Identification of a biosynthesis gene cluster for flocculosin a cellobiose lipid produced by the biocontrol agent Pseudozyma flocculosa

A unique effector secreted by Pseudozyma flocculosa mediates its biocontrol activity

BACKGROUND

Pseudozyma flocculosa is a highly efficient biocontrol agent (BCA) of powdery mildews whose mode of action remains elusive. It is known to secrete unique effectors during its interaction with powdery mildews but effectors have never been shown to be part of the arsenal of a BCA. Here, we characterize the role of the effector Pf2826 released by Pseudozyma flocculosa during its tripartite interaction with barley and the pathogen fungus Blumeria graminis f. sp. hordei.

RESULTS

We utilized CRISPR-Cas9-based genome editing and confirmed that secreted P. flocculosa effector Pf2826 is required for full biocontrol activity. We monitored the localization of the effector Pf2826 with C-terminal mCherry tag and found it localized around the haustoria and on powdery mildew spores. His-tagged Pf2826 recombinant protein was expressed, purified, and used as bait in a pull-down assay from total proteins extracted during the tripartite interaction. Potential interactors were identified by LC-MS/MS analysis after removing unspecific interactions found in the negative controls. A two-way yeast two-hybrid assay validated that Pf2826 interacted with barley pathogenesis-related (PR) proteins HvPR1a and chitinase and with an effector protein from powdery mildew.

CONCLUSIONS

In contrast to the usual modes of action of competition, parasitism, and antibiosis ascribed to BCAs, this study shows that effector pf2826 plays a vital role in the biocontrol activity of P. flocculosa by interacting with plant PR proteins and a powdery mildew effector, altering the host-pathogen interaction.

Progress in pathogenesis research of Ustilago maydis, and the metabolites involved along with their biosynthesis

Ustilago maydis is a pathogenic fungus that causes corn smut. Because of its easy cultivation and genetic transformation, U. maydis has become an important model organism for plant-pathogenic basidiomycetes. U. maydis is able to infect maize by producing effectors and secreted proteins as well as surfactant-like metabolites. In addition, the production of melanin and iron carriers is also associated with its pathogenicity. Here, advances in our understanding of the pathogenicity of U. maydis, the metabolites involved in the pathogenic process, and the biosynthesis of these metabolites, are reviewed and discussed. This summary will provide new insights into the pathogenicity of U. maydis and the functions of associated metabolites, as well as new clues for deciphering the biosynthesis of metabolites.

Massoia Lactone Displays Strong Antifungal Property Against Many Crop Pathogens and Its Potential Application

Massoia lactone could be released from liamocins produced by Aureobasidium melanogenum M39. The obtained Massoia lactone was very stable and highly active against many fungal crop pathogens which cause many plant diseases and food unsafety. Massoia lactone treatment not only could effectively inhibit their hyphal growth and spore germination, but also caused pore formation in cell membrane, reduction of ergosterol content, rise in intracellular ROS levels, and leakage of intracellular components, consequently leading to cellular necrosis and cell death. The direct contact of Massoia lactone with Fusarium graminearum spores could stop the development of Fusarium head blight symptom in the diseased wheats. Therefore, Massoia lactone could be a promising candidate for development as an effective and green bio-fungicide because of its high anti-fungal activity and the multiplicity of mode of its action.

Phase Behaviour, Functionality, and Physicochemical Characteristics of Glycolipid Surfactants of Microbial Origin

Growing demand for biosurfactants as environmentally friendly counterparts of chemically derived surfactants enhances the extensive search for surface-active compounds of biological (microbial) origin. The understanding of the physicochemical properties of biosurfactants such as surface tension reduction, dispersion, emulsifying, foaming or micelle formation is essential for the successful application of biosurfactants in many branches of industry. Glycolipids, which belong to the class of low molecular weight surfactants are currently gaining a lot of interest for industrial applications. For this reason, we focus mainly on this class of biosurfactants with particular emphasis on rhamnolipids and sophorolipids, the most studied of the glycolipids.

