Preferred Nitrogen Source Research Articles

Nutrient content in tissues of Groenlandia densa, Myriophyllum spicatum and Zannichellia palustris: an attempt to understand the intercompartmental relationships in a small stream in the Middle Atlas Mountains of Morocco

Research has long focused on the relative importance of leaves and roots as sources of nutrient supply for macrophytes, as well as the function each stream compartment plays in their growth and development. This study aims to expand the debate on aquatic ecology and to better understand the connection between compartments in aquatic systems by highlighting the relationship observed in rivers between nutrients in macrophytes tissues, water, and sediments. We measured the concentrations of P-PO4, N-NO3 and N-NH4 in three different compartments of the Amengous stream in the Middle Atlas of Morocco. Myriophyllum spicatum (L.), Groenlandia densa (L.) Fourr. and Zannichellia palustris (L.) were selected as plant species. Our results show that even if the species coexist in the same habitat, they respond differently to nutrient richness. G. densa has a higher nutrient accumulation capacity than M. spicatum and Z. palustris and prefers the water compartment as a nutrient source. Although M. spicatum can accumulate phosphate compounds from water and sediment, ammonium is not its preferred nitrogen source. Z. palustris shows a tendency to accumulate nitrogen compounds through the roots, while it prefers the assimilation of phosphorus compounds through the leaves rather than the roots.

The Nitrogen Preference of Cactus Pear (Opuntia ficus-indica): A Sand Culture Snapshot.

Cactus pear (Opuntia-ficus indica (L.) Mill.) is an important agricultural crassulacean acid metabolism (CAM) species used as a source of food, forage, fodder, and secondary products and as a biofuel feedstock. However, the preferred source of nitrogen for this species, whether it be nitrate (NO3-), ammonium (NH4+), or a combination of both, is not well understood. To investigate the nitrate and ammonium preference of cactus pear, we grew cladodes in sand culture with deionized water as a control or with a cross-factorial set of nutrient solutions of 0.0, 2.5, 5.0, and 10.0 mmol of nitrate and/or ammonium for one month. We then assessed a set of physiological parameters including cladode growth, relative water content, chlorophyll, tissue acidity, soluble sugars, starch, nitrate, ammonium, glyoxylic acid, nitrate reductase activity, and nitrogen and carbon content. We found significant differences in all measured parameters except for cladode length, relative water content, and carbon content. Cladodes provided with only deionized water produced no new cladodes and showed decreased soluble sugar content, increased starch content, and increased tissue acidity. We also determined the relative steady-state transcript abundance of genes that encode enzymes involved in N metabolism and CAM. Compared with control cladodes, nutrient-supplied cladodes generally showed increased or variable steady-state mRNA expression of selected CAM-related genes and nitrogen-metabolism-related genes. Our results suggest that O. ficus-indica prefers fertilizers containing either equal concentrations nitrate and ammonium or more nitrate than ammonium.

Biological Characteristics, Pathogenicity, and Sensitivity to Fungicides of Four Species of Lasiodiplodia on Avocado Fruits

This study focuses on four species of Lasiodiplodia (L. euphorbiaceicola, L. mahajangana, L. theobromae, and L. pseudotheobromae), which are associated with avocado stem end rot (SER) in Hainan, China. The factors affecting the growth of Lasiodiplodia, pathogenicity to avocado and other tropical fruits, and sensitivity to 12 fungicides, were tested. All Lasiodiplodia spp. isolates were grown between 10 °C and 40 °C, with optimal growth temperature ranging from 28 to 30 °C; the lethal temperature ranged from 51 to 53 °C for 10 min. Optimal growth pH ranged from 5 to 6. The most suitable medium was PDA, the preferred carbon sources were D–fructose and soluble starch, and the preferred nitrogen sources were yeast and beef extract. All Lasiodiplodia spp. isolates were highly pathogenic to avocado fruit. In addition, their pathogenicity to six tropical fruits (banana guava, mango, papaya, pitaya, and soursop) was evaluated, and the results reveal that all four species of Lasiodiplodia are able to infect these fruits to various degrees of severity. The pathogenicity of both L. theobromae and L. pseudotheobromae was the highest among all the species tested. All Lasiodiplodia spp. isolates were highly susceptible to the fungicides fludioxonil, carbendazim, thiophanate–methyl, tetramycin, iprodione, tebuconazole, prochloraz, and imazalil, which are good candidates for controlling avocado SER. The results of the present study provide important information on the biological characteristics of these four species of Lasiodiplodia and provide a basis for the management of SER in avocado.

