Paul Magnano:Week 3 Individual Journal

Outline

Experiment

• sacchromyces cerevisiae was grown in continuous culture, with varying ammonia input concentrations, while ammonia assiilation rates remained constant
• ammonia is a preffered nitrogen source for s. cerevisiae, because it results in faster growth than other sources
• in this study, cultures were grown with same flux (relationship b/w external ammonia concentration and rte of assimilation) but different inflow ammonia concentrations
• Physiological parameters:
  • S. cerevisiae SU32 grown in continuous cultures with ammonia inflow concentrations ranging from 29 to 118mM
  • fixed glucose concentration of 100mM
• Fig 1A
  • increase of ammonia concentration from 29 to 61mM resulted in increase of biomass from 4.9 to 8.2 g/liter
  • ammonia concentration above 61mM biomass remained at 8.2 g/liter
  • over trhe entire range of ammonia concentrations the ammonia flux into biomass was 1.1 mmol/gh
• Fig 1B
  • input ammonia concentration above 44mM resulted in (c02 production/02 consumption) remained constant
  • with ammonia limitation (ammonia input below 44mM) c02 production and 02 consumption values differed
  • no changes in the residual glucose concentration were seen
  • no significant changes in carbon metabolism occured when the culture was switched from ammonia excess to ammonia limitation
• Fig 1C
  • ammonia within the cells reacts with ketoglutarate to produce glutamate which is converted to glutamine
  • ketoglutarate concentration decreased from 10 to 5 umol/g when the ammonia concentration changed from limited to excess
  • glutamate concentration increased within the cell, linearly
  • increaing ammonia concentrations caused the concentrations of glutamate and glutamine within the cell to increase

Northern Analyses

• RNA analyses were done to see if RNA levels of nitrogen regulating genes changed with increased ammonia concentrations
• genes GDH1, GDH2,GLN1 were determined to study responses to ammonia levels
• Fig 2
  • increasing ammonia levels resulted in GDH1 levels staying the same
  • ammonia concentrations of 29-44mM there was no GDH2, but with increase to 61mM GDH2 level increased
  • maximum GLN1 expression was observed at 61mM
  • overall it was seen that ammonia concentration both repressed GDH1 and caused the expression of GDH2