Optimization of phenol degradation by Candida tropicalis Z-04 using Plackett-Burman design and response surface methodology

Statistical experimental designs were used to optimize the process of phenol degradation by Candida tropicalis Z-04, isolated from phenol-degrading aerobic granules. The most important factors influencing phenol degradation （p 〈 0.05）, as identified by a two-level Plackett-Burman design with 11 variables, were yeast extract, phenol, inoculum size, and temperature. Steepest ascent method was undertaken to determine the optimal regions of these four significant factors. Central composite design （CCD） and response surface analysis were adopted to further investigate the mutual interactions between these variables and to identify their optimal values that would generate maximum phenol degradation. The analysis results indicated that interactions between yeast extract and temperature, phenol and temperature, inocuhim size and temperature affected the response variable （phenol degradation） significantly. The predicted results showed that the maximum removal efficiency of phenol （99.10%） could be obtained under the optimum conditions of yeast extract 0.41 g/L, phenol 1.03 g/L, inoculum size 1.43% （V/V） and temperature 30.04℃. These predicted values were further verified by validation experiments. The excellent correlation between predicted and experimental values confirmed the validity and practicability of this statistical optimum strategy. This study indicated the excellent ability of C. tropicalis Z-04 in degrading high-strength phenol. Optimal conditions obtained in this experiment laid a solid foundation for further use of this microorganism in the treatment of highstrength phenol effluents.

Biodegradation of aniline by Candida tropicalis AN1 isolated from aerobic granular sludge

Aniline-degrading microbes were cultivated and acclimated with the initial activated sludge collected from a chemical wastewater treatment plant. During the acclimation processes, aerobic granular sludge being able to effectively degrade aniline was successfully formed, from which a preponderant bacterial strain was isolated and named as AN1. Effects of factors including pH, temperature, and second carbon/nitrogen source on the biodegradation of aniline were investigated. Results showed that the optimal conditions for the biodegradation of aniline by the strain AN1 were at pH 7.0 and 28–35°C. At the optimal pH and temperature, the biodegradation rate of aniline could reach as high as 17.8 mg/（L·hr） when the initial aniline concentration was 400 mg/L. Further studies revealed that the addition of 1 g/L glucose or ammonium chloride as a second carbon or nitrogen source could slightly enhance the biodegradation efficiency from 93.0% to 95.1%–98.5%. However, even more addition of glucose or ammonium could not further enhance the biodegradation process but delayed the biodegradation of aniline by the strain AN1. Based on morphological and physiological characteristics as well as the phylogenetic analysis of 26S rDNA sequences, the strain AN1 was identified as Candida tropicalis.

Multilocus sequence typing indicates diverse origins of invasive Candida tropicalis isolates in China

Background According to data from the China Hospital Invasive Fungal Surveillance Net （CHIF-NET） 2010, Candida tropica/is （C. tropica/is） is the third most common pathogen causing invasive candidiasis. Moreover, the majority of fluconazole-resistant C. tropicalis isolates were from a single hospital. Therefore, a molecular epidemiological survey is necessary to investigate the genetic relatedness of C. tropica/is isolates in China. Methods In this study, 48 C. tropicalis isolates causing invasive fungal infections from four tertiary hospitals in China were studied. All the isolates were identified by sequencing the internal transcribed spacer region. Antifungal susceptibility to triazoles, amphotericin B, and caspofungin was determined by the Clinical and Laboratory Standards Institute standard broth microdilution method. Multilocus sequence typing （MLST） was performed, and phylogenetic analysis was further performed by the eBURST and maximum parsimony （MP） methods to characterize the genetic relatedness of isolates. Results MLST discriminated 40 diploid sequence types （DSTs） among 48 isolates, including 36 novel DSTs, and the XYR1 gene showed the highest discriminatory power. The DSTs obtained from this study were compared with those of previously reported C. tropicalis isolates, and there was poor type alignment with regional strains. Nine groups and 11 singletons were identified by eBURST, whereas two groups and 10 subgroups were clustered by MP analysis. Generally, there were no obvious correlations between clonal clusters generated and the specimen source or hospital origin. Seven fiuconazole-resistant isolates were confirmed and assigned to three distinguishable branches. Conclusions The results suggested diverse origins of invasive C. tropicalis isolates in China. Although most invasive C. tropicalis strains in the mainland of China were clustered with previously characterized Asian isolates, major C. tropicalis clusters identified in this study were genetically distinct from those of other geographic regions.

热带念珠菌临床分离株对氟康唑耐药分子机制的研究(英文)

Objective This study aimed to investigate the molecular mechanisms responsible for fluconazole resistance in clinical isolates of this pathogenic yeast.Methods A total of 41 Candida tropicalis strains were collected from the clinical laboratory of Taiyuan City Central Hospital.Antifungal susceptibility testing was performed by ATB FUNGU 3 method.The 14 α-demethylase (ERG11) gene in all clinical isolates of Candida tropicalis were amplified by PCR,and their nucleotide sequences were determined in order to detect point mutations.Likewise,efflux transporters (CDR1 and MDR1) and ERG11 genes were tested by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) for their expression in Candida tropicalis cells at the mRNA level.Results The fluconazole-resistant rate of 41 Candida tropicalis was 12.2%.The amino acid substitutions in ERG11p of R245K,Y221F and V362I were found in fluconazole-resistant isolates.And no amino acid substitution was detected in fluconazole-susceptible ones.The mRNA level of CDR1,MDR1 and ERG11 genes in fluconazole-resistant isolates all showed overexpression compared with fluconazole-susceptible ones.Conclusions Missense mutations in ERG11 gene associated with overexpression of CDR1,MDR1 and ERG11 gene seemed to be responsible for the acquired fluconazole resistance of these clinical isolates.