Anaerobic gut fungi are an untapped reservoir of natural products.

Anaerobic fungi (class Neocallimastigomycetes) thrive as low-abundance members of the herbivore digestive tract. The genomes of anaerobic gut fungi are poorly characterized and have not been extensively mined for the biosynthetic enzymes of natural products such as antibiotics. Here, we investigate the potential of anaerobic gut fungi to synthesize natural products that could regulate membership within the gut microbiome. Complementary 'omics' approaches were combined to catalog the natural products of anaerobic gut fungi from four different representative species: Anaeromyces robustus (Arobustus), Caecomyces churrovis (Cchurrovis), Neocallimastix californiae (Ncaliforniae), and Piromyces finnis (Pfinnis). In total, 146 genes were identified that encode biosynthetic enzymes for diverse types of natural products, including nonribosomal peptide synthetases and polyketide synthases. In addition, N. californiae and C. churrovis genomes encoded seven putative bacteriocins, a class of antimicrobial peptides typically produced by bacteria. During standard laboratory growth on plant biomass or soluble substrates, 26% of total core biosynthetic genes in all four strains were transcribed. Across all four fungal strains, 30% of total biosynthetic gene products were detected via proteomics when grown on cellobiose. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) characterization of fungal supernatants detected 72 likely natural products from A. robustus alone. A compound produced by all four strains of anaerobic fungi was putatively identified as the polyketide-related styrylpyrone baumin. Molecular networking quantified similarities between tandem mass spectrometry (MS/MS) spectra among these fungi, enabling three groups of natural products to be identified that are unique to anaerobic fungi. Overall, these results support the finding that anaerobic gut fungi synthesize natural products, which could be harnessed as a source of antimicrobials, therapeutics, and other bioactive compounds.

Engineered GH11 xylanases from Orpinomyces sp. PC-2 improve techno-functional properties of bread dough.

BACKGROUND: Endo-1,4-ß-xylanases have marked hydrolytic activity towards arabinoxylans. Xylanases (xynA) produced by the anaerobic fungus Orpinomyces sp. strain PC-2 have been shown to be superior in specific activity, which strongly suggests their applicability in the bakery industry for the processing of whole-wheat flour containing xylans. In the present study, two xylanases from this source, the small wild-type xylanase SWT and the small mutant xylanase SM2 (V108A, A199T), were expressed in Escherichia coli, purified, characterized, tested for their ability to hydrolyze whole-wheat flour and applied in dough processing. RESULTS: Both purified SM2 and SWT showed high specific activity against oat spelt xylan and wheat arabinoxylan, exhibiting maximum activity at pH 3-7 and 60 °C. SM2 was more thermostable than SWT, which suggests that the mutations enhanced its stability. Both SWT and SM2 were able to hydrolyze whole-wheat flour, and evaluation of their applicability in dough processing by the sponge method indicated that use of these enzymes increased dough volume by 60% and reduced texture hardness by more than 50%, while gumminess and chewiness were reduced by 40%. CONCLUSION: The recombinant xylanases showed potential for application in bakery processing and can improve techno-functional properties in sponges. © 2018 Society of Chemical Industry.

Anaeromyces contortus, sp. nov., a new anaerobic gut fungal species (Neocallimastigomycota) isolated from the feces of cow and goat.

Ten different anaerobic gut fungal strains were isolated from fecal samples of cow and goat in Oklahoma, USA. The isolates displayed polycentric thalli, uniflagellated zoospores, and sausage-shaped hyphal constrictions, all characteristic of the genus Anaeromyces, and lobed or appressorium-like structures on the hyphae, previously reported in Anaeromyces elegans but not in A. mucronatus or A. robustus. Further, the strains exhibited highly coiled and entangled hyphae previously unreported in the Neocallimastigomycota, but resembling fungal traps previously observed in multiple nematophagous fungi. Scanning electron micrographs of isolates grown on switchgrass showed entrapment of plant material by the hyphal coils and the penetration of plant fibers at various sites by the appressorium-like structures. Molecular analysis based on sequences of both partial nuc rDNA ITS1 spacer region and the D1-D2 domains of the nuc28S rDNA confirmed the classification of all isolates in Anaeromyces and confirmed their phylogenetic distance from the available A. mucronatus and A. robustus sequences. On the basis of morphological and phylogenetic distinctions, we conclude that these strains represent a new Anaeromyces species, for which A. contortus is proposed.

