Nitrogen-limiting Conditions Research Articles

Multi-omics analysis reveals the mechanism of torularhodin accumulation in the mutant Rhodosporidium toruloides A1-15 under nitrogen-limited conditions.

A carotenoid production strain Rhodosporidium toruloides NP11 and its mutant strain R. toruloides A1-15 were studied under chemostat nitrogen-limited cultivation. Multi-omics analysis (metabolomics, lipidomics and transcriptomics) was used to investigate the different mechanisms of torularhodin accumulation between NP11 and A1-15. The results showed that the carotenoid synthesis pathway was significantly enhanced in A1-15 compared to NP11 under nitrogen limitation, due to the significant increase of torularhodin. Under nitrogen-limited conditions, higher levels of β-oxidation were present in A1-15 compared to those in NP11, which provided sufficient precursors for carotenoid synthesis. In addition, ROS stress accelerated the intracellular transport of iron ions, promoted the expression of CRTI and CRTY genes, and reduced the transcript levels of FNTB1 and FNTB2 in the bypass pathway, and these factors may be responsible for the regulation of high torularhodin production in A1-15. This study provided insights into the selective production of torularhodin.

Nitrogen limitation prevents the effects of iron or dust additions on biological carbon fixation in the Gulf of California

This paper reports the effect of dissolved iron (dFe) and dust additions on the Biological Carbon Fixation (BCF) rates in the surface layer of the central Gulf of California (GC). Two on deck experiments were conducted in the summer of 2016 at an oceanographic station located in the Guaymas Basin. Each experiment consisted in the incubation of natural phytoplankton assemblages collected at three distinct depths within the upper 50 m layer and amended either with iron (FeCl3) or dust leachate, followed by the quantification of BCF rates using the 13C assimilation method. A very warm (∼30 °C) water column strongly stratified and with reduced phytoplankton biomass (<1 mg chlorophyll a m−3) was indicative of an oligotrophic environment. In addition, the surface levels of NO3−+NO2− (<0.1 μM), dFe (1.71 ± 1.04 nM), as well as the Fe:N (78 ± 47 nmol μmol−1) and N:P (0.04 ± 0.01) ratios revealed that phytoplankton was under conditions of inorganic nitrogen limitation. BCF rates measured during the experiments ranged between 0.46 ± 0.04 and 6.24 ± 0.34 mg C m−3 h−1 with the highest values at the maximum of fluorescence and their vertical distribution was associated with the carbon biomass of picophytoplankton and diatoms. Despite the oligotrophic condition that predominated during the cruise, most of the Fe or dust additions did not show a significant effect (p > 0.05) on the magnitude of BCF rates, which was attributed to the fact that N, rather than Fe, was the limiting nutrient for phytoplankton production. However, Fe limitation cannot be completely ruled out as two samples (one for each treatment) showed a significant increase (p < 0.05) in BCF rates. We suggest that atmospheric supply of dust during the summer could play a relevant biological role maintaining high concentrations of dFe (and other bioactive metals) in the surface waters of central GC.

Exploration of two-stage cultivation strategy using nitrogen limited and phosphorus sufficient to simultaneously improve the biomass and lipid productivity in Desmodesmus intermedius Z8

In this work, the effects of nine different nitrogen and phosphorus conditions on the growth and lipid production of Desmodesmus intermedius Z8 were investigated. The highest lipid concentration of 0.89 g·L−1 was obtained at 6 days under the Nlim&P (nitrogen limited and phosphorus sufficient) condition. To further enhance the total lipid production, the two-stage cultivation strategy was performed. The results show that the addition of 750.0 mg·L−1 of nitrogen and 40.00 mg·L−1 of phosphorus at the end of the second day of incubation could effectively improve the lipid productivity. Under this condition, they could reach 244.69 mg·(L·d)−1, which was 1.66-folds higher than that of the control group. Furthermore, the fatty acid composition analysis indicates that the lipid could meet the standards of biodiesel. Therefore, the two-stage regulation strategy, according to the results in this study, is an effective and simple method to realize high lipid production and quality, and then showing its potential for biodiesel production.

