熟生物膜的转变需要导电菌毛的表达，这与这些细胞外蛋白质附属物作为生物膜各层间电子传导管道的重要作用相一致。基因筛选还鉴定出了以前未与生物膜形成相关联的细胞包膜过程、调控途径和电子传递成分。这些基因有助于深入了解构建电活性生物膜所需的细胞重编程。重要的是，它们可作为嗜硫还原地杆菌生物膜在有毒金属和放射性核素生物修复以及生物电化学系统中电流收集过程中的生理学和还原能力的预测标志物。
