Monday, July 25, 2011
Grand Ballroom, 5th fl (Sheraton New Orleans)
Lactococcus lactis is widely used microorganism in food related biotechnology. Having multiple auxotrophies for amino acids the growth conditions are crucial for balancing amino acid metabolism. Steady state metabolism of amino acids in L. lactis at different specific growth rates (μ) has been analyzed using simplified metabolic flux analysis and absolute proteomic and transcriptomic data. The total carbon consumption showed increase of growth efficiency at higher μ values. Main metabolic route for carbon was glycolysis and degradation fluxes of individual amino acids were two magnitudes smaller covering altogether 16% of total carbon flows. Two different phases of amino acid metabolism can be seen: wasting phase (μ 0.1 to 0.4 h-1) and balanced phase (μ 0.4 to 0.55 h-1). In the first phase up to two-thirds of nitrogen is over-consumed mainly through metabolism of arginine, asparagine and glutamine and ammonia efflux, not supporting the biomass production. The wasted amino acids are used to balance the shortage of ATP, α-ketoglutarate and glycolytic intermediates for biosynthesis. At maximal μ amino acids are mainly used for biosynthesis except those related to nucleotide metabolism, suggesting that synthesis of nucleotides might be the key parameters for efficient growth of L. lactis. Balanced metabolism of amino acids accompanied with decrease of energy spilling and increase of ATP incorporation for biosynthesis indicates that energetic limitations at lower μ are also important in wasting of amino acids. In conclusion, more efficient bioprocesses can be developed by varying the growth conditions that result in balanced amino acid consumption of cells.