Utility of anthesis–silking interval information to predict grain yield under water and nitrogen limited conditions

AbstractDelayed silking relative to pollen shed, measured as the anthesis–silking interval (ASI, the period between pollen shed and silking), is a good indicator of response to abiotic stresses in maize (Zea mays L.). This research was conducted to investigate how ASI is affected by nitrogen (N) and water availability and to assess the utility of ASI to indirectly predict grain yield (GY) under contrasting water and N treatments. Two experiments were conducted in Hancock, WI, in 2018 and 2019. One experiment (Diverse hybrids) included 302 hybrids resulting from the cross of diverse inbred lines by a single tester evaluated at four different treatment levels resulting from combining nonlimited and low N with nonlimited and low water treatments. The second experiment (NSS FAC) included a set of 408 hybrids derived from the cross of biparental doubled‐haploid lines from 13 factorial populations and evaluated under nonlimited and low N treatments. Anthesis and silk time in growing degree days, and GY (Mg ha−1) were measured. Genomic prediction was assessed using a genomic best linear unbiased prediction model, and predictive ability was calculated as the correlation between genomic predictions and adjusted means in the different treatments. Predictive ability ranged from .15 to .49 for NSS FAC and from .06 to .51 for Diverse hybrids across traits and treatments. The ASI was a good indicator of stress and showed higher heritability than GY in the limited treatments for both experiments; however, it did not improve yield predictability.

Alanine synthesized by alanine dehydrogenase enables ammonium-tolerant nitrogen fixation in Paenibacillus sabinae T27

Most diazotrophs fix nitrogen only under nitrogen-limiting conditions, for example, in the presence of relatively low concentrations of NH4+ (0 to 2 mM). However, Paenibacillus sabinae T27 exhibits an unusual pattern of nitrogen regulation of nitrogen fixation, since although nitrogenase activities are high under nitrogen-limiting conditions (0 to 3mM NH4+) and are repressed under conditions of nitrogen sufficiency (4to 30mM NH4+), nitrogenase activity is reestablished when very high levels of NH4+ (30 to 300 mM) are present in the medium. To further understand this pattern of nitrogen fixation regulation, we carried out transcriptome analyses of P. sabinae T27 in response to increasing ammonium concentrations. As anticipated, the nif genes were highly expressed, either in the absence of fixed nitrogen or in the presence of a high concentration of NH4+ (100 mM), but were subject to negative feedback regulation at an intermediate concentration of NH4+ (10 mM). Among the differentially expressed genes, ald1, encoding alanine dehydrogenase (ADH1), was highly expressed in the presence of a high level of NH4+ (100 mM). Mutation and complementation experiments revealed that ald1 is required for nitrogen fixation at high ammonium concentrations. We demonstrate that alanine, synthesized by ADH1 from pyruvate and NH4+, inhibits GS activity, leading to a low intracellular glutamine concentration that prevents feedback inhibition of GS and mimics nitrogen limitation, enabling activation of nif transcription by the nitrogen-responsive regulator GlnR in the presence of high levels of extracellular ammonium.

Effects of nitrogen limitation on Leymus Chinensis clonal growth form and bud bank

Nitrogen is an important element which affects the growth and clonal growth of plant species in grassland. Leymus chinensis (Trin.) Tzvel is a dominant species in grasslands with a high nutritional quality; however, data on the effects of low nitrogen concentration on L. chinensis clonal growth strategy are limited. The aim of this study is to evaluate the response of clonal growth of L. chinensis to low nitrogen concentrations. The growth form and biomass allocation ratios of L. chinensis under different low nitrogen concentrations were evaluated, and the quantitative characteristics of three bud types were analyzed. The proportion of spreading ramets was favored by low nitrogen supply, indicating that L. chinensis under low nitrogen conditions primarily exhibits a guerrilla growth form, meaning a long mean spacer length and production of spreading ramets. Under limited nitrogen conditions, biomass distribution was mainly concentrated in underground organs (including the roots and rhizomes), while the high proportion of axillary rhizome buds suggested that L. chinensis grows primarily by occupying effective living spaces under low nitrogen conditions. The balance between two clonal growth form and the change in the proportion of different types of buds is an important strategy for L. chinensis to cope with nutrient limitations.

