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#microbial activity

3 public questions tagged with this topic.

Bioremediation

Surfactants enhance bioremediation by increasing:

Hydrophobic organic pollutants including crude oil aliphatic and polycyclic aromatic hydrocarbons, polychlorinated biphenyls and creosote components exhibit low aqueous solubility below 1 mg per L, strong sorption to soil organic matter estimated by high Koc, and presence as non-aqueous phase liquids limiting mass transfer to bacterial cells even when degradative enzymes encoded by alkB and nahAc are present. Addition of biosurfactants such as rhamnolipids composed of rhamnose glycosidically linked to beta-hydroxydecanoic acid from Pseudomonas aeruginosa, surfactin cyclic lipopeptide from Bacillus subtilis, or synthetic surfactants Tween 80 and Triton X-100 at concentrations near critical micelle concentration 10 to 200 mg per L lowers surface tension from 72 to 30 milliNewton per meter and interfacial tension, emulsifying oil into micelles 5 to 100 nanometer diameter and pseudo-solubilizing hydrocarbons into aqueous phase, dramatically increasing interfacial area and apparent solubility. This desorption from particles improves direct cell-substrate contact, enhances chemotactic attraction, modulates cell surface hydrophobicity via lipopolysaccharide alteration and increases membrane permeability without necessarily causing lethal lysis at sub-critical micelle doses. Genes rhlAB for rhamnolipid synthesis induced under nitrogen limitation illustrate regulated bioavailability enhancement, measurable as increased CO2 evolution and disappearance of parent compound.

Ref: Pacwa-Płociniczak et al. International Journal Molecular Sciences 2011 biosurfactants bioremediation; EPA surfactant enhanced recovery guide.

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Bioremediation

Intrinsic bioremediation is characterized by:

Intrinsic bioremediation operates as unassisted self-purification process driven solely by resident soil and groundwater microbiota that have evolved under chronic contaminant exposure, without any engineered addition of nutrients, oxygen-releasing compounds, or exogenous inocula. Native bacteria possessing catabolic plasmids like OCT encoding octane oxidation, NAH for naphthalene dioxygenase, or chromosomal pathways for monoaromatic degradation use industrial pollutants as carbon and electron donors, converting them through peripheral pathways to central intermediates catechol then to tricarboxylic acid cycle, releasing CO2 and water. Environmental conditions including temperature 15 to 25 Celsius, pH 6 to 8, moisture 60 percent field capacity and intrinsic oxygen flux from diffusion support basal activity. Rates remain slower than engineered biostimulation because growth limited by naturally available nitrogen and phosphorus, so doubling times longer and kinetics follow first-order decay with half-lives months to years. Evidence for adaptation includes increased copy numbers of nahAc and alkB genes via quantitative PCR over time due to natural selection. This concept underscores fundamental ecosystem resilience and capacity for self-restoration, forming baseline against which active remediation enhancements judged, and informs risk-based corrective action where natural processes acceptable.

Ref: EPA Natural Attenuation Technical Guide 1999; Prescott Microbiology environmental chapters; PubMed intrinsic bioremediation PMID 10463030.

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Bioremediation

Biostimulation refers to:

Biostimulation enhances pollutant degradation capacity of indigenous microbial communities already adapted to site conditions without introducing foreign organisms, focusing instead on relieving nutritional, redox or environmental constraints limiting rate. Petroleum hydrocarbons, chlorinated solvents and pesticides often persist not due to absence of degraders carrying alkB alkane hydroxylase, xylE catechol dioxygenase or dehH haloacid dehalogenase genes, but because electron acceptor oxygen, nitrogen as ammonium, phosphorus as phosphate, or carbon as electron donor scarce, causing C:N:P imbalance away from optimal 100:10:1 for microbial growth. Addition of slow-release oleophilic fertilizers such as Customblen, Inipol EAP22 containing oleic acid, urea and lauryl phosphate, oxygen releasing compounds magnesium peroxide OrCal, or molasses as carbon source stimulates bloom, increasing viable counts from 10^4 to 10^7 colony forming units per gram within weeks and accelerating mineralization kinetics described by Monod equation. Marine oil spills Exxon Valdez demonstrated success of nutrient augmentation. Unlike bioaugmentation seeding lab-grown strains facing intense competition and predation, biostimulation leverages already competitive autochthonous microbiota reducing ecological risk and cost, with monitoring via quantitative PCR of catabolic genes confirming stimulation effect rather than mere microbial presence.

Ref: Adams et al. Frontiers Microbiology 2015 Biostimulation vs Bioaugmentation; EPA Technical Guide biostimulation; PubMed comparison.

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