I wonder what is the solubility of any EPS? Does it contributes to alkalinity/acidity of a medium? What is the pKa/pKb? Does it really depends on the functional groups of the EPS?
The solubility of EPS varies greatly, depending on its composition. Even within a single organism, such as certain Lactobacilli, homopolymers can vary greatly, depending on their structure. For example, Streptococcus spp. produce two types of glucose polymers: water-soluble dextran and water-insoluble mutan, as well as intermediate combination forms of both.
Regarding the pKa and acidity, that also depends on the EPS structure. In the case of neutral polysaccharides, composed of neutral sugars like glucose or mannose, it's not much of an issue. In the instance of acidic polysaccharides like bacterial alginate, it MAY be an issue. However, these usually exist in the salt form at physiological pH, rather than in the protonated, acidic form. The presence of acidic carboxylate groups will definitely affect the buffering capacity and metal-binding capacity of such biofilms. So, yes, it can depend on the functional groups within the EPS.
The solubility of EPS varies greatly, depending on its composition. Even within a single organism, such as certain Lactobacilli, homopolymers can vary greatly, depending on their structure. For example, Streptococcus spp. produce two types of glucose polymers: water-soluble dextran and water-insoluble mutan, as well as intermediate combination forms of both.
Regarding the pKa and acidity, that also depends on the EPS structure. In the case of neutral polysaccharides, composed of neutral sugars like glucose or mannose, it's not much of an issue. In the instance of acidic polysaccharides like bacterial alginate, it MAY be an issue. However, these usually exist in the salt form at physiological pH, rather than in the protonated, acidic form. The presence of acidic carboxylate groups will definitely affect the buffering capacity and metal-binding capacity of such biofilms. So, yes, it can depend on the functional groups within the EPS.
I agree with Greg that all depends on the EPS composition but acidic groups are very common in environmental microbial communities. I recommend you this paper
Environmental Microbiology (2003) 5(4), 231–237
In my opinion most of the epipolysaccharides r nonsoluble and thus have little effect on pH of the medium.
Dear Chin,
It depends fully on the EPS natural PH. All the bacterial EPS have particularly iso electric point.
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 CaCO3 precipitation was determined from acid-base titrations and calcium-binding experiments
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