Cellulolytic activity of Thermomonospora curvata: nutritional requirments for cellulase production

The use of a minimal medium for cellulase (C(1) and C(x)) production by Thermomonospora curvata increased extracellular C(1) activity (measured by rate of cotton fiber hydrolysis) 11-fold compared with the previously used yeast extract medium. Ground cotton fibers supported the highest cellulase production when compared to other soluble and insoluble carbohydrate sources. Maximal cellulase production occurred at 45 C, slightly less at 55 C, and was insignificant at 65 C (the highest temperature at which cellulase activity appeared stable). At a temperature of 55 C, an optimal pH of 8.0, and a cotton fiber concentration of 8 mg/ml, shake cultures of T. curvata degraded about 75% of the cellulose during the 10-day period.

Regulation of cellulase from Ruminococcus

The regulation of cellulase was examined in Ruminococcus albus and R. flavefaciens. Hydrolysis of cellulose, as shown by the formation of clear zones around the colonies of bacteria grown in cellulose-agar roll tubes, was inhibited by moderate levels of cellobiose. An intermediate in the metabolism of cellobiose may be responsible for the inhibition since strains which can use either sucrose or lactose were similarly inhibited by these energy sources. The inhibition of cellulase was examined in relation to either repression of enzyme synthesis or product inhibition of the enzyme activity. There was no inhibition by cellobiose added either to the routine enzymatic assay or to assays using low concentrations of carboxymethylcellulose. A repression mechanism was indicated by the decrease in specific activity of cultures grown in higher concentrations of cellobiose. The specific activity was calculated as the enzymatic activity on carboxymethylcellulose with respect to cell growth. The mechanism of repression was not distinguished between the model proposed by Jacob and Monod and catabolite repression. The growth of R. albus cultured in cellobiose–cellulose liquid medium exhibited a diauxic pattern similar to that described by Monod.

Cellulolytic activity in municipal solid waste composting

A study was made of the open windrow method of municipal solid waste composting as related to those factors that might influence cellulose decomposition. Composting temperatures reached a maximum (55–65 °C) at 3 weeks and then gradually decreased during the rest of the 49-day process. The pH values of compost samples homogenized in distilled water decreased slightly during the initial stages of the process and then increased gradually to final values of 7.0–8.5. Clarified compost extracts were assayed for cellulase activity by measuring the hydrolysis rate of carboxymethylcellulose (CMC). Maximal cellulase activity occurred at 65 °C, pH 6.0, with a CMC concentration of 2.5%. The cellulase activity of compost increased 10-fold at a logarithmic rate while the cellulose content decreased 50%. In a preliminary search for microorganisms active in cellulose degradation during the composting process, three cellulolytic species were isolated; these were identified as Aspergillus fumigatus, a Bacillus species, and a Thermoactinomyces species of the Actinobifida group.

The formation of short fibres from native cellulose by components of Trichoderma koningii cellulase

Cellulolytic enzyme components of culture filtrates of Trichoderma koningii were fractionated on ionic and non-ionic forms of Sephadex and on cellulose powder (Whatman) and examined for their ability to hydrolyse soluble carboxymethyl-cellulose, and to saccharify, solubilize and form short fibres from native undegraded cellulose of the type found in cotton. DEAE-Sephadex provided two CM-cellulase components and a C(1) component; the C(1) component acted weakly and solely on cotton, forming soluble products but not short fibres. The ability to form short fibres was confined almost wholly to one of the CM-cellulase components which completely degraded cotton, minimally to soluble products and extensively to short fibres. The latter action was unaffected by the presence of the other two components. The two CM-cellulase components solubilized cellulose synergistically whereas the short-fibre-forming component and C(1) component were inhibitory.

The Choline and Serum Protein Requirements of Mouse Fibroblast Cells (Strain LS) in Culture

The maximum cell population density of mouse fibroblast (strain LS) cells growing in static suspension culture was found to be directly proportional to the dialysed calf serum concentration. This was due to choline limitation and the fact that serum protein was a major source of choline. The growth yield (Y) was 3.2 x 105 cells/µg choline chloride.

Studies on the role of serum in the presence of excess choline showed the following. When protein was omitted from the medium, cell death occurred. Whole serum protein could be replaced by either (1) bovine serum albumin fraction V, or (2) crystalline bovine serum albumin + sodium pyruvate and α-ketoglutarate, or (3) polyvinylpyrrolidone + methylcellulose + pyruvate and α-ketoglutarate.

The population doubling time was 24 h in the presence of whole serum protein and increased considerably with the substitutes (1-3). The increase in maximum cell population density (without medium changes) exceeded 2.9 x 106 cells/ml with either whole serum protein or substitutes (1) and (2). With serum substitute (3) the maximum increase in population density was reduced to 1.6 x 106 cells/ml.

