Nitrilase enzymes and their role in plant-microbe interactions

Isolation and Characterization of a Nitrilase-Producing Geotrichum Strain and Optimization of the Fermentation Conditions

Glufosinate ammonium is a fast-acting herbicide that was originally discovered as a natural product and is currently the only herbicide that targets glutamine synthetase. Nitrilase was found to catalyze synthesis of glufosinate ammonium. In this study, a fungus, Ytz23, with higher nitrilase activity, was isolated from seabed silt samples and was found to belong to the Geotrichum genus based on morphological, biochemical, and molecular characterization. It was found that Ytz23 had high specificity for the catalysis of fatty nitriles, including acrylonitrile, 3-aminopropanenitrile, and 2-amino-4-(hydroxymethylphosphono)-butanenitrile. The optimal concentrations of variables in the fermentation reaction were assessed. It was found that the optimal carbon and nitrogen sources were glycerol 20 g/L, yeast extract 20, and 0.2 g/L of 2-amino-4-(hydroxymethylphosphono)-butanenitrile, with optimal fermentation conditions of pH 7.0, 30 °C, and shaking at 220 rpm. Under these optimal conditions, the enzyme activity of the nitrilase was 10.2 U/mL. These findings provide a basis for the biosynthesis of glufosinate ammonium and have potential for application in the industrial production of glufosinate ammonium.

Genomic factors limiting the diversity of Saccharomycotina plant pathogens

The Saccharomycotina fungi have evolved to inhabit a vast diversity of habitats over their 400-million-year evolution. There are, however, only a few known fungal pathogens of plants in this subphylum, primarily belonging to the genera Eremothecium and Geotrichum. We compared the genomes of 12 plant-pathogenic Saccharomycotina strains to 360 plant-associated strains to identify features unique to the phytopathogens. Characterization of the oxylipin synthesis genes, a compound believed to be involved in Eremothecium pathogenicity, did not reveal any differences in gene presence within or between the plant-pathogenic and plant-associated strains. A reverse-ecological approach, however, revealed that plant pathogens lack several metabolic enzymes known to assist other phytopathogens in overcoming plant defenses. This includes L-rhamnose metabolism, formamidase and nitrilase genes. This result suggests that the Saccharomycotina plant pathogens are limited to infecting ripening fruits as they are without the necessary enzymes to degrade common phytohormones and secondary metabolites produced by plants.

Protein Engineering of Substrate Specificity toward Nitrilases: Strategies and Challenges

Nitrilase is extensively applied across diverse sectors owing to its unique catalytic properties. Nevertheless, in industrial production, nitrilases often face issues such as low catalytic efficiency, limited substrate range, suboptimal selectivity, and side reaction products, which have garnered heightened attention. With the widespread recognition that the structure of enzymes has a direct impact on their catalytic properties, an increasing number of researchers are beginning to optimize the functional characteristics of nitrilases by modifying their structures, in order to meet specific industrial or biotechnology application needs. Particularly in the artificial intelligence era, the innovative application of computer-aided design in enzyme engineering offers remarkable opportunities to tailor nitrilases for the widespread production of high-value products. In this discussion, we will briefly examine the structural mechanism of nitrilase. An overview of the protein engineering strategies of substrate preference, regioselectivity and stereoselectivity are explored combined with some representative examples recently in terms of the substrate specificity of enzyme. The future research trends in this field are also prospected.

A multi-omics approach reveals a link between ribosomal protein alterations and proteome rebalancing in Arabidopsis thaliana seeds

The ability of seeds to restore their amino acid content and composition after the elimination of the most abundant seed storage proteins (SSPs) is well-documented, yet the underlying mechanisms remain unclear. To better understand how seeds compensate for major proteomic disruptions, we conducted a comprehensive analysis on an Arabidopsis mutant lacking the three most abundant SSPs, the cruciferins. Our initial findings indicated that carbon, nitrogen, and sulfur levels, as well as total protein and oil content, remained unchanged in these mutants suggesting rebalanced seeds. Transcriptomics and proteomics performed during seed maturation of Col-0 and the triple mutant revealed significant modulation in many components of the translational machinery, especially ribosomal proteins (RPs), and in the antioxidation response in the mutant. These findings suggest that RPs play a critical role in facilitating proteomic homeostasis during seed maturation when proteomic perturbation occurs. Biochemical and metabolic analyses of the triple mutant dry seeds revealed increased protein carbonylation and elevated glutathione levels further supporting the link between SSP accumulation and seed redox homeostasis. Overall, we propose that in response to significant proteomic perturbations, changes in the proteome and amino acid composition of seeds are accompanied by a broad remodeling of the translation apparatus. We postulate that these alterations are key elements in seed adaptability and robustness to large proteomic perturbations during seed maturation.

Genome-based taxonomy and functional prediction of Sphingomonas fuzhouensis sp. nov. and Massilia phyllosphaerae sp. nov. isolated from Pennisetum sp. with plant growth-promoting potential

Two facultatively aerobic strains, designated SGZ-02T and SGZ-792T, were isolated from plant Pennisetum sp., exhibiting the highest 16S rRNA gene sequence similarities with the type strains of Sphingomonas zeae LMG 28739T (98.6%) and Massilia forsythiae NBRC 114511T (98.4%), respectively. SGZ-02T grew between 5 and 45 °C, pH 5.0-11.0 and tolerated NaCl concentrations of 0-4% (w/v), whereas SGZ-792T thrived at 5-40 °C, pH 5.0-11.0 and NaCl tolerance to 0-3.5% (w/v). The major quinone of SGZ-02T was ubiquinone-10, with the dominant fatty acids being C16:0 (13.5%), Summed Feature 3 (6.3%), C14:02-OH (5.3%) and Summed Feature 8 (66.3%). SGZ-792T predominantly contained ubiquinone-8, with major fatty acids being C16:0 (20.3%), Summed Feature 3 (5.0%) and Summed Feature 8 (54.7%). Average nucleotide identity and digital DNA-DNA hybridization values between two strains and their closest references strains were below the bacterial species threshold. Based on genotypic and phenotypic characteristics, strains SGZ-02T and SGZ-792T are proposed as novel species within the genera Sphingomonas and Massilia, respectively. The suggested names for the new species are Sphingomonas fuzhouensis sp. nov. (SGZ-02T = GDMCC 1.4033T = JCM 36769T) and Massilia phyllosphaerae sp. nov. (SGZ-792T = GDMCC 1.4211T = JCM 36643T), respectively.

Molecular Modification Strategies of Nitrilase for Its Potential Application in Agriculture

Some feed source plants will produce secondary metabolites such as cyanogenic glycosides during metabolism, which will produce some poisonous nitrile compounds after hydrolysis and remain in plant tissues. The consumption of feed-source plants without proper treatment affect the health of the animals' bodies. Nitrilases can convert nitriles and have been used in industry as green biocatalysts. However, due to their bottleneck problems, their application in agriculture is still facing challenges. Acid-resistant nitrilase preparations, high-temperature resistance, antiprotease activity, strong activity, and strict reaction specificity urgently need to be developed. In this paper, the application potential of nitrilase in agriculture, especially in feed processing industry was explored, the source properties and catalytic mechanism of nitrilase were reviewed, and modification strategies for nitrilase application in agriculture were proposed to provide references for future research and application of nitrilase in agricultural and especially in the biological feed scene.

