Molecular source of biomarkers by genetic engineering techniques

The mutant lacking ORF469 fragment inSynechocystis sp. PCC 6803 (cyanobacterium) was created by means of DNA recombination. In its genome,ORF ₄₆₉, the key DNA fragment controlling the light-independent pathway of chlorophyll biosynthesis was deleted and replaced by erythromycin resistance cassette. The operation resulted in the fact that the content of chlorophyll in mutant cells was fully controlled by illumination and two kinds of cells were harvested, one is high chlorophyll with concentration of 9.427 μg· mg⁻¹ and the other is low chlorophyll with concentration of 0.695 μg · mg¹. They were subjected to thermal simulation respectively at 300°C for 100 h. The alkanes biomarkers from pyrolysates were analyzed by GC-MS and main difference between high and low chlorophyll cells was found at their contents of isoprenoid hydrocarbons. Pr/nC₁₇ and Ph/nC₁₈ from pyrolysate of low chlorophyll cells were 0.192 and 0.216 respectively, which were about 1/3 and 1/7 of that from high chlorophyll cells. The results provide direct evidence that isoprenoid hydrocarbons such as phytane(Ph) and pristane (Pr) could be derived from chlorophyll. The lipids in algal cells would be the most important contributors to hydrocarbon production in their thermal degradation. The results also indicated that the combination of molecular biology and organic geochemistry would provide a new path to investigate the molecular sources of biomarkers.