Impact of the removal of N-terminal non-structured amino acids on activity and stability of xylanases from Orpinomyces sp. PC-2.

Xylanases catalyze the random hydrolysis of xylan backbone from plant biomass and thus, they have application in the production of biofuels, Kraft pulps biobleaching and feed industry. Here, xylanases derived from Orpinomyces sp. PC-2 were engineered guided by molecular dynamics methods to obtain more thermostable enzymes. Based on these models, 27 amino acid residues from the N-terminal were predicted to reduce protein stability and the impact of this removal was validated to two enzyme constructs: small xylanase Wild-Type (SWT) obtained from Wild-Type xylanase (WT) and small xylanase Mutant (SM2) generated from M2 mutant xylanase (V135A, A226T). The tail removal promoted increase in specific activity of purified SWT and SM2, which achieved 5,801.7 and 5,106.8Umg-1 of protein, respectively, while the WT activity was 444.1Umg-1 of protein. WT, SWT and SM2 showed half-life values at 50°C of 0.8, 2.3 and 29.5h, respectively. Overall, in view of the results, we propose that the presence of non-structured amino acid in the N-terminal leads to destabilization of the xylanases and may promote less access of the substrate to the active site. Therefore, its removal may promote increased stability and enzymatic activity, interesting properties that make them suitable for biotechnological applications.

Transcriptome changes in adaptive evolution of xylose-fermenting industrial Saccharomyces cerevisiae strains with δ-integration of different xylA genes.

It is of utmost importance to construct industrial xylose-fermenting Saccharomyces cerevisiae strains for lignocellulosic bioethanol production. In this study, two xylose isomerase-based industrial S. cerevisiae strains, O7 and P5, were constructed by δ-integration of the xylose isomerase (XI) gene xylA from the fungus Orpinomyces sp. and from the bacterium Prevotella ruminicola, respectively. The xylose consumption of the strains O7 and P5 at 48-h fermentation was 17.71 and 26.10 g/L, respectively, in synthetic medium with xylose as the sole sugar source. Adaptive evolution further improved the xylose fermentation capacity of the two strains to 51.0 and 28.9% in average, respectively. The transcriptomes of these two strains before and after evolution were analyzed using RNA-Seq. The expression levels of the genes involved in cell integrity, non-optimal sugar utilization, and stress response to environment were significantly up-regulated after evolution and did not depend on the origin of xylA; the expression levels of the genes involved in transmembrane transport, rRNA processing, cytoplasmic translation, and other processes were down-regulated. The expression of genes involved in central carbon metabolism was fine-tuned after the evolution. The analysis of transcription factors (TFs) indicated that most of the genes with significant differential expression were regulated by the TFs related to cell division, DNA damage response, or non-optimal carbon source utilization. The results of this study could provide valuable references for the construction of efficient xylose-fermenting XI strains.

A parts list for fungal cellulosomes revealed by comparative genomics.

