, Volume 39, Issue 1, pp 92-99

Physiological Status and Community Composition of Microbial Mats of the Ebro Delta, Spain, by Signature Lipid Biomarkers

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Physiological status of microbial mats of the Ebro Delta (Tarragona, Spain) based on the extraction of lipids considered ``signature lipid biomarkers'' (SLB) from the cell membranes and walls of microorganisms has been analyzed. Data from a day–night cycle show significant differences in viable cells countings (PLFA cells counts) ranging from 1.5 × 1010 to 5.0 × 1010 cells g−1 of sediment. Minimum values were observed at 18:00 and 6:00, when physicochemical conditions change drastically. The diversity of the microbial community was assessed by GC/MS analysis of phospholipid fatty acids (PLFA). The ratio of PLFA, representative of Gram-negative bacteria, comprises 47.8% of the total PLFA of the microbial mat community. The remaining PLFA was representative of Gram-positive (10.0%), anaerobic (5.7%), and eukaryotic microorganisms (5.7%), and other common lipids. Two different approaches were used as a comparative study to assess the physiological status of the microbial mats. Two parameters (cyclopropane fatty acids/ω7c monoenoic fatty acids, and measurement of the trans/cis monoenoic PLFA ratio) showed a minimum at midnight, suggesting the highest microbial activity. Higher values were observed at 18:00 and 6:00, coinciding with lower PLFA cell counts.

Received: 14 May 1999; Accepted: 6 September 1999; Online Publication: 24 March 2000