Optimisation of coumaric acid production from aromatic amino acids in Kluyveromyces marxianus

Yeasts are attractive hosts for the production of heterologous products due to their genetic tractability and relative ease of growth. While the baker’s yeast Saccharomyces cerevisiae is a powerful workhorse of the biotechnology industry, the species has metabolic limitations and it is critical that we develop alternative platforms that will facilitate the development of bioprocesses that rely on sustainable feedstocks. In this study, we used synthetic biology tools to construct coumaric acid–producing strains of Kluyveromyces marxianus, a yeast whose physiological traits render it attractive for biotechnology applications. Coumaric acid is a building block in the synthesis of many different families of aromatics and is a key precursor for the synthesis of complect phenylpropanoid molecules, including many flavours and aromas. The starting point for this work was a K. marxianus chassis strain that has increased flux towards the synthesis of tyrosine and phenylalanine, the aromatic amino acids that can serve as starting points for coumaric acid synthesis. Following principles of synthetic biology, a modular approach was taken to identify the best solution to different metabolic possibilities and these were then combined in different ways. For the first step, it was established that the route from phenylalanine was superior to that from tyrosine and the combined overexpression of PlPAL, AtC4H and AtCPR1 delivered the highest yield of coumaric acid. Next, it was established that while Pdc5 and Aro10 both had phenylpyruvate decarboxylase activity, inactivation of ARO10 was sufficient to prevent flux loss in the pathway. Since phenylalanine is the starting point, efforts were made to improve efficiency of its production. It was found that glutamate was a preferred nitrogen source for coumaric acid production, and this knowledge was used to engineer a strain that overexpressed S. cerevisiae GDH1 and delivered higher yields of coumaric acid. Ultimately, this strategy led to the development of strains that has yields of up to 48 mg coumaric acid /g glucose. Strains were evaluated in bioreactors to investigate the effects of different process parameters. These analyses indicated that engineered strains face some redox balance challenges and further work will be required overcome these to develop strains that can perform well under industrial conditions.

Preliminary study on Cyclocodon lancifolius leaf blight and screening of Bacillus subtilis as a biocontrol agent.

This study aimed to identify the pathogen responsible for leaf blight in Cyclocodon lancifolius, investigate its biological characteristics, and identify effective synthetic fungicides. Additionally, this study examined changes in physiological and biochemical indices of leaves following pathogen infection and screened biocontrol bacteria that inhibit the pathogen growth, providing a scientific basis for preventing and managing leaf blight in C. lancifolius. Pathogens were isolated from the interface of healthy and infected leaf tissues and identified through morphological and molecular biological methods. Amplification and sequencing of three genomic DNA regions-internal transcribed spacer region, translation elongation factor 1-α, and glyceraldehyde-3-phosphate dehydrogenase of ribosomal DNA-were performed, followed by the construction of a phylogenetic tree. The biological characteristics of pathogens under various temperature and pH conditions and different nitrogen and carbon sources were analyzed using the mycelial growth rate method. The antifungal effects of 13 chemical agents were evaluated using the poisoned medium method and mycelial growth rate method. Changes in physiological and biochemical indicators post-infection were also assessed. An antagonistic experiment was conducted to screen for biocontrol bacteria. A total of 29 potential pathogenic strains were isolated from infected leaf tissues, with Koch's Postulates confirming Stemphylium lycopersici as a key pathogen causing the disease. Growth analysis of S. lycopersici revealed optimal growth at 20°C and pH 6, with lactose or maltose serving as the most suitable carbon source and histidine as the preferred nitrogen source. Among the 13 synthetic fungicides tested, strain DHY4 exhibited the greatest sensitivity to 400 g/L flusilazole. Significant differences (p < 0.05) were observed in superoxide dismutase, phenylalanine ammonia-lyase, peroxidase, polyphenol oxidase, catalase, and malondialdehyde levels between treated and control groups 3 days post-inoculation. The biocontrol strain DYHS2, identified as a strain of Bacillus subtilis, demonstrated an inhibition rate of 51.80% against S. lycopersici in dual-culture experiments and showed a relative inhibition rate of 78.82% in detached leaf assays. These findings provide valuable insights into the newly identified causal agent of leaf blight in C. lancifolius and its biological characteristics, underscoring the potential of B. subtilis DYHS2 and synthetic fungicides such as flusilazole as effective disease management strategies.

