2 Experimental
2.1 Cultivation of bacteria and harvesting of EPS
In this project, several bacterial strains have been applied
for cultivation and EPS production [60]. D. vulgaris – as a
representative strain of corrosive SRB – was also cultivated and
applied for experiments simulating MIC [60]. The composition of
the appropriate growth medium for D. vulgaris is based on the
Postgate C medium (PGC) as given by the German Collection of
Microorganisms and Cell Cultures (DSMZ, Desulfovibrio medium
no. 63). And was modified according to von Re`ge [72] (cf. Table 1).
D. vulgaris was obtained from the German Collection of
Microorganisms and Cell Cultures (DSMZ, DSM 644) and
cultivated in PGC at 30 8C in the dark without shaking for 3 days
and kept as stock culture at 4 8C for 4–6 weeks. A 1% inoculum
was used to inoculate the experiments.
For EPS harvesting D. vulgaris was cultivated for 3 days: the
culture solutions were centrifuged (30 min, 12 000g, 108C)
(Kontron Hermle Centrikon H-401). In order to eliminate
remaining cells the supernatant was filtrated through sterile
cellulose acetate filters (0.2 mm, Sartorius). Afterwards, the sterile
supernatant was dialysed using a membrane of 3500 kDa
molecular weight cut-off (Spectrapor 6 MWCO 3500). Dialysis
was performed overnight against streaming deionized water and
subsequently two times for 3 h against double deionized water
under agitation. Finally the EPS have been evaporated in order to
minimize the volume for the subsequent freeze-drying process.
The absence of viable bacteria cells in the thus treated EPS was
checked by application of the MPN (most probable number)
method according to de Man [73].
2.2 Preparation of modified Postgate C medium [72]
2 Experimental2.1 Cultivation of bacteria and harvesting of EPSIn this project, several bacterial strains have been appliedfor cultivation and EPS production [60]. D. vulgaris – as arepresentative strain of corrosive SRB – was also cultivated andapplied for experiments simulating MIC [60]. The composition ofthe appropriate growth medium for D. vulgaris is based on thePostgate C medium (PGC) as given by the German Collection ofMicroorganisms and Cell Cultures (DSMZ, Desulfovibrio mediumno. 63). And was modified according to von Re`ge [72] (cf. Table 1).D. vulgaris was obtained from the German Collection ofMicroorganisms and Cell Cultures (DSMZ, DSM 644) andcultivated in PGC at 30 8C in the dark without shaking for 3 daysand kept as stock culture at 4 8C for 4–6 weeks. A 1% inoculumwas used to inoculate the experiments.For EPS harvesting D. vulgaris was cultivated for 3 days: theculture solutions were centrifuged (30 min, 12 000g, 108C)(Kontron Hermle Centrikon H-401). In order to eliminateremaining cells the supernatant was filtrated through sterilecellulose acetate filters (0.2 mm, Sartorius). Afterwards, the sterilesupernatant was dialysed using a membrane of 3500 kDamolecular weight cut-off (Spectrapor 6 MWCO 3500). Dialysiswas performed overnight against streaming deionized water andsubsequently two times for 3 h against double deionized waterunder agitation. Finally the EPS have been evaporated in order tominimize the volume for the subsequent freeze-drying process.The absence of viable bacteria cells in the thus treated EPS waschecked by application of the MPN (most probable number)method according to de Man [73].2.2 Preparation of modified Postgate C medium [72]
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