Biotechnological production of sugar-alcohols: Focus on Yarrowia lipolytica and edible/medicinal mushrooms

In the present review-article several aspects dealing with the biotechnological production of three major sugar-alcohols, viz. erythritol, mannitol and arabitol, are developed. Emphasis is given on the extra-cellular production of these sugar-alcohols by species of the yeast cell factory Yarrowia lipolytica and/or their intra-cellular accumulation in genera/species (mostly Agaricus and Pleurotus) of edible and medicinal mushrooms. Indications concerning the presence of soluble sugars inside the fungal mycelia and fruit-bodies of various types of mushrooms are also added. Initially, general information concerning the mentioned sugar-alcohols as well as others that are produced by biotechnological means, their roles, and their functionalities, are presented. The biochemistry of the synthesis of erythritol, mannitol and arabitol in the yeast cells and fungal mycelia when the main carbon sources employed in the Industrial Biotechnology (viz. glucose/fructose, lignocellulosic compounds/xylose, hydrophobic materials, glycerol) are used is presented and critically discussed. Given that the yeast Y. lipolytica is a major candidate that has been/is implicated in the production of the mentioned sugar-alcohols together with other compounds that are synthesized through similar metabolic pathways (viz. microbial lipids and citric acid, produced as the mentioned polyols during the imbalanced growth phase and after carbon-excess and nitrogen-limited conditions) various considerations concerning the biotechnological potential of this yeast species with emphasis of the production of sugar-alcohols are developed and assessed. Finally, presentations concerning the production of sugar-alcohols and other soluble sugars through the cultivation of various types of edible/medicinal mushrooms in several types of fermentation configurations are critically assessed.

Neighbours in nodules: the interactions between Frankia sp. ACN10a and non-Frankia nodular endophytes of alder.

In the present study, we report the in vitro interactions between Frankia sp. ACN10a and non-Frankia nodular endophytes (NFNE) isolated from alder. The supernatant of NFNE grown in nitrogen-replete medium had neutral or negative effects on Frankia growth; none had a stimulatory effect. Inhibitory effects were observed for supernatants of some NFNE, notably Micromonospora, Pseudomonas, Serratia and Stenotrophomonas isolates. However, some NFNE-Frankia coculture supernatants could stimulate Frankia growth when used as a culture medium supplement. This was observed for supernatants of Frankia cocultured with Microvirga and Streptomyces isolates. In nitrogen-limited conditions, cocultures of Frankia with some NFNE, including some rhizobia and Cytobacillus, resulted in higher total biomass than Frankia-only cultures, suggesting cooperation, while other NFNE were strongly antagonistic. Microscopic observation of cocultures also revealed compromised Frankia membrane integrity, and some differentiation into stress resistance-associated morphotypes such as sporangia and reproductive torulose hyphae (RTH). Furthermore, the coculture of Frankia with Serratia sp. isolates resulted in higher concentrations of the auxinic plant hormone indole-3-acetic acid (IAA) and related indolic compounds in the culture supernatant. This study sheds new light on the breadth of microbial interactions that occur amongst bacteria that inhabit the understudied ecological niche of the alder nodule.

Combinatorial Metabolic Engineering Strategies for the Enhanced Production of Free Fatty Acids in Escherichia coli.

In this study, we evaluated the effects of several metabolic engineering strategies in a systematic and combinatorial manner to enhance the free fatty acid (FFA) production in Escherichia coli. The strategies included (i) overexpression of mutant thioesterase I ('TesAR64C) to efficiently release the FFAs from fatty acyl-ACP; (ii) coexpression of global regulatory protein FadR; (iii) heterologous expression of methylmalonyl-CoA carboxyltransferase and phosphoenolpyruvate carboxylase to synthesize fatty acid precursor molecule malonyl-CoA; and (iv) disruption of genes associated with membrane proteins (GusC, MdlA, and EnvR) to improve the cellular state and export the FFAs outside the cell. The synergistic effects of these genetic modifications in strain SBF50 yielded 7.2 ± 0.11 g/L FFAs at the shake flask level. In fed-batch cultivation under nitrogen-limiting conditions, strain SBF50 produced 33.6 ± 0.02 g/L FFAs with a productivity of 0.7 g/L/h from glucose, which is the maximum titer reported in E. coli to date. Combinatorial metabolic engineering approaches can prove to be highly useful for the large-scale production of FA-derived chemicals and fuels.