A review on biosurfactants: properties, applications and current developments

Microbial surfactants are a large number of amphipathic biomolecules with a myriad of biomolecule constituents from various microbial sources that have been studied for their surface tension reduction activities. With unique properties, their applications have been increased in different areas including environment, medicine, healthcare, agriculture and industries. The present review aims to study the biochemistry and biosynthesis of biosurfactants exhibiting varying biomolecular structures which are produced by different microbial sources. It also provides details on roles played by biosurfactants in nature as well as their potential applications in various sectors. Basic biomolecule content of all the biosurfactants studied showed presence of carbohydrates, aminoacids, lipids and fattyacids. The data presented here would help in designing, synthesis and application of tailor-made novel biosurfactants. This would pave a way for perspectives of research on biosurfactants to overcome the existing bottlenecks in this field.

A reassessment of flocculosin-mediated biocontrol activity of Pseudozyma flocculosa through CRISPR/Cas9 gene editing

Pseudozyma flocculosa is an epiphytic yeast with powerful antagonistic activity against powdery mildews. This activity has been associated with the production of a rare antifungal glycolipid, flocculosin. In spite of the discovery of a specific gene cluster for flocculosin synthesis, attempts to ascribe a functional role to the molecule have been hampered by the inability to efficiently transform P. flocculosa. In this study, two different approaches, target gene replacement by homologous recombination (HR) and CRISPR-Cas9 based genome-editing, were utilized to decipher the role of flocculosin in the biocontrol activity of P.flocculosa. It was possible to alter the production of flocculosin through edition of fat1 by HR, but such mutants displayed abnormal phenotypes and the inability to produce sporidia. Sequencing analyses revealed that transformation by HR led to multiple insertions in the genome explaining the pleiotrophic effects of the approach. On the other hand, CRISPR-Cas9 transformation yielded one mutant that was altered specifically in the proper synthesis of flocculosin. Notwithstanding the loss of flocculosin production, such mutant was phenotypically similar to the wild-type, and when tested for its biocontrol activity against powdery mildew, displayed the same efficacy. These results offer strong evidence that flocculosin-mediated antibiosis is not responsible for the mode of action of P. flocculosa and highlight the potential of CRISPR-Cas9 for functional studies of otherwise difficult-to-transform fungi such as P. flocculosa.

Perspectives for the application of Ustilaginaceae as biotech cell factories

Basidiomycetes fungi of the family Ustilaginaceae are mainly known as plant pathogens causing smut disease on crops and grasses. However, they are also natural producers of value-added substances like glycolipids, organic acids, polyols, and harbor secretory enzymes with promising hydrolytic activities. These attributes recently evoked increasing interest in their biotechnological exploitation. The corn smut fungus Ustilago maydis is the best characterized member of the Ustilaginaceae. After decades of research in the fields of genetics and plant pathology, a broad method portfolio and detailed knowledge on its biology and biochemistry are available. As a consequence, U. maydis has developed into a versatile model organism not only for fundamental research but also for applied biotechnology. Novel genetic, synthetic biology, and process development approaches have been implemented to engineer yields and product specificity as well as for the expansion of the repertoire of produced substances. Furthermore, research on U. maydis also substantially promoted the interest in other members of the Ustilaginaceae, for which the available tools can be adapted. Here, we review the latest developments in applied research on Ustilaginaceae towards their establishment as future biotech cell factories.

The role of transport proteins in the production of microbial glycolipid biosurfactants

Several microorganisms are currently being used as production platform for glycolipid biosurfactants, providing a greener alternative to chemical biosurfactants. One of the reasons why these processes are commercially competitive is the fact that microbial producers can efficiently export their product to the extracellular environment, reaching high product titers. Glycolipid biosynthetic genes are often found in a dedicated cluster, amidst which genes encoding a dedicated transporter committed to shuttle the glycolipid to the extracellular environment are often found, as is the case for many other secondary metabolites. Knowing this, one can rely on gene clustering features to screen for novel putative transporters, as described and performed in this review. The above strategy proves to be very powerful to identify glycolipid transporters in fungi but is less valid for bacterial systems. Indeed, the genetics of these export systems are currently largely unknown, but some hints are given. Apart from the direct export of the glycolipid, several other transport systems have an indirect effect on glycolipid production. Specific importers dictate which hydrophilic and hydrophobic substrates can be used for production and influence the final yields. In eukaryotes, cellular compartmentalization allows the assembly of glycolipid building blocks in a highly specialized and efficient way. Yet, this requires controlled transport across intracellular membranes. Next to the direct export of glycolipids, the current state of the art regarding this indirect involvement of transporter systems in microbial glycolipid synthesis is summarized in this review. KEY POINTS: • Transporters are directly and indirectly involved in microbial glycolipid synthesis. • Yeast glycolipid transporters are found in their biosynthetic gene cluster. • Hydrophilic and hydrophobic substrate uptake influence microbial glycolipid synthesis.

