Mutagenesis and Adaptation of the Psychrotrophic Fungus Chrysosporium pannorum A-1 as a Method for Improving β-pinene Bioconversion

Mutagenesis and adaptation of the psychrotrophic fungus Chrysosporium pannorum A-1 to the toxic substrate β-pinene were used to obtain a biocatalyst with increased resistance to this terpene and improved bioconversion properties. Mutants of the parental strain were induced with UV light and N-methyl-N′-nitro-N-nitrosoguanidine. Mutants resistant to β-pinene were isolated using agar plates with a linear gradient of substrate concentrations. Active mutants were selected based on their general metabolic activity (GMA) expressed as oxygen consumption rate. Compared to the parental strain, the most active mutant showed an enhanced biotransformation ability to convert β-pinene to trans-pinocarveol (315 mg per g of dry mycelium), a 4.3-fold greater biocatalytic activity, and a higher resistance to H2O2-induced oxidative stress. Biotransformation using adapted mutants yielded twice as much trans-pinocarveol as the reaction catalyzed by non-adapted mutants. The results indicate that mutagenesis and adaptation of C. pannorum A-1 is an effective method of enhancing β-bioconversion of terpenes.

MATHEMATICAL MODELLING AND STATIONARY CHARACTERISTICS OF A TWO-PHASE FLUIDISED-BED BIOREACTOR WITH EXTERNAL AERATION

A mathematical model for a two-phase fluidised bed bioreactor with liquid recirculation and an external aerator was proposed. A stationary nonlinear analysis of such a bioreactor for an aerobic process with double-substrate kinetics was carried out. The influences of a volumetric fraction of solid carriers in the liquid phase, the rate of active biomass transfer from the biofilm to the liquid, the concentration of carbonaceous substrate, the mean residence time of the liquid and the efficiency of the external aerator on the steady state characteristics of the bioreactor were described. A method for determination of the minimal recirculation ratio related to oxygen demand and fluidised bed conditions was presented. On the basis of the obtained results, it is possible to choose reasonable operating conditions of such plants and to determine constraints, while considering acceptable concentrations of a toxic substrate being degraded.

The Cation Transporter SLC22A16 Is Expressed in Pediatric Acute Lymphoblastic Leukemia

Hydrophilic drugs require transport proteins to traverse the cell membrane, and the selective expression of these membrane transporters can confer selective sensitivity to their toxic substrates. Therefore, identification of a transport gene with restricted expression on tumor cells represents an opportunity to target that transporter with a selective, toxic substrate. We previously have demonstrated that the organic cation transport gene SLC22A16 (OCT6) is highly expressed in the leukemia cell line HL-60, and its RNA levels were at least 2 orders of magnitude higher in 25 unique specimens of adult leukemic blasts than in liver, placenta and kidney, the tissues that usually have high expression of SLC22 transporters (Gong, S. et al. Experimental Hematology, 30, 1–8, 2002). To determine the relevance of SLC22A16 gene expression in pediatric acute lymphoblastic leukemia (ALL), we examined its expression using an Affymetrix U133B gene expression microarray in 132 primary pediatric ALL specimens. SLC22A16 was broadly and highly expressed in these pediatric ALL primary specimens. The gene was represented by 2 probesets, with average expression levels of 922 ± 344 in one probeset and 1715 ± 857 in the other. Analysis of subgroups revealed that overall expression was highest in hyperdiploid (>50) ALL specimens (n=17), and lowest in T cell ALL (n=14). The gene with highest correlation with SLC22A16 on the U133B array was ERG (Pearson p=2.4 × 10−8; False Discovery Rate (FDR) =5.2 × 10−5), a member of the Ets family of transcription factors that are implicated in leukemogenesis. MLL gene expression correlated with SLC22A16 expression with a Pearson p=3.3 × 10−5 and FDR=0.005. Other genes of special interest in leukemia biology with significant expression correlation to SLC22A16 included LIMD1, a member of the ZYXIN family (Pearson p=2.3 × 10−6, FDR=0.001), PPAR-alpha (Pearson p=4.5 × 10−7, FDR=0.0004), and STS-1 (Pearson p=7 × 10−7, FDR=0.0005). To examine protein expression of SLC22A16 in pediatric ALL, a polyclonal antibody to SLC22A16, that recognizes a protein of expected size in HL-60 cells, demonstrated expression of this protein at a level comparable to HL-60 cells in 3 of 6 primary pediatric B-precursor ALL specimens. These results suggest that an SLC22A16 substrate plays a physiologic role in pediatric ALL, and that SLC22A16 is a new therapeutic target for pediatric ALL that could be exploited by SLC22A16-specific toxins and antibodies.

Modeling of the acclimation/deacclimation process of a mixed culture degrading 4-chlorophenol

The variation of concentration of the toxic substrate has a negative effect on the sludge activity. Although this loss of activity of the microorganisms under toxic starvation has been reported, this variable is not taken into account in the operation of biological wastewater treatment plants. In order to monitor and control the biological plant with a certain confidence it is necessary to consider the acclimation and deacclimation processes to avoid the reactor malfunctioning, resulting in loss of efficiency or in false data acquisition during monitoring. This paper proposes a model for the acclimation/deacclimation process. The experiments have been done in a sequencing batch reactor during the 4-chlorophenol degradation. The basic idea of the model is to consider the variation of the kinetic parameters of the Haldane law in terms of the acclimation and deacclimation state. The idea is discussed, and the results obtained are presented.