Ileana Stoica

Increase of Saccharomyces cerevisiae plating efficiency after treatment with bipolar electric pulses

Abstract Survival rate of yeast cells after electroporation with a succession of bipolar pulses was investigated. Field strength values from 0 to 1.5 kV/cm with a 8 ms width of pulses succession were used. After the electric treatment, cells were immediately inoculated in YEPG medium and kept 2 h at 30°C. Then cells were plated on standard solid medium and two days later, platting efficiency was recorded. A maximum of UFC appears around the value of 0.85 kV/cm, the number of the obtained colonies being about 100% higher than the lowest value of the field used.

Newly isolated alkalophilic Advenella species bioaugmented in activated sludge for high p-cresol removal.

In this work, an alkalophilic bacterium (LVX-4) capable of using p-cresol as sole source of carbon and energy was screened and isolated from soil polluted by used oil. Phylogenetic (16S rRNA) and phenotypic characterization using Biolog GN microplates and API 20NE strips indicated that LVX-4 strain is a new Advenella species. It showed both the capability to degrade of p-cresol at high concentrations (750 mg/L) and to use p-cresol for growth in a pH from 7 to 10, although the optimum pH was 9. Moreover bioaugmentation of activated sludge with this strain lead to the complete removal of p-cresol in less than 100 h. This is the first study that shows the potential of Advenella sp. to be bioaugmented in activated sludge system for p-cresol biodegradation.

Fatty Acids Effect on Lipase and Biosurfactant Induction in Rhodotorula Glutinis CMGB-RG5

Abstract Fatty acids represent important substrates for obtaining microbial lipases and biosurfactants. The yeast strain CMGBRG5 was identified as Rhodotorula glutinis using the BIOLOG MicroLog System. The opacity screening tests showed that R. glutinis CMGB-RG5 was able to produce lipases in presence of 1% Tween 80 after three days of incubation. Lipase induction was estimated as cell growth in presence of Tween 80, Tween 20, olive oil and tributyrin. After 48 hours, best results were obtained in presence of butyric acid, respectively, oleic acid: 2.2 × 107 cells/ml on tributyrin and 1.0 × 107 cells/ml on olive oil. Biosurfactant production was evaluated as emulsification index (E24%). After one week, high E24 values were obtained on fried sunflower oil (53%) and olive oil (35%). Crude and concentrated biosurfactants were tested against nine Candida strains. Best antimicrobial activity was observed for [20X] biosurfactants against C. tropicalis, C. guilliermondii and C. krusei. In conclusion, R. glutinis CGB-RG5 shows high potential for using fatty acids from various sources as unique carbon substrates for synthesis of biocompounds with high economic and biotechnological value.

Complete genome sequence of Tsukamurella sp. MH1: A wide-chain length alkane-degrading actinomycete

Tsukamurella sp. strain MH1, capable to use a wide range of n-alkanes as the only carbon source, was isolated from petroleum-contaminated soil (Pitești, Romania) and its complete genome was sequenced. The 4,922,396 bp genome contains only one circular chromosome with a G + C content of 71.12%, much higher than the type strains of this genus (68.4%). Based on the 16S rRNA genes sequence similarity, strain MH1 was taxonomically identified as Tsukamurella carboxydivorans. Genome analyses revealed that strain MH1 is harboring only one gene encoding for the alkB-like hydroxylase, arranged in a complete alkane monooxygenase operon. This is the first complete genome of the specie T. carboxydivorans, which will provide insights into the potential of Tsukamurella sp. MH1 and related strains for bioremediation of petroleum hydrocarbons-contaminated sites and into the environmental role of these bacteria.

Microbial Community Dynamics in Field-Scale Biopile Bioremediation

Understanding the microbial communities responses to biopile procedures is an essential step in the field of microbial ecology and in bioremediation applications. In order to estimate metabolic dynamics at a microbial community level, we used Biolog Ecoplates. Assays showed that the bacterial communities from all samples were capable of utilizing a great variety from the 31 carbon substrates. Shannon’s diversity index values were between 2.711±0.303 in August and 3.262±0.062 in April, recording a general variation of 0.5 that is similar to other studies. Statistical analysis showed a good correlation coeficient for 2-hydroxybenzoic acid, a compound that is metabolized through the nafhthalene degradation pathway. Results showed a metabolic shift of the microbial community determined by temperature and the decrease of aromatic hydrocarbon concentrations. The shift was observed in the dynamics of MPN from 9x106 to 1x109 cell/g of soil. Even if the initial total petroleum hydrocarbon concentration from the biopile matrix was much higher than in other studies (10.25 g/kg), at the end of the evaluation the pollutant content of the biopile matrix had a removal rate between 92-98% for monoaromatic hydrocarbons and 57-75% for poliaromatic hydrocarbons.

Phenotypic and genotypic assessment of Lactobacillus plantarum influence on Candida albicans fluconazole resistance

Lactobacilli are the most common genera of vaginal microbiota in healthy women, being involved in maintaining the microbial barrier against the development of pathogenic microorganisms in the urogenital tract. Recent studies have shown that the disturbance of microbial environmental balance in the vagina is associated with an increasing risk to develop infections. Over the last years, Candida albicans has continued to be the most frequent species isolated from vaginal yeast infections. The main goal of our studies was to determine the potential influence of lactic acid bacteria strains on the expression of C. albicans CMGBy 13 fluconazole resistance. The present study included 153 lactic acid bacteria strains isolated from fermented food products and human gastrointestinal tracts and one strain of C. albicans CMGBy13 isolated from a patient with vaginal infection. Preliminary analysis included the qualitative screening by disk diffusion assay of lactic acid bacteria strains capacity to increase the fluconazole susceptibility of yeast cells. Two lactic acid bacteria strains, Lactobacillus plantarum CMGB 1 and L. rhamnosus CMGB 38, were selected for further fluorescence microscopy and flow cytometry assays in order to establish their influence on C. albicans efflux pumps activity and, respectively, on the fluconazole resistance genes expression by RT-PCR.