Living in mangroves: a syntrophic scenario unveiling a resourceful microbiome

BACKGROUND

Mangroves are complex and dynamic coastal ecosystems under frequent fluctuations in physicochemical conditions related to the tidal regime. The frequent variation in organic matter concentration, nutrients, and oxygen availability, among other factors, drives the microbial community composition, favoring syntrophic populations harboring a rich and diverse, stress-driven metabolism. Mangroves are known for their carbon sequestration capability, and their complex and integrated metabolic activity is essential to global biogeochemical cycling. Here, we present a metabolic reconstruction based on the genomic functional capability and flux profile between sympatric MAGs co-assembled from a tropical restored mangrove.

RESULTS

Eleven MAGs were assigned to six Bacteria phyla, all distantly related to the available reference genomes. The metabolic reconstruction showed several potential coupling points and shortcuts between complementary routes and predicted syntrophic interactions. Two metabolic scenarios were drawn: a heterotrophic scenario with plenty of carbon sources and an autotrophic scenario with limited carbon sources or under inhibitory conditions. The sulfur cycle was dominant over methane and the major pathways identified were acetate oxidation coupled to sulfate reduction, heterotrophic acetogenesis coupled to carbohydrate catabolism, ethanol production and carbon fixation. Interestingly, several gene sets and metabolic routes similar to those described for wastewater and organic effluent treatment processes were identified.

CONCLUSION

The mangrove microbial community metabolic reconstruction reflected the flexibility required to survive in fluctuating environments as the microhabitats created by the tidal regime in mangrove sediments. The metabolic components related to wastewater and organic effluent treatment processes identified strongly suggest that mangrove microbial communities could represent a resourceful microbial model for biotechnological applications that occur naturally in the environment.

Maximizing the potential of nitrilase: Unveiling their diversity, catalytic proficiency, and versatile applications

Nitrilases represent a distinct class of enzymes that play a pivotal role in catalyzing the hydrolysis of nitrile compounds, leading to the formation of corresponding carboxylic acids. These enzymatic entities have garnered significant attention across a spectrum of industries, encompassing pharmaceuticals, agrochemicals, and fine chemicals. Moreover, their significance has been accentuated by mounting environmental pressures, propelling them into the forefront of biodegradation and bioremediation endeavors. Nevertheless, the natural nitrilases exhibit intrinsic limitations such as low thermal stability, narrow substrate selectivity, and inadaptability to varying environmental conditions. In the past decade, substantial efforts have been made in elucidating the structural underpinnings and catalytic mechanisms of nitrilase, providing basis for engineering of nitrilases. Significant breakthroughs have been made in the regulation of nitrilases with ideal catalytic properties and application of the enzymes for industrial productions. This review endeavors to provide a comprehensive discourse and summary of recent research advancements related to nitrilases, with a particular emphasis on the elucidation of the structural attributes, catalytic mechanisms, catalytic characteristics, and strategies for improving catalytic performance of nitrilases. Moreover, the exploration extends to the domain of process engineering and the multifarious applications of nitrilases. Furthermore, the future development trend of nitrilases is prospected, providing important guidance for research and application in the related fields.

Arylacetonitrilases: Potential Biocatalysts for Green Chemistry

Nitrilases are the enzymes that catalyze the hydrolysis of nitriles to corresponding carboxylic acid and ammonia. They are broadly categorized into aromatic, aliphatic, and arylacetonitrilases based on their substrate specificity. Most of the studies pertaining to these enzymes in the literature have focused on aromatic and aliphatic nitrilases. However, arylacetonitrilases have attracted the attention of academia and industry in the last several years due to their aryl specificity and enantioselectivity. They have emerged as interesting biocatalytic tools in green chemistry to synthesize useful aryl acids such as mandelic acid and derivatives of phenylacetic acid. The aim of the present review is to collate information on the arylacetonitrilases and their catalytic properties including enantioselectivity and potential applications in organic synthesis.

Mycoparasitism related targets of Tmk1 indicate stimulating regulatory functions of this MAP kinase in Trichoderma atroviride

Mycoparasitism is a key feature of Trichoderma (Hypocreales, Ascomycota) biocontrol agents. Recent studies of intracellular signal transduction pathways of the potent mycoparasite Trichoderma atroviride revealed the involvement of Tmk1, a mitogen-activated protein kinase (MAPK), in triggering the mycoparasitic response. We previously showed that mutants missing Tmk1 exhibit reduced mycoparasitic activity against several plant pathogenic fungi. In this study, we identified the most robustly regulated targets that were governed by Tmk1 during mycoparasitism using transcriptome and proteome profiling. Tmk1 mainly exerts a stimulating function for T. atroviride during its mycoparasitic interaction with the fungal plant pathogen Rhizoctonia solani, as reflected by 89% of strongly differently responding genes in the ∆tmk1 mutant compared to the wild type. Specifically, 54% of these genes showed strong downregulation in the response with a deletion of the tmk1 gene, whereas in the wild type the same genes were strongly upregulated during the interaction with the fungal host. These included the gene encoding the mycoparasitism-related proteinase Prb1; genes involved in signal transduction pathways such as a candidate coding for a conserved 14-3-3 protein, and a gene coding for Tmk2, the T. atroviride cell-wall integrity MAP kinase; genes encoding a specific siderophore synthetase, and multiple FAD-dependent oxidoreductases and aminotransferases. Due to the phosphorylating activity of Tmk1, different (phospho-)proteomics approaches were applied and identified proteins associated with cellular metabolism, energy production, protein synthesis and fate, and cell organization. Members of FAD- and NAD/NADP-binding-domain proteins, vesicular trafficking of molecules between cellular organelles, fungal translational, as well as protein folding apparatus were among others found to be phosphorylated by Tmk1 during mycoparasitism. Outstanding downregulation in the response of the ∆tmk1 mutant to the fungal host compared to the wild type at both the transcriptome and the proteome levels was observed for nitrilase, indicating that its defense and detoxification functions might be greatly dependent on Tmk1 during T. atroviride mycoparasitism. An intersection network analysis between the identified transcripts and proteins revealed a strong involvement of Tmk1 in molecular functions with GTPase and oxidoreductase activity. These data suggest that during T. atroviride mycoparasitism this MAPK mainly governs processes regulating cell responses to extracellular signals and those involved in reactive oxygen stress.

Functional Group Properties and Position Drive Differences in Xenobiotic Plant Uptake Rates, but Metabolism Shares a Similar Pathway

Plant uptake of xenobiotic compounds is crucial for phytoremediation (including green stormwater infrastructure) and exposure potential during crop irrigation with recycled water. Experimentally determining the plant uptake for every relevant chemical is impractical; therefore, illuminating the role of specific functional groups on the uptake of trace organic contaminants is needed to enhance predictive power. We used benzimidazole derivatives to probe the impact of functional group electrostatic properties and position on plant uptake and metabolism using the hydroponic model plant Arabidopsis thaliana. The greatest plant uptake rates occurred with an electron-withdrawing functional group at the 2 position; however, uptake was still observed with an electron-donating group. An electron-donating group at the 1 position significantly slowed uptake for both benzimidazole- and benzotriazole-based molecules used in this study, indicating possible steric effects. For unsubstituted benzimidazole and benzotriazole structures, the additional heterocyclic nitrogen in benzotriazole increased plant uptake rates compared to benzimidazole. Analysis of quantitative structure-activity relationship parameters for the studied compounds implicates energy-related molecular descriptors as uptake drivers. Despite significantly varied uptake rates, compounds with different functional groups yielded shared metabolites, including an impact on endogenous glutathione production. Although the topic is complex and influenced by multiple factors in the field, this study provides insights into the impact of functional groups on plant uptake, with implications for environmental fate and consumer exposure.

