Combined submerged and solid substrate fermentation for the bioconversion of lignocellulose

A novel two-stage bioreactor has been designed for a combined submerged (SF) and solid substrate fermentation (SSF) of wheat straw. The straw was pretreated with steam, and cellulases from the culture fluid of Trichoderma reesei were adsorbed on it for increased bioconvertibility. SSF was conducted in the top part of the bioreactor by inoculating the straw with a 36-h mycelial culture of T. reesei, or Coriolus versicolor. In the bottom part of the fermenter, Endomycopsis fibuliger was grown in SF. The SF liquor was recirculated through the SSF stage at 24 h intervals to remove glucose and other metabolites that may inhibit growth, and to maintain optimum moisture level and temperature. The removed glucose and other metabolites provided nutrients for the yeast in the SF stage. The combined fermentation resulted in overall higher biomass yield, increased bioconversion, increased cellulase production, and increased digestibility compared with single SSF or SF.     

Antibacterial Action of Essential Oils of Artemisia as an Ecological Factor: II. Antibacterial Action of the Volatile Oils of Artemisia tridentata (Big Sagebrush) on Bacteria from the Rumen of Mule Deer

Rumen microorganisms of wild and captive deer were subjected to increasing amounts of volatile oils. The oils had a marked antibacterial effect on the rumen bacteria when the concentration reached approximately 16 muliters of oil per 10 ml of rumen fluid nutrient broth. The gross reactions of rumen bacteria obtained from wild, as well as captive, deer to the volatile oils seemed to be of the same magnitude; thus no adaptation by the bacteria to the oils was apparent.     

Lignocellulolytic enzyme production on pretreated poplar wood by filamentous fungi

Gliocladium sp. TUB F-498, a wild strain of a lignocellulolytic fungus with a fast growth rate and enzyme production rate was selected as a potential in situ enzyme source for the bioprocessing of pretreated poplar wood (PPW) to ethanol in a simultaneous saccharification and fermentation process. TUB F-498 produced 77 filter paper units of cellulase activity and 246 IU of -glucosidase activity per g dry weight of substrate utilized, as compared with the highly successful mutant reference strain Trichoderma reesei Rut-C30, which produced 100 filter paper units and 92 IU per g dry weight substrate in a stirred-tank fermentation. TUB F-498 also produced more xylanase and endoglucanase activity than Rut-C30 on PPW in shake-flask fermentations.     

Production of phytase by Mucor racemosus in solid-state fermentation

Phytase production was studied by three Mucor and eight Rhizopus strains by solid-state fermentation (SSF) on three commonly used natural feed ingredients (canola meal, coconut oil cake, wheat bran). Mucor racemosus NRRL 1994 (ATCC 46129) gave the highest yield (14.5 IU/g dry matter phytase activity) on coconut oil cake. Optimizing the supplementation of coconut oil cake with glucose, casein and (NH(4))(2)SO(4), phytase production in solid-state fermentation was increased to 26 IU/g dry matter (DM). Optimization was carried out by Plackett-Burman and central composite experimental designs. Using the optimized medium phytase, alpha-amylase and lipase production of Mucor racemosus NRRL 1994 was compared in solid-state fermentation and in shake flask (SF) fermentation. SSF yielded higher phytase activity than did SF based on mass of initial substrate. Because this particular isolate is a food-grade fungus that has been used for sufu fermentation in China, the whole SSF material (crude enzyme, in situ enzyme) may be used directly in animal feed rations with enhanced cost efficiency.     

Evaporative temperature and moisture control in a rocking reactor for solid substrate fermentation

Summary In the solid substrate fermentation of cooked yellow corn grits with Rhizopus oligosporus in a rocking drum fermenter, temperature was controlled by blowing air through the substrate, forcing water evaporation. The rate of evaporation was controlled by the relative humidity of the air, according to the rate of heat generation during fermentation. Moisture content was maintained constant by spraying cold water on the substrate regulated by the water balance equation of the system. Both controls were operated by computer programs. The rocking motion in the reactor allowed even distribution of air and water in the substrate without disturbing the growing mycelia.     