Cellulosomes are large, multiprotein complexes that tether plant biomass-degrading enzymes together for improved hydrolysis1. These complexes were first described in anaerobic bacteria, where species-specific dockerin domains mediate the assembly of enzymes onto cohesin motifs interspersed within protein scaffolds1. The versatile protein assembly mechanism conferred by the bacterial cohesin-dockerin interaction is now a standard design principle for synthetic biology2,3. For decades, analogous structures have been reported in anaerobic fungi, which are known to assemble by sequence-divergent non-catalytic dockerin domains (NCDDs)4. However, the components, modular assembly mechanism and functional role of fungal cellulosomes remain unknown5,6. Here, we describe a comprehensive set of proteins critical to fungal cellulosome assembly, including conserved scaffolding proteins unique to the Neocallimastigomycota. High-quality genomes of the anaerobic fungi Anaeromyces robustus, Neocallimastix californiae and Piromyces finnis were assembled with long-read, single-molecule technology. Genomic analysis coupled with proteomic validation revealed an average of 312 NCDD-containing proteins per fungal strain, which were overwhelmingly carbohydrate active enzymes (CAZymes), with 95 large fungal scaffoldins identified across four genera that bind to NCDDs. Fungal dockerin and scaffoldin domains have no similarity to their bacterial counterparts, yet several catalytic domains originated via horizontal gene transfer with gut bacteria. However, the biocatalytic activity of anaerobic fungal cellulosomes is expanded by the inclusion of GH3, GH6 and GH45 enzymes. These findings suggest that the fungal cellulosome is an evolutionarily chimaeric structure-an independently evolved fungal complex that co-opted useful activities from bacterial neighbours within the gut microbiome.

Mapping the membrane proteome of anaerobic gut fungi identifies a wealth of carbohydrate binding proteins and transporters.

BACKGROUND: Engineered cell factories that convert biomass into value-added compounds are emerging as a timely alternative to petroleum-based industries. Although often overlooked, integral membrane proteins such as solute transporters are pivotal for engineering efficient microbial chassis. Anaerobic gut fungi, adapted to degrade raw plant biomass in the intestines of herbivores, are a potential source of valuable transporters for biotechnology, yet very little is known about the membrane constituents of these non-conventional organisms. Here, we mined the transcriptome of three recently isolated strains of anaerobic fungi to identify membrane proteins responsible for sensing and transporting biomass hydrolysates within a competitive and rather extreme environment. RESULTS: Using sequence analyses and homology, we identified membrane protein-coding sequences from assembled transcriptomes from three strains of anaerobic gut fungi: Neocallimastix californiae, Anaeromyces robustus, and Piromyces finnis. We identified nearly 2000 transporter components: about half of these are involved in the general secretory pathway and intracellular sorting of proteins; the rest are predicted to be small-solute transporters. Unexpectedly, we found a number of putative sugar binding proteins that are associated with prokaryotic uptake systems; and approximately 100 class C G-protein coupled receptors (GPCRs) with non-canonical putative sugar binding domains. CONCLUSIONS: We report the first comprehensive characterization of the membrane protein machinery of biotechnologically relevant anaerobic gut fungi. Apart from identifying conserved machinery for protein sorting and secretion, we identify a large number of putative solute transporters that are of interest for biotechnological applications. Notably, our data suggests that the fungi display a plethora of carbohydrate binding domains at their surface, perhaps as a means to sense and sequester some of the sugars that their biomass degrading, extracellular enzymes produce.

Functional expression of xylose isomerase in flocculating industrial Saccharomyces cerevisiae strain for bioethanol production.

Saccharomyces cerevisiae strains with xylose isomerase (XI) pathway were constructed using a flocculating industrial strain (YC-8) as the host. Both strains expressing wild-type xylA (coding XI) from the fungus Orpinomyces sp. and the bacterium Prevotella ruminicola, respectively, showed better growth ability and fermentation capacity when using xylose as the sole sugar than most of the reported strains expressing XI. Codon optimization of both XIs did not improve the xylose fermentation ability of the strains. Adaption significantly increased XI activity resulting in improved growth and fermentation. The strains expressing codon-optimized XI showed a higher increase in xylose consumption and ethanol production compared to strains expressing wild XI. Among all strains, the adapted strain YCPA2E expressing XI from P. ruminicola showed the best performance in the fermentation of xylose to ethanol. After 48 h of fermentation, YCPA2E assimilated 16.95 g/L xylose and produced 6.98 g/L ethanol. These results indicate that YC-8 is a suitable host strain for XI expression, especially for the codon-optimized XI originating from P. ruminicola.

A new anaerobic fungus (Oontomyces anksri gen. nov., sp. nov.) from the digestive tract of the Indian camel (Camelus dromedarius).

