Diversity of cellulolytic bacteria in landfill

Nine of 37 cellulolytic bacterial isolates obtained from landfill waste could be easily differentiated on the basis of gross morphological characteristics. Four isolates were selected for further characterization and on the basis of initial results appear to be previously unidentified cellulolytic species of bacteria. An aerotolerant anaerobic, cellulolytic Clostridium and three obligately anaerobic cellulolytic Eubacterium isolates are described. The Clostridium has an unusually high pH optimum for growth of 7.7. The optimum temperature for growth is 50°C. The pH growth optimum of each of the Eubacterium isolates is around pH 7.0 while temperature optima are 37° 45° and 50°C for LFI, LF4 and LF5 respectively. Most isolates had growth optima in the thermophilic range. The ease with which apparently previously unidentified species could be isolated is a reflection of the unique and highly variable, heterogeneous environment within landfill waste.     

Enumeration and characterization of cellulolytic bacteria from refuse of a landfill

Enumeration and phenotypic characterization of aerobic cellulolytic bacteria were performed on fresh, 1 year old and 5 years old refuse samples of a French landfill site. Numbers of cellulolytic bacteria ranged from 1.1x10(6) to 2.3x10(8) c.f.u. (g dry wt.)(-1) and were lower in 5 years old refuse samples. A numerical analysis of phenotypic data based on 80 biochemical tests and performed on 321 Gram-positive isolates from refuse, revealed a high phenotypic diversity of cellulolytic bacteria which were distributed into 21 clusters. Based on the phenotypic analysis and the sequencing of 16S rDNA of five representative strains of major clusters, the predominant cellulolytic groups could be assigned to the family of Bacillaceae and to the genera Cellulomonas, Microbacterium and Lactobacillus. Furthermore, chemical parameters such as pH, carbohydrates and volatile solid contents influenced the composition of the cellulolytic bacterial groups which were reduced essentially to the family of Bacillaceae in the oldest refuse samples.     

Polysulfide as a possible substrate for sulfur-reducing bacteria

Because of its low solubility it is unlikely that elemental sulfur serves as the direct substrate for sulfur-reducing bacteria. To test the hypothesis that polysulfide may represent a soluble intermediate of sulfur reduction, the maximal polysulfide concentrations formed from elemental sulfur in aqueous sulfide solutions were measured at near neutral pH and at temperatures up to 90°C. The saturation concentrations decreased by two orders of magnitude when the pH was lowered from 7 to 6 at a given temperature, and increased about tenfold when the temperature was raised from 37°C to 90°C at a given pH. The dissolution of 0.1 mM zerovalent sulfur in 1 mM sulfide (H₂S+HS^–) required a pH of 7.5 at 20°C and of only 6.1 at 100°C. A comparison with the growth optima of sulfur-reducers suggests that polysulfide is present at sufficient concentration at the growth conditions of the Bacteria and the moderately acidophilic Archaea. Polysulfide is apparently not available at the growth conditions of the extremely acidophilic Archaea. Alternative mechanisms for the sulfur utilization under these conditions are discussed.Abbreviations MOPS Morpholinopropanesulfonate - PIPES 1,4 piperazine-N,N-bis(2-ethanesulfonate) - HEPES N-2-hydroxy-ethylpiperazine-N-ethanesulfonate     

Genomics of cellulolytic bacteria

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Extracellular metabolites of hydrocarbon-oxidizing bacteria as a substrate for sulfate reduction

The relationship between bacterial oxidation of hydrocarbons and sulfate reduction was studied in the experimental system with liquid paraffin was used as a source of organic compounds inoculated with silt taken from a reservoir. Pseudomonads dominated in the hydrocarbon-oxidizing silt bacteriocenosis. However, Rhodococcus and Arthrobacteria amounted to not more than 3%. Arthrobacteria dominated the microbial association formed in the paraffin film of the model system. Sulfate-reducing bacteria were represented by genera Desulfomonas, Desulfotomaculum, and Desulfovibrio. The growth of sulfate-reducing bacteria in media containing with paraffin, successive products of its oxidation (cetyl alcohol, stearate, and acetate), and extracellular metabolites of hydrocarbon-reducing bacteria was studied. The data showed that sulfate-reducing bacteria did not use paraffin or cetyl alcohol as growth substrates. However, active growth of sulfate-reducing bacteria was observed in the presence of stearate and extracellular water-soluble or lipid metabolites of Arthrobacteria.     