Factors Affecting the Synthesis of Cellobiose Lipids by Sporisorium scitamineum

Cellobiose lipids (CL) are extracellular glycolipids that are produced by many microorganisms from the family Ustilaginaceae. The sugarcane smut fungus Sporisorium scitamineum has been long known as a producer of the glycolipids mannosylerythritol lipids (MEL) and was recently described to additionally secrete CL as a byproduct. In fact, we identified 11 homologous genes in S. scitamineum by in silico analysis sharing a high similarity to the CL biosynthesis gene cluster of Ustilago maydis. We here report the first systematic cultivation of S. scitamineum targeting the synthesis of CL with high product titers and its transfer to the bioreactor. In an initial screening we examined different fermentation media compositions, consisting of a mineral salts solution with vitamins and/or trace elements, three carbon sources (glucose, fructose, sucrose), three pH values (2.5, 4.0, 6.7) and three levels of C/N values (42.2, 83.8, 167.2 mol_C⋅mol_N ^-1) with urea as nitrogen source. A pH of 2.5 proved to result in the highest product titers. An increase of urea concentration from 0.6 to 1.2 g⋅L^-1 had a positive effect on biomass formation, however the glycolipid formation was favored at a C/N ratio of 83.8 mol_C⋅mol_N ^-1, using 0.6 g⋅L^-1 urea. Amongst the examined carbon sources, sucrose resulted in an increase in the secretion of cellobiose lipids, compared to glucose. Comparing different media compositions, vitamins were identified as not necessary for CL synthesis. We obtained a concentration of cellobiose lipids of 8.3 ± 1.0 g⋅L^-1 in shaking flasks. This increased to 17.6 g⋅L^-1 in the 1 L bioreactor with additional feeding of carbon source, with a final purity of 85-93%. As a side product, erythritol and mannosylerythritol lipids (MEL) were also synthesized. Via HPTLC coupled MALDI-TOF MS we were able to analyze the secreted CL structures. S. scitamineum produces a mixture of acylated low molecular weight D-glucolipids, linked to a 2,15,16-trihydroxy-hexadecanoic acid via their ω-hydroxyl group (CL-B). The produced cellobiose lipids precipitate as needle like crystals at an acidic pH value of 2.5.

An Ustilago maydis chassis for itaconic acid production without by-products

Ustilago maydis is a promising yeast for the production of a range of valuable metabolites, including itaconate, malate, glycolipids and triacylglycerols. However, wild-type strains generally produce a potpourri of all of these metabolites, which hinders efficient production of single target chemicals. In this study, the diverse by-product spectrum of U. maydis was reduced through strain engineering using CRISPR/Cas9 and FLP/FRT, greatly increasing the metabolic flux into the targeted itaconate biosynthesis pathway. With this strategy, a marker-free chassis strain could be engineered, which produces itaconate from glucose with significantly enhanced titre, rate and yield. The lack of by-product formation not only benefited itaconate production, it also increases the efficiency of downstream processing improving cell handling and product purity.

Biocontrol yeasts: mechanisms and applications

Yeasts occur in all environments and have been described as potent antagonists of various plant pathogens. Due to their antagonistic ability, undemanding cultivation requirements, and limited biosafety concerns, many of these unicellular fungi have been considered for biocontrol applications. Here, we review the fundamental research on the mechanisms (e.g., competition, enzyme secretion, toxin production, volatiles, mycoparasitism, induction of resistance) by which biocontrol yeasts exert their activity as plant protection agents. In a second part, we focus on five yeast species (Candida oleophila, Aureobasidium pullulans, Metschnikowia fructicola, Cryptococcus albidus, Saccharomyces cerevisiae) that are or have been registered for the application as biocontrol products. These examples demonstrate the potential of yeasts for commercial biocontrol usage, but this review also highlights the scarcity of fundamental studies on yeast biocontrol mechanisms and of registered yeast-based biocontrol products. Yeast biocontrol mechanisms thus represent a largely unexplored field of research and plentiful opportunities for the development of commercial, yeast-based applications for plant protection exist.