Two cultures of anaerobic fungi were isolated from the forestomach of an Indian camel (Camelus dromedarius). Phylogenetic analysis using both the internal transcribed spacer (ITS) and large-subunit (LSU) regions of the rRNA locus demonstrated that these isolates were identical and formed a distinct clade within the anaerobic fungi (phylum Neocallimastigomycota). Morphological examination showed that these fungi formed monocentric thalli with filamentous rhizoids and uniflagellate zoospores, broadly similar to members of the genus Piromyces. However, distinctive morphological features were observed, notably the pinching of the cytoplasm in the sporangiophore and the formation of intercalary rhizoidal swellings. Since genetic analyses demonstrated this fungus was only distantly related to Piromyces spp. and closer to the polycentric Anaeromyces clade, we have assigned it to a new genus and species Oontomyces anksri gen. nov., sp. nov. Interrogation of the GenBank database identified several closely related ITS sequences, which were all environmental sequences obtained from camels, raising the possibility that this fungus may be specific to camelids.

A highly active beta-glucanase from a new strain of rumen fungus Orpinomyces sp.Y102 exhibits cellobiohydrolase and cellotriohydrolase activities.

A new strain of rumen fungus was isolated from Bos taurus, identified and designated Orpinomyces sp.Y102. A clone, celC7, isolated from the cDNA library of Orpinomyces sp.Y102, was predicted to encode a protein containing a signal peptide (Residues 1-17), an N-terminal dockerin-containing domain, and a C-terminal cellobiohydrolase catalytic domain of glycoside hydrolase family 6. CelC7 was insoluble when expressed in Escherichia coli. Deletion of 17 or 105 residues from the N-terminus significantly improved its solubility. The resulting enzymes, CelC7(-17) and CelC7(-105), were highly active to ß-glucan substrates and were stable between pH 5.0 and 11.0. CelC7(-105) worked as an exocellulase releasing cellobiose and cellotriose from acid-swollen Avicel and cellooligosaccharides, and displayed a Vmax of 6321.64µmole/min/mg and a Km of 2.18mg/ml to barley ß-glucan. Further, the crude extract of CelC7(-105) facilitated ethanol fermentation from cellulose. Thus, CelC7(-105) is a good candidate for industrial applications such as biofuel production.

The genome of the anaerobic fungus Orpinomyces sp. strain C1A reveals the unique evolutionary history of a remarkable plant biomass degrader.

Anaerobic gut fungi represent a distinct early-branching fungal phylum (Neocallimastigomycota) and reside in the rumen, hindgut, and feces of ruminant and nonruminant herbivores. The genome of an anaerobic fungal isolate, Orpinomyces sp. strain C1A, was sequenced using a combination of Illumina and PacBio single-molecule real-time (SMRT) technologies. The large genome (100.95 Mb, 16,347 genes) displayed extremely low G+C content (17.0%), large noncoding intergenic regions (73.1%), proliferation of microsatellite repeats (4.9%), and multiple gene duplications. Comparative genomic analysis identified multiple genes and pathways that are absent in Dikarya genomes but present in early-branching fungal lineages and/or nonfungal Opisthokonta. These included genes for posttranslational fucosylation, the production of specific intramembrane proteases and extracellular protease inhibitors, the formation of a complete axoneme and intraflagellar trafficking machinery, and a near-complete focal adhesion machinery. Analysis of the lignocellulolytic machinery in the C1A genome revealed an extremely rich repertoire, with evidence of horizontal gene acquisition from multiple bacterial lineages. Experimental analysis indicated that strain C1A is a remarkable biomass degrader, capable of simultaneous saccharification and fermentation of the cellulosic and hemicellulosic fractions in multiple untreated grasses and crop residues examined, with the process significantly enhanced by mild pretreatments. This capability, acquired during its separate evolutionary trajectory in the rumen, along with its resilience and invasiveness compared to prokaryotic anaerobes, renders anaerobic fungi promising agents for consolidated bioprocessing schemes in biofuels production.

Shifts in the rumen microbiota due to the type of carbohydrate and level of protein ingested by dairy cattle are associated with changes in rumen fermentation.