[First evidence of nitrilase enzymatic activity of Xylaria sp. and its relationship with the biosynthesis of indole-3-acetic acid]

Endophytic fungi inhabit plant tissues internally and asymptomatically, and many of them are involved in the synthesis of bioactive metabolites of antifungal and therapeutic nature, as well as other compounds of biotechnological importance including indole derivatives, among many others. Ecologically, they provide some benefits to plants including protection against phytopathogens and promotion of root growth. In this sense, Xylaria sp. is a cellulose-decomposing fungus with biotechnological potential. It is worth mentioning that indole-3-acetic acid (IAA) also plays an extremely important role in plant-micro-organism interactions, as it is essential for physiology and proper plant morphological development. It is known that nitrile-hydrolytic enzymes (nitrilases) are involved in the synthesis of plant indole compounds; however, relatively little information is available concerning the nature of these enzymes in the fungal kingdom. In view of the above, through a biochemical and molecular-genetic approach, it has been demonstrated for the first time that Xylaria sp. carries out nitrile-hydrolytic enzyme activity using nitrogen and carbon-rich compounds as substrate. The studied strain increased its relative gene expression levels and showed mycelial growth, both in the presence of chemical compounds such as cyanobenzene and KCN. Thus, the results of this work suggest that the micro-organism is capable of degrading complex nitrogenous molecules. On the other hand, through fungal biofertilization, it was observed that Xylaria sp. promotes the development of the root system of Arabidopsis thaliana seedlings, in addition to synthesizing IAA.

A Proterozoic microbial origin of extant cyanide-hydrolyzing enzyme diversity

In addition to its role as a toxic environmental contaminant, cyanide has been hypothesized to play a key role in prebiotic chemistry and early biogeochemical evolution. While cyanide-hydrolyzing enzymes have been studied and engineered for bioremediation, the extant diversity of these enzymes remains underexplored. Additionally, the age and evolution of microbial cyanide metabolisms is poorly constrained. Here we provide comprehensive phylogenetic and molecular clock analyses of the distribution and evolution of the Class I nitrilases, thiocyanate hydrolases, and nitrile hydratases. Molecular clock analyses indicate that bacterial cyanide-reducing nitrilases were present by the Paleo- to Mesoproterozoic, and were subsequently horizontally transferred into eukaryotes. These results present a broad diversity of microbial enzymes that could be optimized for cyanide bioremediation.

Recent Progress in the Production of Cyanide-Converting Nitrilases—Comparison with Nitrile-Hydrolyzing Enzymes

Nitrilases have a high potential for application in organic chemistry, environmental technology, and analytics. However, their industrial uses require that they are produced in highly active and robust forms at a reasonable cost. Some organic syntheses catalyzed by nitrilases have already reached a high level of technological readiness. This has been enabled by the large-scale production of recombinant catalysts. Despite some promising small-scale methods being proposed, the production of cyanide-converting nitrilases (cyanide hydratase and cyanide dihydratase) is lagging in this regard. This review focuses on the prospects of cyanide(di)hydratase-based catalysts. The current knowledge of these enzymes is summarized and discussed in terms of the origin and distribution of their sequences, gene expression, structure, assays, purification, immobilization, and uses. Progresses in the production of other nitrilase catalysts are also tackled, as it may inspire the development of the preparation processes of cyanide(di)hydratases.

Control of Pre-formed Halogenated Disinfection Byproducts with Reuse Biofiltration

Disinfection byproduct (DBP) pre-formation is a major issue when prechlorination is used before or during advanced treatment of impacted drinking water sources. Control strategies for pre-formed DBPs before final disinfection, especially for currently nonregulated although highly toxic DBP species, are not yet established. This study evaluated the biodegradation potential of pre-formed DBPs, including haloacetonitriles (HANs), haloacetamides (HAMs), and haloacetaldehydes (HALs), during biofiltration with sand, anthracite, and biological activated carbon of three wastewater effluents under potable reuse conditions. Up to 90%+ removal of di- and trihalogenated HANs, HAMs, and HALs was observed, and removal was associated with active heterotrophic biomass and removal of biodegradable organic carbon. Unlike the microbial dehalogenation pathway of haloacetic acids (HAAs), removal of HANs and HAMs appeared to result from a biologically mediated hydrolysis pathway (i.e., HANs to HAMs and HAAs) that may be prone to inhibition. After prechlorination, biofiltration effectively controlled pre-formed DBP concentrations (e.g., from 271 μg/L to as low as 22 μg/L in total) and DBP-associated calculated toxicity (e.g., 96%+ reduction). Abiotic residual adsorption capacity in biological activated carbon media was important for controlling trihalomethanes. Overall, the toxicity-driving DBP species exhibited high biodegradation potential and biofiltration showed significant promise as a pre-formed DBP control technology.

The Influence of Symbiosis on the Proteome of the Exaiptasia Endosymbiont Breviolum minutum

The cellular mechanisms responsible for the regulation of nutrient exchange, immune response, and symbiont population growth in the cnidarian-dinoflagellate symbiosis are poorly resolved. Here, we employed liquid chromatography-mass spectrometry to elucidate proteomic changes associated with symbiosis in Breviolum minutum, a native symbiont of the sea anemone Exaiptasia diaphana ('Aiptasia'). We manipulated nutrients available to the algae in culture and to the holobiont in hospite (i.e., in symbiosis) and then monitored the impacts of our treatments on host-endosymbiont interactions. Both the symbiotic and nutritional states had significant impacts on the B. minutum proteome. B. minutum in hospite showed an increased abundance of proteins involved in phosphoinositol metabolism (e.g., glycerophosphoinositol permease 1 and phosphatidylinositol phosphatase) relative to the free-living alga, potentially reflecting inter-partner signalling that promotes the stability of the symbiosis. Proteins potentially involved in concentrating and fixing inorganic carbon (e.g., carbonic anhydrase, V-type ATPase) and in the assimilation of nitrogen (e.g., glutamine synthase) were more abundant in free-living B. minutum than in hospite, possibly due to host-facilitated access to inorganic carbon and nitrogen limitation by the host when in hospite. Photosystem proteins increased in abundance at high nutrient levels irrespective of the symbiotic state, as did proteins involved in antioxidant defences (e.g., superoxide dismutase, glutathione s-transferase). Proteins involved in iron metabolism were also affected by the nutritional state, with an increased iron demand and uptake under low nutrient treatments. These results detail the changes in symbiont physiology in response to the host microenvironment and nutrient availability and indicate potential symbiont-driven mechanisms that regulate the cnidarian-dinoflagellate symbiosis.

Quantitative Proteomic Analysis Reveals the Key Molecular Events Driving Phaeocystis globosa Bloom and Dissipation

Phaeocystis globosa is a marine-bloom-forming haptophyte with a polymorphic life cycle alternating between free-living cells and a colonial morphotype, that produces high biomass and impacts ecological structure and function. The mechanisms of P. globosa bloom formation have been extensively studied, and various environmental factors are believed to trigger these events. However, little is known about the intrinsic biological processes that drive the bloom process, and the mechanisms underlying P. globosa bloom formation remain enigmatic. Here, we investigated a P. globosa bloom occurring along the Chinese coast and compared the proteomes of in situ P. globosa colonies from bloom and dissipation phases using a tandem mass tag (TMT)-based quantitative proteomic approach. Among the 5540 proteins identified, 191 and 109 proteins displayed higher abundances in the bloom and dissipation phases, respectively. The levels of proteins involved in photosynthesis, pigment metabolism, nitrogen metabolism, and matrix substrate biosynthesis were distinctly different between these two phases. Ambient nitrate is a key trigger of P. globosa bloom formation, while the enhanced light harvest and multiple inorganic carbon-concentrating mechanisms support the prosperousness of colonies in the bloom phase. Additionally, colonies in the bloom phase have greater carbon fixation potential, with more carbon and energy being fixed and flowing toward the colonial matrix biosynthesis. Our study revealed the key biological processes underlying P. globosa blooms and provides new insights into the mechanisms behind bloom formation.

