Biofilm microbial ability

Aside from adding defined compounds, experimental additions of natural DOM mixtures suspected to vary in lability have helped test ideas about the contribution of various DOM sources to aquatic ecosystems. In a nice example using manipulation of natural DOM sources, Battin et al. (1999) used flowthrough microcosms to measure the relative uptake rates of allochthonous and autochthonous DOM by stream sediments. They documented greater than fivefold differences or more in uptake and respiration, depending on whether the DOM was extracted from soil or periphyton. Moreover, they were able to show, via transplant experiments, several cases where prior exposure to a particular source of DOM increased the ability of that community to metabolize the DOM supplied. There appears to be some preadaptation of microbial catabolic capacity when these stream biofilms were re-exposed to a familiar type of DOM. Similarly, the response of heterotrophic bacteria to carbon or nutrient addition was greatest when the source community was particularly active (Foreman et al., 1998). Kaplan et al. (1996) showed that fixed film bioreactors, colonized on one water source, were unable to rapidly metabolize DOC in water from another source. 

Attached-growth (or fixed-film) systems rely on the ability of microorganisms to attach themselves to inert surfaces. Contaminated water is passed through a bioreactor that houses such media, where the resulting microbial growth attaches and forms a thick film called biofilm. The biomass remains in the reactor except for the part that sloughs off the supporting media. 

The ability of the stone-colonizing microflora to cover and even penetrate material surface layers by the excretion of organic extracellular polymeric substances (EPS) leads to the formation of complex slimes, or biofilms, in which the microbial cells are embedded. Phototrophic organisms usually initiate colonisation by establishing a visible, nutrient-rich biofilm on new stone from which they can penetrate the material below to seek protection from high light intensities or desiccation. Stone EPS trap aerosols, dust and nutrients, minerals,... 

The increased resistance of bacteria to antibiotic therapy is a growing concern for doctors and medical officials worldwide. In the last two decades bacteria have developed resistance to almost all the commercially available antibiotics and the number of new antibiotics expected to enter the market is limited. One of the modes by which bacteria exert this resistance is their ability to develop biofilms. Biofilms are bacterial communities encased in a hydrated polymeric matrix. Biofilm development is known to follow a series of complex but discrete and well-regulated steps (Fig. 4.1) (1) microbial attachment to the surface, (2) growth and aggregation of cells into microcolonies, (3) maturation, and (4) dissemination of progeny cells for new colony formalion (87,88). 

Important pathogenic factors for catheter contamination are related to (1) the properties of the material constituting the device, (2) host factors, and (3) the intrinsic virulence factors of the involved microorganisms (ability to form biofilm). In Table 12.3, the factors controlling microbial adhesion to abiotic surfaces are listed. 

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