Balancing energy and nitrogen in the rumen is a key to both profitability and environmental sustainability. Four dairy cows were used in a Latin square experimental design to investigate the effect of severe nitrogen underfeeding (110 vs. 80% of requirements) and the type of carbohydrate consumed [neutral detergent fiber rich (FIB) vs. starch rich (STA)] on the rumen ecosystem. These dietary treatments modified both rumen fermentation and microbial populations. Compared with STA diets, consumption of FIB diets increased bacterial and fungal diversity in the rumen and also increased the concentrations of cellulolytic microorganisms, including protozoa (+38%), anaerobic fungi (+59%), and methanogens (+27%). This microbial adaptation to fiber utilization led to similar digestibility values for the 2 carbohydrate sources and was accompanied by a shift in the rumen fermentation patterns; when the FIB diets were consumed, the cows had greater ruminal pH, ammonia concentrations, and molar proportions of acetate and propionate compared with when they consumed the STA diets. Certain rumen microorganisms were sensitive to a shortage of nitrogen; rumen concentrations of ammonia were 49% lower when the low-protein (LP) diets were consumed as were total bacteria (-13%), anaerobic fungi (-28%), methanogens (-27%), protozoa (-19%), cellulolytic bacteria, and microbial diversity compared with when the high-protein (HP) diets were consumed. As a result, the digestibility of the LP diets was less than that of the HP diets. These findings demonstrated that the rumen microbial ecosystem is directly linked to the rumen fermentation pattern and, to some extent, to the efficiency of diet utilization by dairy cattle.

D1/D2 domain of large-subunit ribosomal DNA for differentiation of Orpinomyces spp.

This study presents the suitability of D1/D2 domain of large-subunit (LSU) ribosomal DNA (rDNA) for differentiation of Orpinomyces joyonii and Orpinomyces intercalaris based on PCR-restriction fragment length polymorphism (RFLP). A variation of G/T in O. intercalaris created an additional restriction site for AluI, which was used as an RFLP marker. The results demonstrate adequate heterogeneity in the LSU rDNA for species-level differentiation.

Expression of an endo-ß-1,4-glucanase gene from orpinomyces PC-2 in Pichia pastoris.

The endo-ß-1,4-glucanase gene celE from the anaerobic fungus Orpinomyces PC-2 was placed under the control of an alcohol oxidase promoter (AOX1) in the plasmid pPIC9K, and integrated into the genome of a methylotrophic yeast P. pastoris GS115 by electroporation. The strain with highest endo-ß-1,4-glucanase activity was selected and designed as P. pastoris egE, and cultivated in shaking flasks. The culture supernatant was assayed by SDS-polyacrylamide gel electrophoresis and showed a single band at about 52 kDa. Furthermore, the recombinant P. pastoris egE was proved to possess the ability to utilize sodium carboxymethyl cellulose as a carbon source. The recombinant endoglucanase produced by P. pastoris showed maximum activity at pH 6.0 and temperature 45 °C, indicating it was a mesophilic neutral endo-ß-1,4-glucanase, suitable for denim biofinishing/washing. Further research was carried out in suitable fermentation medium in shaking flasks. The most favorable methanol addition concentration was discussed and given as 1.0%. After methanol induction for 96 h, the endo-ß-1,4-glucanase activity reached 72.5 IU mL(-1). This is the first report on expression and characterization of endo-ß-1,4-glucanase from Orpinomyces in P. pastoris. The endo-ß-1,4-glucanase secreted by recombinant P. pastoris represents an attractive potential for both academic research and textile industry application.

Isolation and characterization of a ferulic acid esterase (Fae1A) from the rumen fungus Anaeromyces mucronatus.

