Composition, biomass proteins

For anabolic reactions, which result in the production of new cells, it is important to know the approximate chemical composition of the biomass. The bacterial protoplasm comprises 75 to 80% water. The solid material is composed of several complex organic molecules, such as proteins, carbohydrates, and DNA. The mean composition of these molecules can be approximated by a relatively simple empirical formula, C60H87O23N12P, or in an even more simple form as C5H7O2N10.Numerous other elements such as sulfur, sodium, potassium, calcium, magnesium,... 

However, the research of the conversion of the biomass containing cellulose, such as com stalk, into biohydrogen is lacking. In general, it is hard to convert directly raw crop stalk wastes into biohydrogen gas by microbe anaerobic fermentation because of their complex chemical composition, e.g., cellulose, hemicellulose, lignin, protein, fat. 

Changes in biomass concentration throughout the fermentation process were followed by optical density (OD) measurement at 580 nm using an Ultrospec 2000 Spectrophotometer. Quantitative biomass concentration was assayed applying microbiuret cell protein determination (16). Biomass concentration was expressed in grams of dry matter per liter of fermentation broth by assuming a twofold multiplication constant for microbial protein to cell mass. For carbon balance calculations, the elemental composition of C. saccharolyticus was assumed to be CH1 8O0 5N0 2 (24.6 mg/mmol). 

Macromolecular biomass composition is of obvious interest when the biomass itself is the product, such as algal biomass in [18], or for production of singlecell protein, for e.g. animal feedstock. Moreover, for a precise metabolic flux analysis, changes in biomass composition should be taken in account. For example, Henriksen et al. [19] observed with E. coli under different growth rates, that the levels of DNA and lipids were relatively constant, whereas the proteins and stable RNA levels increased with the specific growth rate and the total amount of carbohydrates decreased. 

An alternative, at least semi-quantitative method to follow changes in biomass composition is infrared (IR) spectroscopy [22]. From dried samples of microbial cells, IR spectra can be obtained which contain information on all major cell components. The spectra are analysed as a multi-component mixture Characteristic bands in the spectra are identified, the extinction coefficients for each component (protein, carbohydrate, lipid, and nucleic acids) at each band are determined, and the concentrations are calculated by a system of linear equations. The method gives results on all major cell components simultaneously, and is relatively quick and easy to perform, compared to the chemical analysis methods. For details see Sect. 8.4 below. 

Biomass can be divided mainly into three compound classes - namely, lignocellulose, lipids, and proteins. These may come from different feedstocks and may differ in composition but should need only different steps in preprocessing to obtain a... 

Davis et al (1985) screened 57 dif rent woody and herbaceous biomass feedstocks for their production of liquid hiel constituents from indirect liquefaction of powdered materials in a fluidized b. Composition metrics in Davis studies were ash, proteins, polyphenols, oil, and hydrocarbon content as defined and measured by the USOA (Ibr example, in Adams, et al, 1986 Buchanan, et al, 1980a Roth et al, 1984 Swanson, et al 1979). We will call the USDA-measured compositions traditional" fcr purposes of this article. These feed compositions were correlated with pyrolysis gas production of hydrogen, CO, CjH4, total olefins, paraffins, and H2/CO ratio using direct regression equations of the quadratic type, but tar/char production was not addressed. 

The USDA characterized a large number of biomass species for their traditional composition fractions of ash, crude protein, polyphenols, oils and hydrocarbons among others. These fiactions were defined operationally by the USDA botanochemical screening project their sample analysis and fraction partitioning scheme is summarized in Fig. 1. Of interest were extractives, components that can he separated/paititioned from the plant by solvents. The major extractives included various oils, terpenes, fatty acids, unsaponiflables, aromatic compounds, tannins, and quinones. In exceptional cases extractives composed over 15% of the biomass (especially ash) but generally they did not exceed S-10%. 

Statistical manipulations on the USDA database (cluster analysis, principal component analysis with varimax rotation e.g., Everitt, 1980) revealed subsets of represent ve species, as idealized in Fig 2b, but with dif ent variables (orthogonal principal components) than traditional fractions as measured by USDA. A set cf species from each orthogonal subset appears in Table 1. The Latin names, and where available, the common names of the biomass species are given. The extractives ranges are ash content, 4 to 17% protein content, 5 to 14% polyphenol, 3 to 11% and oil content, 1 to 4%. However no species contains extremes of all 4 variables. Nor can species be found, retaining native compositions, at extremes of just one extractive composition, while the other fractions are present at constant levels. Thus we use orthogonal but non-intuitive compositions in this work, then rank pyrolysis effects in terms of traditional extractives content to get an understanding of their impact on biomass pyrolysis. 

The desired product from the fermentation process is E. coli cells. At the end of the fermentation process, the assumed E. coli cell concentration is 30 g/liter (dry cell weight) in which the protein content is assumed to be 20% of the dry cell mass. The composition (mass basis) of the outlet stream from the fermentor comprises 2.95% biomass, 4.00% glucose, 0.58% salts, and 92.46% water. 

As said above, plant root chemistry may also influence deeply alpine soil microorganism s biomass. It turns out that the particular chemical composition of exudates is a strong selective force in favour of bacteria that can catabolize particular compounds. Plants support heterotrophic microorganisms by way of rhizodeposition of root exudates and litter from dead tissue that include phenolic acids, flavonoids, terpenoids, carbohydrates, hydroxamic acids, aminoacids, denatured protein from dying root cells, CO2, and ethylene (Wardle, 1992). In certain plants, as much as 20-30% of fixed carbon may be lost as rhizodeposition (Lynch and Whipps, 1990). Most of these compounds enter the soil nutrient cycle by way of the soil microbiota, giving rise to competition between the myriad species living there, from microarthropods and nematodes to mycorrhiza and bacteria, for these resources (e.g. Hoover and Crossley, 1995). There is evidence that root phenolic exudates are metabolized preferentially by some soil microbes, while the same compounds are toxic to others. Phenolic acids usually occur in small concentration in soil chiefly because of soil metabolism while adsorption in clay and other soil particles plays a minor role (Bliun et al., 1999). However, their phytotoxicity is compounded by synergism between particular mixtures (Blum, 1996). 

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