Antimicrobial Applications of Rhamnolipid Biosurfactant Produced from Achromobacter sp. (PS1) Isolate Using Lignocellulosic Hydrolysate

Heterogeneous mixture of partially purified rhamnolipid (RL) produced from Achromobacter sp. (PS1) using lignocellulosic rice straw (RS) sugar hydrolysate medium revealed six different congeners- Rha- C10-C10, Rha-C8-C10/Rha-C10-C8, Rha- C12-C10 / Rha- C10-C12, referring mono-rhamnolipids amounting to total 68.23 % and Rha-Rha-C10-C10, Rha-Rha-C8-C10/Rha-Rha-C10-C8, Rha-Rha-C10-C12/Rha-Rha-C12-C10, referring di-rhamnolipids amounting to 31.73 %, with Mono to Di- RL in the ratio of 2.1:1. This mixture's antimicrobial action containing more mono-rhamnolipids analyzed using broth macro-dilution method exhibited a broad-spectrum antibacterial activity showing ≥ 90 % growth inhibition of both Gram-positive and Gram-negative pathogenic bacteria at MIC ranging from 1.25 mg/mL to 10 mg/mL of total rhamnolipids. This might be due to the more hydrophobic character of mono-rhamnolipids containing a single rhamnosyl group and showing high surface activities. On the other hand, the non-antifungal activity may be attributed to the lower percentage of di-rhamnolipids in the partially purified mixture.

Bioreactor Rhamnolipid Production Using Palm Oil Agricultural Refinery By-Products

Palm fatty acid distillate (PFAD) and fatty acid methyl ester (FAME) are used by P. aeruginosa PAO1 to produce rhamnolipid biosurfactant. The process of fermentation producing of biosurfactant was structured in a 2 L bioreactor using 2% of PFAD and FAME as carbon sources in minimal medium and with a nitrogen concentration of 1 g L−1. Mass spectrometry results show the crude biosurfactant produced was predominantly monorhamnolipid (Rha-C10-C10) and dirhamnolipid (Rha-Rha-C10-C10) at 503 and 649 m/z value for both substrates. Maximum production of crude rhamnolipid for PFAD was 1.06 g L−1 whereas for FAME it was 2.1 g L−1, with a reduction in surface tension of Tris-HCl pH 8.0 solution to 28 mN m−1 and a critical micelle concentration (CMC) of 26 mg L−1 measured for both products. Furthermore, the 24 h emulsification indexes in kerosene, hexadecane, sunflower oil, and rapeseed oil using 1 g L−1 of crude rhamnolipid were in the range 20–50%. Consequently, PFAD and FAME, by-products from the agricultural refining of palm oil, may result in a product that has a higher added-value, rhamnolipid biosurfactant, in the process of integrated biorefinery.

On the Evaluation of Rhamnolipid Biosurfactant Adsorption Performance on Amberlite XAD-2 Using Machine Learning Techniques

Biosurfactants are a series of organic compounds that are composed of two parts, hydrophobic and hydrophilic, and since they have properties such as less toxicity and biodegradation, they are widely used in the food industry. Important applications include healthy products, oil recycling, and biological refining. In this research, to calculate the curves of rhamnolipid adsorption compared to Amberlite XAD-2, the least-squares vector machine algorithm has been used. Then, the obtained model is formed by 204 adsorption data points. Various graphical and statistical approaches are applied to ensure the correctness of the model output. The findings of this study are compared with studies that have used artificial neural network (ANN) and data group management method (GMDH) models. The model used in this study has a lower percentage of absolute mean deviation than ANN and GMDH models, which is estimated to be 1.71%.The least-squares support vector machine (LSSVM) is very valuable for investigating the breakthrough curve of rhamnolipid, and it can also be used to help chemists working on biosurfactants. Moreover, our graphical interface program can assist everyone to determine easily the curves of rhamnolipid adsorption on Amberlite XAD-2.

Enzymatic Treatment of Phenolic Wastewater: Effects of Salinity and Biosurfactant Addition

Water contaminated with phenols is produced from several oil and gas related industries. Although there are a number of treatment methods, enzymatic wastewater treatment is more attractive due to its sustainability, environmental-friendliness, and mild nature. A key limitation of this process, however, is the enzymatic deactivation (whether complete or partial) during the treatment process. This limitation might be addressed to a certain extent through the addition of biosurfactants to the reaction medium. Thus, the key aim of this study is to utilize laccase (an oxidoreductase enzyme from Trametes versicolor) to remove bisphenol A (BPA) from wastewaters in the presence of rhamnolipid biosurfactant. Since most wastewaters contain inorganic salts, the efficacy of enzymatic treatment of high saline wastewaters has been evaluated. The beneficial effect of the biosurfactant addition during the enzymatic treatment of highly saline phenolic wastewater has been also assessed. Additionally, the effect of increasing the biocatalyst and the phenolic pollutant concentrations have been also probed. The results showed that the BPA degradation rate increases with increasing the enzyme concentration. The extent of BPA removal also increased with increasing the biocatalyst concentration, approaching almost a complete removal at an enzyme concentration of 400 ppm. The BPA degradation rate also increased almost linearly with increasing its initial concentration; however, its removal extent showed the opposite trend. The addition of as low as 1 ppm rhamnolipid biosurfactant to the reaction medium increased both the BPA degradation rate and the removal extent relative to the biosurfactant-free wastewater samples. The addition of the biosurfactant to the reaction medium boosted the BPA degradation rate and the removal extent by 1.1- to 1.23-fold. The highest BPA degradation rate and removal enhancement (about 23% higher than those in the absence of the biosurfactant) was obtained for BPA-rhamnolipid mass ratio of 50:1. The presence of salt severely reduced the BPA degradation rate and removal. The addition of 20 mM NaCl resulted in about 1.7-fold drop in the BPA degradation rate and removal. The drop in the BPA degradation rate and removal reached more than 3.6-fold at 500 mM NaCl. The addition of 1 ppm rhamnolipid partially compensated the negative effect of salinity, providing relatively higher BPA degradation rate and removal at all examined salinity levels. The findings reported herein reveal the positive effect of biosurfactant addition to the enzymatic reaction medium and the need for the salt removal prior to subjecting the saline wastewaters to enzymatic treatment.