AIMS: A novel ferulic acid esterase gene from rumen fungus Anaeromyces mucronatus was cloned, heteroexpressed in Escherichia coli and characterized. METHODS AND RESULTS: A total of 30 clones exhibiting activity on α-naphthyl acetate (α-NA) were isolated from an A. mucronatus YE505 cDNA library. Sequence analysis revealed that these clones represented two esterase-coding sequences. The gene, fae1A, showed highest amino acid sequence identity to CE family 1 esterases from anaerobic micro-organisms such as Orpinomyces sp., Ruminococcus albus and Clostridium thermocellum. The gene comprised 828 nucleotides encoding a polypeptide of 275 amino acids. The coding sequence was cloned into the pET30a expression vector and overexpressed in E. coli BL21 (DE3). Gene product Fae1A was found to exhibit activity against a number of substrates including naphthyl fatty acid esters, p-nitrophenyl fatty acid esters and hydroxylcinnamic acid esters. CONCLUSIONS: Fae1A exhibited a lower K(m) and higher catalytic efficiency (k(cat) /K(m) ) on ferulic acid esters than on α-NA or p-nitrophenyl acetate, suggesting that it has a higher affinity for ethyl and methyl ferulate than for the acetyl esters. It releases ferulic acid and p-coumaric acid from barley straw. Activity of Fae1A was inhibited by the serine-specific protease inhibitor, phenylmethylsulfonyl fluoride, indicating that a serine residue plays a role in its activity. SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first report of characterization of carbohydrate esterase gene from the genus of Anaeromyces.

Construction of a xylose-metabolizing yeast by genome integration of xylose isomerase gene and investigation of the effect of xylitol on fermentation.

A yeast with the xylose isomerase (XI) pathway was constructed by the multicopy integration of XI overexpression cassettes into the genome of the Saccharomyces cerevisiae MT8-1 strain. The resulting yeast strain successfully produced ethanol from both xylose as the sole carbon source and a mixed sugar, consisting of xylose and glucose, without any adaptation procedure. Ethanol yields in the fermentation from xylose and mixed sugar were 61.9% and 62.2% of the theoretical carbon recovery, respectively. Knockout of GRE3, a gene encoding nonspecific aldose reductase, of the host yeast strain improved the fermentation profile. Not only specific ethanol production rates but also xylose consumption rates was improved more than twice that of xylose-metabolizing yeast with the XI pathway using GRE3 active yeast as the host strain. In addition, it was demonstrated that xylitol in the medium exhibits a concentration-dependent inhibition effect on the ethanol production from xylose with the yeast harboring the XI-based xylose metabolic pathway. From our findings, the combination of XI-pathway integration and GRE3 knockout could be result in a consolidated xylose assimilation pathway and increased ethanol productivity.

Xylose isomerase from polycentric fungus Orpinomyces: gene sequencing, cloning, and expression in Saccharomyces cerevisiae for bioconversion of xylose to ethanol.

The cDNA sequence of the gene for xylose isomerase from the rumen fungus Orpinomyces was elucidated by rapid amplification of cDNA ends. The 1,314-nucleotide gene was cloned and expressed constitutively in Saccharomyces cerevisiae. The deduced polypeptide sequence encoded a protein of 437 amino acids which showed the highest similarity to the family II xylose isomerases. Further, characterization revealed that the recombinant enzyme was a homodimer with a subunit of molecular mass 49 kDa. Cell extract of the recombinant strain exhibited high specific xylose isomerase activity. The pH optimum of the enzyme was 7.5, while the low temperature optimum at 37 degrees C was the property that differed significantly from the majority of the reported thermophilic xylose isomerases. In addition to the xylose isomerase gene, the overexpression of the S. cerevisiae endogenous xylulokinase gene and the Pichia stipitis SUT1 gene for sugar transporter in the recombinant yeast facilitated the efficient production of ethanol from xylose.

Molecular diversity of the rumen microbiome of Norwegian reindeer on natural summer pasture.