Smut infection of perennial hosts: the genome and the transcriptome of the Brassicaceae smut fungus Thecaphora thlaspeos reveal functionally conserved and novel effectors

Biotrophic fungal plant pathogens can balance their virulence and form intricate relationships with their hosts. Sometimes, this leads to systemic host colonization over long time scales without macroscopic symptoms. However, how plant-pathogenic endophytes manage to establish their sustained systemic infection remains largely unknown. Here, we present a genomic and transcriptomic analysis of Thecaphora thlaspeos. This relative of the well studied grass smut Ustilago maydis is the only smut fungus adapted to Brassicaceae hosts. Its ability to overwinter with perennial hosts and its systemic plant infection including roots are unique characteristics among smut fungi. The T. thlaspeos genome was assembled to the chromosome level. It is a typical smut genome in terms of size and genome characteristics. In silico prediction of candidate effector genes revealed common smut effector proteins and unique members. For three candidates, we have functionally demonstrated effector activity. One of these, TtTue1, suggests a potential link to cold acclimation. On the plant side, we found evidence for a typical immune response as it is present in other infection systems, despite the absence of any macroscopic symptoms during infection. Our findings suggest that T. thlaspeos distinctly balances its virulence during biotrophic growth ultimately allowing for long-lived infection of its perennial hosts.

Effectors involved in fungal-fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent-powdery mildew-plant

Tritrophic interactions involving a biocontrol agent, a pathogen and a plant have been analyzed predominantly from the perspective of the biocontrol agent. We have conducted the first comprehensive transcriptomic analysis of all three organisms in an effort to understand the elusive properties of Pseudozyma flocculosa in the context of its biocontrol activity against Blumeria graminis f.sp. hordei as it parasitizes Hordeum vulgare. After inoculation of P. flocculosa, the tripartite interaction was monitored over time and samples collected for scanning electron microscopy and RNA sequencing. Based on our observations, P. flocculosa indirectly parasitizes barley, albeit transiently, by diverting nutrients extracted by B. graminis from barley leaves through a process involving unique effectors. This brings novel evidence that such molecules can also influence fungal-fungal interactions. Their release is synchronized with a higher expression of powdery mildew haustorial effectors, a sharp decline in the photosynthetic machinery of barley and a developmental peak in P. flocculosa. The interaction culminates with a collapse of B. graminis haustoria, thereby stopping P. flocculosa growth, as barley plants show higher metabolic activity. To conclude, our study has uncovered a complex and intricate phenomenon, described here as hyperbiotrophy, only achievable through the conjugated action of the three protagonists.

Promoters from the itaconate cluster of Ustilago maydis are induced by nitrogen depletion

Background

Ustilago maydis is known for its natural potential to produce a broad range of valuable chemicals, such as itaconate, from both industrial carbon waste streams and renewable biomass. Production of itaconate, and many other secondary metabolites, is induced by nitrogen limitation in U. maydis. The clustered genes responsible for itaconate production have recently been identified, enabling the development of new expression tools that are compatible with biotechnological processes.

Results

Here we report on the investigation of two of the native promoters, P_tad1 and P_mtt1, from the itaconate cluster of U. maydis MB215. For both promoters the specific activation upon nitrogen limitation, which is known to be the trigger for itaconate production in Ustilago, could be demonstrated by gfp expression. The promoters cover a broad range of expression levels, especially when combined with the possibility to create single- and multicopy construct integration events. In addition, these reporter constructs enable a functional characterization of gene induction patterns associated with itaconate production.

Conclusions

The promoters are well suited to induce gene expression in response to nitrogen limitation, coupled to the itaconate production phase, which contributes towards the further improvement of organic acid production with Ustilago.