Extending the benefits of PGPR to bioremediation of nitrile pollution in crop lands for enhancing crop productivity

Incessant release of nitrile group of compounds such as cyanides into agricultural land through industrial effluents and excessive use of nitrile pesticides has resulted in increased nitrile pollution. Release of nitrile compounds (NCs) as plant root exudates is also contributing to the problem. The released NCs interact with soil elements and persists for a long time. Persistent higher concentration of NCs in soil cause toxicity to beneficial microflora and affect crop productivity. The NCs can cause more problems to human health if they reach groundwater and enter the food chain. Nitrile degradation by soil bacteria can be a solution to the problem if thoroughly exploited. However, the impact of such bacteria in plant and soil environments is still not properly explored. Plant growth-promoting rhizobacteria (PGPR) with nitrilase activity has recently gained attention as potential solution to address the problem. This paper reviews the core issue of nitrile pollution in soil and the prospects of application of nitrile degrading bacteria for soil remediation, soil health improvement and plant growth promotion in nitrile-polluted soils. The possible mechanisms of PGPR that can be exploited to degrade NCs, converting them into plant useful compounds and synthesis of the phytohormone IAA from degraded NCs are also discussed at length.

The hidden world within plants: metatranscriptomics unveils the complexity of wood microbiomes

The importance of plants as complex entities influenced by genomes of the associated microorganisms is now seen as a new source of variability for a more sustainable agriculture, also in the light of ongoing climate change. For this reason, we investigated through metatranscriptomics whether the taxa profile and behaviour of microbial communities associated with the wood of 20-year-old grapevine plants are influenced by the health status of the host. We report for the first time a metatranscriptome from a complex tissue in a real environment, highlighting that this approach is able to define the microbial community better than referenced transcriptomic approaches. In parallel, the use of total RNA enabled the identification of bacterial taxa in healthy samples that, once isolated from the original wood tissue, displayed potential biocontrol activities against a wood-degrading fungal taxon. Furthermore, we revealed an unprecedented high number of new viral entities (~120 new viral species among 180 identified) associated with a single and limited environment and with potential impact on the whole holobiont. Taken together, our results suggest a complex multitrophic interaction in which the viral community also plays a crucial role in raising new ecological questions for the exploitation of microbial-assisted sustainable agriculture.

Characterization of nitrilases from Variovorax boronicumulans that functions in insecticide flonicamid degradation and β-cyano-L-alanine detoxification

AIMS

To characterize the functions of nitrilases of Variovorax boronicumulans CGMCC 4969 and evaluate flonicamid (FLO) degradation and β-cyano-L-alanine (Ala(CN)) detoxification by this bacterium.

METHODS AND RESULTS

V. boronicumulans CGMCC 4969 nitrilases (NitA and NitB) were purified and substrate specificity assay indicated that both of them degraded insecticide FLO to N-(4-trifluoromethylnicotinoyl)glycinamide (TFNG-AM) and 4-(trifluoromethyl)nicotinol glycine (TFNG). Ala(CN), a plant detoxification intermediate, was hydrolyzed by NitB. Escherichia coli overexpressing NitA and NitB degraded 41.2 and 93.8% of FLO (0.87 mmol·L^-1 ) within 1 h, with half-lives of 1.30 and 0.25 h, respectively. NitB exhibited the highest nitrilase activity toward FLO. FLO was used as a substrate to compare their enzymatic properties. NitB was more tolerant to acidic conditions and organic solvents than NitA. Conversely, NitA was more tolerant to metal ions than NitB. CGMCC 4969 facilitated FLO degradation in soil and surface water and utilized Ala(CN) as a sole nitrogen source for growth.

CONCLUSIONS

CGMCC 4969 efficiently degraded FLO mediated by NitA and NitB; NitB was involved in Ala(CN) detoxification.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study promotes our understanding of versatile functions of nitrilases from CGMCC 4969 that is promising for environmental remediation.

Metabolism of Aldoximes and Nitriles in Plant-Associated Bacteria and Its Potential in Plant-Bacteria Interactions

In plants, aldoximes per se act as defense compounds and are precursors of complex defense compounds such as cyanogenic glucosides and glucosinolates. Bacteria rarely produce aldoximes, but some are able to transform them by aldoxime dehydratase (Oxd), followed by nitrilase (NLase) or nitrile hydratase (NHase) catalyzed transformations. Oxds are often encoded together with NLases or NHases in a single operon, forming the aldoxime-nitrile pathway. Previous reviews have largely focused on the use of Oxds and NLases or NHases in organic synthesis. In contrast, the focus of this review is on the contribution of these enzymes to plant-bacteria interactions. Therefore, we summarize the substrate specificities of the enzymes for plant compounds. We also analyze the taxonomic and ecological distribution of the enzymes. In addition, we discuss their importance in selected plant symbionts. The data show that Oxds, NLases, and NHases are abundant in Actinobacteria and Proteobacteria. The enzymes seem to be important for breaking through plant defenses and utilizing oximes or nitriles as nutrients. They may also contribute, e.g., to the synthesis of the phytohormone indole-3-acetic acid. We conclude that the bacterial and plant metabolism of aldoximes and nitriles may interfere in several ways. However, further in vitro and in vivo studies are needed to better understand this underexplored aspect of plant-bacteria interactions.

Alternative Pathway for 3-Cyanoalanine Assimilation in Pseudomonas pseudoalcaligenes CECT5344 under Noncyanotrophic Conditions

3-Cyanoalanine and cyanohydrins are intermediate nitriles produced in cyanide degradation pathways in plants and bacteria. 3-Cyanoalanine is generated from cyanide by the 3-cyanoalanine synthase, an enzyme mainly characterized in cyanogenic plants. NIT4-type nitrilases use 3-cyanoalanine as a substrate, forming ammonium and aspartate. In some organisms, this enzyme also generates asparagine through an additional nitrile hydratase activity. The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 assimilates cyanide through an intermediate cyanohydrin, which is further converted into ammonium by the nitrilase NitC. This bacterium also contains three additional nitrilases, including Nit4. In this work, a proteomic analysis of P. pseudoalcaligenes CECT5344 cells grown with 3-cyanoalanine as the sole nitrogen source has revealed the overproduction of different proteins involved in nitrogen metabolism, including the nitrilase NitC. In contrast, the nitrilase Nit4 was not induced by 3-cyanoalanine, and it was only overproduced in cells grown with a cyanide-containing jewelry-manufacturing residue. Phenotypes of single and double mutant strains defective in nit4 or/and nitC revealed the implication of the nitrilase NitC in the assimilation of 3-cyanoalanine and suggest that the 3-cyanoalanine assimilation pathway in P. pseudoalcaligenes CECT5344 depends on the presence or absence of cyanide. When cyanide is present, 3-cyanoalanine is assimilated via Nit4, but in the absence of cyanide, a novel pathway for 3-cyanoalanine assimilation, in which the nitrilase NitC uses the nitrile generated after deamination of the α-amino group from 3-cyanoalanine, is proposed. IMPORTANCE Nitriles are organic cyanides with important industrial applications, but they are also found in nature. 3-Cyanoalanine is synthesized by plants and some bacteria to detoxify cyanide from endogenous or exogenous sources, but this nitrile may be also involved in other processes such as stress tolerance, nitrogen and sulfur metabolism, and signaling. The cyanide-degrading bacterium Pseudomonas pseudoalcaligenes CECT5344 grows with 3-cyanoalanine as the sole nitrogen source, but it does not use this nitrile as an intermediate in the cyanide assimilation pathway. In this work, a quantitative proteomic analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to study, for the first time, the response to 3-cyanoalanine at the proteomic level. Proteomic data, together with phenotypes of different nitrilase-defective mutants of P. pseudoalcaligenes CECT5344, provide evidence that in the absence of cyanide, the nitrilase Nit4 is not involved in 3-cyanoalanine assimilation, and instead, the nitrilase NitC participates in a novel alternative 3-cyanoalanine assimilation pathway.

