Shewanella oneidensis MR-1, a model species of exoelectrogenic bacteria (EEB), has been widely applied in bioelectrochemical systems. Biofilms of EEB grown on electrodes are essential in governing the current output and power density of bioelectrochemical systems. The MR-1 genome is exceptionally dynamic due to the existence of a large number of insertion sequence (IS) elements. However, to date, the impacts of IS elements on the biofilm-forming capacity of EEB and performance of bioelectrochemical systems remain unrevealed. Herein, we isolated a non-motile mutant (NMM) with biofilm-deficient phenotype from MR-1. We found that the insertion of an ISSod2 element into the flrA (encoding the master regulator for flagella synthesis and assembly) of MR-1 resulted in the non-motile and biofilm-deficient phenotypes in NMM cells. Notably, such a variant was readily confused with the wild-type strain because there were no obvious differences in growth rates and colonial morphologies between the two strains. However, the reduced biofilm formation on the electrodes and the deteriorated performances of bioelectrochemical systems and Cr(VI) immobilization for the strain NMM were observed. Given the wide distribution of IS elements in EEB, appropriate cultivation and preservation conditions should be adopted to reduce the likelihood that IS elements-mediated mutation occurs in EEB. These findings reveal the negative impacts of IS elements on the biofilm-forming capacity of EEB and performance of bioelectrochemical systems and suggest that great attention should be given to the actual physiological states of EEB before their applications.

希瓦氏菌（Shewanella oneidensis） MR-1是外生电细菌（EEB）的模型物种，已广泛应用于生物电化学系统。在电极上生长的EEB生物膜对于控制生物电化学系统的电流输出和功率密度至关重要。由于存在大量插入序列（IS）元素，因此MR-1基因组异常动态。但是，迄今为止，IS元素对EEB的生物膜形成能力和生物电化学系统性能的影响仍然没有得到揭示。本文中，我们从MR-1中分离出了一种具有生物膜缺陷型的非运动型突变体（NMM）。我们发现将IS Sod2元素插入flrA（编码鞭毛合成和组装的主调节剂）的MR-1在NMM细胞中导致非运动型和生物膜缺陷型。值得注意的是，这种变体很容易与野生型菌株混淆，因为两种菌株之间的生长速率和菌落形态没有明显差异。但是，观察到电极上生物膜形成减少，生物电化学系统性能下降，Cr（VI）固定化，导致菌株NMM变质。鉴于IS元素在EEB中的分布广泛，应采取适当的培养和保存条件以减少IS元素介导的突变在EEB中发生的可能性。