Antimicrobial assay and genetic screening of selected freshwater Cyanobacteria and identification of a biomolecule dihydro-2H-pyran-2-one derivative

AIMS

Explorations of freshwater Cyanobacteria as antimicrobial (bacteria, fungi and methicillin-resistant Staphylococcus aureus (MRSA) strains) drug resource using bioassay, NRPS (non-ribosomal polypeptide synthetase) and PKS (polyketide synthase) genes, as well as in silico approach.

METHODS AND RESULTS

We have bioassayed the extracts of Phormidium CCC727, Geitlerinema CCC728, Arthrospira CCC729, Leptolyngbya CCC732, Phormidium CCC730, Phormidium CCC731 against six pathogenic bacteria comprising Gram (+ve): S. aureus including seven clinical MRSA and Enterococcus faecalis, Gram (-ve): Escherichia coli, Salmonella Typhimurium, Klebsiella pneumoniae and Shigella boydii along with non-pathogenic Enterobacter aerogenes as well as fungal strains (Cryptococcus neoformans and Candida albicans, C. krusei, C. tropicalis and Aspergillus niger) exhibiting antimicrobial potential. The NRPS and PKS genes of the target strains were also amplified and sequenced. The putative protein structures were predicted using bioinformatics approach.

CONCLUSION

PKS gene expression indicated β keto-acyl synthase as one of the important active domains in the biomolecules related to antitumour and antifungal group. The simultaneous identification of the biomolecule (dihydro-2H-pyran-2-one derivative) was also inferred spectroscopically.

SIGNIFICANCE AND IMPACT OF THE STUDY

Freshwater Cyanobacteria are prolific producers of secondary metabolite(s) that may act as the antimicrobial drug resource in addition to their much explored marine counterpart.

A Gene Cluster for Biosynthesis of Mannosylerythritol Lipids Consisted of 4-O-β-D-Mannopyranosyl-(2R,3S)-Erythritol as the Sugar Moiety in a Basidiomycetous Yeast Pseudozyma tsukubaensis

Mannosylerythritol lipids (MELs) belong to the glycolipid biosurfactants and are produced by various fungi. The basidiomycetous yeast Pseudozyma tsukubaensis produces diastereomer type of MEL-B, which contains 4-O-β-D-mannopyranosyl-(2R,3S)-erythritol (R-form) as the sugar moiety. In this respect it differs from conventional type of MELs, which contain 4-O-β-D-mannopyranosyl-(2S,3R)-erythritol (S-form) as the sugar moiety. While the biosynthetic gene cluster for conventional type of MELs has been previously identified in Ustilago maydis and Pseudozyma antarctica, the genetic basis for MEL biosynthesis in P. tsukubaensis is unknown. Here, we identified a gene cluster involved in MEL biosynthesis in P. tsukubaensis. Among these genes, PtEMT1, which encodes erythritol/mannose transferase, had greater than 69% identity with homologs from strains in the genera Ustilago, Melanopsichium, Sporisorium and Pseudozyma. However, phylogenetic analysis placed PtEMT1p in a separate clade from the other proteins. To investigate the function of PtEMT1, we introduced the gene into a P. antarctica mutant strain, ΔPaEMT1, which lacks MEL biosynthesis ability owing to the deletion of PaEMT1. Using NMR spectroscopy, we identified the biosynthetic product as MEL-A with altered sugar conformation. These results indicate that PtEMT1p catalyzes the sugar conformation of MELs. This is the first report of a gene cluster for the biosynthesis of diastereomer type of MEL.

Biological control of the cucurbit powdery mildew pathogen Podosphaera xanthii by means of the epiphytic fungus Pseudozyma aphidis and parasitism as a mode of action

Epiphytic yeasts, which colonize plant surfaces, may possess activity that can be harnessed to help plants defend themselves against various pathogens. Due to their unique characteristics, epiphytic yeasts belonging to the genus Pseudozyma hold great potential for use as biocontrol agents. We identified a unique, biologically active isolate of the epiphytic yeast Pseudozyma aphidis that is capable of inhibiting Botrytis cinerea via a dual mode of action, namely induced resistance and antibiosis. Here, we show that strain L12 of P. aphidis can reduce the severity of powdery mildew caused by Podosphaera xanthii on cucumber plants with an efficacy of 75%. Confocal and scanning electron microscopy analyses demonstrated P. aphidis proliferation on infected tissue and its production of long hyphae that parasitize the powdery mildew hyphae and spores as an ectoparasite. We also show that crude extract of P. aphidis metabolites can inhibit P. xanthii spore germination in planta. Our results suggest that in addition to its antibiosis as mode of action, P. aphidis may also act as an ectoparasite on P. xanthii. These results indicate that P. aphidis strain L12 has the potential to control powdery mildew.