An Azospirillum brasilense chemoreceptor that mediates nitrate chemotaxis has conditional roles in the colonization of plant roots.

Motile plant-associated bacteria use chemotaxis and dedicated chemoreceptors to navigate gradients in their surroundings and to colonize host plant surfaces. Here, we characterize a chemoreceptor that we named Tlp2 in the soil alphaproteobacterium Azospirillum brasilense. We show that the Tlp2 ligand-binding domain is related to the 4-helix bundle family and is conserved in chemoreceptors found in the genomes of many soil- and sediment-dwelling alphaproteobacteria. The promoter of tlp2 is regulated in an NtrC- and RpoN-dependent manner and is most upregulated under conditions of nitrogen fixation or in the presence of nitrate. Using fluorescently tagged Tlp2 (Tlp2-YFP), we show that this chemoreceptor is present in low abundance in chemotaxis-signaling clusters and is prone to degradation. We also obtained evidence that the presence of ammonium rapidly disrupts Tlp2-YFP localization. Behavioral experiments using a strain lacking Tlp2 and variants of Tlp2 lacking conserved arginine residues suggest that Tlp2 mediates chemotaxis in gradients of nitrate and nitrite, with the R159 residue being essential for Tlp2 function. We also provide evidence that Tlp2 is essential for root surface colonization of some plants (teff, red clover, and cowpea) but not others (wheat, sorghum, alfalfa, and pea). These results highlight the selective role of nitrate sensing and chemotaxis in plant root surface colonization and illustrate the relative contribution of chemoreceptors to chemotaxis and root surface colonization.IMPORTANCEBacterial chemotaxis mediates host-microbe associations, including the association of beneficial bacteria with the roots of host plants. Dedicated chemoreceptors specify sensory preferences during chemotaxis. Here, we show that a chemoreceptor mediating chemotaxis to nitrate is important in the beneficial soil bacterium colonization of some but not all plant hosts tested. Nitrate is the preferred nitrogen source for plant nutrition, and plants sense and tightly control nitrate transport, resulting in varying nitrate uptake rates depending on the plant and its physiological state. Nitrate is thus a limiting nutrient in the rhizosphere. Chemotaxis and dedicated chemoreceptors for nitrate likely provide motile bacteria with a competitive advantage to access this nutrient in the rhizosphere.

Association between organic nitrogen substrates and the optical purity of d-lactic acid during the fermentation by Sporolactobacillus terrae SBT-1

The development of biotechnological lactic acid production has attracted attention to the potential production of an optically pure isomer of lactic acid, although the relationship between fermentation and the biosynthesis of highly optically pure d-lactic acid remains poorly understood. Sporolactobacillus terrae SBT-1 is an excellent d-lactic acid producer that depends on cultivation conditions. Herein, three enzymes responsible for synthesizing optically pure d-lactic acid, including d-lactate dehydrogenase (D-LDH; encoded by ldhDs), l-lactate dehydrogenase (L-LDH; encoded by ldhLs), and lactate racemase (Lar; encoded by larA), were quantified under different organic nitrogen sources and concentration to study the relationship between fermentation conditions and synthesis pathway of optically pure lactic acid. Different organic nitrogen sources and concentrations significantly affected the quantity and quality of d-lactic acid produced by strain SBT-1 as well as the synthetic optically pure lactic acid pathway. Yeast extract is a preferred organic nitrogen source for achieving high catalytic efficiency of d-lactate dehydrogenase and increasing the transcription level of ldhA2, indicating that this enzyme plays a major role in d-lactic acid formation in S. terrae SBT-1. Furthermore, lactate racemization activity could be regulated by the presence of d-lactic acid. The results of this study suggest that specific nutrient requirements are necessary to achieve a stable and highly productive fermentation process for the d-lactic acid of an individual strain.