Examination of the Catalytic Role of the Axial Cystine Ligand in the Co-Type Nitrile Hydratase from Pseudonocardia thermophila JCM 3095

The strictly conserved αSer162 residue in the Co-type nitrile hydratase from Pseudonocardia thermophila JCM 3095 (PtNHase), which forms a hydrogen bond to the axial αCys108-S atom, was mutated into an Ala residue. The αSer162Ala yielded two different protein species: one was the apoform (αSerA) that exhibited no observable activity, and the second (αSerB) contained its full complement of cobalt ions and was active with a kcat value of 63 ± 3 s−1 towards acrylonitrile at pH 7.5. The X-ray crystal structure of αSerA was determined at 1.85 Å resolution and contained no detectable cobalt per α2β2 heterotetramer. The axial αCys108 ligand itself was also mutated into Ser, Met, and His ligands. All three of these αCys108 mutant enzymes contained only half of the cobalt complement of wild-type PtNHase, but were able to hydrate acrylonitrile with kcat values of 120 ± 6, 29 ± 3, and 14 ± 1 s−1 for the αCys108His, Ser, and Met mutant enzymes, respectively. As all three of these mutant enzymes are catalytically competent, these data provide the first experimental evidence that transient disulfide bond formation is not catalytically essential for NHases.

Natural Feedstock in Catalysis: A Sustainable Route Towards Organic Transformations

Catalysts are the jewel in the crown of the chemical industry, accelerating reaction kinetics and augmenting the efficiency of desired reaction paths. Natural feedstock is a renewable resource capable of providing valuable functional products; in addition, it confers an opportunity to create catalysts. As an alternative to stoichiometric reagents, and as a part of a sustainable approach, the implications of using natural feedstocks as a source of new catalysts has attracted considerable interest. Natural feedstock-derived catalysts can promote chemical transformations more efficiently. Recent reports have highlighted the significant role of these biogenic, cost-effective, innocuous, biodegradable materials as catalysts in many biologically and pharmacologically important protocols. This review outlines the decisive organic transformations for which feedstock-derived catalysts have been employed effectively and successfully, along with their economic and environmental benefits over traditional catalytic systems.

Modulating response of sunflower (Hellianthus annuus) to induced salinity stress through application of engineered urea functionalized hydroxyapatite nanoparticles

Agro-nanotechnology aims to improve the quality and quantity of plants and plant products while preserving environmental health. Contemporary anecdotal studies that provide representation of the use of nanostructures as fertilizers, pesticides, and plant growth regulators have highlighted the need to determine the effect of such modified nanofertilizers on transforming plant yield under abiotic stress. Present study was performed to modulate the physiological response of Hellianthus annuus through the application of Urea capped hydroxyapatite nanoparticles (Urea-HANPs) in stressed environment. Hydroxyapatite nanoparticles were synthesized via co-precipitation method, functionalized with urea and characterized through a series of contemporary techniques of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. We observed that Urea-HANPs significantly (p < .05) ameliorated resistivity in plant to osmotic stress by enhancing agronomic and physiobiochemical attributes. Elevated chlorophyll contents were reported from tested leaves treated with Urea-HANPs in T6 (0.05 M NaCl + 10 μg/ml Urea-HANP) under induced salinity stress. Data revealed significant decrease in osmolytes at T3 (0.1 M NaCl), and T4 (0.2 M NaCl) which was significantly ameliorated in T9 (0.1 M NaCl + 10 μg/ml Urea-HANPs) and T12 (0.2 M NaCl + 10 μg/ml Urea-HANPs). The antioxidant system was boosted up by the application of Urea-HANPs preventing the plant from oxidative stress by scavenging reactive oxygen species (ROS). It has been concluded that alleviation in impact of osmotic stress on plant through the use of Urea-HANPs was coupled with elevation in photosynthetic performance, stimulation of osmolytes and boosting antioxidant system of plants.

Cyanide Hydratase Modification Using Computational Design and Docking Analysis for Improved Binding Affinity in Cyanide Detoxification

Cyanide is a hazardous and detrimental chemical that causes the inactivation of the respiration system through the inactivation of cytochrome c oxidase. Because of the limitation in the number of cyanide-degrading enzymes, there is a great demand to design and introduce new enzymes with better functionality. This study developed an integrated method of protein-homology-modelling and ligand-docking protein-design approaches that reconstructs a better active site from cyanide hydratase (CHT) structure. Designing a mutant CHT (mCHT) can improve the CHT performance. A computational design procedure that focuses on mutation for constructing a new model of cyanide hydratase with better activity was used. In fact, this study predicted the three-dimensional (3D) structure of CHT for subsequent analysis. Inducing mutation on CHT of Trichoderma harzianum was performed and molecular docking was used to compare protein interaction with cyanide as a ligand in both CHT and mCHT. By combining multiple designed mutations, a significant improvement in docking for CHT was obtained. The results demonstrate computational capabilities for enhancing and accelerating enzyme activity. The result of sequence alignment and homology modeling show that catalytic triad (Cys-Glu-Lys) was conserved in CHT of Trichoderma harzianum. By inducing mutation in CHT structure, MolDock score enhanced from −18.1752 to −23.8575, thus the nucleophilic attack can occur rapidly by adding Cys in the catalytic cavity and the total charge of protein in pH 6.5 is increased from −6.0004 to −5.0004. Also, molecular dynamic simulation shows a stable protein-ligand complex model. These changes would help in the cyanide degradation process by mCHT.

Nitrilase: a promising biocatalyst in industrial applications for green chemistry

Nitrilases are widely distributed in nature and are able to hydrolyze nitriles into their corresponding carboxylic acids and ammonia. In industry, nitrilases have been used as green biocatalysts for the production of high value-added products. To date, biocatalysts are considered to be important alternatives to chemical catalysts due to increasing environmental problems and resource scarcity. This review provides an overview of recent advances of nitrilases in aspects of distribution, enzyme screening, molecular structure and catalytic mechanism, protein engineering, and their potential applications in industry.

Genome-Based Insights into the Production of Carotenoids by Antarctic Bacteria, Planococcus sp. ANT_H30 and Rhodococcus sp. ANT_H53B

Antarctic regions are characterized by low temperatures and strong UV radiation. This harsh environment is inhabited by psychrophilic and psychrotolerant organisms, which have developed several adaptive features. In this study, we analyzed two Antarctic bacterial strains, Planococcus sp. ANT_H30 and Rhodococcus sp. ANT_H53B. The physiological analysis of these strains revealed their potential to produce various biotechnologically valuable secondary metabolites, including surfactants, siderophores, and orange pigments. The genomic characterization of ANT_H30 and ANT_H53B allowed the identification of genes responsible for the production of carotenoids and the in silico reconstruction of the pigment biosynthesis pathways. The complex manual annotation of the bacterial genomes revealed the metabolic potential to degrade a wide variety of compounds, including xenobiotics and waste materials. Carotenoids produced by these bacteria were analyzed chromatographically, and we proved their activity as scavengers of free radicals. The quantity of crude carotenoid extracts produced at two temperatures using various media was also determined. This was a step toward the optimization of carotenoid production by Antarctic bacteria on a larger scale.

