One of the main industrial uses of microorganisms has been alcoholic fermenta­tion. The giant “microbial libraries” in current vogue can be studied for microbes that convert cheaper carbohydrates into value-added products, which can serve as raw materials for the fermentation of hemicellulosic-derived sugars into valuable commercial commodities [30]. The bioconversion process holds more promise of utilizing both hexose and pentose sugars from lignocellulosic materials. Microbial

conversion of hexose sugars into chemicals is well established; however, the ability of these organisms to ferment pentose sugars is somewhat less so. The use­ful exploitation of lignocellulosics by fermentation can be enhanced by efficient utilization of the pentosanic fraction along with hexoses.

Yeasts that have been studied extensively for use in xylose fermentation include Pachysolen tannophilus, Candida shehatae, Pichia stiptis, and Kluveromyces marxi — anus [3]. The optimal performance of these microorganisms is usually controlled by the air supply. Other yeasts investigated for their xylose-fermenting ability include Brettanomyces, Clavispora, Schizosaccharomyces, several other species of Candida viz. C. tenius, C. tropicalis, C. utilis, C. blankii, C. friedrichii, C. solani, and C. parapsilosis, and species of Debaromyces viz. D. nepalensis and D. polymorpha. Maleszka and Schneider [31] screened 15 yeast strains for their ability to utilize D-xylose, D-xylulose, and xylitol for ethanol production under aerobic, microaero­bic (low aeration), and anaerobic conditions using rich undefined or defined media. In almost all cases, ethanol production by P. tannophilus and species belonging to Candida and Pichia was better on rich media under microaerobic conditions [3,4, 31].

Several pentose-utilizing fungal species like Fusarium oxysporum, Rhizopus sp., Monilia sp., Neurospora crassa, Paecilomyces sp., Mucor sp., Neurospora crassa, and F oxysporum and bacterial species like Bacillus macerans, B. polymyxa, Kiebsiella pneumoniae, Clostridium acetobutylicum, Aeromonas hydrophila, Aerobacter sp., Erwinia sp., Leuconostoc sp., Lactobacillus sp., Clostridium ther — mocellum, C. thermohydrsulfurium, C. thermosaccharolyticum, and C. thermosul — furogenes utilizing pentose, hexose, and lignocellulose hydrolysates for ethanol production have been extensively reviewed [32].