New halo- and thermotolerant fermenting bacteria producing surface-active compounds

Abstract

Two new strains of fermenting bacteria were isolated from oily sludge under conditions of enhanced salt concentration (approx. 8% w/v) and temperature (50°C). They produced considerable amounts of surface-active compounds that were detected by a newly developed quick and easy half-quantitative test of emulsion stabilization, and were quantified by tensiometry. The chemical structure of the surfactant is unknown. The strains grew fast with inexpensive substrates such as sugars and might be of interest for application in microbially improved oil recovery. Morphological, cytological, and physiological characterization allowed affiliation of the two strains to the genus Bacteroides.

Anaerophaga thermohalophila gen. nov., sp. nov., a moderately thermohalophilic, strictly anaerobic fermentative bacterium.

“…Strain Fru22 T and a similar strain, Glc12, had been enriched originally from blackish-oily sedimentary residues of an oil separation tank near Hannover, Germany. The mineral salts medium for enrichment and cultivation was bicarbonate-buffered (50 mM), cysteine-reduced (1 mM) and contained, together with other minerals, 75 g NaCl l − " and 4n0 g MgCl Denger & Schink, 1995). The pH was 6n7-6n8.…”

“…Subcultures were inoculated with oily drops from the surface of the preculture. All details concerning cultivation and physiological characterization have been described by Denger & Schink (1995). Pigment characterization.…”

“…Possible hydrolysis by enzymes was checked for by incubation experiments with proteinase K (from Tritirachium album, 150 µg ml − " ; Merck) or trypsin (from pig pancreas, 150 µg ml − " ; Merck) in 10 mM Tris\HCl buffer, pH 8n0, or lipase (from Candida cylindrica, 100 µg ml − " ; Merck) in 10 mM Tris\HCl buffer, pH 7n5. Culture supernatant was incubated at 37 mC for 1 h and surface activity was measured by a test checking for stabilization of an oil-water emulsion (Denger & Schink, 1995). For enrichment of the surface-active compound, the culture supernatant was titrated to pH 2n0 with 25 % (w\v) HCl.…”

“…In an effort to provide suitable organisms for microbially enhanced oil recovery, we isolated strains of moderately thermophilic and halophilic bacteria which could thrive in such environments and be applied to improve oil recovery. Two such strains have been described with respect to their nutritional, morphological and physiological properties (Denger & Schink, 1995). In the present paper, one of these isolates, strain Fru22 T , is described in more detail, also with respect to the production of a pigment and of an extracellular surface-active agent.…”

“…The isolated strains were unusual also in their fermentation patterns (Denger & Schink, 1995). Hexoses and pentoses were fermented to equal molar amounts of acetate, propionate and succinate, according to the following equations :…”