A rhamnolipid biosurfactant increased bacterial population size but hindered hydrocarbon biodegradation in weathered contaminated soils.

Surfactants are used to enhance the bioavailability of recalcitrant residual petroleum contamination during bioremediation. However, surfactants in some cases inhibit biodegradation, which is often attributed to their toxicity. Herein, we show that a rhamnolipid biosurfactant likely served as a carbon source and exhibited physiological inhibition on petroleum biodegradation. The addition of biosurfactants in mixed, batch, slurry bioreactors with soils from a petroleum-contaminated site led to a dose-dependent shift in the microbial community with a decrease in diversity and increase in population size and delayed biodegradation. Microbial community analysis indicated the enrichment of Alphaproteobacteria affiliated taxa such as Sphingomonadaceae in systems amended with biosurfactant. The diversity was significantly lower in systems with higher doses of biosurfactants compared to systems without biosurfactant. Droplet Digital PCR indicated a 30-90 fold increase in 16S rRNA copy numbers in systems with higher doses of biosurfactant than control systems without surfactant and nutrients, whereas the nutrient amendment alone led to a two-fold increase in population size. Total petroleum hydrocarbon analysis showed that the biodegradation extent was negatively impacted by rhamnolipid at the highest dose compared to lower doses (23% vs. 40%) or without the biosurfactant. Indigenous isolates cultivated from the oil-amended soil exhibited growth on rhamnolipid as a sole carbon source. A novel insight gained is how dose-dependent responses of microbial communities to biosurfactants alter the biodegradation time profile of hydrocarbons. The study highlights the significance of microbial assessment prior to surfactant-mediated bioremediation practices.

The antiradical activity of some plant raw materials and extracts obtained from these raw materials.

INTRODUCTION: Free radicals and reactive oxygen species are compounds usually present in healthy organisms as natural products of many metabolic pathways, and they are important in cell signaling and homeostasis. As a source of reactive oxygen species one can mention phagocytic cells and enzymes such as xanthine oxidase. Sometimes the level of reactive oxygen species strongly increases. This may lead to damage of very important cell structures such as nucleic acids, proteins or lipids. In this situation one should provide the organism with powerful antioxidants as a medicine or in the diet. A rich source of strong antioxidants such as phenolic compounds is plant raw materials, which are the subject of our study. MATERIAL/METHODS: Antiradical potential of extracts was measured with DPPH radical (2,2-diphenyl-1-picrylhydrazyl) and was expressed as the number of units per mg of extracts (TAU(515/mg)) and per g of raw material (TAU(515/g)). The amount of phenolic compounds was determined colorimetrically using Folin-Ciocalteu phenol reagent (3H2O • P2O5 • 13WO3 • 5MoO3 • 10H2O). RESULTS: The strongest antiradical activity was noted for extracts obtained from Cinnamomi cortex; the number of antiradical units per mg of extract (TAU(515/mg)) was 10.31±1.052. The lowest antiradical features were exhibited by extract from Zingiberis rhizoma (0.28±0.174) and extract from Cichorii radix (0.38±0.669). The highest amount of phenolic compounds was measured for extracts from Bistortae rhizoma, with a value (in percentage) of 78.6±13.5. The correlation coefficient between the number of antiradical units in extracts and amount of phenolic compounds in these extracts was 0.7273. When the number of antiradical units was calculated per g of raw material (TAU(515/g)) the strongest antiradical properties were noted for Bistortae rhizoma (1406±274.9), the weakest for Cichorii radix (122±158.3).