Elevated intracellular cyclic‐di‐GMP level in Shewanella oneidensis increases expression of c‐type cytochromes

Abstract

Electrochemically active biofilms are capable of exchanging electrons with solid electron acceptors and have many energy and environmental applications such as bioelectricity generation and environmental remediation. The performance of electrochemically active biofilms is usually dependent on c-type cytochromes, while biofilm development is controlled by a signal cascade mediated by the intracellular secondary messenger bis-(3ʹ-5ʹ) cyclic dimeric guanosine monophosphate (c-di-GMP). However, it is unclear whether there are any links between the c-di-GMP regulatory system and the expression of c-type cytochromes. In this study, we constructed a S. oneidensis MR-1 strain with a higher cytoplasmic c-di-GMP level by constitutively expressing a c-di-GMP synthase and it exhibited expected c-di-GMP-influenced traits, such as lowered motility and increased biofilm formation. Compared to MR-1 wild-type strain, the high c-di-GMP strain had a higher Fe(III) reduction rate (21.58 vs 11.88 pM of Fe(III)/h cell) and greater expression of genes that code for the proteins involved in the Mtr pathway, including CymA, MtrA, MtrB, MtrC and OmcA. Furthermore, single-cell Raman microspectroscopy (SCRM) revealed a great increase of c-type cytochromes in the high c-di-GMP strain as compared to MR-1 wild-type strain. Our results reveal for the first time that the c-di-GMP regulation system indirectly or directly positively regulates the expression of cytochromes involved in the extracellular electron transport (EET) in S. oneidensis, which would help to understand the regulatory mechanism of c-di-GMP on electricity production in bacteria.

Coupling riboflavin de novo biosynthesis and cytochrome expression for improving extracellular electron transfer efficiency in Shewanella oneidensis

“…Biofilm formation of the CY3 strain (solely engineering c ‐Cyts) and RF‐CY (co‐engineering of RF and c ‐Cyts) strain on the carbon cloth were substantially thicker than that of the DL0 strain. The results demonstrated that the reinforcement of c ‐Cyts could increase the thickness of biofilm, thereby improving the EET efficiency, which was consistent with previous reports (Jing et al, 2020; Mukherjee et al, 2020; Ng et al, 2020). In summary, the elevated RF production was capable of promoting MET, and the synergistic expression of c ‐Cyts promoted biofilm formation, thereby remarkably enhancing the efficiency of EET.…”

Respiration-induced biofilm formation as a driver for bacterial niche colonization

“…In an analysis of proteins involved in c-di-GMP homeostasis of 42 algae strains, six novel sensory domains have been recently described [18], including a novel CSS domain variant in a c-di-GMP phosphodiesterase presumably involved in sensing the redox state of the periplasm [79]. High c-di-GMP content is associated with higher expression of c-type cytochromes in S. oneidensis MR-1 [80], and represents a primary candidate to mediate RIBF in Shewanella. Other nucleotide secondmessenger pathways, such as cyclic di-GMP-AMP (cGAMP) signaling, may play regulatory roles in distinct bacterial species.…”

Shewanella oneidensis MR-1 as a bacterial platform for electro-biotechnology

“…A subsequent study has shown that the diguanylate synthase is involved in regulating the global level of cyclic-di-GMP (c-di-GMP) in MR-1 cells and facilitating biofilm formation on electrodes [52]. In addition, another study has also suggested that elevated intracellular c-di-GMP levels in MR-1 increase the expression of c-type cytochromes, thereby correlating the biofilm formation with EET [53]. However, since these studies have been conducted independently using different experimental settings, our knowledge on the formation and functioning of EABFs seems to be fragmentary.…”