Microorganisms for fermentation of lignocellulosic hydrolyzates

Abstract

Velika količina lignoceluloznog otpada, kojeg čine uglavnom celuloza, hemiceluloza i lignin, nastaju u šumarstvu, poljoprivredi i prehrambenoj industriji. Lignoceluloza je jeftina, ali i kompleksna obnovljiva sirovina koja se može prevesti u razne visokovrijedne biotehnološke proizvode. Da bi se iskoristio potencijal lignoceluloze potrebno je primijeniti prikladne metode predobrade. Lignocelulozni hidrolizati su složene smjese heksoza i pentoza te drugih spojeva od kojih neki mogu djelovati kao inhibitori fermentacije. Optimalni radni mikroorganizam trebao bi fermentirati pentoze i heksoze pri čemu se preferira da ih troši istodobno. Također bi trebao imati visoku toleranciju prema inhibitorima i produktima fermentacije, biti otporan na mikrobiološke kontaminacije te postizati visoku produktivnost i prinos proizvoda. Uz to, trebao bi tolerirati visoke temperature i niske pH-vrijednosti kako bi se smanjio rizik od kontaminacije. Poželjno je da radni mikroorganizam posjeduje i izlučuje celulolitičke i hemicelulolitičke enzime. Ova svojstva mogu biti prirodno prisutna u mikroorganizmu ili se mogu postići primjenom metoda genetičkog inženjerstva. U ovom radu dan je pregled prokariotskih i eukariotskih mikroorganizama koji su istraživani za dobivanje etanola, ali i nekih drugih ekonomski važnih proizvoda koji se mogu dobiti biotehnološkom preradom lignoceluloznih sirovina.Huge amounts of lignocellulosic waste, consisting mainly of cellulose, hemicellulose and lignin, are generated through forestry, agriculture and food industry. Lignocellulose is a cheap but complex renewable raw material that can potentially be converted into various value-added biotechnological products. In order to exploit lignocellulose potential, it is necessary to implement appropriate pretreatment methods. Lignocellulosic hydrolysates are complex mixtures of hexoses, pentoses and other compounds, some of which may act as inhibitors of fermentation. Optimal working microorganism should ferment pentoses and hexoses, which should be preferentially simultaneously consumed. It should also have a high tolerance to inhibitors and fermentation products, to be resistant to microbiological contamination as well as to achieve a high productivity and high product yields. In addition, it should tolerate high temperatures and low pH-values in order to reduce the risk of contamination. It is also desirable for working microorganism to produce and secrete cellulolytic and hemicellulolytic enzymes. These properties can be naturally present in the microorganism or can be achieved by using genetic engineering methods. This paper gives an overview of prokaryotic and eukaryotic microorganisms which have been investigated for production of ethanol as well as other economically important products which can be obtained by biotechnological processing of lignocellulosic raw materials