Metabolic Network Reconstruction of Algal Strains of <em>Chlorella species</em>

Abstract

<em>Chlorella</em> is a photosynthetic, eukaryotic microalgae that has received profound interest as a prospective feed source for the production of biofuels. For efficient biotechnological application, the high light tolerance and thereby accelerated growth of some species is of special interest. To uncover the genetic basis of high light tolerance, genome metabolic network reconstruction of high light sensitive and tolerant strains was performed. <br/> For this thesis research work, four <em>Chlorella</em> strains are used for a comparative analysis. Three strains were high light tolerant while one was high light sensitive. The genomes of these algal strains were annotated with gene ontology terms and EC numbers by using InterProScan, InterPro2GO and EC2GO mapping. <br/> With <em>Arabidopsis thaliana</em> as reference genome, ortholog prediction was conducted by using OrthoMCL. BLASTP was used for sequence similarity analysis, whereas for pathway mapping KEGG Pathways mapping tool was used. <br/> Pathway coverage of shared and strain-specific genes was analysed. The results show that in the Oxidative Phosphorylation pathway there is a missing gene in the sensitive strain (Cv11b). This gene belongs to NADH dehydrogenase, Complex-I and functions in the transfer of electrons from NADH to the respiratory chain, while it is present in tolerant strains. The glycerophospholipid metabolism pathway also shows a missing enzyme, PSD3, in the sensitive strain (Cv11b). This gene is present in all tolerant strains. Subsequently, synteny analysis was conducted for the PSD genomic region. The alignment of Cv264 and Cv11b algal strains showed that PSD3-neighbouring genes were located on contig node-207 of the sensitive algal strain Cv11b, however flanking genes to one side of the expected PSD3 location were found in reverse order and orientation in Cv11b. However, the PSD3 gene itself could not be mapped to the Cv11b genome sequence. This indicates that the genomic region of PSD3 is sequenced and assembled in Cv11b, however the PSD3 gene has presumably been deleted. <br/> These differences in metabolic networks could be candidates for further studies regarding their potential to enhance lipid production by using metabolic engineering. Especially PSD3 appears to be an interesting target for high light tolerance as it may be linked to lipid production and the capacity of membranes to maintain function under high light stress.