Production of bacterial exopolysaccharides by solid substrate fermentation
Introduction
Bacterial exopolysaccharides (EPS) have found a wide range of applications as thickeners, stabilisers, emulsifiers, binders, film former, gelling and suspending agents, based on their structural properties and rheological behaviour. Nevertheless, plant and algal polysaccharides still dominate the natural gum market, due to lower production costs. With microbial EPS, the costs of nutrient substrate, bioprocess and recovering process add up to the final price, which must be moderate to be competitive with that of algal and plant products [1], [2], [3].
The production of bacterial EPS in submerged cultivation is often accompanied by a substantial increase in the fermentation broth viscosity, which results in impaired air distribution in the medium. Under these conditions, oxygen availability might become the limiting factor for cell metabolism, thus negatively affecting EPS synthesis and quality [4], [5], [6]. In addition, the agitation of viscous culture fluids is much more costly, both in terms of energy expenditure and of stirring equipment, than in low viscosity broths [1], [2].
Solid substrate fermentation (SSF) has been suggested as a suitable alternative to submerged fermentation in order to prevent the problems connected with high viscosity of culture broths. A further advantage of SSF is that cheap and easily available substrates, such as agriculture and food industry by-products might he used in this process. Many processes based on SSF have been developed for the production of enzymes, organic acids, alcohol, protein enriched feed, secondary metabolites, unsaturated fatty acids and other microbial products [7], [8], [9], [10], [11], [12], [13], [14], [15]. The production of xanthan by surface cultivation on vegetable cubes has also been published [16].
In this work, the efficiency of SSF for EPS production was evaluated, as compared to submerged fermentation, on the lab-scale. EPS producing microorganisms were selected among those which prosper in a solid environment (soil, plants), as SSF ideally simulates their natural hahitat.
Section snippets
Bacteria
Rhizobium meliloti SU-47 and R. trifolii TA-1 were kindly supplied by Prof. Zevenhuizen (Agricultural University, Wageningen, The Netherlands); Rhizobium sp AAD8, R. galega and R. hedysari HCNT1 were provided by Dr Tombolini, (University of Padova, Italy); Agrobacterium tumefaciens PT45 was obtained as a spontaneous variant of the strain Agrobacterium tumefaciens PD51 (Culture Collection of Plant Protection Service, Wageningen, The Netherlands); Xanthomonas campestris PD656 and PD659 were also
Choice of substrate
The solid matter used in SSFs usually contains most, if not all of the nutrients supporting microbial growth and/or product formation. Alternatively, an inert matrix might be used as a support for growth after impregnation with the appropriate nutrient solution. In this study the latter option was chosen in order to compare EPS productivity in solid and in submerged cultivation, using the same liquid medium composition.
Critical requirements of the solid support to be used were a high absorption
Conclusions
In this work the production of EPS by various bacterial species was favoured in solid substrate fermentation, as compared to submerged cultivation, on the laboratory scale. Spent malt grains, the use of which has been reported as a growth support for polyunsaturated fatty acids producing fungi [25], proved to be an excellent support for bacterial growth and exopolysaccharide production, after impregnation with the appropriate nutrient solution.
While in the case of xanthan the yields obtained in
References (25)
- Margaritis, A. and Pace, G. W., In Comprehensive Biotechnology, ed. M. Moo-Young. Pergamon Press, Oxford, 1985 pp....
- Galindo, E., Aspects of the process for xanthan production. TransICHemE 1994, 72, (Part C)...
- Papoutsopoulou. S. V., Ekaterinidiadou, L. V., and Kyriadis. D. A., Genetic construction of Xanthomonas campestris and...
- Wernau, W. C., Fermentation methods for the production of polysaccharides. Developments in Indian Microbiology 1985,...
- Wecker, A. and Onken, V., Influence of dissolved oxygen concentration and shear rate on the production of pullulan by...
- Peter, H. V., Herbst, H., Hesselink, P. G. M., Lünsdorf, H., Schumpe, A., and Deckwer, W. D., The influence of...
- Rolz, C. E., In Solid Substrate Cultivation, eds H. W. Doelle, D. A. Mitchell, C. E. Rolz, Elsevier Science Publishers...