Functional gene categories differentiate maize leaf drought-related microbial epiphytic communities

The phyllosphere epiphytic microbiome is composed of microorganisms that colonize the external aerial portions of plants. Relationships of plant responses to specific microorganisms–both pathogenic and beneficial–have been examined, but the phyllosphere microbiome functional and metabolic profile responses are not well described. Changing crop growth conditions, such as increased drought, can have profound impacts on crop productivity. Also, epiphytic microbial communities provide a new target for crop yield optimization. We compared Zea mays leaf microbiomes collected under drought and well-watered conditions by examining functional gene annotation patterns across three physically disparate locations each with and without drought treatment, through the application of short read metagenomic sequencing. Drought samples exhibited different functional sequence compositions at each of the three field sites. Maize phyllosphere functional profiles revealed a wide variety of metabolic and regulatory processes that differed in drought and normal water conditions and provide key baseline information for future selective breeding.

Plant Nitrilase Homologues in Fungi: Phylogenetic and Functional Analysis with Focus on Nitrilases in Trametes versicolor and Agaricus bisporus

Fungi contain many plant-nitrilase (NLase) homologues according to database searches. In this study, enzymes NitTv1 from Trametes versicolor and NitAb from Agaricus bisporus were purified and characterized as the representatives of this type of fungal NLase. Both enzymes were slightly more similar to NIT4 type than to NIT1/NIT2/NIT3 type of plant NLases in terms of their amino acid sequences. Expression of the synthetic genes in Escherichia coli Origami B (DE3) was induced with 0.02 mM isopropyl β-D-1-thiogalactopyranoside at 20 °C. Purification of NitTv1 and NitAb by cobalt affinity chromatography gave ca. 6.6 mg and 9.6 mg of protein per 100 mL of culture medium, respectively. Their activities were determined with 25 mM of nitriles in 50 mM Tris/HCl buffer, pH 8.0, at 30 °C. NitTv1 and NitAb transformed β-cyano-L-alanine (β-CA) with the highest specific activities (ca. 132 and 40 U mg⁻¹, respectively) similar to plant NLase NIT4. β-CA was transformed into Asn and Asp as in NIT4 but at lower Asn:Asp ratios. The fungal NLases also exhibited significant activities for (aryl)aliphatic nitriles such as 3-phenylpropionitrile, cinnamonitrile and fumaronitrile (substrates of NLase NIT1). NitTv1 was more stable than NitAb (at pH 5–9 vs. pH 5–7). These NLases may participate in plant–fungus interactions by detoxifying plant nitriles and/or producing plant hormones. Their homology models elucidated the molecular interactions with various nitriles in their active sites.

From sequence to function: a new workflow for nitrilase identification

Abstract

Nitrilases are industrially important biocatalysts due to their ability to degrade nitriles to carboxylic acids and ammonia. In this study, a workflow for simple and fast recovery of nitrilase candidates from metagenomes is presented. For identification of active enzymes, a NADH-coupled high-throughput assay was established. Purification of enzymes could be omitted as the assay is based on crude extract containing the expressed putative nitrilases. In addition, long incubation times were avoided by combining nitrile and NADH conversion in a single reaction. This allowed the direct measurement of nitrile degradation and provided not only insights into substrate spectrum and specificity but also in degradation efficiency. The novel assay was used for investigation of candidate nitrilase-encoding genes. Seventy putative nitrilase-encoding gene and the corresponding deduced protein sequences identified during sequence-based screens of metagenomes derived from nitrile-treated microbial communities were analyzed. Subsequently, the assay was applied to 13 selected candidate genes and proteins. Six of the generated corresponding Escherichia coli clones produced nitrilases that showed activity and one unusual nitrilase was purified and analyzed. The activity of the novel arylacetonitrilase Nit09 exhibited a broad pH range and a high long-term stability. The enzyme showed high activity for arylacetonitriles with a K_M of 1.29 mM and a V_max of 13.85 U/mg protein for phenylacetonitrile. In conclusion, we provided a setup for simple and rapid analysis of putative nitrilase-encoding genes from sequence to function. The suitability was demonstrated by identification, isolation, and characterization of the arylacetonitrilase.

Key points

• A simple and fast high-throughput nitrilase screening was developed.

• A set of putative nitrilases was successfully screened with the assay.

• A novel arylacetonitrilase was identified, purified, and characterized in detail.

Electronic supplementary material

The online version of this article (10.1007/s00253-020-10544-9) contains supplementary material, which is available to authorized users.

Genome-Scale Investigation of the Metabolic Determinants Generating Bacterial Fastidious Growth

Xylella fastidiosa is one of the most important threats to plant health worldwide, causing disease in the Americas on a range of agricultural crops and trees, and recently associated with a critical epidemic affecting olive trees in Europe. A main challenge for the detection of the pathogen and the development of physiological studies is its fastidious growth, as the generation time can vary from 10 to 100 h for some strains. This physiological peculiarity is shared with several human pathogens and is poorly understood. We performed an analysis of the metabolic capabilities of X. fastidiosa through a genome-scale metabolic model of the bacterium. This model was reconstructed and manually curated using experiments and bibliographical evidence. Our study revealed that fastidious growth most probably results from different metabolic specificities such as the absence of highly efficient enzymes or a global inefficiency in virulence factor production. These results support the idea that the fragility of the metabolic network may have been shaped during evolution to lead to the self-limiting behavior of X. fastidiosa.

High proliferation rate and robustness are vital characteristics of bacterial pathogens that successfully colonize their hosts. The observation of drastically slow growth in some pathogens is thus paradoxical and remains unexplained. In this study, we sought to understand the slow (fastidious) growth of the plant pathogen Xylella fastidiosa. Using genome-scale metabolic network reconstruction, modeling, and experimental validation, we explored its metabolic capabilities. Despite genome reduction and slow growth, the pathogen’s metabolic network is complete but strikingly minimalist and lacking in robustness. Most alternative reactions were missing, especially those favoring fast growth, and were replaced by less efficient paths. We also found that the production of some virulence factors imposes a heavy burden on growth. Interestingly, some specific determinants of fastidious growth were also found in other slow-growing pathogens, enriching the view that these metabolic peculiarities are a pathogenicity strategy to remain at a low population level.

IMPORTANCEXylella fastidiosa is one of the most important threats to plant health worldwide, causing disease in the Americas on a range of agricultural crops and trees, and recently associated with a critical epidemic affecting olive trees in Europe. A main challenge for the detection of the pathogen and the development of physiological studies is its fastidious growth, as the generation time can vary from 10 to 100 h for some strains. This physiological peculiarity is shared with several human pathogens and is poorly understood. We performed an analysis of the metabolic capabilities of X. fastidiosa through a genome-scale metabolic model of the bacterium. This model was reconstructed and manually curated using experiments and bibliographical evidence. Our study revealed that fastidious growth most probably results from different metabolic specificities such as the absence of highly efficient enzymes or a global inefficiency in virulence factor production. These results support the idea that the fragility of the metabolic network may have been shaped during evolution to lead to the self-limiting behavior of X. fastidiosa.

