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Understanding bacteria and the lag phase.

Salmonella remains a serious cause of food poisoning in the United Kingdom and elsewhere, in part due to its ability to thrive and quickly adapt to the different environments in which it can grow. Now a team of scientists at the Institute of Food Research (IFR) has taken the first detailed look at what Salmonella does when it enters a new environment, which could help find ways to reduce its transmission through the food chain and prevent human illness.

Bacteria can multiply rapidly, potentially doubling every 20 minutes under ideal conditions. However, this exponential growth phase is preceded by a lag phase, when no increase in cell number occurs. Lag phase was assumed to be needed by bacteria to prepare to exploit new environmental conditions. Bacteria are metabolically active in this period.

Researchers at IFR, along with colleagues at Campden BRI, Gloucestershire, U.K., have developed a system for studying the biology of Salmonella during its lag phase. In this system, the lag phase lasts about two hours, but the cells sense their new environment remarkably quickly, and within four minutes switch on a specific set of genes, including some that control the uptake of specific nutrients.

For example, one nutrient accumulated was phosphate, which is needed for many cellular processes, and a gene encoding a phosphate transporter was the most upregulated gene during the first four minutes of the lag phase. The cellular uptake mechanisms for iron were also activated during the lag phase. Iron is needed for key aspects of bacterial metabolism. This increase in iron leads to a short-term sensitivity to oxidative damage. Manganese and calcium were also accumulated in lag phase, but were lost from the cell during exponential growth.

This new understanding of Salmonella's metabolism during lag phase shows how rapidly Salmonella senses favorable conditions and builds up the materials needed for growth. Future research to determine the regulatory mechanisms behind these processes and the switch from lag phase to exponential growth will tell us more about how Salmonella can flourish in different environments, and could point to new ways of controlling its transmission in the food chain.

Further information. Mike Peck, Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, U.K.; phone: 1603 255000; fax: 1603 507723; email:
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Publication:Emerging Food R&D Report
Geographic Code:4EUUK
Date:Apr 1, 2012
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