Optimal chemostat cascades for periplasmic protein production.

This theoretical work predicts the optimal system design for the steady-state production of secreted protein in a chemostat cascade, using bakers' yeast (Saccharomyces cerevisiae) as the host organism. The protein of interest, mutant invertase, is secreted to the periplasmic space instead of the culture medium on account of its large size. This work uses the secretion model developed and tested by Park and Ramirez (1988). It is shown that the highest productivity is achieved when the chemostat cascade contains two stages, although the improvement over the single-stage productivity is small. When no recycle is used, the advantage of two stages results from the tradeoff between maximizing the cell concentration and maximizing the rate of protein production per cell. When recycle is used, the cell concentration and protein productivity are increased, and the advantage of two stages results from the tradeoff between maximizing the specific protein production rate and maximizing the specific protein secretion rate. Cascades with three stages were also investigated, but these were found to have no improvement over the corresponding two-stage cascades.     

CpG methylation recruits sequence specific transcription factors essential for tissue specific gene expression

CG methylation is an epigenetically inherited chemical modification of DNA found in plants and animals. In mammals it is essential for accurate regulation of gene expression and normal development. Mammalian genomes are depleted for the CG dinucleotide, a result of the chemical deamination of methyl-cytosine in CG resulting in TpG. Most CG dinucleotides are methylated, but ~ 15% are unmethylated. Five percent of CGs cluster into ~ 20,000 regions termed CG islands (CGI) which are generally unmethylated. About half of CGIs are associated with housekeeping genes. In contrast, the gene body, repeats and transposable elements in which CGs are generally methylated. Unraveling the epigenetic machinery operating in normal cells is important for understanding the epigenetic aberrations that are involved in human diseases including cancer. With the advent of high-throughput sequencing technologies, it is possible to identify the CG methylation status of all 30 million unique CGs in the human genome, and monitor differences in distinct cell types during differentiation and development. Here we summarize the present understanding of DNA methylation in normal cells and discuss recent observations that CG methylation can have an effect on tissue specific gene expression. We also discuss how aberrant CG methylation can lead to cancer. This article is part of a Special Issue entitled: Chromatin in time and space.     

Malathion biodegradation by a psychrotolerant bacteria Ochrobactrum sp. M1D and metabolic pathway analysis

An organophosphorus pesticide malathion biodegradation was investigated by using the bacteria Ochrobactrum sp. M1D isolated from a soil sample of peach orchards in Palampur, District Kangra, Himachal Pradesh (India). The bacterium was able to utilize malathion as the sole source of carbon and energy. The isolated bacterium was found psychrotolerant and could degrade 100% of 100 mg l⁻¹ malathion in minimal salt medium at 20°C, pH 7·0 within 12 days with no major significant metabolites left at the end of the study. Through GCMS analysis, methyl phosphate, diethyl maleate, and diethyl 2-mercaptosuccinate were detected and identified as the major pathway metabolites. Based on the GCMS profile, three probable degradation pathways were interpreted. The present study is the first report of malathion biodegradation at both the psychrophilic and mesophilic conditions by any psychrotolerant strain and also through multiple degradation pathways. In the future, the strain can be explored to bio-remediate the malathion contaminated soil in the cold climatic region and to utilize the enzymatic systems for advanced biotechnology applications.     

Influence of antibiotics and trace salts on lysine production by arthrobacter globiformis

A hydrocarbon utilizing strain of Arthrobacter globiformis Lb isolated from local soil has been found to yield lysine 3.4 g l^?1, keeping the medium optimal for pH, C- and N-sources. Addition of antibiotics and micronutrients to that optimal media stimulated cell growth and enhanced lysine yield.