Cellulolysis by Mucor pusillus

Culture filtrates of Mucor pusillus NRRL 2543 contained hydrolytic enzymes that attacked native cellulose, acid-swollen cellulose, carboxymethylcellulose, and cellobiose. The distribution profiles of cellulolytic and beta-glucosidase activities after gel filtration on Sephadex G-75 showed the presence of several active peaks. Glucose was the only product of hydrolysis when native cellulose was used as the substrate. Acid-swollen cellulose, when treated with cellulase free of beta-glucosidase activity, gave rise to glucose, cellobiose, and at least two higher molecular weight components which were also hydrolyzed in turn to cellobiose and glucose. The presence of a multiple cellulolytic enzyme system was indicated, the components of which may have specific roles in the degradation of cellulose.

Cellulolytic enzymes during morphogenesis in Dictyostelium discoideum

Extracts from Dictyostelium discoideum at the sorocarp stage of development catalyzed the degradation of acid-swollen cellulose to d-glucose at an optimal pH of about 4.5; cellobiose and cellotriose were the major products from this degradation at pH 7.0. The optimal temperature at pH 7.0, when swollen cellulose was used as substrate, was about 45 to 48 C, and was somewhat lower at pH 4.2 to 4.5, i.e., about 40 C. To account for this degradation pattern, two types of enzymes have been characterized, cellulase(s) and beta-glucosidase. With carboxymethyl cellulose as substrate, cellulase activity was not found in extracts prior to the sorocarp stage of development, but increased rapidly during aging of the sorocarp. Evidence is presented that at earlier stages of development the cellulase(s) is present in an inactive form. An inhibitor found in these extracts is heat-labile and probably of protein nature. The beta-glucosidase is present at all stages of development and the specific activity changes about fourfold, the highest activity occurring during the culmination and sorocarp stages of development.

Mechanism of isolated hemicellulose and xylan degradation by cellulolytic rumen bacteria

Although certain strains of cellulolytic rumen bacteria cannot utilize isolated hemicelluloses or xylan as a source of energy, all strains examined can degrade or solubilize these materials from an 80% ethyl alcohol insoluble to a soluble form. Centrifugation and washing of the cellobiose-grown bacterial cells did not affect the rate or extent of utilization or degradation or both. When the level of a nonutilizing culture inoculum (either normal or washed) was doubled, a corresponding increase in the initial rate of degradation was observed. With a nitrogen-free medium, utilization of xylan was almost completely inhibited for a utilizing strain, whereas degradation by either type of organism was not markedly affected. Cellobiose medium cell-free culture filtrates from a nonutilizing strain were able to degrade or solubilize xylan. The percentage of degradation increased with the volume of cell-free filtrate, and all activity was lost when the filtrate was boiled. No utilization (loss in total pentose) was observed with cell-free filtrates from utilizing or nonutilizing strains. The release of free hexose from insoluble cellulose by culture filtrates from a nonutilizing strain was very limited. On the other hand, carboxymethylcellulose (CMC-70L) and cellulodextrins were degraded to an 80% ethyl alcohol soluble form by filtrates from both types of organisms. Similar enzyme activity was obtained in cell-free culture filtrates from four additional strains of cellulolytic rumen bacteria (one xylan utilizer and three nonutilizers). When the assays were carried out aerobically, CMC-70L solubilization was reduced to a much greater extent than xylan or cellulodextrin solubilization. The enzyme or enzymes responsible for the degradation of hemicellulose by cellololytic rumen bacteria unable to utilize the hemicellulose as an energy source appear to be constitutive in nature, and this activity may be a nonspecific action of a beta-1, 4-glucosidase or -cellulase.

Trace-metal requirements of NCTC clone 929 strain L cells

The effects of iron, zinc, copper, manganese, and Methocel on the growth of L cells in a synthetic medium were studied. The medium was iron-deficient unless a supplement of 1.0 g/liter Methocel HG (4,000 centipoises), Methocel ash equivalent to 1.0 g/liter Methocel, or 1.0 microM FeSO4 was added. Cells grew faster in the presence of FeSO4 or Methocel ash (generation time = 40 hours) than of Methocel (generation time = 110 hours), but Methocel was needed to protect cells from mechanical destruction. Treating the growth medium with Dowex A-1 chelating resin produced a medium deficient in both iron and zinc. The iron requirement in this medium varied between 0.6 and 1.4 microM, depending on the concentrations of other cations added to the medium. A copper concentration of at least 0.4 microM was beneficial as it reduced the amount of iron necessary for cell growth. No manganese was required in this medium; any added manganese produced an inhibition of cell growth. Additional iron could reverse this inhibition. The minimum iron requirement for the production of L cells was 3 nmoles/mg cell nitrogen produced. Approximately 0.6 microM zinc was required for maximum cell growth in resin-treated medium.