Recovery of protein and chlorophyll from alfalfa by simultaneous lactic acid fermentation and enzyme hydrolysis (ENLAC)

Simultaneous lactic acid fermentation and enzyme hydrolysis by cell wall degrading enzymes (ENLAC for short) was tested for improving the recovery of cell content, such as protein and chlorophyll, from alfalfa. Alfalfa was ensiled with the addition of 1.0% (wet weight) of a variety of commercial enzymes or enzyme cocktails. The best result was achieved by the addition of a 1:1 mixture of Novo Viscozyme (containing mainly hemicellulases, cellulases, and pectinases) and Novo Celluclast 1.5 L or Genencore Cellulase 150 L (containing T. reesei cellulases). ENLAC improved the recovery of protein by 160%, chlorophyll by 240%. The same enzyme treatment in a 24-h reaction without ensiling resulted in only a 14% increase in protein recovery. ENLAC provided optimal acidic conditions for enzyme action, and due to the preservation of the plant material during ensiling, it made possible the efficient use of a low concentration of enzymes during a longer reaction time, compared to conventional 24-h enzyme treatments.     

Inhibition of microbial growth and metabolism by excess turbulence

Excess turbulence caused by high-intensity stirring inhibited microbial growth and metabolism. In stirred tank bioreactors, the growth rate and lysine biosynthesis decreased in Brevibacterium flavum beyond 900 rpm, the growth rate of Trichoderma reesei on wheat straw beyond 150 rpm, and the growth rate of Saccharomyces cerevisae beyond 800 rpm. The term turbohypobiosis was introduced to describe this inhibition. Turbohypobiosis was characterized by a stress factor F(str) expressing the interaction of medium flow with microbial cells in local turbulent zones, dependent on the energy distribution of the stirring regime. Lysine synthesis was inhibited at significantly lower F(str) values than the growth of B. flavum. The main reason for the inhibition was shear effects causing decreased adenosine triphosphate (ATP) generation, lower O(2) uptake, and lower specific growth rate of bacteria.     

Cellulase production by mixed fungi in solid-substrate fermentation of bagasse

Ammonia-treated bagasse with 80%(w/w) moisture content was subjected to mixed-culture solid-substrate fermentation (SSF) with Trichoderma reesei LM-UC4 and Aspergillus phoenicis QM 329, in flask or pot fermenters, for cellulase production. Significantly higher activities of all the enzymes of the cellulase complex were achieved in 4 days of mixed-culture SSF than in single-culture (T. reesei) SSF. The highest filter-paper-cellulase and -glucosidase activities seen in mixed-culture SSF were 18.7 and 38.6 IU/g dry wt, respectively, representing approx. 3- and 6-fold increases over the activities attained in single-culture SSF. The mixed-culture SSF process also converted about 46% of the cellulose and hemicellulose to reducing sugars and enriched the product with 13% fungal protein. The biomass productivity, 0.29 gl^-1.h, and enzyme productivity, 28.0 IU I^-1.h, were about twice as high in the mixed-culture than in the single-culture.R. Dueñas is with the Departamento de Biologia, Universidad Nacional San Antonio Abad, Cusco, Peru. R. Tengerdy is with the Department of Microbiology, Colorado State University, Fort Collins, CO 80523, USA. M. Gutierrez-Correa is with the Laboratorio de Micologia y Biotecnologia, Universidad Nacional Agraria La Molina, Apdo. Postal 456, Lima 1. Peru;     

Production of cellulase on sugar cane bagasse by fungal mixed culture solid substrate fermentation

Trichoderma reesei LM-UC4 and its mutant LM-UC4E1 were co-cultured with Aspergillus phoenicis QM329 for cellu-lase production on bagasse by mixed culture solid substrate fermentation. A mutual synergism was observed between the parent Trichoderma strain and the Aspergillus, resulting in enhanced combined biomass production and corresponding increased in cellulase, endoglucanase and b-glucosidase activities. Such synergism was absent with the mutant Trichoderma strain suggesting that in the hypermutation the ability for cooperative interaction with other microbes was lost.