Mixed culture solid substrate fermentation for cellulolytic enzyme production

Summary Cellulolytic and hemicellulolytic enzymes were produced on extracted sweet sorghum silage by mixed culture solid substrate fermentation with Trichoderma reesei LM-1 (a Peruvian mutant) and Aspergillus niger ATCC 10864. Optimal cellulose and xylanase levels of 4 IU/g dry weight (DW) and 180 IU/g DW, respectively, were achieved in 120 h-fermentation when T. reesei, inoculated at 0 h, was followed by the inoculation of A. niger at 48 h.     

Starvation of bacteria as a stress caused by substrate limitation

The analysis of literature has made it possible to establish the priority of Russian research works made in the 1970-80s on the subject of starvation of bacteria caused by substrate limitation as well as research made in the 1990s concerning starvation of bacteria. This state is characterized by synthesis of additional proteins, so-called stress proteins, which not only ensure the survival of bacteria under the conditions of substrate limitation, but also protect them from a number of other stressors. In spite of the fact that genetic mechanisms regulating the synthesis of some stressor proteins have been revealed their significance for microbiological technology is not yet clear.     

Fermentation of methylcellulose by a cellulolytic and a non-cellulolytic marine bacteria

Summary Two microorganisms originally existing in cellulose enrichmet cultures obtained from lagoon sediments, were isolated for mono-and cocultures studies. Methylcellulose was degraded faster with the coculture than with the cellulolytic bacterium alone, and with a product pattern reflecting the non-cellulolytic bacterium.     

Growth of cellulolytic bacteria on sugarcane bagasse

The growth behavior of Cellulomonas has been examined in fermentation system using alkali pretreated sugarcane bagasse. During the batch operation diauxic growth was found which would not seem to be explained by catabolic repression. The relative variation of cellulose and hemicellulose during the fermentation process suggests the initial utilization of easily degradable substrate, i.e., hemicellulose and amorphous cellulose, until their concentration becomes limiting, followed by utilization of the crystalline cellulose. The conversion of substrate was 70% with a yield of 0.355 g of biomass per gram of bagasse feed.     

Characterization of rat cecum cellulolytic bacteria.

Cellulose-degrading bacteria previously isolated from the ceca of rats have been characterized and identified. The most commonly isolated type was rods identified as Bacteroides succinogenes. These bacteria fermented only cellulose (e.g., pebble-milled Whatman no. 1 filter paper), cellobiose, and in 43 of 47 strains, glucose, with succinic and acetic acids as the major products. The only organic growth factors found to be required by selected strains were p-aminobenzoic acid, cyanocobalamine, thiamine, and a straight-chain and a branched-chain volatile fatty acid. These vitamin requirements differ from those of rumen strains of B. succinogenes, indicating the rat strains may form a distinct subgroup within the species. The mole percent guanine plus cytosine was 45%, a value lower than those (48 to 51%) found for three rumen strains of B. succinogenes included in this study. Cellulolytic cocci were isolated less frequently than the rods and were identified as Rumminococcus flavefaciens. Most strains fermented only cellulose and cellobiose, and their major fermentation products were also succinic and acetic acids. Their required growth factors were not identified but were supplied by rumen fluid.     

