Lipid production and molecular dynamics simulation for regulation of accD gene in cyanobacteria under different N and P regimes

Roshan Kumar,Koushik Biswas,Pankaj Kumar Singh,Puneet Kumar Singh,Sanniyasi Elumalai,Sunil Pabbi,Pratyoosh Shukla

doi:10.1186/s13068-017-0776-2

Abstract

BackgroundMicroalgae grown under different nutrient deficient conditions present a good source of natural lipids with applications for several types of biofuels. The expression of acetyl-CoA carboxylase gene can further provide an insight to the mechanisms leading to enhanced lipid production under such stresses. In this study, two nutrients viz. nitrogen and phosphorus were modulated to see its effect on lipid productivity in selected cyanobacteria and its correlation with Accase followed by molecular dynamics simulation.ResultsSelected cyanobacteria viz. Oscillatoria sp. (SP8), Anabaena sp. (SP12), Anabaena sp. (SP13), Microcoleus sp. (SP18), and Nostoc sp. (SP20) varied in their ability to accumulate lipids which ranged from a lowest of 0.13% in Anabaena sp. (SP13) to the maximum of 7.24% in Microcoleus sp. (SP18). Microcoleus sp. (SP18) also recorded highest lipid accumulation at both N (6 mM NaNO3) and P (0.20 mM K2HPO4) limiting conditions. The overall expression of accD was found to be upregulated in both Oscillatoria sp. (SP8) and Microcoleus sp. (SP18) for all nitrogen concentrations but was differentially regulated with both positive and negative induction under phosphorus stress conditions. Maximum induction was observed in Microcoleus sp. (SP18) at 0.20 mM K2HPO4. The obtained 3D structure of SP8 protein (21.8 kDa) showed six alpha helices, while SP18 protein (16.7 kDa) exhibited four alpha helices and four beta sheets. The phi (ϕ)/psi(ψ) angles of the amino acid residues observed in Ramachandran plot analysis showed that both SP8 and SP18 proteins were highly stable with more than 90% amino acids in allowed regions. The molecular dynamics simulation results also indicated the stability of ligand-bound protein complexes.ConclusionIt has been demonstrated that cyanobacterial isolates are affected differently by nutrient limitation leading to variation in their lipid productivity. The same has been revealed by the behavior of accD gene expression which was regulated more by nutrients concentrations rather than the organism. However, the ligand-bound protein complexes were stable throughout MD simulations.

Highlights

Microalgae grown under different nutrient deficient conditions present a good source of natural lipids with applications for several types of biofuels
It was very interesting to note that Oscillatoria sp. (SP8) and Microcoleus sp. (SP18) which did not survive at lower nitrogen concentration of 3 mM showed maximum fold increase in total lipid accumulation when grown at 6 mM nitrogen
Maximum percentage increase of 26.8% in lipid production was achieved in Microcoleus sp. (SP18) at 6 mM nitrogen concentration after 35 days of incubation (Fig. 1)

Summary

Introduction

Microalgae grown under different nutrient deficient conditions present a good source of natural lipids with applications for several types of biofuels. The available alternative sources such as solar, wind, geothermal, wave, and nuclear energy have many benefits but these are generally limited to producing electricity rather than liquid and gaseous energy storage forms and do not provide a solution for other products derived from petroleum. Biological systems have the potential to function as feedstock for producing liquid or gaseous fuels and biomass-based fuels are ideal as these are renewable, can achieve high efficiencies and are generally well distributed geographically. Many cyanobacteria have the capacity to accumulate substantial amounts of triacylglyceride (TAG) as a storage lipid (ranging from 20 to 50% of cell dry weight) under photo-oxidative stress condition or other environmental stress condition and depending on the species/strain, can produce different kinds of lipids

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Conclusion