S. Krishnakumar's Talk

Aug 12, 2013 - 00:41

Aug 12, 2013 - 00:41

Chemical Engineering room no 118

Seminars

S. Krishnakumar who is a PhD student working with Professors Pramod Wangikar and Ganesh Viswanathan

Abstract: Cyanobacteria are a group of photosynthetic prokaryotes that inhabit in diverse ecosystems with simple oxygen (O2) evolving mechanism similar to that in higher plants. They are believed to be responsible for the creation of oxygenic atmosphere on earth and are credited with 20-30% of the global photosynthesis currently. Cyanobacteria use light energy from the sunlight to fix atmospheric CO2 and convert it into energy rich sugar molecules for their growth development and metabolic process. Cyanothece sp. ATCC 51142 a non-heterocystous diazotrophic unicellular organism is one amongst the photosynthetic cyanobacterial community known well to perform both oxygenic photosynthesis and oxygen-sensitive nitrogenfixation temporally. This organism has extraordinary metabolic capabilities and is reported to produce higher amount of hydrogen (H2) under nitrogen fixing conditions. However commercial considerations in growing this type cultures typically demand high cell density cultivations which usually result in photo-limitation or photo-inhibition due to self-shading and uneven light distribution at high cell growth. A potential remedy would be culturing these cells under turbulent condition which could alleviate such problems as a result of flashing light effect and cyclic movement of cells between light and dark zones. However introducing turbulence along with aeration in reactor vessel can increase the oxygen tension in the media which may affect nitrogen fixation and growth under nitrogen fixing conditions. We demonstrate the robustness and metabolic potential of Cyanothece 51142 at nitrogen fixing conditions through analyzing the online exhaust gas CO2 and O2 profiles under the influence of varying the agitation rates. From this study we ascertain that the agitation speed at 600 rpm in stirred vessel provide optimal growth for this organism than the conventional shake flask and flat panel bioreactor studies. Further Cyanothece 51142 tend to oscillate between day and night time metabolisms in response to light/dark (LD) or continuous light (LL) cycles we therefore investigate the periodicity behavioral pattern and robustness of free-run metabolic oscillations in tandem with gene expression studies under prolonged LL condition. We show that Cyanothece 51142 exhibit ~11h period sustained oscillations under extended LL condition with fair synchronization between the online exhaust gas profiles and the results of biochemical and gene expression analysis. We also develop and demonstrate a novel functional re-annotation tool called “SHARP” (Systematic Homology-based Automated Re-annotation for Prokaryotes) to predict the Gene-Protein-Reaction (GPR) associations based on distant context-specific sequence similarities and probabilistic optimization approach predominantly from cyanobacterial species. The predicted GPR associations using SHARP led to the identification of several important pathways which can provide new directions in performing metabolic engineering studies to produce useful products.