Impact of nickel and cobalt on biogas production and process stability during semi-continuous anaerobic fermentation of a model substrate for maize silage.

The importance of nickel and cobalt on anaerobic degradation of a defined model substrate for maize was demonstrated. Five semi-continuous reactors were operated for 250 days at 35 °C and a well-defined trace metal solution was added to all reactors. Two reactors each were limited regarding the concentration of Ni(2+) and Co(2+), respectively, for certain time intervals. The required nickel concentration was depending on the organic loading rates (OLR) while, for example, above 2.6 g ODM L(-1) d(-1) nickel concentrations below 0.06 mg kg(-1) FM in the process significantly decreased biogas production by up to 25% compared to a control reactor containing 0.8 mg Ni(2+) kg(-1) FM. Similarly, limitation of cobalt to 0.02 mg kg(-1) FM decreased biogas production by about 10%. Limitations of nickel as well as cobalt lead to process instability. However, after gradual addition of nickel till 0.6 mg and cobalt till 0.05 mg kg(-1) FM the OLR was again increased to 4.3 g ODM L(-1) d(-1) while process stability was recovered and a fast metabolisation of acetic and propionic acid was detected. An increase of nickel to 0.88 mg kg(-1) FM did not enhance biogas performance. Furthermore, the increase of cobalt from 0.05 mg kg(-1) FM up to 0.07 mg kg(-1) FM did not exhibit a change in anaerobic fermentation and biogas production.

Characterization of an anaerobic population digesting a model substrate for maize in the presence of trace metals.

The influence of a defined trace metal solution and additionally Ni(2+) on anaerobic digestion of biomass was investigated. A novel synthetic model substrate was designed consisting of cellulose, starch and urea as carbon and nitrogen source in a ratio mimicking the basic composition of maize silage. Two independent batch fermentations were carried out over 21 d with the synthetic model substrate in the presence of the trace metal solution. Particularly an increase in nickel concentrations (17 and 34 microM) enhanced methane formation by up to 20%. This increased activity was also corroborated by fluorescence microscopy measurements based on cofactor F(420). The eubacterial and methanogenic population was characterized with the single strand conformational polymorphism analysis and the amplified 16S rDNA restriction analysis of 16S rRNA genes amplified by different primer systems. Nearly the half of the analyzed bacteria were identified as Firmicutes while 70% in this phylum belonged to the class of Clostridiales and 30% to the class of Bacilli. Bacteroides and uncultured bacteria represented each a quarter of the analyzed community. Methanogenic archaea were investigated with ARDRA, too. The hydrogenotrophic Methanoculleus sp. was the dominant genus which is commonly described for maize digestion thus confirming the value of the model substrate.

Influence of trace elements on methane formation from a synthetic model substrate for maize silage.

The effect of a well-defined trace element solution and the elements nickel, cobalt and molybdenum on anaerobic digestion of a synthetic model substrate for maize silage was studied in batch reactor experiments at 35 degrees C. The defined substrate (dS) consisted of xylan and starch as the main carbon source, urea as nitrogen source and phosphorus from a 0.1M potassium phosphate buffer. Batch reactors were operated for 30 days with 1.5% organic dry matter (ODM) of inoculum sludge from a mono-maize biogas plant and 1% ODM of the defined substrate. Results showed an increase of methane yield of up to 30% upon addition of the trace element solution. With an addition of nickel at 10.6 microM, a final yield of 407 l kg(-1) ODM was reached and an enhanced methane production by 25% at day 25 of operation was observed. Total elimination of nickel from the trace element solution highly decreased methane formation and process stability. Cobalt in a concentration range of 0.4 up to 2.0 microM increased the methane production by 10% approximately. Interestingly, addition of molybdenum did not significantly effect methane production.

A novel aryl acylamidase from Nocardia farcinica hydrolyses polyamide.

An alkali stable polyamidase was isolated from a new strain of Nocardia farcinica. The enzyme consists of four subunits with a total molecular weight of 190 kDa. The polyamidase cleaved amide and ester bonds of water insoluble model substrates like adipic acid bishexylamide and bis(benzoyloxyethyl)terephthalate and hydrolyzed different soluble amides to the corresponding acid. Treatment of polyamide 6 with this amidase led to an increased hydrophilicity based on rising height and tensiometry measurements and evidence of surface hydrolysis of polyamide 6 is shown. In addition to amidase activity, the enzyme showed activity on p-nitrophenylbutyrate. On hexanoamide the amidase exhibited a K(m) value of 5.5 mM compared to 0.07 mM for p-nitroacetanilide. The polyamidase belongs to the amidase signature family and is closely related to aryl acylamidases from different strains/species of Nocardia and to the 6-aminohexanoate-cyclic dimer hydrolase (EI) from Arthrobacter sp. KI72.

New model substrates for enzymes hydrolysing polyethyleneterephthalate and polyamide fibres.

Recently the potential of enzymes for surface hydrophilisation and/or functionalisation of polyethyleneterephthalate (PET) and polyamide (PA) has been discovered. However, there was no correlation between enzyme class/activity (e.g. esterase, lipase, cutinase) and surface hydrolysis of these polymers and consequently no simple assay to estimate this capability. Enzymes active on the model substrates bis (benzoyloxyethyl) terephthalate and adipic acid bishexyl-amide, were also capable of increasing the hydrophilicity of PET and PA. When dosed at the identical activity on 4-nitrophenyl butyrate, only enzymes from Thermobifida fusca, Aspergillus sp., Beauveria sp. and commercial enzymes (TEXAZYME PES sp5 and Lipase PS) increased the hydrophilicity of PET fibres while other esterases and lipases did not show any effect. Activity on PET correlated with the activity on the model substrate. Hydrophilicity of fibres was greatly improved based on increases in rising height of up to 4.3 cm and the relative decrease of water absorption time between control and sample of the water was up to 76%. Similarly, enzymes increasing the hydrophilicity of PA fibres such as from Nocardia sp., Beauveria sp. and F. solani hydrolysed the model substrate; however, there was no common enzyme activity (e.g. protease, esterase, amidase) which could be attributed to all these enzymes.