Transcriptome analysis of pellicle formation of Shewanella oneidensis

Bacterial Cellulose Applied in Wound Dressing Materials: Production and Functional Modification - A Review

In recent years, the development of new type wound dressings has gradually attracted more attention. Bacterial cellulose (BC) is a natural polymer material with various unique properties, such as ultrafine 3D nanonetwork structure, high water retention capacity, and biocompatibility. These properties allow BC to be used independently or in combination with different components (such as biopolymers and nanoparticles) to achieve diverse effects. This means that BC has great potential as a wound dressing. However, systematic summaries for the production and commercial application of BC-based wound dressings are still lacking. Therefore, this review provides a detailed introduction to the production fermentation process of BC, including various production strains and their biosynthetic mechanisms. Subsequently, with regard to the functional deficiencies of bacterial cellulose as a wound dressing, recent research progress in this area is enumerated. Finally, prospects are discussed for the low-cost production and high-value-added product development of BC-based wound dressings.

Enhancement of hexavalent chromium reduction by Shewanella oneidensis MR-1 in presence of copper nanoparticles via stimulating bacterial extracellular electron transfer and environmental adaptability

The bioreduction of hexavalent chromium (Cr(VI)) depends highly on bacterial activity, while the release of copper nanoparticles (Cu NPs) poses threats to microorganisms in the environment. This work demonstrated that Cr(VI) reduction efficiency of Shewanella oneidensis MR-1 was remarkably enhanced by 83.7% under 20 mg/L Cu NPs exposure. Cu NPs improved the electron migration capacity of Shewanella oneidensis MR-1 by enhancing bioelectrochemical performance and flavin mononucleotide secretion. Moreover, key genes related to extracellular electron transfer pathways, including direct electron transfer through outer-membrane proteins, flavin-mediated electron transfer, and conductive flagella, were generally upregulated under Cu NPs exposure. In addition, environmental adaptability of Shewanella oneidensis MR-1 was enhanced under Cu NPs exposure by improving environmental information processing and energy and reducing power production, promoting Cr(VI) reduction by Shewanella oneidensis MR-1. This work indicated that Cu NPs could enhance Cr(VI) reduction by Shewanella oneidensis MR-1 through regulating extracellular electron transfer and environmental adaptability.

Research progress of the biosynthetic strains and pathways of bacterial cellulose

Bacterial cellulose is a glucose biopolymer produced by microorganisms and widely used as a natural renewable and sustainable resource in the world. However, few bacterial cellulose-producing strains and low yield of cellulose greatly limited the development of bacterial cellulose. In this review, we summarized the 30 cellulose-producing bacteria reported so far, including the physiological functions and the metabolic synthesis mechanism of bacterial cellulose, and the involved three kinds of cellulose synthases (type I, type II, and type III), which are expected to provide a reference for the exploration of new cellulose-producing microbes.

Pellicle development of Shewanella oneidensis is an aerotaxis-piloted and energy-dependent process

Pellicles are biofilms found at the air-liquid interface and are widely distributed in natural environments. In this study, a simple pellicle detection method was established, and using this new method, the pellicle formation activities of Shewanella oneidensis MR-1 and its 42 cytochrome c mutants were analysed. The results showed that the pellicle was initiated at very early stages of incubation. Aerotaxis was the major external factor, while energy acquirement was the main internal factor for pellicle initiation. Among the 42 cytochrome c mutants, 17 mutants, including those deficient in aerobic respiration, sulfur or sulfite/sulfate respiration, nitrite respiration, metal respiration, DMSO respiration and fumarate respiration, exhibited delayed pellicle initiation. The results suggest that S. oneidensis utilizes the electron acceptors simultaneously under anoxic conditions and that the disruption of any of these anaerobic respiration routes would retard pellicle initiation.

Regulation of biofilm formation by BpfA, BpfD, and BpfG in Shewanella oneidensis

Bacteria switch between two distinct life styles – planktonic (free living) and biofilm forming – in keeping with their ever-changing environment. Such switch involves sophisticated signaling and tight regulation, which provides a fascinating portal for studying gene function and orchestrated protein interactions. In this work, we investigated the molecular mechanism underlying biofilm formation in Shewanella oneidensis MR-1, an environmentally important model bacterium renowned for respiratory diversities, and uncovered a gene cluster coding for seven proteins involved in this process. The three key proteins, BpfA, BpfG, and BpfD, were studied in detail for the first time. BpfA directly participates in biofilm formation as extracellular “glue” BpfG is not only indispensable for BpfA export during biofilm forming but also functions to turn BpfA into active form for biofilm dispersing. BpfD regulates biofilm development by interacting with both BpfA and BpfG, likely in response to signal molecule c-di-GMP. In addition, we found that 1:1 stoichiometry between BpfD and BpfG is critical for biofilm formation. Furthermore, we demonstrated that a biofilm over-producing phenotype can be induced by C116S mutation but not loss of BpfG.

