Molecular source of biomarkers by genetic engineering techniques

The mutant lacking ORF469 fragment in Synechocystis sp. PCC 6803 (cyanobact erium) was created by means of DNA recombination. In its genome, ORF469, th e 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 muta nt cells was fully controlled by illumination and two kinds of cells were h arvested, one is high chlorophyll with concentration of 9.427 mu g . mg(-1) and the other is low chlorophyll with concentration of 0.695 mu g . mg(-1) . They were subjected to thermal simulation respectively at 300 degrees C f or 100 h. The alkanes biomarkers from pyrolysates were analyzed by GC-MS an d main difference between high and low chlorophyll cells was found at their contents of isoprenoid hydrocarbons. Pr/nC(17) and Ph/nC(18) from pyrolysa te of low chlorophyll cells were 0.192 and 0.216 respectively, which were a bout 1/3 and 1/7 of that from high chlorophyll cells, The results provide d irect evidence that isoprenoid hydrocarbons such as phytane(Ph) and pristan e (Pr) could be derived from chlorophyll. The lipids in algal cells would b e the most important contributors to hydrocarbon production in their therma l degradation. The results also indicated that the combination of molecular biology and organic geochemistry would provide a new path to investigate t he molecular sources of biomarkers.