Degradation of cellulose by thermophilic bacteria

Degradation of 1—.10% crystalline cellulose and concentration of:free reducing sugars in the medium, were studied during cultivation of a wild coculture of obligately thermphilic bacteria in 3-L fermentors at 60^°C and pH 7.0 under anaerobic conditions. The coculture was composed of five different species ofBacillus and a single cellulolytic species lof Clostridium. The proportion of degraded substrate was inversely proportional to the initial concentration of cellulose. The higher the initial substrate concentration the lower the proportion of its.degradation. Cellulose at 1 — 2 % concentration is best degraded (98 % in:5.d). The fermentation time increases with increasing cellulose concentration, the level of reducing saccharides increases together with the initial rate of substrate degradation. In the presence of 10 %) cellulose the rate of degradation within a period of a 1-d fermentation is close toV, being 0.455 g L^-1 h^-1withK _m of 12.5 g/L. However, during further cultivation (1—3 d) the rate of degradation of 4—10 % cellulose decreases, probably due to the effect of accumulated reducing saccharides whose levels reach 55—60 mg/L.     

Ethanol formation from cellulose by thermophilic bacteria

Summary A wild coculture of obligately thermophilic bacteria, including only a single cellulolytic species Clostridium, ferments 2% crystalline cellulose and produces 4.6–5.1 g·l^–1 of ethanol at 55°–60° C; that is, 0.96–1.1 moles of ethanol from 1 mole of glucose equivalent of cellulose degraded. However, the ethanol yield decreases with increasing cellulose concentration. Ethanolacetic acid ratio varies around 1 and cannot be influenced by substrate concentration. However, this ratio can be influenced by changing pH and temperature. For the ethanol production from cellulose, neutral and weekly alkaline media with a pH of 7.0–8.0 and a temperature of 55° C are optimal. Experiments in which the coculture was subjected to high ethanol concentrations showed that higher concentrations of added ethanol (up to 20 g·l^–1) suppress cellulose degradation by 50% and inhibit the actual production of ethanol.     

Carboxymethyl cellulose decomposition by intestinal bacteria of cockroaches

The effect of freeze-drying on phenotypic reversion of amino acid auxotrophy to prototrophy was studied in Escherichia coli. In a radioresistant strain, E. coli H/r 30 (uvr+ exr+), which can repair the deoxyribonucleic acid damaged due to freeze-drying, an increased mutation frequency from auxotrophy to prototrophy was observed with increased time of freeze-drying of the cells. On the other hand, in a radiosensitive strain, E. coli NG 30 (recA), which cannot repair the damaged deoxyribonucleic acid due to a lack of repair enzyme system, no significant reversion occurred, although the survival rate was very low. The rate of phenotypic reversion dut to freeze-drying in both E. coli RIMD 0509109 (uvr+ exr+) and RIMD 0509115 (uvr exr+) was almost the same, indicating that the phenomenon is independent of the uvr character. From these results it is concluded that mutation was induced in E. coli cells during the rehydration when the damaged deoxyribonucleic acid was repaired by exr character of the cells. Thus, we propose that a serious consideration should be paid to the freeze-drying technique to preserve bacterial cells.     

Biodegradation of dibenzothiophene by thermophilic bacteria

Anaerobic microbial biodegradation of dibenzothiophene (DBT) was studied using thermophilic bacteria obtained from crude oil. A mixed culture was obtained that degraded 98% of DBT at 0.5 mg ml^–1 at 65 °C over 15 days both in the presence and in the absence of Methyl Viologen.     

Production of ethanol by thermophilic bacteria

Doubts about the viability of using classical yeast fermentations to produce ethanol have led in recent years to a search for alternative microbes capable of ethanol production. Among the front-runners for consideration are the thermophilic bacteria and this article shows how close these extraordinary microbes have come to replacing yeast in ethanol production.     