Enhanced biofilm formation and melanin synthesis by the oyster settlement-promoting Shewanella colwelliana is related to hydrophobic surface and simulated intertidal environment

A direct relationship between biofilm formation and melanogenesis in Shewanella colwelliana with increased oyster recruitment is already established. Previously, S. colwelliana was grown in a newly patented biofilm-cultivation device, the conico-cylindrical flask (CCF), offering interchangeable hydrophobic/hydrophilic surfaces. Melanization was enhanced when S. colwelliana was cultivated in a hydrophobic vessel compared with a hydrophilic vessel. In the present study, melanogenesis in the CCF was positively correlated with increased architectural parameters of the biofilm (mean thickness and biovolume obtained by confocal laser scanning microscopy) and melanin gene (melA) expression observed by densitometry. Niche intertidal conditions were mimicked in a process operated in an ultra-low-speed rotating disk bioreactor, which demonstrated enhanced biofilm formation, melanogenesis, exopolysaccharide synthesis and melA gene expression compared with a process where 12-h periodic immersion and emersion was prevented. The wettability properties of the settling plane as well as intermittent wetting and drying, which influenced biofilm formation and melA expression, may affect oyster settlement in nature.

Oxygen promotes biofilm formation of Shewanella putrefaciens CN32 through a diguanylate cyclase and an adhesin

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.

Investigation of roles of divalent cations in Shewanella oneidensis pellicle formation reveals unique impacts of insoluble iron

BACKGROUND

Bacteria adopt a variety of lifestyles in their natural habitats and can alternate among different lifestyles in response to environmental changes. At high cell densities, bacteria can form extracellular matrix encased cell population on submerged tangible surfaces (biofilms), or at the air-liquid interface (pellicles). Compared to biofilm, pellicle lifestyle allows for better oxygen access, but is metabolically more costly to maintain. Further understanding of pellicle formation and environmental cues that influence cellular choices between these lifestyles will definitely improve our appreciation of bacterial interaction with their environments.

METHODS

Shewanella oneidensis cells were cultured in 24-well plates with supplementation of varied divalent cations, and pellicles formed under such conditions were evaluated. Mutants defective in respiration of divalent cations were used to further characterize and confirm unique impacts of iron.

RESULTS AND CONCLUSIONS

Small amount of Fe(2+) was essential for pellicle formation, but presence of over-abundant iron (0.3mM Fe(2+) or Fe(3+)) led to pellicle disassociation without impairing growth. Such impacts were found due to S. oneidensis-mediated formation of insoluble alternative electron acceptors (i.e., Fe3O4) under physiologically relevant conditions. Furthermore, we demonstrated that cells preferred a lifestyle of forming biofilm and respiring on such insoluble electron acceptors under tested conditions, even to living in pellicles.

GENERAL SIGNIFICANCE

Our finding suggests that bacterial lifestyle choice involves balanced evaluation of multiple aspects of environmental conditions, and yet-to-be-characterized signaling mechanism is very likely underlying such processes.

Transcriptome analysis of early surface-associated growth of Shewanella oneidensis MR-1

Bacterial biofilm formation starts with single cells attaching to a surface, however, little is known about the initial attachment steps and the adaptation to the surface-associated life style. Here, we describe a hydrodynamic system that allows easy harvest of cells at very early biofilm stages. Using the metal ion-reducing gammaproteobacterium Shewanella oneidensis MR-1 as a model organism, we analyzed the transcriptional changes occurring during surface-associated growth between 15 and 60 minutes after attachment. 230 genes were significantly upregulated and 333 were downregulated by a factor of ≥2. Main functional categories of the corresponding gene products comprise metabolism, uptake and transport, regulation, and hypothetical proteins. Among the genes highly upregulated those implicated in iron uptake are highly overrepresented, strongly indicating that S. oneidensis MR-1 has a high demand for iron during surface attachment and initial biofilm stages. Subsequent microscopic analysis of biofilm formation under hydrodynamic conditions revealed that addition of Fe(II) significantly stimulated biofilm formation of S. oneidensis MR-1 while planktonic growth was not affected. Our approach to harvest cells for transcriptional analysis of early biofilm stages is expected to be easily adapted to other bacterial species.