生物膜（Biofilm）

2015年8月5日
讀畢需時 6 分鐘

A biofilm is any group of microorganisms in which cells stick to each other on a surface. Theseadherent(粘连物) cells are frequently embedded(嵌入) within a self-produced matrix(矩阵) ofextracellular polymeric substance(物质) (EPS). Biofilm(生物膜) EPS, which is also referred to asslime 黏质物(although not everything described as slime is a biofilm), is a polymeric conglomeration(聚集) generally composed(构成) of extracellular(细胞外的) DNA, proteins, and polysaccharides.

生物膜有一群微生物构成。生物膜内细胞在一个表面上紧连一起。这些粘连细胞常常被嵌入到自己分泌的矩阵物质中，这些矩阵物质被称为EPS。

Biofilms(生物膜) may form on living or non-living surfaces and can be prevalent(流行的) in natural, industrial(工业的) and hospital settings.[2][3] The microbial(微生物的) cells growing in a biofilm are physiologically distinct from planktonic 浮游生物的cells of the same organism(有机体), which, by contrast(对比), are single-cells that may float or swim in a liquid medium(方法).

Microbes(细菌) form a biofilm in response to many factors(因素), which may include cellular(细胞的) recognition(识别) of specific(特殊的) or non-specific(不明确的) attachment(附件) sites on a surface, nutritional(营养的) cues(提示), or in some cases, by exposure(暴露) of planktonic(浮游生物的) cells to sub-inhibitory concentrations(浓度) of antibiotics(抗生素).[4][5] When a cellswitches(开关) to the biofilm(生物膜) mode of growth, it undergoes(经历) a phenotypic 表型的shift(移动)in behavior(行为) in which large suites of genes are differentially(微分的) regulated.

微生物形成生物膜的原因有很多。

Formation

Formation(形成) of a biofilm(生物膜) begins with the attachment(附件) of free-floatingmicroorganisms(微生物) to a surface. These first colonists(殖民者) adhere(坚持) to the surface initially through weak, reversible(可逆的) adhesion(粘附) via van der Waals forces.

生物膜形成第一阶段：一群自由移动的微生物依靠范德瓦尔斯力，沾附在一个表面上。这期间，细菌沾附是可逆的，虚弱的。

If the colonists are not immediately separated from the surface, they can anchor(抛锚) themselves more permanently(永久地) using cell adhesion structures such as pili.

如果沾附细菌不能立即清除表面，它们可依靠pili细胞沾附结构，永久驻留表面。

Hydrophobicity 疏水性also plays an important role in determining the ability of bacteria to form biofilms, as those with increased hydrophobicity(疏水性) have reduced repulsion(排斥) between the extracellular matrix细胞外基质 and the bacterium.

疏水性帮助减少细胞外基质和细菌的排斥性。基质是由生物大分子构成的无定形胶状物，无色透明，具有一定黏性，孔隙中有组织液。

Some species(物种) are not able to attach(依附) to a surface on their own but are sometimes able to anchor(抛锚) themselves to the matrix(基质) or directly to earlier colonists(殖民者).

一些物种不能依附在表面，但有时能依附在基质上或之前细菌上。

It is during this colonization(殖民) that the cells are able to communicate via quorum sensing using products such as AHL. Some bacteria are unable to form biofilms(生物膜) as successfully due to their limited motility(运动性).

这阶段，细胞可以通过群体感应交流。一些细菌移动性不够，不能形成生物膜。

Nonmotile(无运动的) bacteria cannot recognize the surface or aggregate(集合) together as easily as motile(能动的) bacteria.

无运动能力细菌不能识别表面或在表面聚集。但能运动细菌可以做到

Once colonization has begun, the biofilm grows through a combination(结合) of cell division and recruitment(补充).Polysaccharide matrices(基质) typically(典型的) enclose(围绕) bacterial(细菌的) biofilms. In addition to the polysaccharides(多糖), these matrices may also contain material from the surrounding environment, including but not limited to minerals, soil particles(颗粒), and bloodcomponents(成分), such as erythrocytes(红细胞) and fibrin(纤维蛋白).[10] The final stage of biofilm formation(形成) is known as dispersion(散布), and is the stage in which the biofilm isestablished(确定的) and may only change in shape and size. The development of a biofilm may allow for an aggregate cell colony(殖民地) (or colonies) to be increasingly antibiotic(抗生的)resistant(抵抗者).