Biotechnological opportunities in biosurfactant production

In the recent years, biosurfactants proved to be an interesting alternative to petrochemically derived surfactants. Two classes of biosurfactants, namely glycolipids and lipopeptides, have attracted significant commercial interest. Despite their environmental advantages and equal performance, commercialization of these molecules remains a challenge due to missing acquaintance of the applicants, higher price and lack of structural variation. The latter two issues can partially be tackled by screening for novel and better wild-type producers and optimizing the fermentation process. Yet, these traditional approaches cannot overcome all hurdles. In this review, an overview is given on how biotechnology offers opportunities for increased biosurfactant production and the creation of new types of molecules, in this way enhancing their commercial potential.

Hassallidins, antifungal glycolipopeptides, are widespread among cyanobacteria and are the end-product of a nonribosomal pathway

Cyanobacteria produce a wide variety of cyclic peptides, including the widespread hepatotoxins microcystins and nodularins. Another class of peptides, cyclic glycosylated lipopeptides called hassallidins, show antifungal activity. Previously, two hassallidins (A and B) were reported from an epilithic cyanobacterium Hassallia sp. and found to be active against opportunistic human pathogenic fungi. Bioinformatic analysis of the Anabaena sp. 90 genome identified a 59-kb cryptic inactive nonribosomal peptide synthetase gene cluster proposed to be responsible for hassallidin biosynthesis. Here we describe the hassallidin biosynthetic pathway from Anabaena sp. SYKE748A, as well as the large chemical variation and common occurrence of hassallidins in filamentous cyanobacteria. Analysis demonstrated that 20 strains of the genus Anabaena carry hassallidin synthetase genes and produce a multitude of hassallidin variants that exhibit activity against Candida albicans. The compounds discovered here were distinct from previously reported hassallidins A and B. The IC50 of hassallidin D was 0.29-1.0 µM against Candida strains. A large variation in amino acids, sugars, their degree of acetylation, and fatty acid side chain length was detected. In addition, hassallidins were detected in other cyanobacteria including Aphanizomenon, Cylindrospermopsis raciborskii, Nostoc, and Tolypothrix. These compounds may protect some of the most important bloom-forming and globally distributed cyanobacteria against attacks by parasitic fungi.

Biosurfactant gene clusters in eukaryotes: regulation and biotechnological potential

Biosurfactants (BSs) are a class of secondary metabolites representing a wide variety of structures that can be produced from renewable feedstock by a wide variety of micro-organisms. They have (potential) applications in the medical world, personal care sector, mining processes, food industry, cosmetics, crop protection, pharmaceuticals, bio-remediation, household detergents, paper and pulp industry, textiles, paint industries, etc. Especially glycolipid BSs like sophorolipids (SLs), rhamnolipids (RLs), mannosylerythritol lipids (MELs) and cellobioselipids (CBLs) have been described to provide significant opportunities to (partially) replace chemical surfactants. The major two factors currently limiting the penetration of BSs into the market are firstly the limited structural variety and secondly the rather high production price linked with the productivity. One of the keys to resolve the above mentioned bottlenecks can be found in the genetic engineering of natural producers. This could not only result in more efficient (economical) recombinant producers, but also in a diversification of the spectrum of available BSs as such resolving both limiting factors at once. Unraveling the genetics behind the biosynthesis of these interesting biological compounds is indispensable for the tinkering, fine tuning and rearrangement of these biological pathways with the aim of obtaining higher yields and a more extensive structural variety. Therefore, this review focuses on recent developments in the investigation of the biosynthesis, genetics and regulation of some important members of the family of the eukaryotic glycolipid BSs (MELs, CBLs and SLs). Moreover, recent biotechnological achievements and the industrial potential of engineered strains are discussed.

