Amino acids and proteomic acclimation of Staphylococcus aureus when incubated in a defined minimal medium supplemented with 5% sodium chloride

Abstract

Staphylococcus aureus is a versatile bacterium that can adapt to survive and grow in a wide range of salt concentrations. This study investigated whether the cells could mount a response to survive a challenge of 5% NaCl in a minimal incubation medium that would not support cell replication. Cells were grown in liquid culture, washed and then incubated for 90 min at 37°C in a medium that contained only glycine and glucose as substrates in PBS plus trace elements. The control cells were compared with a treatment group which was incubated with an additional 5% NaCl. Significantly more glycine was taken up by the cells exposed to 5% NaCl compared with control cells, and both groups consumed 99% of the glucose supplied. The NaCl treated cells had significantly higher cytoplasmic levels of proline and glutamic acid as well as lower levels of alanine and methionine compared with the controls ( p < 0.05). The levels of the two major cytoplasmic amino acids, aspartic acid and glycine, remained constant in control and treated cells. Proteomic analyses revealed that 10 proteins showed differential responses between the control and treatment groups. The reductions in proteins were primarily associated with processes of protein biosynthesis, pathogenicity, and cell adhesion. Since cell numbers remained constant during the incubation period in minimal medium, it was concluded that there was no cell division to support population growth. The results provided evidence that the cells in the minimal medium exposed to the NaCl treatment underwent in situ homeostatic changes to adjust to the new environmental conditions. It was proposed that this represented a phenotypic shift to form cells akin to small colony variants, with lower metabolic rates and lower levels of key proteins associated with pathogenicity.

The Uptake and Release of Amino Acids by Staphylococcus aureus at Mid-Exponential and Stationary Phases and Their Corresponding Responses to Changes in Temperature, pH and Osmolality

“…This was proposed as an adaptive mechanism by the bacteria to utilize amino acids for energy and alternative resources to support growth based on nutrient availabilities from the surrounding environment (Zhu et al, 2007;Stipetic et al, 2016). To date, the studies have demonstrated that the exposure of S. aureus to subtle variations in temperature, pH and NaCl resulted in significant alterations in cytoplasmic amino acids, proteins and external morphological structures compared with bacterial cells grown under normal conditions (Crompton et al, 2014;Wehrli et al, 2014;Alreshidi et al, 2015;Alreshidi et al, 2016;Alreshidi et al, 2019). It has also been shown that S. aureus consumed a significant amount of glycine when incubated in minimal media supplemented with 5% NaCl compared to the cells grown in normal conditions (Alreshidi et al, 2019).…”

Transporters and Efflux Pumps Are the Main Mechanisms Involved in Staphylococcus epidermidis Adaptation and Tolerance to Didecyldimethylammonium Chloride

“…Modifications to the metabolic pathways are related to decreasing cell size, although many different pathways were detected using the RNA−seq analysis here. The reduction in growth and regulation of the basal metabolic activity of cells represent adaptation responses and survival strategies, along with other metabolic changes, to reduce the harmful effects of antimicrobials [63,65,67].…”

“…Modifications to the amino-acid profile influence many biological pathways in cells, as amino acids are required for protein synthesis, and used for synthesis of the cell-wall and nucleic acids, and they can be used as energy substrates [64]. Reductions in cytoplasmic amino acids has been associated with slower rates of metabolism, to conserve energy for basal metabolism [65]. Modifications to cell membranes and the cell wall are known to be important to maintain cellular homeostasis, by the protection of cells from changes in the environment.…”

Metabolic Profiles of Clinical Strain of Staphylococcus aureus to Subtle Changes in the Environmental Parameters at Different Phases of Growth

“…aureus used in the current study was isolated from patients who were suffering from chronic muscle pain 14 . This bacterium was used in following investigations to study metabolic and proteomic adaptation to alterations in the environmental factors 5,6,9 .…”

“…When S. aureus was grown under sub-optimal conditions, significant changes in the cytoplasmic amino acid, fatty acid and protein patterns were observed 6,8 . Thus, it was assumed that characteristic and specific changes in the amino acid and fatty acid metabolites as well as protein composition led to the survival of S. aureus when exposed to confined nutrition in combination with higher concentrations of NaCl 9 . A recent study indicated that hydrogen peroxide (H 2 O 2 ) combined with various temperatures and pH induced alterations in the amino acid profiles of clinical isolate of S. aureus 10 .…”