Nele Ilmberger

Applying metagenomics for the identification of bacterial cellulases that are stable in ionic liquids

Ionic liquids (ILs) are novel and chemically inert solvents for a wide range of reactions in organic synthesis and biocatalysis, and at least one of them is known to dissolve cellulose. ILs would provide novel options for cellulose degradation in homogenous catalysis if cellulases were sufficiently stable and active. By screening metagenomic libraries 24 novel cellulase clones were identified and tested for their performance in the presence of ILs. Most enzyme clones showed only very poor or no activities. Three enzyme clones (i.e. pCosJP10, pCosJP20 and pCosJP24) were moderately active and stable in the presence of 1-butyl-1-methyl-pyrrolidinium trifluoromethanesulfonate. The corresponding genes of these environment-derived cosmids were similar to known cellulases from Cellvibrio japonicus and a salt-tolerant cellulase from an uncultured microorganism, S. Voget, H. L. Steele and W. R. Streit, J. Biotechnol., 2006, 126, 26-36.1 The most active protein (CelA10) belonged to GH5 family cellulases and was active at IL concentrations of up to 30% (v/v). Recombinant CelA10 was extremely tolerant to 4 M NaCl and KCl. Furthermore improved cellulase variants of CelA10 were isolated in a directed evolution experiment employing SeSaM-technology. Analysis of these variants revealed that the N-terminal cellulose binding domain plays a pivotal role for IL resistance.

Functional Screening of Metagenome and Genome Libraries for Detection of Novel Flavonoid-Modifying Enzymes

ABSTRACT The functional detection of novel enzymes other than hydrolases from metagenomes is limited since only a very few reliable screening procedures are available that allow the rapid screening of large clone libraries. For the discovery of flavonoid-modifying enzymes in genome and metagenome clone libraries, we have developed a new screening system based on high-performance thin-layer chromatography (HPTLC). This metagenome extract thin-layer chromatography analysis (META) allows the rapid detection of glycosyltransferase (GT) and also other flavonoid-modifying activities. The developed screening method is highly sensitive, and an amount of 4 ng of modified flavonoid molecules can be detected. This novel technology was validated against a control library of 1,920 fosmid clones generated from a single Bacillus cereus isolate and then used to analyze more than 38,000 clones derived from two different metagenomic preparations. Thereby we identified two novel UDP glycosyltransferase (UGT) genes. The metagenome-derived gtfC gene encoded a 52-kDa protein, and the deduced amino acid sequence was weakly similar to sequences of putative UGTs from Fibrisoma and Dyadobacter. GtfC mediated the transfer of different hexose moieties and exhibited high activities on flavones, flavonols, flavanones, and stilbenes and also accepted isoflavones and chalcones. From the control library we identified a novel macroside glycosyltransferase (MGT) with a calculated molecular mass of 46 kDa. The deduced amino acid sequence was highly similar to sequences of MGTs from Bacillus thuringiensis. Recombinant MgtB transferred the sugar residue from UDP-glucose effectively to flavones, flavonols, isoflavones, and flavanones. Moreover, MgtB exhibited high activity on larger flavonoid molecules such as tiliroside.

A comparative metagenome survey of the fecal microbiota of a breast- and a plant-fed Asian elephant reveals an unexpectedly high diversity of glycoside hydrolase family enzymes.

A phylogenetic and metagenomic study of elephant feces samples (derived from a three-weeks-old and a six-years-old Asian elephant) was conducted in order to describe the microbiota inhabiting this large land-living animal. The microbial diversity was examined via 16S rRNA gene analysis. We generated more than 44,000 GS-FLX+454 reads for each animal. For the baby elephant, 380 operational taxonomic units (OTUs) were identified at 97% sequence identity level; in the six-years-old animal, close to 3,000 OTUs were identified, suggesting high microbial diversity in the older animal. In both animals most OTUs belonged to Bacteroidetes and Firmicutes. Additionally, for the baby elephant a high number of Proteobacteria was detected. A metagenomic sequencing approach using Illumina technology resulted in the generation of 1.1 Gbp assembled DNA in contigs with a maximum size of 0.6 Mbp. A KEGG pathway analysis suggested high metabolic diversity regarding the use of polymers and aromatic and non-aromatic compounds. In line with the high phylogenetic diversity, a surprising and not previously described biodiversity of glycoside hydrolase (GH) genes was found. Enzymes of 84 GH families were detected. Polysaccharide utilization loci (PULs), which are found in Bacteroidetes, were highly abundant in the dataset; some of these comprised cellulase genes. Furthermore the highest coverage for GH5 and GH9 family enzymes was detected for Bacteroidetes, suggesting that bacteria of this phylum are mainly responsible for the degradation of cellulose in the Asian elephant. Altogether, this study delivers insight into the biomass conversion by one of the largest plant-fed and land-living animals.

