Extracellular polymeric substances and structural stability of aerobic granule

ABSTRACT Extracellular DNA (eDNA) is a biofilm component that contributes to the formation and structural stability of biofilms. Streptococcus mutans, a major cariogenic bacterium, induces eDNA-dependent biofilm formation under specific conditions. Since cell death can result in the release and accumulation of DNA, the dead cells in biofilms are a source of eDNA. However, it remains unknown how eDNA is released from dead cells and is localized within S. mutans biofilms. We focused on cell death induced by the extracellular signaling peptide called competence-stimulating peptide (CSP). We demonstrate that nucleic acid release into the extracellular environment occurs in a subpopulation of dead cells. eDNA production induced by CSP was highly dependent on the lytF gene, which encodes an autolysin. Although lytF expression was induced bimodally by CSP, lytF-expressing cells further divided into surviving cells and eDNA-producing dead cells. Moreover, we found that lytF-expressing cells were abundant near the bottom of the biofilm, even when all cells in the biofilm received the CSP signal. Dead cells and eDNA were also abundantly present near the bottom of the biofilm. The number of lytF-expressing cells in biofilms was significantly higher than that in planktonic cultures, which suggests that adhesion to the substratum surface is important for the induction of lytF expression. The deletion of lytF resulted in reduced adherence to a polystyrene surface. These results suggest that lytF expression and eDNA production induced near the bottom of the biofilm contribute to a firmly attached and structurally stable biofilm. IMPORTANCE Bacterial communities encased by self-produced extracellular polymeric substances (EPSs), known as biofilms, have a wide influence on human health and environmental problems. The importance of biofilm research has increased, as biofilms are the preferred bacterial lifestyle in nature. Furthermore, in recent years it has been noted that the contribution of phenotypic heterogeneity within biofilms requires analysis at the single-cell or subpopulation level to understand bacterial life strategies. In Streptococcus mutans, a cariogenic bacterium, extracellular DNA (eDNA) contributes to biofilm formation. However, it remains unclear how and where the cells produce eDNA within the biofilm. We focused on LytF, an autolysin that is induced by extracellular peptide signals. We used single-cell level imaging techniques to analyze lytF expression in the biofilm population. Here, we show that S. mutans generates eDNA by inducing lytF expression near the bottom of the biofilm, thereby enhancing biofilm adhesion and structural stability.

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Soil Structural Stability and Extracellular Polymeric Substances (EPS): transient binding agents affected by land-use.

10.5194/egusphere-egu2020-5742 ◽

2020 ◽

Author(s):

Marc Redmile-Gordon

Keyword(s):

Land Use ◽

Organic Carbon ◽

Soil Organic Carbon ◽

Structural Stability ◽

Extracellular Polymeric Substances ◽

Aggregate Stability ◽

Land Uses ◽

Total Soil ◽

Binding Agents ◽

Soil Structural Stability

Structural stability in agricultural soils is said to be maintained through production of &#8216;biological binding agents&#8217;, including temporary binding agents (fungi, roots), transient binding agents (EPS), and persistent binding agents (of less certain origin). We sampled soils from a long-term field trial, comprising previous grassland, arable and fallow land-uses in factorial combination with current land-uses of the same type: previous 3 land-uses &#160;x current 3 land-uses = 9 treatments (Redmile-Gordon et al., 2020). Total soil organic carbon (SOC), EPS (including protein, and polysaccharide fractions; Redmile-Gordon et al., 2014), and mean weight diameter (MWD) of water stable aggregates (Le Bissonnais, 1996) were quantified.Both EPS and MWD were correlated, and were both strongly influenced by current land-use (implemented 2.5 years before sampling), but not by previous land-use (implemented > 50 years ago, terminated 2.5 years before sampling). While exopolysaccharides were significantly correlated to the soil&#8217;s structural stability (p = 0.027), proteinaceous EPS were more closely related to the associated gains in soil aggregate stability (p = 0.002).In contrast to EPS and soil stability, total soil organic carbon (SOC) was strongly influenced by previous land-use. Importantly, this indicates that any capacity for relatively stable organic matter to contribute to the soil&#8217;s structural stability is overwhelmed by temporary/transient effects owed to current land-use. This is cause for optimism, as it seems the physical quality of soils might be improved by short-term application of managements that favour EPS production. This approach would represent a qualitative step beyond that of building total SOC, which can be difficult for land-managers to achieve. This study is the first to simultaneously assess the effects of land-use on proteinaceous and polysaccharide content of EPS, and link this to the structural stability of soils. Further understanding surrounding the ecology of EPS production, and disentangling the contributions of temporary (largely physical) vs. transient (biochemical) binding agents is hoped to contribute to the development of more efficient land-management strategies.&#160;References:Le Bissonnais, Y., 1996. Aggregate stability and assessment of soil crustability and erodibility. 1. Theory and methodology. Eur. J. Soil Sci. 47, 425&#8211;437.Redmile-Gordon, M., Brookes, P.C., Evershed, R.P., Goulding, K.W.T., Hirsch, P.R., 2014. Measuring the soil-microbial interface: extraction of extracellular polymeric substances (EPS) from soil biofilms. Soil Biol. Biochem. 72, 163&#8211;171.Redmile-Gordon, M., Gregory, A.S., White, R.P., Watts, C.W. 2020. Soil organic carbon, extracellular polymeric substances (EPS), and soil structural stability as affected by previous and current land-use. Geoderma, 363. https://doi.org/10.1016/j.geoderma.2019.114143

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Time-resolved high-resolution electron microscopy of structural stability in mgo clusters

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100165823 ◽

1996 ◽

Vol 54 ◽

pp. 672-673

Author(s):

T. Kizuka ◽

N. Tanaka

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Magnesium Oxide ◽

Structural Stability ◽

High Resolution Electron Microscopy ◽

Video Tape ◽

Solid State Physics ◽

Time Resolved ◽

Resolution Electron ◽

Structural And Functional Properties

Structure and stability of atomic clusters have been studied by time-resolved high-resolution electron microscopy (TRHREM). Typical examples are observations of structural fluctuation in gold (Au) clusters supported on silicon oxide films, graphtized carbon films and magnesium oxide (MgO) films. All the observations have been performed on the clusters consisted of single metal element. Structural stability of ceramics clusters, such as metal-oxide, metal-nitride and metal-carbide clusters, has not been observed by TRHREM although the clusters show anomalous structural and functional properties concerning to solid state physics and materials science.In the present study, the behavior of ceramic, magnesium oxide (MgO) clusters is for the first time observed by TRHREM at 1/60 s time resolution and at atomic resolution down to 0.2 nm.MgO and gold were subsequently deposited on sodium chloride (001) substrates. The specimens, single crystalline MgO films on which Au particles were dispersed were separated in distilled water and observed by using a 200-kV high-resolution electron microscope (JEOL, JEM2010) equipped with a high sensitive TV camera and a video tape recorder system.

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Structural stability

AccessScience ◽

10.1036/1097-8542.800390 ◽

2015 ◽

Keyword(s):

Structural Stability

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