In Saccharomyces cerevisiae, the accepted theory is that due to TCA cycle dysfunction, the cit1 mutant lacking the mitochondrial enzyme citrate synthase (Cit1) cannot grow on acetate, regardless of the presence of the peroxisomal isoenzyme (Cit2). In this study, we re-evaluated the roles of Cit1 and Cit2 in acetate utilization and examined the pathway of acetate metabolism by analysing mutants defective in TCA or glyoxylate cycle enzymes. Although cit1 cells showed significantly reduced growth on rich acetate medium (YPA), they exhibited growth similar to cit2 and the wild-type cells on minimal acetate medium (YNBA). Impaired acetate utilization by cit1 cit2 cells on YNBA was restored by ectopic expression of either Cit2 or its cytoplasmically localized variants. Deletion of any of the genes for the enzymes solely involved in the TCA cycle (IDH1, KGD1 and LSC1 ), except for SDH1, caused little defect in acetate utilization on YNBA but resulted in significant growth impairment on YPA. In contrast, cells lacking any of the genes involved in the glyoxylate cycle (ACO1, FUM1, MLS1, ICL1 and MDH2 ) did not grow on either YNBA or YPA. Deletion of SFC1 encoding the succinate-fumarate carrier also caused similar growth defects on YNBA. Our results suggest that in S. cerevisiae the glyoxylate cycle functions as a competent metabolic pathway for acetate utilization on YNBA, while both the TCA and glyoxylate cycles are essential for growth on YPA.
In multi-robot systems, each robot needs to have the position and pose information of itself and that of the other cooperative robots. This paper presents a synchronous distributed positioning system that uses a multi-code ultrasonic sensor network and a compensation algorithm using a Kalman filter. The bearings of robots are computed by using their position changes, and then compensated for by using the Kalman filter. The ZigBee sensor network protocol is used for communication among the robots and for the synchronization of the ultrasonic transmission timing. The experimental results show that our system positions multiple robots synchronously without any configured infrastructures. The results have a better accuracy and less accumulative error than those found in positioning systems without compensation.
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