瘤胃中纤维素分解菌的分离、鉴定及其产酶条件的优化

[目的]从新疆细毛羊、牛和骆驼瘤胃液中分离出具有分解纤维素能力的好氧细菌,用于绿色粗饲料微生物添加剂的研发.[方法]采取新鲜瘤胃液,接种于羧甲基纤维素钠平板,通过刚果红染色和液体复筛培养基,筛选出分解纤维素能力强的好氧细菌;形态学、生理生化试验与16S rDNA序列分析方法相结合对细菌进行鉴定;同时对纤维素分解能力强的4株细菌进行不同条件下酶活力测定.[结果]共分离到84株具有分解纤维素能力的细菌,其中筛选出较强分解纤维素能力的40株.该菌包括37株G-菌和3株G+菌;经鉴定40株纤维素分解菌分别属于6个属10个种,其中16株为寡养单胞菌属,10株为苍白杆菌属,5株为鞘氨醇杆菌属,3株为微杆菌属,3株为副球菌属,2株为假单胞菌属.其中产酶能力强的4株菌在不同条件下的酶活力表明,它们在最佳碳源为秸秆粉、pH5.5-6.0的偏中性条件和37℃培养条件下的酶活力较高.不同菌株对不同纤维素类物质的分解能力不一样,同一菌株对不同纤维素碳源的利用能力也不相同.[结论]分离获得的瘤胃纤维素分解菌是从新疆不同地区、干旱半干旱环境下饲养的动物胃液中分离、筛选出来的,有较强的纤维素分解能力,将为高品质、高消化率的青贮饲料生产提供优质菌种资源及一定的科学依据.     

Unravelling carbon metabolism in anaerobic cellulolytic bacteria

Carbon metabolism in anaerobic cellulolytic bacteria has been investigated essentially in Clostridium thermocellum, Clostridium cellulolyticum, Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus. While cellulose depolymerization into soluble sugars by various cellulases is undoubtedly the first step in bacterial metabolisation of cellulose, it is not the only one to consider. Among anaerobic cellulolytic bacteria, C. cellulolyticum has been investigated metabolically the most in the past few years. Summarizing metabolic flux analyses in continuous culture using either cellobiose (a soluble cellodextrin resulting from cellulose hydrolysis) or cellulose (an insoluble biopolymer), this review aims to stress the importance of the insoluble nature of a carbon source on bacterial metabolism. Furthermore, some general and specific traits of anaerobic cellulolytic bacteria trends, namely, the importance and benefits of (i) cellodextrins with degree of polymerization higher than 2, (ii) intracellular phosphorolytic cleavage, (iii) glycogen cycling on cell bioenergetics, and (iv) carbon overflows in regulation of carbon metabolism, as well as detrimental effects of (i) soluble sugars and (ii) acidic environment on bacterial growth. Future directions for improving bacterial cellulose degradation are discussed.     

Optimization of culture medium composition for cellulolytic bacteria by mathematical methods

The culture medium composition for cellulolytic bacteria growing on sugar cane wastes was optimized. A modified method of Rosenbrock was employed for shaker culture medium and a factorial plan design for fermentor culture medium optimization. A much more economical and productive medium was obtained for the production of single cell protein (SCP). A biomass concentration of 4.3 g/L was obtained in the optimized medium in batch fermentation, in comparison with 2.8 g/L previously obtained in the traditional medium under similar conditions.     

Biomethanation of a cellulose-based substrate in the presence and absence of a cellulolytic bacterium

The effect of co-culturing a methanogen isolated from a paper mill waste (PMW) with cellulolytic bacteria isolated from the intestinal fluids of the silver cricket (Lepisma saccharina) on the biomethanation of filter paper strips was examined. The autoclaved filter paper strips were subjected to biomethanation in AC 21 medium inoculated with methanogen PMW in the presence and in absence of a co-culture of cellulolytic bacteria. In spite of poor initial response, methane production in the presence of the cellulolytic co-culture were found to increase gradually upto 25 days, after which a reduction in methane production was observed. Analysis of the results in terms of increased cellulose degradation in the presence of cellulolytic bacteria has been made. This revised version was published online in July 2006 with corrections to the Cover Date.