Prokaryotic community assembly patterns and nitrogen metabolic potential in oxygen minimum zone of Yangtze Estuary water column

It is predicted that oxygen minimum zones (OMZs) in the ocean will expand as a consequence of global warming and environmental pollution. This will affect the overall microbial ecology and microbial nitrogen cycle. As one of the world's largest alluvial estuaries, the Yangtze Estuary has exhibited a seasonal OMZ since the 1980s. In this study, we have uncovered the microbial composition, the patterns of community assembly and the potential for microbial nitrogen cycling within the water column of the Yangtze Estuary, with a particular focus on OMZ. Based on the 16 S rRNA gene sequencing, a specific spatial variation in the composition of prokaryotic communities was observed for each water layer, with the Proteobacteria (46.1%), Bacteroidetes (20.3%), and Cyanobacteria (10.3%) dominant. Stochastic and deterministic processes together shaped the community assembly in the water column. Further, pH was the most important environmental factor influencing prokaryotic composition in the surface water, followed by silicate, PO43−, and distance offshore (p < 0.05). Water depth, NH4+, and PO43− were the main factors in the bottom water (p < 0.05). At last, species analysis and marker gene annotation revealed candidate nitrogen cycling performers, and a rich array of nitrogen cycling potential in the bottom water of the Yangtze Estuary. The determined physiochemical parameters and potential for nitrogen respiration suggested that organic nitrogen and NO3− (or NO2−) are the preferred nitrogen sources for microorganisms in the Yangtze Estuary OMZ. These findings are expected to advance research on the ecological responses of estuarine oxygen minimum zones (OMZs) to future global climate perturbations.

Biological ammonium transporters: evolution and diversification.

Although ammonium is the preferred nitrogen source for microbes and plants, in animal cells it is a toxic product of nitrogen metabolism that needs to be excreted. Thus, ammonium movement across biological membranes, whether for uptake or excretion, is a fundamental and ubiquitous biological process catalysed by the superfamily of the Amt/Mep/Rh transporters. A remarkable feature of the Amt/Mep/Rh family is that they are ubiquitous and, despite sharing low amino acid sequence identity, are highly structurally conserved. Despite sharing a common structure, these proteins have become involved in a diverse range of physiological process spanning all domains of life, with reports describing their involvement in diverse biological processes being published regularly. In this context, we exhaustively present their range of biological roles across the domains of life and after explore current hypotheses concerning their evolution to help to understand how and why the conserved structure fulfils diverse physiological functions.

Taxonomy, biological characterization and fungicide sensitivity assays of Hypomyces cornea sp. nov. causing cobweb disease on Auricularia cornea

Auricularia cornea is an important edible mushroom crop in China but the occurrence of cobweb disease has cause significance economic loss in its production. The rate of disease occurrence is 16.65% all over the country. In the present study, a new pathogen Hypomyces cornea sp. nov. was found to cause the cobweb disease. In July 2021, three strains of fungal pathogen were isolated from infected fruiting bodies and identified as H. cornea based on morphological studies and molecular phylogenetic analysis of internal transcribed spacer (ITS) of nuclear ribosomal DNA, mitochondrial large subunit (LSU) of rRNA and the partial translation elongation factor 1-alpha genes. The representative isolates of the pathogenic Hypomyces species used to perform pathogenicity test with spore suspension that caused similar symptoms as those observed in the cultivated field, and same pathogens could be re-isolated, which fulfill Koch's postulates. The typical biological characterization was examined of the serious pathogen to determine its favorable growth conditions, including suitable temperature, pH, carbon, nitrogen sources and light conditions. The findings revealed an optimum temperature of 25 °C, pH of 6, and soluble starch and peptone as the preferred carbon and nitrogen sources, respectively. The hyphal growth inhibition method was used for primary in vitro screening test of seven common fungicides, and the most suitable fungicide is Prochloraz manganese chloride complex, the EC50 values of cobweb pathogen and mushrooms were 0.085 μg/mL and 2.452 μg/mL, respectively. The results of our research provide an evidence-based basis for the effective prevention and treatment of A. cornea cobweb disease.