最后一阶段生物膜是细菌散布。最后一阶段生物膜是确定的，它只会改变形状和尺寸。生物膜的发展会产生抗生素耐受。

Dispersal

Dispersal(分散) of cells from the biofilm colony(殖民地) is an essential stage of the biofilm life cycle. Dispersal enables biofilms to spread and colonize(移于殖民地) new surfaces. Enzymes(酶)that degrade(贬低) the biofilm(生物膜) extracellular(细胞外的) matrix(矩阵), such as dispersin Band deoxyribonuclease, may play a role in biofilm dispersal(分散).[11][12] Biofilm matrix degrading(贬低) enzymes(酶) may be useful as anti-biofilm agents.[13][14] Recent evidence(证据)has shown that a fatty(胖子) acid(酸) messenger(报信者), cis-2-decenoic acid, is capable(能干的)of inducing(产生诱导作用的) dispersion(散布) and inhibiting(抑制作用的) growth of biofilm(生物膜)colonies(殖民地). Secreted(分泌) by Pseudomonas aeruginosa, this compound(复合的) induces cyclo(三轮车) heteromorphic(异形的) cells in several species(物种) of bacteria and the yeast(酵母) Candida albicans.[15] Nitric(氮的) oxide(氧化物) has also been shown to trigger(引发) the dispersal(分散)of biofilms of several bacteria species [16][17] at sub-toxic concentrations(浓度). Nitric oxide一氧化氮has the potential(潜能) for the treatment of patients that suffer from chronic(慢性的)infections(感染) caused by biofilms.[18]

Properties

Biofilms(生物膜) are usually found on solid substrates submerged(水下的) in or exposed to anaqueous solution, although they can form as floating mats on liquid surfaces and also on the surface of leaves, particularly in high humidity(湿度) climates. Given sufficient(足够的)resources for growth, a biofilm will quickly grow to be macroscopic(宏观的) (visible(可见物) to the naked(裸体的) eye). Biofilms can contain many different types of microorganism(微生物), e.g.bacteria, archaea, protozoa, fungi and algae; each group performs specialized(专门从事) metabolicfunctions. However, some organisms(有机体) will form single-species films under certain conditions. The social structure(结构) (cooperation(合作), competition) within a biofilm(生物膜)highly depends on the different species(物种) present.[19]

生物膜可由单种多种微生物组成。

Extracellular matrix

微生物的胞外聚合物（ECP）是微生物在一定条件下，在其代谢过程中分泌的、包围在微生物细胞壁外的聚合化合物，包括荚膜、粘液层以及其他表面物质。经过分析可以知道，这些聚合物的成分为脂类、多糖、蛋白质等

The biofilm is held together and protected by a matrix(基质) of secreted(分泌) polymericcompounds(化合物) called EPS. EPS is an abbreviation(缩写) for either extracellular(细胞外的)polymeric(聚合的) substance(物质)胞外聚合物 or exopolysaccharide.

生物膜由胞外聚合物形成和保护。基质保护细胞，并促进交流。一些生物膜包含水管道。水管道用于分配营养和信号传递。在一些条件下，基质很顽强，生物膜甚至可以石化。

This matrix protects the cells within it and facilitates(促进) communication among them through biochemical(生物化学的) signals. Some biofilms have been found to contain water channels that help distribute(分配) nutrients and signalling molecules.[20] This matrix(矩阵) is strong enough that under certain conditions,biofilms(生物膜) can become fossilized (Stromatolites).

Bacteria living in a biofilm usually have significantly(意味深长地) different properties from free-floating bacteria of the same species(物种), as the dense(稠密的) and protected environment of the film allows them to cooperate(合作) and interact(互相影响) in various ways.

细菌驻入生物膜后，产生根本变化。它们不在是单一漂浮物，而是稠密聚集在一起，拥有复杂功能。不同细菌互相合作，影响。生物膜可以抵抗去垢剂和抗生素（1000倍以上），胞外聚合物保护内部细菌。之后生物膜细胞实现基因转移，生物膜稳定性更高。

One benefit(利益) of this environment is increased resistance(阻力) to detergents 去垢剂and antibiotics, as the dense extracellular(细胞外的) matrix and the outer layer of cells protect the interior(内部) of the community. In some cases antibiotic(抗生的) resistance can be increased a thousandfold(千倍地).[21] Lateral gene transfer is greatly facilitated(促进) in biofilms and leads to a more stable(马厩) biofilm structure(结构).[22]

However, biofilms(生物膜) are not always less susceptible(易受影响的) to antibiotics(抗生素). Forinstance(举…为例), the biofilm form of Pseudomonas aeruginosa has no greater resistance(阻力) toantimicrobials(抗菌剂) than do stationary-phase planktonic(浮游生物的) cells, although when the biofilm is compared to logarithmic(对数的) phase(相) planktonic cells, the biofilm does have greater resistance to antimicrobials. This resistance to antibiotics in both stationary(固定的)phase cells and biofilms may be due to the presence(存在) of persister cells