Saccharomyces cerevisiae tolerance to hyper-osmolarity in aerobic glucose-limited chemostat culture

Different mechanisms contribute to regulate cellular functions in order to cope with threats from physiological stress conditions. As a fundamental response to balance excess water loss and restore turgor, Saccharomyces cerevisiae subjected to increased osmolarity accelerate intracellular glycerol biosynthesis and accumulation as a compatible solute. This study assessed cellular response to sorbitol-induced osmolarity in aerobic glucose-limited chemostat culture at various levels of the glycerol flux. Cell number declined slightly without any substantial increase in dry weight and total protein contents following exposure to 1M sorbitol that lasted for 90 min. On the other hand, total glycerol levels increased over time in different yeast cultivations corresponding with enhanced glycerol-3-phosphate dehydrogenase 1 (GPD1) transcript levels, which led to a steady and intensified protein product. These results support literature evidence of accumulated intracellular glycerol regulation at different levels and further increase curiosity to understand yeast tolerance in various applications including bakery, brewery and wine making or leavening of bread underdifferent osmotic conditions.

Draft Genome Sequence of Phenol-Degrading Variovorax boronicumulans Strain c24

ABSTRACT We report the draft genome sequence of Variovorax boronicumulans strain c24, which was isolated from a soil-inoculated chemostat culture amended with phenol as a sole carbon and energy source. The genome data will provide insights into phenol and other xenobiotic compound degradation mechanisms for bioremediation applications.

Production of prodigiosin pigment by Serratia marcescens is negatively associated with cellular ATP levels during high-rate, low-cell-density growth

Serratia marcescens is a facultatively anaerobic bacterium and the most recognized producer of the hydrophobic pigment prodigiosin. Previous work has shown that prodigiosin both increases ATP production during population lag phase and approximately doubles the stationary-phase cell yield. Here, we employed both batch and chemostat culture methods to investigate prodigiosin’s role during high rate growth at low cell density as peak cellular ATP levels decline. Batch culture experiments utilizing artificial pigment induction showed an ATP reduction during low cell density growth. In addition, pigment induction during fixed growth rate chemostat culture revealed a negative correlation between cellular levels of prodigiosin and ATP (r = −0.95). Variable growth rate chemostat experiments showed an inverse relationship between ATP per cell and prodigiosin per cell during low-density growth but a direct relationship during high-density growth. Rate modeling of chemostat data quantified the pigment’s effect on cellular levels of ATP for both population growth phases. Finally, prodigiosin production in a heterologous bacterium led to ATP decline. These data with intact cells complement the established in vitro proton import function of prodigiosin pigment and may indicate an energy-spilling function during high rate, low cell density growth.

Draft Genome Sequence of Phenol-Degrading Variovorax boronicumulans Strain HAB-30

We report the draft genome sequence of Variovorax boronicumulans strain HAB-30, which was isolated from a phenol-degrading chemostat culture. This strain contains genes encoding a multicomponent type of phenol hydroxylase, with degradation pathways for catechol and other aromatic compounds. The genome sequence will be useful for understanding the metabolic pathways involved in phenol degradation.

Tandem Amplification of the Staphylococcal Cassette Chromosome mec Element Can Drive High-Level Methicillin Resistance in Methicillin-Resistant Staphylococcus aureus

ABSTRACT Hospital-associated methicillin-resistant Staphylococcus aureus (MRSA) strains typically express high-level, homogeneous (HoR) β-lactam resistance, whereas community-associated MRSA (CA-MRSA) more commonly express low-level heterogeneous (HeR) resistance. Expression of the HoR phenotype typically requires both increased expression of the mecA gene, carried on the staphylococcal cassette chromosome mec element (SCCmec), and additional mutational event(s) elsewhere on the chromosome. Here the oxacillin concentration in a chemostat culture of the CA-MRSA strain USA300 was increased from 8 μg/ml to 130 μg/ml over 13 days to isolate highly oxacillin-resistant derivatives. A stable, small-colony variant, designated HoR34, which had become established in the chemostat culture was found to have acquired mutations in gdpP, clpX, guaA, and camS. Closer inspection of the genome sequence data further revealed that reads covering SCCmec were ∼10 times overrepresented compared to other parts of the chromosome. Quantitative PCR (qPCR) confirmed >10-fold-higher levels of mecA DNA on the HoR34 chromosome, and MinION genome sequencing verified the presence of 10 tandem repeats of the SCCmec element. qPCR further demonstrated that subculture of HoR34 in various concentrations of oxacillin (0 to 100 μg/ml) was accompanied by accordion-like contraction and amplification of the SCCmec element. Although slower growing than strain USA300, HoR34 outcompeted the parent strain in the presence of subinhibitory oxacillin. These data identify tandem amplification of the SCCmec element as a new mechanism of high-level methicillin resistance in MRSA, which may provide a competitive advantage for MRSA under antibiotic selection.