Numerical study of surface dimple phenomenon by starvation in simple sliding contact

Purpose This study aims to use a thermal elastohydrodynamic lubrication (EHL) algorithm incorporating an Eyring flow model to solve a steady-state contact in simple sliding motion. Design/methodology/approach A theoretical model was used to investigate the effect of starvation on the surface dimple phenomenon by gradually reducing the thickness of the inlet oil layer. Findings The increase in the starvation degree reduces the dimple depth, film thickness, the pressure peak and the temperature rise. Under the severe starvation condition, the dimple is eliminated so that the EHL contact becomes partly parched. In elliptical results, for the same starvation parameters, the oil replenishment is stronger than that in circular contact. Originality/value This paper fulfils an exploration to study how the oil starvation influences the surface dimple phenomenon.

Oxygen-limited metabolism in the methanotroph Methylomicrobium buryatense 5GB1C

The bacteria that grow on methane aerobically (methanotrophs) support populations of non-methanotrophs in the natural environment by excreting methane-derived carbon. One group of excreted compounds are short-chain organic acids, generated in highest abundance when cultures are grown under O2-starvation. We examined this O2-starvation condition in the methanotroph Methylomicrobium buryatense 5GB1. The M. buryatense 5GB1 genome contains homologs for all enzymes necessary for a fermentative metabolism, and we hypothesize that a metabolic switch to fermentation can be induced by low-O2 conditions. Under prolonged O2-starvation in a closed vial, this methanotroph increases the amount of acetate excreted about 10-fold, but the formate, lactate, and succinate excreted do not respond to this culture condition. In bioreactor cultures, the amount of each excreted product is similar across a range of growth rates and limiting substrates, including O2-limitation. A set of mutants were generated in genes predicted to be involved in generating or regulating excretion of these compounds and tested for growth defects, and changes in excretion products. The phenotypes and associated metabolic flux modeling suggested that in M. buryatense 5GB1, formate and acetate are excreted in response to redox imbalance. Our results indicate that even under O2-starvation conditions, M. buryatense 5GB1 maintains a metabolic state representing a combination of fermentation and respiration metabolism.

Environmental Factors Regulate the hlyE Gene Expression in Both S. typhi and E. coli in a Similar Way to Display Haemolytic Activity

Haemolysin (HlyE) is an essential virulence factor of Salmonella, Escherichia coli and other enteric bacteria. Although, a substantial degree of haemolytic activity is not seen under normal culture conditions in these organisms, however, the non-haemolytic E. coli K-12 showed significant haemolytic activity under stress conditions. To confirm this phenomenon in other enteric bacteria, in this study, the production of haemolysin in Salmonella enterica serovar Typhi under stress conditions, like oxygen and glucose starvations in vitro was investigated during March-December 2015. For this, S. typhi was cultured under oxygen or glucose starvation condition separately and this organism showed high haemolytic activity. The activity was found to be much higher when both the conditions were applied together. Also, the role of the transcription factor SlyA of S. typhi was investigated on induction of haemolytic activity. When E. coli K-12 was transformed with plasmid containing the gene of SlyA, the recombinant bacteria without any starvation condition, also showed similar haemolytic activity that was exhibited by S. typhi grown under oxygen and glucose starvation conditions. All these findings suggest that both environmental factors like oxygen or glucose starvation and overexpression of the transcription factor SlyA have important role in inducing hlyE gene expression in S. typhi.