Selecting for a high lipid accumulating microalgae culture by dual growth limitation in a continuous bioreactor

A dual-growth-limited continuous operated bioreactor (chemostat) was used to enhance lipid accumulation in an enrichment culture of microalgae. The light intensity and nitrogen concentration where both limiting factors resulting in high lipid accumulation in the mixed culture. Both conditions of light and nitrogen excess and deficiency were tested. Strategies to selectively enrich for a phototrophic lipid-storing community, based on the use of different nitrogen sources (ammonium vs. nitrate) and vitamin B supplementation in the growth medium, were evaluated. The dual limitation of both nitrogen and light enhanced the accumulation of storage compounds. Ammoniacal nitrogen was the preferred nitrogen source. Vitamin B supplementation led to a doubling of the lipid productivity. The availability of vitamins played a key role in selecting an efficient lipid-storing community, primarily consisting of Trebouxiophyceae (with an 82 % relative abundance among eukaryotic microorganisms). The obtained lipid volumetric productivity (387 mg L−1 d−1) was among the highest reported in literature for microalgae bioreactors. Lipid production by the microalgae enrichment surpassed the efficiencies reported for continuous microalgae pure cultures, highlighting the benefits of mixed-culture photo-biotechnologies for fuels and food ingredients in the circular economy.

Novel Phospholipase C with High Catalytic Activity from a Bacillus stearothermophilus Strain: An Ideal Choice for the Oil Degumming Process

A novel thermoactive phosphatidylcholine-specific phospholipase C (PC-PLCBs) was identified from Bacillus stearothermophilus isolated from a soil sample from an olive oil mill. Enhanced PLCBs production was observed after 10 h of incubation at 55 °C in a culture medium containing 1 mM of Zn2+ with an 8% inoculum size and 6 g/L glucose and 4/L yeast extract as the preferred carbon energy and nitrogen sources, respectively. PLCBs was purified to homogeneity by heat treatment, ammonium sulfate fractionation, and anion exchange chromatography, resulting in a purification factor of 17.6 with 39% recovery. Interestingly, this enzyme showed a high specific activity of 8450 U/mg at pH 8–9 and 60 °C, using phosphatidylcholine PC as the substrate, in the presence of 9 mM sodium deoxycholate and 0.4 mM Zn2+. Remarkable stability at acidic and alkali pH and up to 65 °C was also observed. PLCBs displayed a substrate specificity order of phosphatidylcholine &gt; phosphatidylethanolamine &gt; phosphatidylserine &gt; sphingomyelin &gt; phosphatidylinositol &gt; cardiolipin and was classified as a PC-PLC. In contrast to phospholipases C previously isolated from Bacillus strains, this PLCBs substrate specificity was correlated to its hemolytic and anti-bacterial potential against erythrocytes and Gram-positive bacterial membranes, which are rich in glycerophospholipids and cardiolipin. An evaluation of PLCBs soybean degumming process efficiency showed that the purified enzyme reduced the phosphorus content to 35 mg/kg and increased the amount of diacylglycerols released, indicating its ability to hydrolyze phospholipids in the crude soybean oil. Collectively, PLCBs could be considered as a potential catalyst for efficient industrial oil degumming, advancing the edible oil industry by reducing the oil gum volume through transforming non-hydratable phospholipids into their hydratable forms, as well as through generating diacylglycerols, which are miscible with triacylglycerols, thereby reducing losses.

Nitrate alleviates ammonium toxicity in Brassica napus by coordinating rhizosphere and cell pH and ammonium assimilation.