Development of a stable semi-continuous lipid production system of an oleaginous Chlamydomonas sp. mutant using multi-omics profiling

BackgroundMicroalgal lipid production has attracted global attention in next-generation biofuel research. Nitrogen starvation, which drastically suppresses cell growth, is a common and strong trigger for lipid accumulation in microalgae. We previously developed a mutant Chlamydomonas sp. KAC1801, which can accumulate lipids irrespective of the presence or absence of nitrates. This study aimed to develop a feasible strategy for stable and continuous lipid production through semi-continuous culture of KAC1801.ResultsKAC1801 continuously accumulated > 20% lipid throughout the subculture (five generations) when inoculated with a dry cell weight of 0.8–0.9 g L−1 and cultured in a medium containing 18.7 mM nitrate, whereas the parent strain KOR1 accumulated only 9% lipid. Under these conditions, KAC1801 continuously produced biomass and consumed nitrates. Lipid productivity of 116.9 mg L−1 day−1 was achieved by semi-continuous cultivation of KAC1801, which was 2.3-fold higher than that of KOR1 (50.5 mg L−1 day−1). Metabolome and transcriptome analyses revealed a depression in photosynthesis and activation of nitrogen assimilation in KAC1801, which are the typical phenotypes of microalgae under nitrogen starvation.ConclusionsBy optimizing nitrate supply and cell density, a one-step cultivation system for Chlamydomonas sp. KAC1801 under nitrate-replete conditions was successfully developed. KAC1801 achieved a lipid productivity comparable to previously reported levels under nitrogen-limiting conditions. In the culture system of this study, metabolome and transcriptome analyses revealed a nitrogen starvation-like response in KAC1801.

Mathematical models of nitrogen-fixing cell patterns in filamentous cyanobacteria.

The Anabaena genus is a model organism of filamentous cyanobacteria whose vegetative cells can differentiate under nitrogen-limited conditions into a type of cell called a heterocyst. These heterocysts lose the possibility to divide and are necessary for the filament because they can fix and share environmental nitrogen. In order to distribute the nitrogen efficiently, heterocysts are arranged to form a quasi-regular pattern whose features are maintained as the filament grows. Recent efforts have allowed advances in the understanding of the interactions and genetic mechanisms underlying this dynamic pattern. Here, we present a systematic review of the existing theoretical models of nitrogen-fixing cell differentiation in filamentous cyanobacteria. These filaments constitute one of the simplest forms of multicellular organization, and this allows for several modeling scales of this emergent pattern. The system has been approached at three different levels. From bigger to smaller scale, the system has been considered as follows: at the population level, by defining a mean-field simplified system to study the ratio of heterocysts and vegetative cells; at the filament level, with a continuous simplification as a reaction-diffusion system; and at the cellular level, by studying the genetic regulation that produces the patterning for each cell. In this review, we compare these different approaches noting both the virtues and shortcomings of each one of them.

A Wild Rice Rhizobacterium Burkholderiacepacia BRDJ Enhances Nitrogen Use Efficiency in Rice.

Rice domestication has dramatically improved its agronomic traits, albeit with unavoidable significantly reduced genetic diversity. Dongxiang common wild rice, the wild rice species distributed in northernmost China, exhibits excellent resistance against stress and diseases and provides a rich genetic resource for rice breeding. Most of the studies focus on the function of the plant genes, often disregarding the role of the root microbes associated with the plants. In this work, we isolated a Burkholderia strain from the root of Dongxiang wild rice, which we identified as Burkholderia cepacia BRDJ, based on a phylogenetic analysis. This strain promoted the rice growth under greenhouse conditions. The grain yield was higher in a rice line containing a small genomic fragment derived from the Dongxiang wild rice, compared to the indica rice cultivar Zhongzao 35. This new strain also increased the plant biomass under limiting nitrogen conditions. Interestingly, this strain had a differential effect on indica and japonica rice varieties under full nitrogen supply conditions. By genome sequencing and comparison with another two B. cepacia strains, we observed enriched genes related with nitrogen fixation and phytohormone and volatiles biosynthesis that may account for the growth-promoting effects of the BRDJ. BRDJ has the potential to be used as a biofertilizer in promoting nitrogen use efficiency and overall growth in rice.

