M. L. Onnela

Bio: M. L. Onnela is an academic researcher. The author has contributed to research in topics: Cellulase & Gene expression. The author has an hindex of 2, co-authored 2 publications receiving 505 citations.

Regulation of cellulase gene expression in the filamentous fungus Trichoderma reesei.

Abstract: Basic features of regulation of expression of the genes encoding the cellulases of the filamentous fungus Trichoderma reesei QM9414, the genes cbh1 and cbh2 encoding cellobiohydrolases and the genes egl1, egl2 and egl5 encoding endoglucanases, were studied at the mRNA level. The cellulase genes were coordinately expressed under all conditions studied, with the steady-state mRNA levels of cbh1 being the highest. Solka floc cellulose and the disaccharide sophorose induced expression to almost the same level. Moderate expression was observed when cellobiose or lactose was used as the carbon source. It was found that glycerol and sorbitol do not promote expression but, unlike glucose, do not inhibit it either, because the addition of 1 to 2 mM sophorose to glycerol or sorbitol cultures provokes high cellulase expression levels. These carbon sources thus provide a useful means to study cellulase regulation without significantly affecting the growth of the fungus. RNA slot blot experiments showed that no expression could be observed on glucose-containing medium and that high glucose levels abolish the inducing effect of sophorose. The results clearly show that distinct and clear-cut mechanisms of induction and glucose repression regulate cellulase expression in an actively growing fungus. However, derepression of cellulase expression occurs without apparent addition of an inducer once glucose has been depleted from the medium. This expression seems not to arise simply from starvation, since the lack of carbon or nitrogen as such is not sufficient to trigger significant expression.

Regulation of Cellulase Gene Expression in the Filamentous Fungus

Abstract: Basic features of regulation of expression of the genes encoding the cellulases of the filamentous fungus Trichoderma reesei QM9414, the genes cbh1 and cbh2 encoding cellobiohydrolases and the genes egl1, egl2 and egl5 encoding endoglucanases, were studied at the mRNA level. The cellulase genes were coordinately expressed under all conditions studied, with the steady-state mRNA levels of cbh1 being the highest. Solka floc cellulose and the disaccharide sophorose induced expression to almost the same level. Moderate expression was observed when cellobiose or lactose was used as the carbon source. It was found that glycerol and sorbitol do not promote expression but, unlike glucose, do not inhibit it either, because the addition of 1 to 2 mM sophorose to glycerol or sorbitol cultures provokes high cellulase expression levels. These carbon sources thus provide a useful means to study cellulase regulation without significantly affecting the growth of the fungus. RNA slot blot experiments showed that no expression could be observed on glucose-containing medium and that high glucose levels abolish the inducing effect of sophorose. The results clearly show that distinct and clear-cut mechanisms of induction and glucose repression regulate cellulase expression in an actively growing fungus. However, derepression of cellulase expression occurs without apparent addition of an inducer once glucose has been depleted from the medium. This expression seems not to arise simply from starvation, since the lack of carbon or nitrogen as such is not sufficient to trigger significant expression.

Microbial cellulose utilization: fundamentals and biotechnology.

Abstract: Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

Transcriptional regulation of plant cell wall degradation by filamentous fungi

Abstract: Plant cell wall consists mainly of the large biopolymers cellulose, hemicellulose, lignin and pectin. These biopolymers are degraded by many microorganisms, in particular filamentous fungi, with the aid of extracellular enzymes. Filamentous fungi have a key role in degradation of the most abundant biopolymers found in nature, cellulose and hemicelluloses, and therefore are essential for the maintenance of the global carbon cycle. The production of plant cell wall degrading enzymes, cellulases, hemicellulases, ligninases and pectinases, is regulated mainly at the transcriptional level in filamentous fungi. The genes are induced in the presence of the polymers or molecules derived from the polymers and repressed under growth conditions where the production of these enzymes is not necessary, such as on glucose. The expression of the genes encoding the enzymes is regulated by various environmental and cellular factors, some of which are common while others are more unique to either a certain fungus or a class of enzymes. This review summarises our current knowledge on the transcriptional regulation, focusing on the recently characterized transcription factors that regulate genes coding for enzymes involved in the breakdown of plant cell wall biopolymers.

Microbial cellulases ─ Production, applications and challenges

Abstract: Microbial cellulases find applications in various industries and constitute a major group of the industrial enzymes. Recently, there is resurgence in utilization of biomass for fuel production employing cellulases and hence forth in obtaining better yields and novel activities. Improving the economics of such processes will involve cost reduction in cellulase production which may be achieved by better bioprocesses and genetic improvement of cellulase producers to yield more of the enzyme. The review discusses the current knowledge on cellulase production by microorganisms and the genetic controls exercised on it. It discusses the industrial applications of cellulases and the challenges in cellulase research especially in the direction of improving the process economics of enzyme production.