Project description:Oxygen and carbon dioxide are common protective gases used in modified atmosphere packaging (MAP) of meat. Within the package, they selectively suppress members of the spoilage microbiome, reshaping it to adapted species concomitantly growing upon MAP. Thus, this species must exhibit adaptation mechanisms to withstand the inhibitory effect of carbon dioxide and oxygen, and cope with selective nutrition on MAP meat. In order to uncover these mechanisms, the typical representative meat-spoiling bacteria Brochothrix (B.) thermosphacta TMW2.2101 and four lactic acid bacteria (LAB) Carnobacterium (C.) divergens TMW2.1577, C. maltaromaticum TMW2.1581, Leuconostoc (L.) gelidum subsp. gelidum TMW2.1618 and L. gelidum subsp. gasicomitatum TMW2.1619 were grown in a meat simulation medium under a controlled, sterile environment, aerated constantly with either air, 100%_N2, 30%_CO2/70%_O2 or 30%_CO2/70%_N2. Growth dynamics were monitored and a label-free quantitative mass spectrometric approach was employed to determine changes within the bacterial proteomes in response to the different gas atmospheres. Revealed bacterial tolerance to modified atmospheres (MA) comprise two possible scenarios: Either bacteria were intrinsically adapted to MA, exhibiting no proteomic regulation of enzymes (L. gelidum subsp. gelidum and gasicomitatum) or, tolerance was provided by varying specific metabolic adaptation (B. thermosphacta, C. divergens, C. maltaromaticum). In detail, metabolic adaptation mechanisms to oxygen comprised an enhanced oxidative stress reduction response, adjustment of the pyruvate metabolism and catabolic oxygen consuming reactions. Adaptation to carbon dioxide was characterized by an upregulation of proteins involved in intracellular pH homeostasis, maintenance of osmotic balance and alteration of the fatty acid composition of the cell membrane. We furthermore predict species-specific strategies for different and preferential carbon source utilization enabling a non-competitive coexistence on meat and resulting in a synergistic spoilage. We conclude that a gas atmosphere containing 30%_CO2/70%_O2 has no inhibitory effect on the analyzed prominent meat-spoiling bacteria whereas 30%_CO2/70%_N2 predictively inhibits C. divergens TMW21577 and B. thermosphacta TMW2.2101 but not the other three species. This gives a mechanistically explanation of their acknowledged status as typical spoilage organisms on packaged meats.
Project description:Modelling the growth and interaction between Brochothrix thermosphacta, Pseudomonas spp. and Leuconostoc gelidum in minced pork meat samples.