Accumulation of cellobiose lipids under nitrogen-limiting conditions by two ustilaginomycetous yeasts, Pseudozyma aphidis and Pseudozyma hubeiensis

Some basidiomycetous yeast strains extracellularly produce cellobiose lipids (CLs), glycolipid biosurfactants which have strong fungicidal activity. The representative CL producer Ustilago maydis produces CLs together with the other glycolipids, mannosylerythritol lipids (MELs); the preference of the two glycolipids is affected considerably by the nitrogen source. To develop new CL producers, 12 MEL producers were cultured under the nitrogen-limited conditions. Pseudozyma aphidis and Pseudozyma. hubeiensis were characterized as new CL producers. CL production was induced on three strains, P. aphidis, Pseudozyma graminicola, and P. hubeiensis under these conditions. The putative homologous genes of U. maydis cyp1, which encodes a P450 monooxygenase, essential for CL biosynthesis, were partially amplified from their genomic DNA. The nucleotide sequences of the gene fragments from P. hubeiensis and P. aphidis shared identities with U. maydis cyp1 of 99% and 78%, respectively. Furthermore, all of the deduced translation products are tightly clustered in the phylogenic tree of the monooxygenase. These results suggest that the genes involved with CL biosynthesis must be widely distributed in the basidiomycetous fungi as well as the MEL biosynthesis genes, and thus, the genus Pseudozyma has great potential as a biosurfactant producer.

Observing the invisible through imaging mass spectrometry, a window into the metabolic exchange patterns of microbes

Many microbes can be cultured as single-species communities. Often, these colonies are controlled and maintained via the secretion of metabolites. Such metabolites have been an invaluable resource for the discovery of therapeutics (e.g. penicillin, taxol, rapamycin, epothilone). In this article, written for a special issue on imaging mass spectrometry, we show that MALDI-imaging mass spectrometry can be adapted to observe, in a spatial manner, the metabolic exchange patterns of a diverse array of microbes, including thermophilic and mesophilic fungi, cyanobacteria, marine and terrestrial actinobacteria, and pathogenic bacteria. Dependent on media conditions, on average and based on manual analysis, we observed 11.3 molecules associated with each microbial IMS experiment, which was split nearly 50:50 between secreted and colony-associated molecules. The spatial distributions of these metabolic exchange factors are related to the biological and ecological functions of the organisms. This work establishes that MALDI-based IMS can be used as a general tool to study a diverse array of microbes. Furthermore the article forwards the notion of the IMS platform as a window to discover previously unreported molecules by monitoring the metabolic exchange patterns of organisms when grown on agar substrates.

Beta hydroxylation of glycolipids from Ustilago maydis and Pseudozyma flocculosa by an NADPH-dependent β-hydroxylase

Flocculosin and ustilagic acid (UA), two highly similar antifungal cellobiose lipids, are respectively produced by Pseudozyma flocculosa, a biocontrol agent, and Ustilago maydis, a plant pathogen. Both glycolipids contain a short-chain fatty acid hydroxylated at the β position but differ in the long fatty acid, which is hydroxylated at the α position in UA and at the β position in flocculosin. In both organisms, the biosynthesis genes are arranged in large clusters. The functions of most genes have already been characterized, but those of the P. flocculosa fhd1 gene and its homolog from U. maydis, uhd1, have remained undefined. The deduced amino acid sequences of these genes show homology to those of short-chain dehydrogenases and reductases (SDR). We disrupted the uhd1 gene in U. maydis and analyzed the secreted UA. uhd1 deletion strains produced UA lacking the β-hydroxyl group of the short-chain fatty acid. To analyze the function of P. flocculosa Fhd1, the corresponding gene was used to complement U. maydis Δuhd1 mutants. Fhd1 was able to restore wild-type UA production, indicating that Fhd1 is responsible for β hydroxylation of the flocculosin short-chain fatty acid. We also investigated a P. flocculosa homolog of the U. maydis long-chain fatty-acid alpha hydroxylase Ahd1. The P. flocculosa ahd1 gene, which does not reside in the flocculosin gene cluster, was introduced into U. maydis Δahd1 mutant strains. P. flocculosa Ahd1 neither complemented the U. maydis Δahd1 phenotype nor resulted in the production of β-hydroxylated UA. This suggests that P. flocculosa Ahd1 is not involved in flocculosin hydroxylation.