Anaerobic biodegradation of lipids of the marine microalga Nannochloropsissalina

In order to determine the susceptibility to anaerobic biodegradation of the different lipid biomarkers present in a marine microalga containing algaen an, portions of one large batch of cultured Nannochloropsis salina (Eustigm atophyceae) were incubated in anoxic sediment slurries for various times. A fter 442 days, all lipids studied [mono-, di-, and tri-unsaturated hydrocar bons, long-chain unsaturated alcohols and alkyl diets, phytol, sterols, sat urated and (poly)-unsaturated fatty acids] showed a significant decrease in concentration, which was accompanied by a strong production of sulfide and methane. However, the studied compounds showed a wide range of reactivity and different patterns and extent of degradation. Polyunsaturated fatty aci ds, phytol and triunsaturated hydrocarbons were the most labile compounds a nd showed initially rapid degradation rates, followed by a substantial redu ction in degradation rate during the later stages of incubation. Long-chain alkyl diols and unsaturated alkenols, known to constitute the building blo cks of the algaenan of N. salina, showed fluctuating concentrations with ti me clearly indicating their release from bound fractions in parallel with t heir degradation. Other lipids showed a continuous concentration decrease u ntil the end of the incubation, with alkadienes and sterols being the most resistant compounds encountered. Besides providing an extended sequence of reactivity For lipids under anoxic conditions, the results demonstrate that the presence of resistant algaenan in the outer cell wall of microalgae do es not protect the other lipids of the cell From anaerobic microbial degrad ation. (C) 2001 Elsevier Science Ltd. All rights reserved.