The molecular diversity of the rumen microbiome was investigated in five semi-domesticated adult female Norwegian reindeer (Rangifer tarandus tarandus) grazing on natural summer pastures on the coast of northern Norway (71.00 degrees N, 25.30 degrees E). Mean population densities (numbers per gram wet weight) of methanogenic archaea, rumen bacteria and ciliate protozoa, estimated using quantitative real-time polymerase chain reaction (PCR), were 3.17x10(9), 5.17x10(11) and 4.02x10(7), respectively. Molecular diversity of rumen methanogens was revealed using a 16S rRNA gene library (54 clones) constructed using pooled PCR products from the whole rumen contents of the five individual reindeer. Based upon a similarity criterion of <97%, a total of 19 distinct operational taxonomic units (OTUs) were identified, nine of which are potential new species. The 16S rRNA sequences generated from the reindeer rumen exhibited a high degree of sequence similarity to methanogens affiliated with the families Methanobacteriaceae (14 OTUs) and Methanosarcinaceae (one OTU). Four of the OTUs detected belonged to a group of uncultivated archaea previously found in domestic ruminants and thought to be dominant in the rumen together with Methanobrevibacter spp. Denaturing gradient gel electrophoresis profiling of the rumen bacterial 16S rRNA gene and the protozoal 18S rRNA gene indicated a high degree of animal variation, although some bands were common to all individuals. Automated ribosomal intergenic spacer analysis (ARISA) profiling of the ruminal Neocallimastigales population indicated that the reindeer are likely to contain more than one type of anaerobic fungus. The ARISA profile from one animal was distinct from the other four. This is the first molecular investigation of the ruminal methanogenic archaea in reindeer, revealing higher numbers than expected based on methane emission data available. Also, many of the reindeer archaeal 16S rRNA gene sequences were similar to those reported in domesticated ruminants in Australia, Canada, China, New Zealand and Venezuela, supporting previous findings that there seems to be no host type or geographical effect on the methanogenic archaea community structure in ruminants.

Caecomyces sympodialis sp. nov., a new rumen fungus isolated from Bos indicus.

A new anaerobic rumen fungus was isolated from the rumen fluid of a yellow cow (Bos indicus). This fungus appears to be a previously undescribed species of the genus Caecomyces, it possessing uniflagellate zoospores, a spherical holdfast, tubular sporangiophores and bulbous rhizoids. This new fungus also features distinctive multisporangiate thallus sympodially distributed on sporangiophores. The fungus resembles Caecomyces communis and C. equi in that it characterizes bulbous rhizoids and uniflagellate zoospores but differs from C. communis and C. equi in that it possesses multisporangiate and sympodial sporangia. This new fungus and Cyllamyces aberensis both reveal similar morphology during early thallus development in having a spherical holdfast, but they vary from unbranched sporangiophores and additional bulbous rhizoids. In addition, the molecular phylogenetic analyses ITS1 (internal transcribed spacer 1) also conform to the results of the morphological examinations of Caecomyces. For the mentioned reasons, this new species of fungus is described as Caecomyces sympodialis sp. nov. The genera of Neocallimasticaceae and species of Caecomyces are also keyed out.

Expression of an AT-rich xylanase gene from the anaerobic fungus Orpinomyces sp. strain PC-2 in and secretion of the heterologous enzyme by Hypocrea jecorina.

The catalytic domain encoded by an adenine-thymine (AT)-rich xylanase gene (xynA) of the anaerobic fungus Orpinomyces was expressed in Hypocrea jecorina under the control of the cel7A promoter and terminator. No XynA protein was detected in H. jecorina culture supernatants when the original sequence was fused to the H. jecorina cel5A region coding for its signal peptide, carbohydrate-binding module, and hinge. Replacing the xynA (56% AT content) with a synthetic sequence containing lower AT content (39%) supported the extracellular production (150 mg l(-1)) of the fusion xylanase by H. jecorina. Northern analysis revealed that successful production after the decrease in AT content was related to higher levels of the xylanase-specific mRNA. Another construct with an RDKR-coding sequence inserted between the cel5A linker and the xynA catalytic domain allowed production of the fully processed active xylanase catalytic domain. Both the fusion (40 kDa) and the fully processed (28 kDa) forms displayed enzymatic properties of family 11 xylanases. Both the R and the Kex2-like KR sites were recognized during secretion, resulting in a mixture of two amino termini for the 28-kDa xylanase. The work demonstrated for the first time that glycoside hydrolases derived from anaerobic fungi can be produced by H. jecorina.