다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The microorganisms in biofilms live in a self-produced matrix of hydrated extracellular polymeric substances (EPS) that form their immediate environment. EPS are mainly polysaccharides, proteins, nucleic acids and lipids; they provide the mechanical stability of biofilms, mediate their adhesion to surfaces and form a cohesive, three-dimensional polymer network that interconnects and transiently immobilizes biofilm cells. In addition, the biofilm matrix acts as an external digestive system by keeping extracellular enzymes close to the cells, enabling them to metabolize dissolved, colloidal and solid biopolymers. Here we describe the functions, properties and constituents of the EPS matrix that make biofilms the most successful forms of life on earth.

The biofilm matrix

Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Biofilms: an emergent form of bacterial life.

https://web.science.uu.nl/pmi/publications/PDF/2012/TiPS-Berendsen-2012.pdf

The rhizosphere microbiome and plant health

Microbial exopolymer secretions in ocean environments: their role(s) in food webs and marine processes

/pdf/processes-of-carbonate-precipitation-in-modern-microbial-176vfhaypi.pdf

Processes of carbonate precipitation in modern microbial mats

Intertidal marine systems are highly dynamic systems which are characterized by periodic #uctuations in environmental parameters. Microbial processes play critical roles in the remineralization of nutrients and primary production in intertidal systems. Many of the geochemical and biological processes which are mediated by microorganisms occur within microenvironments which can be measured over micrometer spatial scales. These processes are localized by cells within a matrix of extracellular polymeric secretions (EPS), collectively called a ‘microbial bio"lma. Recent examinations of intertidal systems by a range of investigators using new approaches show an abundance of bio"lm communities. The purpose of this overview is to examine recent information concerning the roles of microbial bio"lms in intertidal systems. The microbial bio"lm is a common adaptation of natural bacteria and other microorganisms. In the #uctuating environments of intertidal systems, bio"lms form protective microenvironments and may structure a range of microbial processes. The EPS matrix of bio"lm forms sticky coatings on individual sediment particles and detrital surfaces, which act as a stabilizing anchor to bu!er cells and their extracellular processes during the frequent physical stresses (e.g., changes in salinity and temperature, UV irradiation, dessication). EPS is an operational de"nition designed to encompass a range of large microbially-secreted molecules having widely varying physical and chemical properties, and a range of biological roles. Examinations of EPS using Raman and Fourier-transform infared spectroscopy, and atomicforce microscopy suggest that some EPS gels possess physical and chemical properties which may hasten the development of sharp geochemical gradients, and contribute a protective e!ect to cells. Bio"lm polymers act as a sorptive sponge which binds and concentrates organic molecules and ions close to cells. Concurrently, the EPS appear to localize extracellular enzyme activities of bacteria, and hence contribute to the e$cient biomineralization of organics. At larger spatial scales, the copious secretion of speci"c types of EPS by diatoms on the surfaces of

/pdf/microbial-biofilms-in-intertidal-systems-an-overview-5cawhnq7ke.pdf

Microbial biofilms in intertidal systems: an overview

For three billion years, before the Cambrian diversification of life, laminated carbonate build-ups called stromatolites were widespread in shallow marine seas. These ancient structures are generally thought to be microbial in origin and potentially preserve evidence of the Earth's earliest biosphere. Despite their evolutionary significance, little is known about stromatolite formation, especially the relative roles of microbial and environmental factors in stromatolite accretion. Here we show that growth of modern marine stromatolites represents a dynamic balance between sedimentation and intermittent lithification of cyanobacterial mats. Periods of rapid sediment accretion, during which stromatolite surfaces are dominated by pioneer communities of gliding filamentous cyanobacteria, alternate with hiatal intervals. These discontinuities in sedimentation are characterized by development of surface films of exopolymer and subsequent heterotrophic bacterial decomposition, forming thin crusts of microcrystalline carbonate. During prolonged hiatal periods, climax communities develop, which include endolithic coccoid cyanobacteria. These coccoids modify the sediment, forming thicker lithified laminae. Preservation of lithified layers at depth creates millimetre-scale lamination. This simple model of modern marine stromatolite growth may be applicable to ancient stromatolites.

The role of microbes in accretion, lamination and early lithification of modern marine stromatolites

Sulfate-reducing bacteria (SRB) have been recognized as key players in the precipitation of calcium carbonate in lithifying microbial communities. These bacteria increase the alkalinity by reducing sulfate ions, and consuming organic acids. SRB also produce copious amounts of exopolymeric substances (EPS). All of these processes influence the morphology and mineralogy of the carbonate minerals. Interactions of EPS with metals, calcium in particular, are believed to be the main processes through which the extracellular matrix controls the precipitation of the carbonate minerals. SRB exopolymers were purified from lithifying mat and type cultures, and their potential role in CaCO 3 precipitation was determined from acid-base titrations and calcium-binding experiments. Major EPS characteristics were established using infrared spectroscopy and gas chromatography to characterize the chemical functional groups and the sugar monomers composition. Our results demonstrate that all of the three SRB strains tested were able to produce large amounts of EPS. This EPS exhibited three main buffering capacities, which correspond to carboxylic acids (pK a = 3.0), sulfur-containing groups (thiols, sulfonic and sulfinic acids ‐ pK a = 7.0‐7.1) and amino groups (pK a = 8.4‐9.2). The calcium-binding capacity of these exopolymers in solution at pH 9.0 ranged from 0.12g Ca g EPS ‐1 ‐0.15 g Ca g EPS ‐1 . These results suggest that SRB could play a critical role in the formation of CaCO 3 in lithifying microbial mats. The unusually high sulfur content, which has not been reported for EPS before, indicates a possible strong interaction with iron. In addition to changing the saturation index through metabolic activity, our results imply that SRB affect the rock record through EPS production and its effect on the CaCO 3 precipitation. Furthermore, EPS produced by SRB may account for the incorporation of metals (e.g. Sr, Fe, Mg) associated with carbonate minerals in the rock record.

Alan W. Decho

Papers

Microbial exopolymer secretions in ocean environments: their role(s) in food webs and marine processes

Processes of carbonate precipitation in modern microbial mats

Microbial biofilms in intertidal systems: an overview

The role of microbes in accretion, lamination and early lithification of modern marine stromatolites

Exopolymeric substances of sulfate‐reducing bacteria: Interactions with calcium at alkaline pH and implication for formation of carbonate minerals