Variation in morpho-physiological and metabolic responses to low nitrogen stress across the sorghum association panel

BackgroundAccess to biologically available nitrogen is a key constraint on plant growth in both natural and agricultural settings. Variation in tolerance to nitrogen deficit stress and productivity in nitrogen limited conditions exists both within and between plant species. However, our understanding of changes in different phenotypes under long term low nitrogen stress and their impact on important agronomic traits, such as yield, is still limited.ResultsHere we quantified variation in the metabolic, physiological, and morphological responses of a sorghum association panel assembled to represent global genetic diversity to long term, nitrogen deficit stress and the relationship of these responses to grain yield under both conditions. Grain yield exhibits substantial genotype by environment interaction while many other morphological and physiological traits exhibited consistent responses to nitrogen stress across the population. Large scale nontargeted metabolic profiling for a subset of lines in both conditions identified a range of metabolic responses to long term nitrogen deficit stress. Several metabolites were associated with yield under high and low nitrogen conditions.ConclusionOur results highlight that grain yield in sorghum, unlike many morpho-physiological traits, exhibits substantial variability of genotype specific responses to long term low severity nitrogen deficit stress. Metabolic response to long term nitrogen stress shown higher proportion of variability explained by genotype specific responses than did morpho-pysiological traits and several metabolites were correlated with yield. This suggest, that it might be possible to build predictive models using metabolite abundance to estimate which sorghum genotypes will exhibit greater or lesser decreases in yield in response to nitrogen deficit, however further research needs to be done to evaluate such model.

Structural variability, implementational irregularities in mathematical modelling of polyhydroxyalkanoates (PHAs) production—A state‐of‐the‐art review

The rate and extent of microbial polyhydroxyalkanoates (PHAs) production rely on the availability of substrates, growth of microbial biomass, and intracellular accumulation of polymer under nitrogen-limited conditions. The dynamics of PHAs production captured through various structured or unstructured models can be extended to design an optimal feeding strategy for process intensification. Large variability in process assumptions, choices of kinetics, and model complexity is expected depending on substrate(s), microbial metabolism, and discretization of the process under consideration. This communication attempts to review the estimation of stoichiometric yield coefficients, metabolic modelling, and choices of unstructured kinetics in microbial PHA production. Implementational irregularities in parameter estimation and quality check in modelling exercises have also been reviewed. It is observed that the scope of the majority of the "modelling" studies is confined to the estimation of stoichiometric parameters with limited utility. In dynamic models, microbial growth is often described using either Monod or logistic variants, while PHAs production adopts a Luedeking-Piret expression with or without substrate inhibition. Though model selection, regression with experimental data, parameter estimation, and model validation are integral parts of the exercise, very few provide sufficient coverage on all those aspects. Application of the model to control or optimize the bioprocess has rarely been attempted.

Terminal heterocyst differentiation in the Anabaena patA mutant as a result of post-transcriptional modifications and molecular leakage.

The Anabaena genus is a model organism of filamentous cyanobacteria whose vegetative cells can differentiate under nitrogen-limited conditions into a type of cell called heterocyst. These heterocysts lose the possibility to divide and are necessary for the colony because they can fix and share environmental nitrogen. In order to distribute the nitrogen efficiently, heterocysts are arranged to form a quasi-regular pattern whose features are maintained as the filament grows. Recent efforts have allowed advances in the understanding of the interactions and genetic mechanisms underlying this dynamic pattern. However, the main role of the patA and hetF genes are yet to be clarified; in particular, the patA mutant forms heterocysts almost exclusively in the terminal cells of the filament. In this work, we investigate the function of these genes and provide a theoretical model that explains how they interact within the broader genetic network, reproducing their knock-out phenotypes in several genetic backgrounds, including a nearly uniform concentration of HetR along the filament for the patA mutant. Our results suggest a role of hetF and patA in a post-transcriptional modification of HetR which is essential for its regulatory function. In addition, the existence of molecular leakage out of the filament in its boundary cells is enough to explain the preferential appearance of terminal heterocysts, without any need for a distinct regulatory pathway.