In natural and agricultural situations, ammonium ( ) is a preferred nitrogen (N) source for plants, but excessive amounts can be hazardous to them, known as toxicity. Nitrate ( ) has long been recognized to reduce toxicity. However, little is known about Brassica napus, a major oil crop that is sensitive to high . Here, we found that can mitigate toxicity by balancing rhizosphere and intracellular pH and accelerating ammonium assimilation in B. napus. increased the uptake of and under high circumstances by triggering the expression of and transporters, while and H+ efflux from the cytoplasm to the apoplast was enhanced by promoting the expression of efflux transporters and genes encoding plasma membrane H+ -ATPase. In addition, increased pH in the cytosol, vacuole, and rhizosphere, and down-regulated genes induced by acid stress. Root glutamine synthetase (GS) activity was elevated by under high conditions to enhance the assimilation of into amino acids, thereby reducing accumulation and translocation to shoot in rapeseed. In addition, root GS activity was highly dependent on the environmental pH. might induce metabolites involved in amino acid biosynthesis and malate metabolism in the tricarboxylic acid cycle, and inhibit phenylpropanoid metabolism to mitigate toxicity. Collectively, our results indicate that balances both rhizosphere and intracellular pH via effective transmembrane cycling, accelerates assimilation, and up-regulates malate metabolism to mitigate toxicity in oilseed rape.

Microalgae biofilm photobioreactor and its combined process for long-term stable treatment of high-saline wastewater achieved high pollutant removal efficiency

High-saline wastewater treatment processes have a high energy demand, while microalgae-driven wastewater biotechnology is both economical and environmentally friendly, and the use of microalgae to treat high-saline wastewater can effectively reduce energy consumption. However, it is unclear whether the performance of microalgae reactor can be stable for a long time. In this study, an open continuous-flow biofilm photobioreactor using Dunaliella salina was innovatively constructed, and operated in combination with a membrane bioreactor (MBR) for high-saline wastewater treatment. The purpose of this study was to investigate the long-term performance of MBR, MBPBR alone and their combined operation for the removal of organic matter, phosphorus and nitrogen, explore the pathway and mechanism of nitrogen and phosphorus removal by MBPBR, and evaluate the feasibility of MBPBR-MBR integrated system for the treatment of saline wastewater. The MBR effectively removed most of the organic matter and converted ammonia nitrogen into nitrate nitrogen, which is a preferred nitrogen source for the growth of Dunaliella salina, thereby providing favorable water quality for Dunaliella salina in the subsequent MBPBR. The MBPBR, with a hydraulic retention time (HRT) of 72 h, achieved a NO3--N removal load of 74.9 g N/(m3∙d) and a removal efficiency of approximately 60 %, and the PO43--P removal load of 8.33 g P/(m3∙d) and removal efficiency of over 80 %. The MBR-MBPBR system demonstrated long-term stability, achieving removal efficiencies of 84.3 %, 81.6 %, and 91.0 % for COD, TN and PO43--P, respectively. Within the MBPBR, the growth of algae and their assimilation contributed 44.9 % and 38.7 % of the nitrogen and phosphorus removal, respectively. The abundance of Dunaliella salina in the MBPBR remained at approximately 90 % for over 40 days of operation, providing an opportunity for Dunaliella salina recovery. These findings provide valuable insights into the utilization of microalgae for the treatment of high-salinity wastewater, while also supporting the practical implementation of microalgae-based treatment methods for such wastewater.

Yueomyces silvicola sp. nov., a novel ascomycetous yeast species unable to utilize ammonium, glutamate, and glutamine as sole nitrogen sources.

Five yeast strains isolated from tree bark and rotten wood collected in central and southwestern China, together with four Brazilian strains (three from soil and rotting wood collected in an Amazonian rainforest biome and one from Bromeliad collected in Alagoas state) and one Costa Rican strain isolated from a flower beetle, represent a new species closely related with Yueomyces sinensis in Saccharomycetaceae, as revealed by the 26S ribosomal RNA gene D1/D2 domain and the internal transcribed spacer region sequence analysis. The name Yueomyces silvicola sp. nov. is proposed for this new species with the holotype China General Microbiological Culture Collection Center 2.6469 (= Japan Collection of Microorganisms 34885). The new species exhibits a whole-genome average nucleotide identity value of 77.8% with Y. sinensis. The two Yueomyces species shared unique physiological characteristics of being unable to utilize ammonium and the majority of the amino acids, including glutamate and glutamine, as sole nitrogen sources. Among the 20 amino acids tested, only leucine and tyrosine can be utilized by the Yueomyces species. Genome sequence comparison showed that GAT1, which encodes a GATA family protein participating in transcriptional activation of nitrogen-catabolic genes in Saccharomyces cerevisiae, is absent in the Yueomyces species. However, the failure of the Yueomyces species to utilize ammonium, glutamate, and glutamine, which are generally preferred nitrogen sources for microorganisms, implies that more complicated alterations in the central nitrogen metabolism pathway might occur in the genus Yueomyces.