Screening for Cellulase Encoding Clones in Metagenomic Libraries

Modern biotechnology has the steady need to continuously identify novel enzymes for use in biotechnological applications. In industrial applications, however, enzymes often have to function under extreme and nonnatural conditions (i.e., in the presence of solvents, high temperature and/or at extreme pH values). Cellulases have many industrial applications from the generation of bioethanol, a realistic long-term energy source, to the finishing of textiles. These industrial processes require cellulolytic activity under a range of pH, temperature, and ionic conditions, and they are usually carried out by mixtures of cellulases. Investigation of the broad diversity of cellulolytic enzymes involved in the natural degradation of cellulose is necessary for optimization of these processes.

The metagenome-derived enzyme RhaB opens a new subclass of bacterial B type α-L-rhamnosidases.

A combined sequence- and function-based analysis of a metagenomic library DNA derived from elephant feces led to the identification of a novel bacterial α-l-rhamnosidase belonging to glycoside hydrolase family 78 (GH78). The gene was designated rhaB (4095bp) and encoded for a putative protein of 1364 amino acids. The C-terminal part of the enzyme revealed an amino acid (AA) sequence identity of 58% to a predicted bacterial α-l-rhamnosidase from Bacteroides nordii. Interestingly, the N-terminal region of the deduced enzyme RhaB contained a GDSL-like lipase motif and an acetyl-xylan esterase (DAP2) motif. While heterologous expression of the complete rhaB failed, subcloning of the gene identified the most active open reading frame (ORF) to be of 3081bp, which we designated rhaB1. The enzyme RhaB1 was overexpressed in Escherichia coli BL21 (DE3) and was purified to an amount of 75mg/L of culture medium. In accordance to the intestinal origin, RhaB1 showed a preference for mesophilic conditions with an optimum activity at a temperature TOpt of 40°C and a pHOpt of 6.5, respectively. The recombinant protein had a Km value of 0.79mM and a specific activity vmax of 18.4U for pNP-α-l-rhamnose, a calculated Km of 6.36mM and vmax of 2.9×10(-3)U for naringin, and a Km of 6.75mM and specific activity vmax of 8.63×10(-2)U for rutin, respectively. Phylogenetic analysis and amino acid domain architecture comparison revealed that RhaB1 belongs to a new subclass of bacterial B type α-l-rhamnosidases of GH 78. To our knowledge RhaB1 is the first biochemically-characterized enzyme of this subclass.

Screening for Cellulases with Industrial Value and Their Use in Biomass Conversion

Cellulose is an easily renewable and highly occurring resource. To take advantage of this great potential, there is a constant need of new cellulose degrading enzymes. In industrial applications enzymes have to function under extreme conditions like high temperature, very acidic or basic pH and different solvents. Cellulases have a huge area of application, for example the textile and food industry as well as the generation of bioethanol as an alternative energy source. They have the ability to yield a great energetic potential, but there is still a lack of economical technologies to conquer the stability of the cellulose structure. Via metagenomic research and well-directed screening, it is possible to detect new cellulases, which are active under tough industrial conditions.

Screening Glycosyltransferases for Polyphenol Modifications.

Glycosyltransferases offer the opportunity to glycosylate a variety of substrates including health beneficial molecules like flavonoids in a regiospecific manner. Flavonoids are plant secondary metabolites that have antimicrobial, antioxidative, and health beneficial effects. Glycosylation often has impact on these properties and furthermore enhances the water solubility, the stability, and the bioavailability of the molecules. To detect flavonoid glycosylating enzymes we established a metagenome screen for the discovery of modifying clones. This function based screening technique can furthermore detect other modifications like methylations. The method relies on analysis of the culture supernatant extracts from biotransformation reactions in a thin layer chromatography (TLC) approach.