Erythritol (1,2,3,4-butanetetrol) is a four-carbon sugar alcohol with sweetening properties that is used by the agrofood industry as a food additive. In this study, we demonstrated that metabolic engineering can be used to improve the production of erythritol from glycerol in the yeast Yarrowia lipolytica. The best results were obtained using a mutant that overexpressed GUT1 and TKL1, which encode a glycerol kinase and a transketolase, respectively, and in which EYK1, which encodes erythrulose kinase, was disrupted; the latter enzyme is involved in an early step of erythritol catabolism. In this strain, erythritol productivity was 75% higher than in the wild type; furthermore, the culturing time needed to achieve maximum concentration was reduced by 40%. An additional advantage is that the strain was unable to consume the erythritol it had created, further increasing the process's efficiency. The erythritol productivity values we obtained here are among the highest reported thus far.

Plant-associated Bacillus velezensis and Pseudomonas spp. represent excellent model species as strong producers of bioactive metabolites involved in phytopathogen inhibition and the elicitation of plant immunity. However, the ecological role of these metabolites during microbial interspecies interactions and the way their expression may be modulated under naturally competitive soil conditions has been poorly investigated.

Most isolates belonging to the Bacillus amyloliquefaciens subsp. plantarum clade retain the potential to produce a vast array of structurally diverse antimicrobial compounds that largely contribute to their efficacy as biocontrol agents against numerous plant fungal pathogens. In that context, the role of cyclic lipopeptides (CLPs) has been well-documented but still little is known about the impact of interactions with other soil-inhabiting microbes on the expression of these molecules. In this work, we wanted to investigate the antagonistic activity developed by this bacterium against Rhizomucor variabilis, a pathogen isolated from diseased maize cobs in Democratic Republic of Congo. Our data show that fengycins are the major compounds involved in the inhibitory activity but also that production of this type of CLP is significantly upregulated when co-cultured with the fungus compared to pure cultures. B. amyloliquefaciens is thus able to perceive fungal molecules that are emitted and, as a response, up-regulates the biosynthesis of some specific components of its antimicrobial arsenal.

BackgroundIn recent years, the non-conventional model yeast species Yarrowia lipolytica has received much attention because it is a useful cell factory for producing recombinant proteins. In this species, expression vectors involving LIP2 and POX2 promoters have been developed and used successfully for protein production at yields similar to or even higher than those of other cell factories, such as Pichia pastoris. However, production processes involving these promoters can be difficult to manage, especially if carried out at large scales in fed-batch bioreactors, because they require hydrophobic inducers, such as oleic acid or methyl oleate. Thus, the challenge has become to reduce loads of hydrophobic substrates while simultaneously promoting recombinant protein production. One possible solution is to replace a portion of the inducer with a co-substrate that can serve as an alternative energy source. However, implementing such an approach would require detailed knowledge of how carbon sources impact promoter regulation, which is surprisingly still lacking for the LIP2 and POX2 promoters. This study’s aim was thus to better characterize promoter regulation and cell metabolism in Y. lipolytica cultures grown in media supplemented with different carbon sources.ResultspPOX2 induction could be detected when glucose or glycerol was used as sole carbon source, which meant these carbon source could not prevent promoter induction. In addition, when a mixture of glucose and oleic acid was used in complex medium, pPOX2 induction level was lower that that of pLIP2. In contrast, pLIP2 induction was absent when glucose was present in the culture medium, which meant that cell growth could occur without any recombinant gene expression. When a 40/60 mixture of glucose and oleic acid (w/w) was used, a tenfold increase in promoter induction, as compared to when an oleic-acid-only medium was observed. It was also clear that individual cells were adapting metabolically to use both glucose and oleic acid. Indeed, no distinct subpopulations that specialized on glucose versus oleic acid were observed; such an outcome would have led to producer and non-producer phenotypes. In medium containing both glucose and oleic acid, cells tended to directly metabolize oleic acid instead of storing it in lipid bodies.ConclusionsThis study found that pLIP2 is a promoter of choice as compared to pPOX2 to drive gene expression for recombinant protein production by Y. lipolytica used as cell factory.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0558-8) contains supplementary material, which is available to authorized users.

Within the plant-associated microbiome, some bacterial species are of particular interest due to the disease protective effect they provide via direct pathogen suppression and/or stimulation of host immunity. While these biocontrol mechanisms are quite well characterized, we still poorly understand the molecular basis of the cross talk these beneficial bacteria initiate with their host.