Comparative effects of nitrogen, phosphorus and potassium on Radopholus similis infection in East African highland banana plants as influenced by rhizosphere biota

Root parasitism by Radopholus similis may vary under different nutritional conditions and soil substrates. Such variations in nematode infection may affect deductions from evaluations of pest control measures. Three parallel factorial experiments (nutrients × soil sterility × nematode) were conducted to investigate the effects of N-P-K and soil biota on R. similis infection and banana plant growth. Chlorophyll content was lower in plants receiving N-deficient solution or water only, especially in non-sterile soil. Plants were larger in non-sterile than in sterile soil; but smaller when receiving N-deficient solution or water only. Compared to complete nutrient solution (CNS), R. similis density was higher and root death lower in plants receiving N-deficient solution or water, but not different when P-deficient and K-deficient solutions were applied. Compared to CNS, root necrosis was higher in P-deficient and lower in K-deficient plants, but not different in plants treated with N-deficient solution or water only. Root damage and R. similis density were lower in non-sterile than in sterile soil. Plants inoculated with R. similis were larger and appeared greener with tendency to have higher leaf concentrations of N, P, K, Ca, Mg and Zn, than those without the nematode inoculant when treated with N-deficient solution. Deficiency in N, P or K was associated with reduced root colonization by native Fusarium, but was enhanced by R. similis under N-deficiency. Optical density of root extracts was lower in R. similis-inoculated banana plants when grown in sterile soil, but was higher in the nematode-inoculated banana plants in non-sterile soil. It is concluded that, the multiplication of R. similis in banana roots and its associated root damage and plant growth suppressive activities can vary due to plant N-P-K nutrition and the presence of rhizosphere biota, with the nematode pest even being potentially beneficial to banana plants, especially those growing under nitrogen-limited conditions.

Non-Proteinogenic Amino Acid β-N-Methylamino-L-Alanine (BMAA): Bioactivity and Ecological Significance.

Research interest in a non-protein amino acid β-N-methylamino-L-alanine (BMAA) arose due to the discovery of a connection between exposure to BMAA and the occurrence of neurodegenerative diseases. Previous reviews on this topic either considered BMAA as a risk factor for neurodegenerative diseases or focused on the problems of detecting BMAA in various environmental samples. Our review is devoted to a wide range of fundamental biological problems related to BMAA, including the molecular mechanisms of biological activity of BMAA and the complex relationships between producers of BMAA and the environment in various natural ecosystems. At the beginning, we briefly recall the most important facts about the producers of BMAA (cyanobacteria, microalgae, and bacteria), the pathways of BMAA biosynthesis, and reliable methods of identification of BMAA. The main distinctive feature of our review is a detailed examination of the molecular mechanisms underlying the toxicity of BMAA to living cells. A brand new aspect, not previously discussed in any reviews, is the effect of BMAA on cyanobacterial cells. These recent studies, conducted using transcriptomics and proteomics, revealed potent regulatory effects of BMAA on the basic metabolism and cell development of these ancient photoautotrophic prokaryotes. Exogenous BMAA strongly influences cell differentiation and primary metabolic processes in cyanobacteria, such as nitrogen fixation, photosynthesis, carbon fixation, and various biosynthetic processes involving 2-oxoglutarate and glutamate. Cyanobacteria were found to be more sensitive to exogenous BMAA under nitrogen-limited growth conditions. We suggest a hypothesis that this toxic diaminoacid can be used by phytoplankton organisms as a possible allelopathic tool for controlling the population of cyanobacterial cells during a period of intense competition for nitrogen and other resources in various ecosystems.

Superior Haplotypes for Early Root Vigor Traits in Rice Under Dry Direct Seeded Low Nitrogen Condition Through Genome Wide Association Mapping.