嗜热菌的耐热分子机制

对嗜热菌耐热机制在其细胞表层结构、ＤＮＡ螺旋的热稳定性和嗜热菌酶耐热性等方面的研究作一综述。     

Aerobic thermophilic biodegradation of microbial cells

Summary Results are presented comparing the extent of solubilization/biodegradation of whole yeast cells by mixed thermophilic bacterial cultures under conditions of oxygen, excess and oxygen limitation. The process was most effective at a low dissolved oxygen concentration as suggested by solids removal data and by the production of often considerable quantities of carboxylic acids. The temperature optimum was also investigated and, under oxygen limited conditions, the most consistant results were obtained for operation at 65°C reflecting the true thermophilic nature of the process microbes. An operating temperature of 70°C probably exceeded the optimum for effective functioning of the thermophilic microbes and resulted in a less efficient process, whilst an operating temperature of 60°C was intermediate with respect to its effectiveness.     

Superoxide dismutase biosynthesis by two thermophilic bacteria

Some high-molecular weight antioxidant defense system components of two thermophilic bacteria isolated from spa waters of Serbia (Yugoslavia) and identified as Bacillus stearothermophilus and Thermothrix sp. were studied. In addition to superoxide dismutase (SOD; EC 1.15.1.1), qualitative analyses demonstrated the presence of catalase (EC 1.11.1.6), peroxidases and oxidases in both bacterial strains. Cell-free extracts were subjected to nondenaturing polyacrylamide gel electrophoresis (PAGE) and SOD activity in the eluates of the corresponding bands was examined in the presence of several specific inhibitors. A slight decrease of SOD activity observed in the presence of 0.3 M potassium cyanide and its complete insensitivity to hydrogen peroxide (5 mM) and sodium azide (20 mM) action suggest that the enzyme occurring in the two thermophiles represents Mn SOD. A high SOD activity recorded in cell-free extracts strongly recommends these two bacterial strains as potential producers of this important antioxidant defense system component at industrial scale.     

Physiology of growth of a mixed culture of thermophilic bacteria on cellulose under microaerophilic conditions

Summary A mixed wild culture of thermophilic bacteria degraded 86% of 2% cellulose in 96 h with production of liquid (ethanol, acetic and propionic acids, and ethylesters of these acids) and gaseous products (hydrogen and carbon dioxide).     

Aerobic biodegradation of nonylphenol by cold-adapted bacteria

Three strains capable of mineralizing nonylphenol as sole carbon source were isolated from a sample of contaminated soil and characterized as two Pseudomonas spp. and a Stenotrophomonas sp. The two Pseudomonas spp. expressed characteristics typical of psychrophiles growing optimally of 10 °C and capable of growing at 0 °C. The Stenotrophomonas sp. was more likely psychrotrophic because it had an optimal temperature between 14 and 22 °C although it was not capable of growing at 4 °C. At 14 °C, one of the Pseudomonas spp. exhibited the highest rate of degradation of nonylphenol (4.4 mg l^–1 d^–1), when compared with axenic or mixed cultures of the isolates. This study represents, to the best of our knowledge, the first reported case of cold-adapted microorganisms capable of mineralizing nonylphenol.     

Aerobic biodegradation of propylene glycol by soil bacteria

Propylene glycol (PG) is a main component of aircraft deicing fluids and its extensive use in Northern airports is a source of soil and groundwater contamination. Bacterial consortia able to grow on PG as sole carbon and energy source were selected from soil samples taken along the runways of Oslo Airport Gardermoen site (Norway). DGGE analysis of enrichment cultures showed that PG-degrading populations were mainly composed by Pseudomonas species, although Bacteroidetes were found, as well. Nineteen bacterial strains, able to grow on PG as sole carbon and energy source, were isolated and identified as different Pseudomonas species. Maximum specific growth rate of mixed cultures in the absence of nutrient limitation was 0.014 h^?1 at 4 °C. Substrate C:N:P molar ratios calculated on the basis of measured growth yields are in good agreement with the suggested values for biostimulation reported in literature. Therefore, the addition of nutrients is suggested as a suitable technique to sustain PG aerobic degradation at the maximum rate by autochthonous microorganisms of unsaturated soil profile.