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The large-scale production of recombinant proteins (rProt) is becoming increasingly economically important. Among the different hosts used for rProt production, yeasts are gaining popularity. The socalled non-conventional yeasts, such as the methylotrophic Pichia pastoris and the dimorphic Yarrowia lipolytica, are popular choices due to their favorable characteristics and well-established expression systems. Nevertheless, a direct comparison of the two systems for rProt production and secretion was lacking. This study therefore aimed to directly compare Y. lipolytica and P. pastoris for the production and secretion of lipase CalB in bioreactor. Y. lipolytica produced more than double the biomass and more than 5-fold higher extracellular lipase than P. pastoris. Furthermore, maximal CalB production levels were reached by Y. lipolytica in half the cultivation time required for maximal production by P. pastoris. Conversely, P. pastoris was found to express 7-fold higher levels of CalB mRNA. Secreted enhanced green fluorescent protein -in isolation and fused to CalB-and protease inhibitor MG-132 were used in P. pastoris to further investigate the reasons behind such discrepancy. The most likely explanation was ultimately found to be protein degradation by endoplasmic reticulum-associated protein degradation preceding successful secretion. This study highlighted the multifaceted nature of rProt production, prompting a global outlook for selection of rProt production systems.The production of recombinant proteins (rProt) at industrial scale is of increasing economic importance. Among the different microbial chassis that have been developed for that purpose, yeasts are emerging as the preferred option for the production of recombinant enzymes and therapeutic proteins. The main advantage of yeasts over bacterial systems such as Escherichia coli is the possibility to obtain post-translational modified proteins in the culture supernatant at a gram per liter scale. Historically, Saccharomyces cerevisiae has been used as the reference eukaryotic chassis, however it suffers several drawbacks such as low protein productivity, overflow metabolism and hyperglycosylation of rProt. Moreover, it is less metabolically adapted to catabolize raw carbon and nitrogen sources, which are nowadays increasingly considered as feedstocks in bioprocesses, with the intention of reducing the process costs. Currently, non-conventional yeasts such as Pichia pastoris and Yarrowia lipolytica are considered as realistic alternatives to S. cerevisiae for rProt synthesis. Both species combine the advantages of growth at high cell density and production and secretion of rProt at high yields, with low nutritional requirements, thus allowing growth on raw materials or industrial by-products 1,2 .In most cases, the processes developed for rProt production are two-step systems involving a first phase of biomass generation under repressive or non-inducing conditions, followed by an induction phase during which rProt are synthetized and secreted into the cult...

A metagenomic library was constructed from microorganisms associated with the brown alga Ascophyllum nodosum. Functional screening of this library revealed 13 novel putative esterase loci and two glycoside hydrolase loci. Sequence and gene cluster analysis showed the wide diversity of the identified enzymes and gave an idea of the microbial populations present during the sample collection period. Lastly, an endo-␤-1,4-glucanase having less than 50% identity to sequences of known cellulases was purified and partially characterized, showing activity at low temperature and after prolonged incubation in concentrated salt solutions. Previous surveys have revealed that less than 1% of existing microorganisms can be studied by traditional culturing methods. This leaves most microorganisms and their by-products unknown and unexploited (1, 2) and explains why metagenomics, a culture-independent approach using total microbial genomes from environmental samples, has met with great success over the past decade (3, 4). Sequence-based metagenomics has already provided information about the composition, organization, function, and hierarchy of microbial communities in particular habitats (5). On the other hand, functional genomics applied to metagenomic libraries from diverse environments has led to the discovery of many new enzymes and bioactive compounds and to substantial enrichment of genome databases. To date, most of the enzymes brought to light through metagenomics have been derived from soil (6-9) and gut (10-13) samples.Marine microorganisms represent promising candidate sources of original biocatalysts, as they are exposed to extreme conditions of temperature, pressure, salinity, nutrient availability, etc. Hence, functional screening of marine microbial populations should yield new enzymes with specific and unique physiological and biochemical properties, produced by organisms far different from those usually described in terrestrial environments (14). New enzymes have already been identified in marine metagenomic libraries from seawater samples (15, 16) and from microorganisms in symbiosis with marine organisms such as sponges and corals (17). To our knowledge, however, nobody has yet performed functional screening of metagenomic libraries from algal microbial communities. As algal microbial biofilms are in constant interaction with algal biomass, they represent an interesting source of enzymes and other active compounds (18). Sequence-based studies have already revealed the importance and functions of microbial communities living on the surfaces of algae, showing tight interdependence between algae and their biofilms (19-21). Furthermore, many genes coding for enzymes involved in hydrolyzing algal biomass, such as cellulases, xylanases, ␣-amylases, and specific algal polysaccharidases (e.g., agarases, carrageenases, and alginate lyases), have been identified from cultivable marine bacteria (22,23). Only a few such enzymes have been found in marine metagenomes by functional screening. For example, no cellulase gene...