Biotechnological potential of agro-industrial residues. I: sugarcane bagasse

New developments in solid state fermentation: I-bioprocesses and products.

Despite the increasing number of publications dealing with solid-state (substrate) fermentation (SSF) it is very difficult to draw general conclusion from the data presented This is due to the lack of proper standardisation that would allow objective comparison with other processes Research work has so far focused on the general applicability of SSF for the production of enzymes, metabolites and spores, in that many different solid substrates (agricultural waste) have been combined with many different fungi and the productivity of each fermentation reported On a gram bench-scale SSF appears to be superior to submerged fermentation technology (SmF) in several aspects However, SSF up-scaling, necessary for use on an industrial scale, raises severe engineering problems due to the build-up of temperature, pH, O2, substrate and moisture gradients Hence, most published reviews also focus on progress towards industrial engineering The role of the physiological and genetic properties of the microorganisms used during growth on solid substrates compared with aqueous solutions has so far been all but neglected, despite the fact that it may be the microbiology that makes SSF advantageous against the SmF biotechnology This review will focus on research work allowing comparison of the specific biological particulars of enzyme, metabolite and/or spore production in SSF and in SmF In these respects, SSF appears to possess several biotechnological advantages, though at present on a laboratory scale only, such as higher fermentation productivity, higher end-concentration of products, higher product stability, lower catabolic repression, cultivation of microorganisms specialized for water-insoluble substrates or mixed cultivation of various fungi, and last but not least, lower demand on sterility due to the low water activity used in SSF

Biotechnological advantages of laboratory-scale solid-state fermentation with fungi.

Application of solid-state fermentation to food industry—A review

Differentiation and secondary metabolism are correlated processes in fungi that respond to light. In
Aspergillus nidulans
, light inhibits sexual reproduction as well as secondary metabolism. We identified
the heterotrimeric
velvet
complex VelB/VeA/LaeA connecting light-responding developmental
regulation and control of secondary metabolism. VeA, which is primarily expressed in the dark,
physically interacts with VelB, which is expressed during sexual development. VeA bridges VelB to the
nuclear master regulator of secondary metabolism, LaeA. Deletion of either
velB
or
veA
results in
defects in both sexual fruiting-body formation and the production of secondary metabolites.

VelB/VeA/LaeA Complex CoordinatesLight Signal with Fungal Developmentand Secondary Metabolism

Solid-state fermentation: Physiology of solid medium, its molecular basis and applications

Statins are a group of extremely successful drugs that lower cholesterol levels in blood; decreasing the risk of heath attack or stroke. In recent years, statins have also been reported to have other biological activities and numerous potential therapeutic uses. Natural statins are lovastatin and compactin, while pravastatin is derived from the latter by biotransformation. Simvastatin, the second leading statin in the market, is a lovastatin semisynthetic derivative. Lovastatin is mainly produced by Aspergillus terreus strains, and compactin by Penicillium citrinum. Lovastatin and compactin are produced industrially by liquid submerged fermentation, but can also be produced by the emerging technology of solid-state fermentation, that displays some advantages. Advances in the biochemistry and genetics of lovastatin have allowed the development of new methods for the production of simvastatin. This lovastatin derivative can be efficiently synthesized from monacolin J (lovastatin without the side chain) by a process that uses the Aspergillus terreus enzyme acyltransferase LovD. In a different approach, A. terreus was engineered, using combinational biosynthesis on gene lovF, so that the resulting hybrid polyketide synthase is able to in vivo synthesize 2,2-dimethylbutyrate (the side chain of simvastatin). The resulting transformant strains can produce simvastatin (instead of lovastatin) by direct fermentation.

Biotechnological production and applications of statins.

Penicillin was produced by a non-sterile solid state fermentation (SSF) on bagasse impregnated with culture medium. The use of concentrated media greatly enhanced the antibiotic production in this system. It was observed that adequate initial moisture content (70%) of the impregnated solid medium results in higher production. A comparison between solid and liquid fermentation showed superior yield and productivity.

Penicillin production by solid state fermentation

Microbial secondary metabolites are useful high value products that are normally produced by liquid culture; but could be advantageously produced by solid-state fermentation (SSF). Particularly if SSF could benefit from a deeper understanding of microbial physiology in a solid environment. Recent research indicates that different kind of secondary metabolites can be produced by SSF: antibiotics, phytohormones, food grade pigments, alkaloids, etc. Physiology in SSF shows several similarities with physiology in liquid medium, so similar strategies must be adapted for efficient processes. However, there are certain particularities of idiophase in solid medium which dictate the need for special strains.

Production of Secondary Metabolites by Solid-State Fermentation

Molecular studies were performed to establish the causes of the superior lovastatin productivity of a novel solid-state fermentation (SSF) process, in relation with liquid submerged fermentation (SmF; 20 mg/g vs. 0.65 mg/ml). In SSF, biosynthetic genes lovE and lovF transcripts accumulated to high levels from day 1 to day 7. In this period, lovE transcript showed 4.6-fold higher accumulation levels (transcription) than the highest level detected in SmF (day 5). lovF transcript showed two-fold higher expression than the highest point in SmF. In SmF, the expression was only detected clearly on day 5 and, showing a 50% decrease, on day 7. These results show that the higher lovastatin production in SSF is related to a more intense transcription of these biosynthetic genes. A strong expression of gldB gene in lovastatin SSF indicated that Aspergillus terreus senses osmotic stress during the course of SSF, but not in SmF. However, when a liquid medium of identical concentration was used in SmF, lovastatin production decreased in 50%, while lovE and lovF transcripts accumulation was 20 and six-fold lower than in SSF; showing that physiology is different in SSF, and that osmotic stress alone is not responsible for the higher gene expression in SSF.

Javier Barrios-González

Papers

Solid-state fermentation: Physiology of solid medium, its molecular basis and applications

Biotechnological production and applications of statins.

Penicillin production by solid state fermentation

Production of Secondary Metabolites by Solid-State Fermentation

Lovastatin biosynthetic genes of Aspergillus terreus are expressed differentially in solid-state and in liquid submerged fermentation.