Water and land resources have been aggressively exploited in the recent decades to meet the growing demands for food. The changing climate has prompted rice scientists and farmers of the tropics and subtropics to adopt the direct seeded rice (DSR) system. DSR system of rice cultivation significantly reduces freshwater consumption and labor requirements, while increasing system productivity, resource use efficiency, and reducing greenhouse gas emissions. Early root vigor is an essential trait required in an ideal DSR system of rice cultivation to ensure a good crop stand, adequate uptake of water, nutrients and compete with weeds. The aus subpopulation which is adapted for DSR was evaluated to understand the biology of early root growth under limited nitrogen conditions over two seasons under two-time points (14 and 28 days). The correlation study identified a positive association between shoot dry weight and root dry weight. The genome-wide association study was conducted on root traits of 14 and 28 days with 2 million single-nucleotide polymorphisms (SNPs) using an efficient mixed model. QTLs over a significant threshold of p < 0.0001 and a 10% false discovery rate were selected to identify genes involved in root growth related to root architecture and nutrient acquisition from 97 QTLs. Candidate genes under these QTLs were explored. On chromosome 4, around 30 Mbp are two important peptide transporters (PTR5 and PTR6) involved in mobilizing nitrogen in the root during the early vegetative stage. In addition, several P transporters and expansin genes with superior haplotypes are discussed. A novel QTL from 21.12 to 21.46 Mb on chromosome 7 with two linkage disequilibrium (LD) blocks governing root length at 14 days were identified. The QTLs/candidate genes with superior haplotype for early root vigor reported here could be explored further to develop genotypes for DSR conditions.

Enhanced biohydrogen and lipid coproduction in Chlorella protothecoides under nitrogen-limiting conditions in a closed system

This study was developed to explore the feasibility of achieving enhanced hydrogen (H2) and lipid coproduction mediated by H2-producing microalgae Chlorella protothecoides. C. protothecoides was able to simultaneously produce both H2 and lipids, and this H2 and lipid coproduction was found to be inducible under conditions of nitrogen limitation in a closed system. Specifically, optimal H2 (151.1 mL L−1) and lipid (49.6% DW) coproduction was achieved under 5% N in a closed system. Relative to nitrogen-replete conditions, such nitrogen limitation was able to induce the accumulation of NADPH and reactive oxygen species, thereby directly promoting lipid production. Moreover, in a closed system, these limited nitrogen levels established conditions of anaerobiosis, activating hydrogenase and thereby generating H2 while suppressing respiratory electron transport, ultimately further augmenting lipid production. Together, these results highlight a novel approach to simultaneously producing H2 and lipids and to enhancing such coproduction activity.

Conversion of Short and Medium Chain Fatty Acids into Novel Polyhydroxyalkanoates Copolymers by Aeromonas sp. AC_01.

Polyhydroxyalkanoates (PHAs) production by Aeromonas sp. AC_01 was investigated using synthetic and waste derived short and medium chain fatty acids (SMCFAs). The obtained results revealed that the analyzed bacterial strain was able to grow and synthesize PHAs using SMCFAs. The highest PHA productivity was observed in the cultivation supplemented with a mixture of acetic acid and butyric acid (3.89 mg/L·h). Furthermore, SMCFAs-rich stream, derived from acidogenic mixed culture fermentation of acid whey, was found to be less beneficial for PHA productivity than its synthetic mixture, however the PHA production was favored by the nitrogen-limited condition. Importantly, Aeromonas sp. AC_01 was capable of synthesizing novel scl-mcl copolymers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 3-hydroxytridecanoate (3HtriD) and/or 3-hydroxytetradecaonate (3HTD) with high 3HB and 3HV fractions. They were identified with alterable monomers composition depending on the culture conditions used. Moreover, in-depth thermal analyses proved that they are highly resistant to thermal degradation regardless of their monomeric composition. The obtained results confirm that Aeromonas sp. AC_01 is a promising candidate for the biotechnological production of PHAs from SMCFAs with thermal properties that can be tuned together with their chemical composition by the corresponding adjustment of the cultivation process.