Molecular imprints of plant beneficial Streptomyces sp. AC30 and AC40 reveal differential capabilities and strategies to counter environmental stresses

Streptomyces and their biomolecules are well explored for antibiotics production, bioremediation and alleviating the plant stresses due to their plant beneficial attributes. Therefore, due to plethora of biological attributes, the accurate portraying of molecular capabilities of these microorganisms at genomic level is of paramount importance. Here, we have evaluated biochemical attributes of two Streptomyces sp. AC30and AC40 for different plant beneficial activities which are antagonistic to Fusarium oxysporum, Alternaria solani, Sclerotinia sclerotium and Phytopthora infestans. In parallel, the draft genomes of these strains were deduced to understand their genomic capabilities using Illumina platform. The complete genome of AC30and AC40 were 11,284,599 bp and 12,636,188 bp in size with total G + C content of 62.36 and 54.75 %, respectively. Overall, higher number of genes (14,024) was reported for AC40 as compared to AC30 (12,476). The comparative genome organization revealed sharing of a few biosynthetic clusters as well as some exclusive biosynthetic clusters among both the strains. Further, expansion in the chitinases and glucanases was found in the genome of AC40. In addition, genes for 3-phytase and glycosyl hydrolase family 19 were restricted to AC40 only. The comparative genome study revealed presence of plant induced nitrilase in AC40 which is predicted for its role in IAA biosynthesis, release of ammonia, biotransformation of nitrile compounds to corresponding acids and bioremediation of soil containing nitrile compounds. For IAA and secondary metabolites biosynthesis, flavin-dependent monooxygenase, a rate limiting factor in Trp-dependent auxin biosynthesis pathway was found exclusive to AC30 genome. The comparative study revealed the diversification of few pathways/strategies to suppress plant pathogens and promote plant growth by Streptomyces strains.

Comparative Proteomic Analysis Reveals New Insights Into the Common and Specific Metabolic Regulation of the Diatom Skeletonema dohrnii to the Silicate and Temperature Availability

Silicate (Si) and temperature are essential drivers for diatom growth and development in the ocean. Response of diatoms to these particular stress has been investigated; however, their common and specific responses to regulate intracellular development and growth are not known. Here, we investigated the combination of physiological characteristics and comparative proteomics of the diatom Skeletonema dohrnii grown in silicate- and temperature-limited conditions. Results show that cell carbon and lipid quotas were higher at lower-temperature cells, whereas cellular phosphate was higher in cells grown with lower Si. In silicate-limited cells, nitrate transporters were downregulated and resulted in lower nitrate assimilation, whereas the phosphate transporters and its assimilation were reduced in lower-temperature conditions. In photosynthesis, lower silicate caused impact in the linear electron flow and NADPH production, whereas cycling electron transport and ATP production were affected by the lower temperature. Concerning cell cycle, imbalances in the translation process were observed in lower-silicate cells, whereas impact in the transcription mechanism was observed in lower-temperature cells. However, proteins associated with carbon fixation and photorespiration were downregulated in both stress conditions, while the carbohydrate and lipid synthesis proteins were upregulated. Our results showed new insights into the common and specific responses on the proteome and physiology of S. dohrnii to silicate and temperature limitation, providing particular nutrient (Si)- and temperature-dependent mechanisms in diatoms.

Identification of QTLs Containing Resistance Genes for Sclerotinia Stem Rot in Brassica napus Using Comparative Transcriptomic Studies

Sclerotinia stem rot is a major disease in Brassica napus that causes yield losses of 10-20% and reaching 80% in severely infected fields. SSR not only causes yield reduction but also causes low oil quality by reducing fatty acid content. There is a need to identify resistant genetic sources with functional significance for the breeding of SSR-resistant cultivars. In this study, we identified 17 QTLs involved in SSR resistance in three different seasons using SNP markers and disease lesion development after artificial inoculation. There were no common QTLs in all 3 years, but there were three QTLs that appeared in two seasons covering all seasons with a shared QTL. The QTLs identified in the 2 years were SRA9a, SRC2a and SRC3a with phenotypic effect variances of 14.75 and 11.57% for SRA9a, 7.49 and 10.38% for SRC3a and 7.73 and 6.81% for SRC2a in their 2 years, respectively. The flowering time was also found to have a negative correlation with disease resistance, i.e., early-maturing lines were more susceptible to disease. The stem width has shown a notably weak effect on disease development, causing researchers to ignore its effect. Given that flowering time is an important factor in disease resistance, we used comparative RNA-sequencing analysis of resistant and susceptible lines with consistent performance in 3 years with almost the same flowering time to identify the resistance genes directly involved in resistance within the QTL regions. Overall, there were more genes differentially expressed in resistant lines 19,970 than in susceptible lines 3936 compared to their mock-inoculated lines, demonstrating their tendency to cope with disease. We identified 36 putative candidate genes from the resistant lines that were upregulated in resistant lines compared to resistant mock and susceptible lines that might be involved in resistance to SSR.

Beneficial Endophytic Bacteria-Serendipita indica Interaction for Crop Enhancement and Resistance to Phytopathogens

Serendipita (=Piriformospora) indica is a fungal endophytic symbiont with the capabilities to enhance plant growth and confer resistance to different stresses. However, the application of this fungus in the field has led to inconsistent results, perhaps due to antagonism with other microbes. Here, we studied the impact of individual bacterial isolates from the endophytic bacterial community on the in vitro growth of S. indica. We further analyzed how combinations of bacteria and S. indica influence plant growth and protection against the phytopathogens Fusarium oxysporum and Rhizoctonia solani. Bacterial strains of the genera Bacillus, Enterobacter and Burkholderia negatively affected S. indica growth on plates, whereas Mycolicibacterium, Rhizobium, Paenibacillus strains and several other bacteria from different taxa stimulated fungal growth. To further explore the potential of bacteria positively interacting with S. indica, four of the most promising strains belonging to the genus Mycolicibacterium were selected for further experiments. Some dual inoculations of S. indica and Mycolicibacterium strains boosted the beneficial effects triggered by S. indica, further enhancing the growth of tomato plants, and alleviating the symptoms caused by the phytopathogens F. oxysporum and R. solani. However, some combinations of S. indica and bacteria were less effective than individual inoculations. By analyzing the genomes of the Mycolicibacterium strains, we revealed that these bacteria encode several genes predicted to be involved in the stimulation of S. indica growth, plant development and tolerance to abiotic and biotic stresses. Particularly, a high number of genes related to vitamin and nitrogen metabolism were detected. Taking into consideration multiple interactions on and inside plants, we showed in this study that some bacterial strains may induce beneficial effects on S. indica and could have an outstanding influence on the plant-fungus symbiosis.

Genetic and Functional Diversity of Nitrilases in Agaricomycotina

Nitrilases participate in the nitrile metabolism in microbes and plants. They are widely used to produce carboxylic acids from nitriles. Nitrilases were described in bacteria, Ascomycota and plants. However, they remain unexplored in Basidiomycota. Yet more than 200 putative nitrilases are found in this division via GenBank. The majority of them occur in the subdivision Agaricomycotina. In this work, we analyzed their sequences and classified them into phylogenetic clades. Members of clade 1 (61 proteins) and 2 (25 proteins) are similar to plant nitrilases and nitrilases from Ascomycota, respectively, with sequence identities of around 50%. The searches also identified five putative cyanide hydratases (CynHs). Representatives of clade 1 and 2 (NitTv1 from Trametes versicolor and NitAg from Armillaria gallica, respectively) and a putative CynH (NitSh from Stereum hirsutum) were overproduced in Escherichia coli. The substrates of NitTv1 were fumaronitrile, 3-phenylpropionitrile, β-cyano-l-alanine and 4-cyanopyridine, and those of NitSh were hydrogen cyanide (HCN), 2-cyanopyridine, fumaronitrile and benzonitrile. NitAg only exhibited activities for HCN and fumaronitrile. The substrate specificities of these nitrilases were largely in accordance with substrate docking in their homology models. The phylogenetic distribution of each type of nitrilase was determined for the first time.