- Lonsane, B. K., Ghildyal, N. P., In Solid Substrate Cultivation, eds H. W. Doelle, D. A. Mitchell, C. E. Rolz, Elsevier...
- Johns, M. R., In Solid Substrate Cultivation, eds H. W. Doelle, D. A. Mitchell, C. E. Rolz, Elsevier Science Publishers...
- Pandey, A., Recent process developments in solidstate fermentation. Process Biochemistry 1992, 27,...
Cited by (33)
Sourdough fermentation of whole and sprouted lentil flours: In situ formation of dextran and effects on the nutritional, texture and sensory characteristics of white bread
2021, Food ChemistryCitation Excerpt :Overall, lentil and sprouted lentil flour appeared to be good substrate for EPS production. Stredansky, Conti, Navarini, & Bertocchi (1999) hypothesized that one important factor influencing the yield of synthesized EPS could be the similarity of the substrate to the natural habitat of the microorganisms. This could fit our experimental conditions, since SL flour is the natural habitat which W. confusa SLA4 was isolated (Perri, Calabrese, Rizzello, De Angelis, Gobbetti, & Calasso, 2020).
Semi-continuous production of xanthan in biofilm reactor using Xanthomonas campestris
2021, Journal of BiotechnologyCitation Excerpt :High agitation may be a strategy to overcome this restriction. Stredansky et al. (1999) reported a higher productivity of succinoglycan in solid substrate fermentation compared with a submerged cultivation, due to higher availability of oxygen for Agrobacterium tumefaciens, thus free oxygen may move more rapidly through the spaces between particles and reached to the attached cells, accordingly, a higher growth and productivity of succinoglycan was obtained. Feeding operation may also change the yield of bioproduction of gum (Stredansky et al., 1999).
Cow dung is an ideal fermentation medium for amylase production in solid-state fermentation by Bacillus cereus
2015, Journal of Genetic Engineering and BiotechnologyCitation Excerpt :Agrowastes like wheat bran, rice bran, and coconut oil bran have replaced the high cost media generally used in submerged fermentation for amylase preparation because of their simplicity, low cost, easy availability, and lesser water output. Additionally it solves the pollution problem occurring due to their disposal in the surrounding [19]. Recently, various agrowastes were used as the substrates for the production of amylases in SSF.
Statistical based media optimization and production of naringinase using Aspergillus brasiliensis 1344
2014, International Journal of Biological MacromoleculesCitation Excerpt :SSF has many advantages over submerged fermentation including higher productivity, simple technique, low capital investment, low energy requirement and less water output, thus lesser contamination, lack of foam build up, but improved product recovery. Thus, several advantages have made SSF a method of choice for the production of industrially important compounds [9–11]. Different solid substrates were used for naringinase production under the SSF, including soybean [1], wheat bran, washed sugarcane bagasse [12], and rice bran [13].
Perspective of apple processing wastes as low-cost substrates for bioproduction of high value products: A review
2013, Renewable and Sustainable Energy ReviewsCitation Excerpt :Besides, xanthan gum has been used as emulsifiers, stabilizers and texture enhancers in the food industry [131]. The exopolysaccharide production using SSF has been reported by the group of Stredansky and Conti [158] and Stredansky et al. [159]. X. campestris strains were cultivated on easily available low cost substrates, such as AP, grape pomace and citrus peels, among others, in order to evaluate their ability to produce the exopolysaccharide xanthan.
Alcohol production from sterilized and non-sterilized molasses by Saccharomyces cerevisiae immobilized on brewer's spent grains in two types of continuous bioreactor systems
2012, Biomass and BioenergyCitation Excerpt :Brewer's spent grains (BSG), the main solid residual of the brewing industry, are discarded at large amounts annually but their utilization is still limited. At research level, alternative uses of BSG have been proposed, including protein rich animal feed production, exopolysaccharides, ethanol, enzymes, as well as biocatalysts based on immobilized cells for alcoholic fermentation processes [8,15–19]. Specifically, the use of BSG as solid supports for yeast immobilization, led to the production of biocatalysts, that showed high efficiency in alcoholic fermentation of glucose and molasses as well as in wine making and brewing processes, even at very low temperatures [8,19,20].