Regulation of nutrient utilization in filamentous fungi.

Organisms must accurately sense and respond to nutrients to survive. In filamentous fungi, accurate nutrient sensing is important in the establishment of fungal colonies and in continued, rapid growth for the exploitation of environmental resources. To ensure efficient nutrient utilization, fungi have evolved a combination of activating and repressing genetic networks to tightly regulate metabolic pathways and distinguish between preferred nutrients, which require minimal energy and resources to utilize, and nonpreferred nutrients, which have more energy-intensive catabolic requirements. Genes necessary for the utilization of nonpreferred carbon sources are activated by transcription factors that respond to the presence of the specific nutrient and repressed by transcription factors that respond to the presence of preferred carbohydrates. Utilization of nonpreferred nitrogen sources generally requires two transcription factors. Pathway-specific transcription factors respond to the presence of a specific nonpreferred nitrogen source, while another transcription factor activates genes in the absence of preferred nitrogen sources. In this review, we discuss the roles of transcription factors and upstream regulatory genes that respond to preferred and nonpreferred carbon and nitrogen sources and their roles in regulating carbon and nitrogen catabolism. KEY POINTS: • Interplay of activating and repressing transcriptional networks regulates catabolism. • Nutrient-specific activating transcriptional pathways provide metabolic specificity. • Repressing regulatory systems differentiate nutrients in mixed nutrient environments.

Effect of pH, Carbon and Nitrogen Sources on Antibiotic Production by Actinomycetes Isolates from River Tana and Lake Elementaita, Kenya

The escalating concern over antibiotic resistance and its profound impact on public health have underscored the urgent need to explore alternative reservoirs of antimicrobial agents. In this regard, Actinomycetes have emerged as a compelling area of investigation due to their remarkable capacity to produce bioactive compounds. Therefore, this study sought to investigate the influence of pH and various carbon and nitrogen sources on the antibacterial activity of Actinomycetes isolates collected from Lake Elementaita and River Tana. By examining the effects of these factors, we aimed to gain insights into the optimization of growth conditions and nutrient availability to enhance the production of bioactive compounds with potent antibacterial properties. The Actinomycetes isolates used in this study were from Lake Elementaita and River Tana, known for their diverse ecological characteristics and potential as sources of bioactive compounds. The isolates were subjected to morphological, biochemical, and molecular techniques to ensure accurate identification. To assess the antibacterial activity of the Actinomycetes isolates, they were tested against E. coli using the agar well diffusion method. The independent variables examined in this study were pH levels (4, 7, and 9) as well as different carbon sources (fructose and sucrose) and nitrogen sources (urea and sodium nitrate). The diameter of the inhibition zones served as the dependent variable. The data collected on the effects of pH and nutrients on the inhibition zones of Actinomycetes isolates were subjected to statistical analysis. One-way ANOVA was performed to assess significant differences in antibacterial activity among the isolates under different carbon and nitrogen preference. Mean values were compared using the LSD test at a significance level (α) of 0.05. Furthermore, the Kruskal-Wallis test was utilized to analyze the pH preferences of the Actinomycetes isolates at a significance level (α) of 0.05. The results showed that pH significantly influenced the bioactivity of the Actinomycetes isolates, with pH 7 exhibiting the highest inhibition zones against E. coli. The isolates displayed varied antibacterial activities depending on the carbon and nitrogen sources provided. Sucrose was the most preferred carbon source, followed by fructose, while urea was the preferred nitrogen source, followed by sodium nitrate. The study concluded that pH and nutrient availability play crucial roles in determining the antibacterial activity of Actinomycetes isolates. Other than contributing to our in-depth understanding of the factors influencing the antimicrobial potential of Actinomycetes, the results of this study highlight the importance of optimizing growth conditions and nutrient availability to enhance the production of bioactive compounds with potent antibacterial properties. Further investigations and exploration of Actinomycetes from diverse environments are recommended to discover new bioactive molecules for combating antibiotic resistance.

