Sulfonolipid content of Cytophaga and Flexibacter species isolated from soil and cultured under different nutrient and temperature regimes

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Abstract
Gliding bacteria of the genera Cytophaga and Flexibacter contain an unusual sulfonolipid in their outer membrane that may be a potential biochemical marker for these organisms in soil. The precision with which a marker provides information about biomass varies with the range in marker content within the cells of the taxon under study. To evaluate this, Cytophaga and Flexibacter spp. were isolated from earthworm fecal pellets and soil, batch cultured with [35S]sulfate, and extracted for lipids. Sulfonolipid S was measured using isotope dilution techniques and lipid phosphate was determined by colorimetry. Ratios of sulfonolipid S to protein and to phospholipid P were compared among isolates grown under various conditions. Ratios of sulfonolipid S to phospholipid P from 0.22 to 0.98 confirmed sulfonolipids as major cell components of Cytophaga and Flexibacter spp. Two criteria essential to the success of sulfonolipids as a biomarker for these organisms in soil were met: (i) sulfonolipid concentration among the noncellulolytic isolates, with one exception, spanned a narrow range (40–60 μmol S/g cell protein), and (ii) this range in sulfonolipid concentration was maintained under the range of growth conditions studied here. Cellulolytic cytophagas, however, could be clearly differentiated from other Cytophaga and Flexibacter spp. on the basis of sulfonolipid content, 85–164 μmol S/g cell protein. This dichotomy in sulfonolipid content between cellulolytic and noncellulolytic isolates must be considered when interpreting data where sulfonolipids are used as a quantitative biomarker for Cytophaga and Flexibacter spp. in habitats where cellulolytic cytophagas are dominant.Key words: lipid biomarkers, cellulolytic cytophagas, Cytophaga, Flexibacter, sulfonolipids.

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