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Rhamnolipid production by Pseudomonas aeruginosa under denitrification: effects of limiting nutrients and carbon substrates.

Abstract：

:Being biosurfactants, rhamnolipids create severe foaming when produced in aerobic Pseudomonas aeruginosa fermentation. The necessary reduction of aeration causes oxygen limitation and restricts cell and product concentrations. In this study, we evaluate the new strategy of rhamnolipid production under denitrification conditions. Because hydrocarbons used in earlier aerobic fermentations were not metabolizable in the absence of oxygen, other potential C substrates were examined, including palmitic acid, stearic acid, oleic acid, linoleic acid, glycerol, vegetable oil, and glucose. All were found able to support cell growth under anaerobic denitrification. The growth on the two solid substrates (palmitic acid and stearic acid) was slower but could be enhanced substantially by initial addition of rhamnolipids (0.06 g/L). The effects of different limiting nutrients (N, P, S, Mg, Ca, and Fe) were also investigated. The commonly used N limitation could not be adopted in the denitrifying fermentation because the nitrate added for anaerobic respiration would also be assimilated for growth. P limitation was most effective, giving four- to fivefold higher specific productivity than the conventional N limitation. S limitation was comparable to N limitation; Mg limitation was much poorer. Ca and Fe were ineffective in limiting cell growth. The new strategy was further evaluated in a P-limited fermentation with palmitic acid as the substrate. The fermentation was first carried out under denitrification and later switched to aerobic condition. The specific productivity under denitrification was found to be about one-third that of the aerobic condition. The denitrification process was, however, free of foaming or respiratory limitation. Much higher cell concentrations may be employed to attain higher volumetric productivity and product concentrations, for more economical product recovery and/or purification.

journal_name

Biotechnol Bioeng

journal_title

Biotechnology and bioengineering

authors

Chayabutra C,Wu J,Ju LK

doi

10.1002/1097-0290(20010105)72:1<25::aid-bit4>3.0.c

subject

Has Abstract

pub_date

2001-01-05 00:00:00

pages

25-33

issue

eissn

0006-3592

issn

1097-0290

pii

10.1002/1097-0290(20010105)72:1<25::AID-BIT4>3.0.C

journal_volume

pub_type

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Rhamnolipid production by Pseudomonas aeruginosa under denitrification: effects of limiting nutrients and carbon substrates.