The term biofilm structure mostly refers to the term implicitly than explicitly. This term also refers to the biomass distribution in a biofilm and commutual allotting of biofilm porosity (Zbigniew L., 1998). Tolker-Nielsen et.al, in 2000 observed that biofilm community only had general attributes that could be considered universal but mostly every microbial biofilm depending on its community possessed individual characteristics that lead to its “unique” state.
In the beginning of time, when biofilms were first imaged by light and electron microscopes the researches documented that biofilms were made out of bacterial cells surrounded by extracellular polymer matrix of a uniform thickness and consistency. Researches refer to this images they observed as a “slab” where bacterial cells were observed to be distributed randomly. With development of imaging techniques the term biofilm became a misnomer since, the developed imaging shown a much complex picture than just a continuous surface layer, Instead it was determined that biofilms are heterogeneous (Costerton et.al.,1994).
As an example appearance of a heterogeneous biofilm is described below. This heterogeneous nature of the biofilm was observed when imaged by the confocal scanning laser microscope (CSLM), the image obtained indicated a arrangement of cells in a thin, dense layer where some of the cells were bound whereas others were not. Cells were round in shape with microcolonies that was packed with microorganisms. These microcolonies were seen filled with extracellular polymers but was separated by interstitial voids. Water was seen in-between this voids filling them, in some instances low concentrated polymers were observed replacing water. This whole structure lead to the formation of a network was due the interconnection of the voids leading to a porous structure. (Lewandoswski et.al., 1999)
Stoodley et al., in 1997 describes thin base film lining up from monolayer to several layers, thicker layers, think layers with or without water channels, as general characteristic of any biofilm. As explained before about the “uniqueness” of a biofilm, depending on the organisms or organism composing, the biofilm is main factor determining its structure (Lewandowski et.al., 1999).
Complex Biofilm structures are adapted according to variation of the environment it’s growing; biofilms grown in fast moving water will grow in filamentous streamers. As long as the water biofilm is growing is fast, the biofilm will grow as streamers without considering whether the fast running water is in a drainage or in an acid mine but if grown in river they will grow as periphyton. (Edwards K.J., et.al., 2000) Mushroom shaped structures or mound like structures of biofilms are seen grown in quiescent water.
Available nutrients, nutrient conditions, genetic regulation, selection or both genetic regulation and selection, oxygen limitation (from aerobic to anaerobic), PH, rates of growth, sheer stress, biofilm surface loading, substrate loading rate are factors that could influence the complicity of the structure of a biofilm (Xu K.D., et.al., 2000) (stoodley et.al., 2004) (Lewandowski et.al., 1999).
Therefore structure of a biofilm could be stated as very complex. The first indication of the complex and differentiated architecture of the biofilm was the images obtained by CSLM a detailed picture of a such image observed is explained as the start of the article to explain the complex nature of the biofilm . The structural complexness of a biofilm helps its functions, the channels structures helps transport nutrients from bulk phase into the biofilms. This channel helps exchange of nutrients for waste products. Journal articles by stoodley et.al 1994 states this as the first link between form and function. The complexity of the architecture of the biofilm allows penetration of oxygen and nutrition even of the thickest biofilm.
Function of a biofilm, cannot be defined since there are many functions of a biofilm, and the meaning of “function of a biofilm” may change according to the area of interest of the biofilm. Therefore “function of a biofilm” contains broad spectrum of meanings and should be defined each time the word is used. Complexity of the biofilm structure is linked with various functions of biofilms, such as degree of stability on the environment, antimicrobial resistance etc.
Tolker-Nielsen T, Molin S. Spatial organization of microbial biofilm communities. Microb Ecol 2000;40:75-84.
Costerton J.W., Lewandoswski Z., DeBeer D., Caldwell D., Korber D., James G., (1994) Minireview : biofilms, the customized micronich, J Bacteriology, 176(8), pp 2137-2142
Stoodley P, Boyle JD, Dodds I, Lappin-Scott HM. Consensus model of biofilm structure. In: Wimpenny JWT, Gilbert PS, Lappin-Scott HM, Jones M, editors. Biofilms: community interactions and control. Cardiff, UK: Bioline; 1997. p. 1-9.