tailieunhanh - Báo cáo y học: " Bet hedging in the underworld"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Bet hedging in the underworld. | Zhang and Rainey Genome Biology 2010 11 137 http 2010 11 10 137 w Genome Biology RESEARCH HIGHLIGHT L__ Bet hedging in the underworld Xue-Xian Zhang and Paul B Rainey Abstract Under starvation conditions the soil bacterium Sinorhizobium meliloti divides into two types of daughter cell one suited to short-term and the other to long-term starvation. Soil-dwelling bacteria face the challenge of maintaining fitness in the face of frequent changes in nutrient availability. Many species have evolved mechanisms of food storage which are likely to enhance survival during periods of starvation. The classic example is production of lipid-like poly-3-hydroxybutyrate PHB by bacteria in the family of Rhizobiaceae collectively known as rhizobia . Rhizobia lead a dual life as both soil saprophytes living off dead organic matter and as symbionts of leguminous plants. As plant symbionts they exist in specialized organs known as nodules where they convert atmospheric nitrogen into ammonium for use by the plant. Within the nodule rhizobial activities are powered by carbohydrates from the plant with surplus being partitioned to the storage compound PHB 1 . Stored PHB - a reward from the symbiosis - can exceed 50 of the cellular dry weight of rhizobia and is used to support growth in the nutrient-limited bulk soil after rhizobia are released from senescing nodules. Before reaching the next suitable host rhizobia must decide how to use stored PHB. The critical but unknown factor is the length of time before a new host is encountered. How should the bacterium respond One possibility is to use PHB as fast as possible thus maximizing short-term growth rate - a strategy likely to be successful if a new host is encountered in the near future but disastrous if there is a prolonged period before the next host. Alternatively PHB could be used conservatively thus increasing the likelihood of long-term survival - a strategy likely to be successful if new hosts

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