Although oxygen has been reported to regulate biofilm formation by several Shewanella species, the exact regulatory mechanism mostly remains unclear. Here, we identify a direct oxygen-sensing diguanylate cyclase (DosD) and reveal its regulatory role in biofilm formation by Shewanella putrefaciens CN32 under aerobic conditions. In vitro and in vivo analyses revealed that the activity of DosD culminates to synthesis of cyclic diguanylate (c-di-GMP) in the presence of oxygen. DosD regulates the transcription of bpfA operon which encodes seven proteins including a large repetitive adhesin BpfA and its cognate type I secretion system (TISS). Regulation of DosD in aerobic biofilms is heavily dependent on an adhesin BpfA and the TISS. This study offers an insight into the molecular mechanism of oxygen-stimulated biofilm formation by S. putrefaciens CN32.
Biofabrication of nanomaterials is currently constrained by a low production efficiency and poor controllability on product quality compared to chemical synthetic routes. In this work, we show an attractive new biosynthesis system to break these limitations. A directed production of selenium-containing nanoparticles in Shewanella oneidensis MR-1 cells, with fine-tuned composition and subcellular synthetic location, was achieved by modifying the extracellular electron transfer chain. By taking advantage of its untapped intracellular detoxification and synthetic power, we obtained high-purity, uniform-sized cadmium selenide nanoparticles in the cytoplasm, with the production rates and fluorescent intensities far exceeding the state-of-the-art biosystems. These findings may fundamentally change our perception of nanomaterial biosynthesis process and lead to the development of fine-controllable nanoparticles biosynthesis technologies.
Biosynthesis
offers opportunities for cost-effective and sustainable
production of semiconductor quantum dots (QDs), but is currently restricted
by poor controllability on the synthesis process, resulting from limited
knowledge on the assembly mechanisms and the lack of effective control
strategies. In this work, we provide molecular-level insights into
the formation mechanism of biogenic QDs (Bio-QDs) and its connection
with the cellular substrate metabolism in Escherichia coli. Strengthening the substrate metabolism for producing more reducing
power was found to stimulate the production of several reduced thiol-containing
proteins (including glutaredoxin and thioredoxin) that play key roles
in Bio-QDs assembly. This effectively diverted the transformation
route of the selenium (Se) and cadmium (Cd) metabolic from Cd3(PO4)2 formation to CdS
x
Se1–x
QDs assembly,
yielding fine-sized (2.0 ± 0.4 nm), high-quality Bio-QDs with
quantum yield (5.2%) and fluorescence lifetime (99.19 ns) far exceeding
the existing counterparts. The underlying mechanisms of Bio-QDs crystallization
and development were elucidated by density functional theory calculations
and molecular dynamics simulation. The resulting Bio-QDs were successfully
used for bioimaging of cancer cells and tumor tissue of mice without
extra modification. Our work provides fundamental knowledge on the
Bio-QDs assembly mechanisms and proposes an effective, facile regulation
strategy, which may inspire advances in controlled synthesis and practical
applications of Bio-QDs as well as other bionanomaterials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.