Novel mannanases from industrially relevant microorganisms

Abstract

Microalgal feedstock are gaining more and more attention due to a wide range of potential and emerging commercial and industrial applications, from biofuel production to nutrition, cosmetics and pigment extraction among others. The presence and roles of mannans and endomannanases in three industrially relevant microalgaes were studied in this project. Chlorella vulgaris has seven putative endomannanase genes in the genome, but no activity has been detected in the experimental work and its cell wall has a low mannan content (<5%). Chlorella protothecoides has similar amounts of mannan in the cell wall, but mannanase activity was detected when grown in a mannan-rich media. This mannanase could perhaps be involved in mannan uptake and degradation. Scenedesmus quadricauda seems to have endomannanase activity when grown without mannan in the media. Furthermore, an endomannanase from Bacillus cellulosilyticus with four carbohydrate binding modules and extreme optimum conditions (60ºC and pH 11) has been cloned, characterized and proven to be able to degrade the microalgal cell-wall, being a good candidate to be industrially used with this purpose.

Popular Abstract

All living organisms are equipped with sets of tools that allow them to perform reactions and functions that otherwise they couldn’t accomplish because they would occur too slow or not happen at all. These powerful tools are called enzymes, and they work by catalyzing biologically relevant chemical reactions
In this work, a specific type of enzymes called mannanases are studied. Mannanases are responsible of the breakdown of long and complex chains of sugars, called mannan polysaccharides, into the small primary subunits which form these complex chains. This process is similar to the one that occurs when we eat starch (a slow energy release carbohydrate), in which the small primary subunits of sugar are released by enzymes to be used as energy for our cells. The main differences between starch and mannans are the primary sugar subunits used and the bond used to link them together.
Mannan polysaccharides constitute approximately 20% of the soft wood, and are one of the main residues of the paper industry which, right now, are mainly released in side-streams or waste. It thus is an enormous potential source of energy, as once the sugars are released from the complex chains they can be used with feeding purposes or biofuel production like biodiesel or biogas among others. Another, in essence unutilized, resource are the mannans present in the cell-walls of some industrial microalgaes. Mannans thus have a great potential to be established as a renewable resource and its increased utilization will contribute to a sustainable society based on the so-called “bioeconomy” which will be less dependent on fossil resources.
The aim of this work is to identify and characterize mannanases from types of organisms previously not studied for this purpose. These organisms were a type of soil bacteria (Bacillus cellulosilyticus) and three microalgaes (Chlorella vulgaris CCAP211/52, Chlorella protothecoides CCAP211/8D, Scenedesmus quadricauda CCAP276/4B) where S. quadricauda was shown to have mannan in the cell wall. The mannanases may be assumed to have different functions: Either modification/modulation of endogenous cell-wall mannan (which might serve as a model for plant mannans) or degradation of environmental mannans. The latter might have properties relevant for industrial processes (e.g. conversion of plan or microalgal waste-mannans).
Thus, four organisms have been involved in this study. The first of them, a soil bacteria called Bacillus cellulosilyticus, was found to have a mannanase which is able to work in really alkaline environments, temperatures as high as 60ºC, and seems to tolerate chemicals, making it a really good candidate for industrial scale processes where the normal working conditions are similar to the ones the enzyme seems to prefer.
The other organisms involved in the study are microalgaes used for biofuel production, Chlorella and Scenedesmus. Its cell debris, which can be around half of its dry weight, is rich in mannan polysaccharides. At the same time, it contains mannanases which can degrade them. The interesting part of this is the possibility of using Chlorella’s own tools to degrade its cell debris, achieving a process where nothing is left behind and everything is used. There are evidences that mannanases exist in Chlorella, but more work is needed to be able to use them in industrial process as the tip of this iceberg has just been glimpsed.

• author: Carrasco Flores, David
• supervisor: Evelina Kulcinskaja; Johan Svantesson Sjöberg
• organization: Department of Chemistry
• course: KEMT30 20132
• year: 2014
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: proteinvetenskap, protein science
• language: English
• id: 4645245
• date added to LUP: 2014-09-12 16:35:49
• date last changed: 2014-09-12 16:35:49