Functional Insights Into Protein Acetylation in the Hyperthermophilic Archaeon Sulfolobus islandicus

Proteins undergo acetylation at the Nε-amino group of lysine residues and the Nα-amino group of the N terminus in Archaea as in Bacteria and Eukarya. However, the extent, pattern and roles of the modifications in Archaea remain poorly understood. Here we report the proteomic analyses of a wild-type Sulfolobus islandicus strain and its mutant derivative strains lacking either a homolog of the protein acetyltransferase Pat (ΔSisPat) or a homolog of the Nt-acetyltransferase Ard1 (ΔSisArd1). A total of 1708 Nε-acetylated lysine residues in 684 proteins (26% of the total proteins), and 158 Nt-acetylated proteins (44% of the identified proteins) were found in S. islandicus ΔSisArd1 grew more slowly than the parental strain, whereas ΔSisPat showed no significant growth defects. Only 24 out of the 1503 quantifiable Nε-acetylated lysine residues were differentially acetylated, and all but one of the 24 residues were less acetylated by >1.3 fold in ΔSisPat than in the parental strain, indicating the narrow substrate specificity of the enzyme. Six acyl-CoA synthetases were the preferred substrates of SisPat in vivo, suggesting that Nε-acetylation by the acetyltransferase is involved in maintaining metabolic balance in the cell. Acetylation of acyl-CoA synthetases by SisPat occurred at a sequence motif conserved among all three domains of life. On the other hand, 92% of the acetylated N termini identified were acetylated by SisArd1 in the cell. The enzyme exhibited broad substrate specificity and could modify nearly all types of the target N termini of human NatA-NatF. The deletion of the SisArd1 gene altered the cellular levels of 18% of the quantifiable proteins (1518) by >1.5 fold. Consistent with the growth phenotype of ΔSisArd1, the cellular levels of proteins involved in cell division and cell cycle control, DNA replication, and purine synthesis were significantly lowered in the mutant than those in the parental strain.

Comparative genomics of Paraburkholderia kururiensis and its potential in bioremediation, biofertilization, and biocontrol of plant pathogens

Burkholderia harbors versatile Gram-negative species and is β-Proteobacteria. Recently, it was proposed to split the genus in two main branches: one of animal and plant pathogens and another, Paraburkholderia, harboring environmental and plant-beneficial species. Currently, Paraburkholderia comprises more than 70 species with ability to occupy very diverse environmental niches. Herein, we sequenced and analyzed the genome of Paraburkholderia kururiensis type strain KP23T , and compared to P. kururiensis M130, isolated in Brazil, and P. kururiensis susbp. thiooxydans, from Korea. This study focused on the gene content of the three genomes with special emphasis on their potential of plant-association, biocontrol, and bioremediation. The comparative analyses revealed several genes related to plant benefits, including biosynthesis of IAA, ACC deaminase, multiple efflux pumps, dioxygenases, and degradation of aromatic compounds. Importantly, a range of genes for protein secretion systems (type III, IV, V, and VI) were characterized, potentially involved in P. kururiensis well documented ability to establish endophytic association with plants. These findings shed light onto bacteria-plant interaction mechanisms at molecular level, adding novel information that supports their potential application in bioremediation, biofertilization, and biocontrol of plant pathogens. P. kururiensis emerges as a promising model to investigate adaptation mechanisms in different ecological niches.

The nematicide Serratia plymuthica M24T3 colonizes Arabidopsis thaliana, stimulates plant growth, and presents plant beneficial potential

Nine bacterial strains were previously isolated in association with pinewood nematode (PWN) from wilted pine trees. They proved to be nematicidal in vitro, and one of the highest activities, with potential to control PWN, was showed by Serratia sp. M24T3. Its ecology in association with plants remains unclear. This study aimed to evaluate the ability of strain M24T3 to colonize the internal tissues of the model plant Arabidopsis thaliana using confocal microscopy. Plant growth-promoting bacteria (PGPB) functional traits were tested and retrieved in the genome of strain M24T3. In greenhouse conditions, the bacterial effects of all nematicidal strains were also evaluated, co-inoculated or not with Bradyrhizobium sp. 3267, on Vigna unguiculata fitness. Inoculation of strain M24T3 increased the number of A. thaliana lateral roots and the confocal analysis confirmed effective bacterial colonization in the plant. Strain M24T3 showed cellulolytic activity, siderophores production, phosphate and zinc solubilization ability, and indole acetic acid production independent of supplementation with L-tryptophan. In the genome of strain M24T3, genes involved in the interaction with the plants such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase, chitinolytic activity, and quorum sensing were also detected. The genomic organization showed ACC deaminase and its leucine-responsive transcriptional regulator, and the activity of ACC deaminase was 594.6 nmol α-ketobutyrate μg protein^-1 μl^-1. Strain M24T3 in co-inoculation with Bradyrhizobium sp. 3267 promoted the growth of V. unguiculata. In conclusion, this study demonstrated the ability of strain M24T3 to colonize other plants besides pine trees as an endophyte and displays PGPB traits that probably increased plant tolerance to stresses.

Plant nitrilase: a new job for an old enzyme

Nitrilases are versatile enzymes that hydrolyze nitriles to carboxylic acids and ammonia, but many members of this family lack defined biological functions. In plants, nitrilases have been associated with detoxification of cyanide-containing compounds and auxin biosynthesis; however, recent work suggests that the chemical versatility of these proteins contributes to metabolite repair. In this issue of the Biochemical Journal, Niehaus et al. demonstrate that the Nit1 nitrilase from Arabidopsis thaliana functions as a metabolite repair enzyme that removes deaminated glutathione from the cytoplasm and plastids.

Comparative Genomic Analyses Reveal Core-Genome-Wide Genes Under Positive Selection and Major Regulatory Hubs in Outlier Strains of Pseudomonas aeruginosa

Genomic information for outlier strains of Pseudomonas aeruginosa is exiguous when compared with classical strains. We sequenced and constructed the complete genome of an environmental strain CR1 of P. aeruginosa and performed the comparative genomic analysis. It clustered with the outlier group, hence we scaled up the analyses to understand the differences in environmental and clinical outlier strains. We identified eight new regions of genomic plasticity and a plasmid pCR1 with a VirB/D4 complex followed by trimeric auto-transporter that can induce virulence phenotype in the genome of strain CR1. Virulence genotype analysis revealed that strain CR1 lacked hemolytic phospholipase C and D, three genes for LPS biosynthesis and had reduced antibiotic resistance genes when compared with clinical strains. Genes belonging to proteases, bacterial exporters and DNA stabilization were found to be under strong positive selection, thus facilitating pathogenicity and survival of the outliers. The outliers had the complete operon for the production of vibrioferrin, a siderophore present in plant growth promoting bacteria. The competence to acquire multidrug resistance and new virulence factors makes these strains a potential threat. However, we identified major regulatory hubs that can be used as drug targets against both the classical and outlier groups.

Interplay of nucleophilic catalysis with proton transfer in the nitrile reductase QueF from Escherichia coli

Proton relay through an active-site network of hydrogen bonds promotes enzymatic nitrile reduction to amine via a covalent thioimidate enzyme intermediate.

The use of clade-specific PCR assays to identify novel nitrilase genes from environmental isolates

Nitrilase enzymes (EC 3.5.5.1) are responsible for the direct hydration of nitriles to their corresponding carboxylic acids and ammonia. The utilization of nitrilase enzymes in biocatalysis toward bio-pharmaceuticals and industrial applications facilitates the move towards green chemistry. The body of research presented describes a novel clade-specific touchdown PCR protocol for the detection of novel nitrilase genes. The presented study identified partial sequences of 15 novel nitrilase genes across 7 genera, with partial DNA sequence homology (%) displayed across an additional 16 genera. This research will prove valuable in the screening of microorganisms for the identification of novel clade-specific nitrilase genes, with predicted enantioselective profiles as determined by their clade characterizations.