Effects of Various Nitrogen Sources on the Growth and Biochemical Composition of &lt;I&gt;Chlorella&lt;/I&gt; sp.

Highlight Research Each species of microalga has a preferable nitrogen source for their optimal growth. The nitrogen sources in the grown media affected the growth rate and biochemical composition of Chlorella FNUB01. (NH2)2CO (urea) was found to be the best alternative nitrogen source for Chlorella FNUB01. For producing 1 g of Chlorella FNUB01, the use of urea reduced the cost of medium by 72.6%. Abstract Chlorella sp. is a potential microalgae species to be produced commercially for feed, growth accelerator, and immuno-modulator in fish and shrimp culture. This study aimed to evaluate the various nitrogen sources on the growth, biomass production, and biochemical composition of Chlorella sp. FNUB01. The nitrogen sources used in this study were urea (NH2)2CO, potassium nitrate (KNO3), and ammonium nitrate (NH4NO3). Sodium nitrate (NaNO3) was used as a control as it is a part of the commercial medium BG-11. Generally, the sources of nitrogen in the media affected the growth and chemical composition of Chlorella sp. FNUB01. This green microalga grew better in the urea-containing medium which accounted for 1.5 times the concentration of that cultured in BG-11 (40 x106 cells. mL-1). Meanwhile, this microalgae species experienced the lowest growth when cultured in NH4NO3-containing medium. The biomass productivity of Chlorella sp. FNUB01 cultured in urea (0.93 g.L-1) was comparable to those grown with NaNO3 as the N source. A similar pattern was recorded for protein, chlorophyll, and carotenoid content as these biochemical contents were affected by N availability in the medium. Urea was an alternative low-cost N source for the culture of Chlorella sp. FNUB01. Replacement of NaNO3 with urea could reduce the cost of the medium by 72.6%.

Controlling the nitrogen environment for optimal Rhodomonas salina production

AbstractThe microalga Rhodomonas salina is a widely used species for rearing live feed organisms in the aquaculture feed market. A species-specific medium is an essential step towards enhancing productivity and decreasing production costs for microalgae cultivation. However, relevant aspects of medium composition such as nitrogen source and elemental ratio have not yet been characterized for this alga. This study aimed to optimize the following three aspects of culture media: 1) optimal ratio between nitrogen and phosphorus (N:P ratio); 2) preferred source of nitrogen; and 3) tolerance of R. salina towards free ammonia. To investigate this, we conducted a series of controlled laboratory experiments in shake flasks. Our experiments revealed a 45% increase in growth rate when an N:P ratio of 15:1 was used compared to the standard ratio of 25:1. Ammonium and nitrate were equally well accepted as a nitrogen source, however, a mix of ammonium and nitrate resulted in significant growth reduction. Free ammonia did not affect growth of the alga at the tested concentrations of up to 5 mg ammonia–nitrogen L−1. We conclude that for optimal R. salina cultivation, an N:P ratio of 15:1 is strongly preferred, as it leads to a significant increase in growth rate. Further, media with a single source of nitrogen promote faster growth over media with mixed sources, and ammonium may safely be used as a nitrogen source, since R. salina tolerates certain levels of free ammonia. Overall, this work provides insights into the optimal cultivation conditions for R. salina, allowing for more efficient and reliable production of this relevant species.

Adaptive Laboratory Evolution of Bacillus subtilis 168 for Efficient Production of Surfactin Using NH4Cl as a Nitrogen Source

Bacillus subtilis strain 168 is commonly used as a host to produce recombinant proteins and as a chassis for bio-based chemicals production. However, its preferred nitrogen source is organic nitrogen, which greatly increases production costs. In this study, adaptive laboratory evolution (ALE) was used to improve B. subtilis 168 growth using NH4Cl as the sole nitrogen source. The cell density (OD600) of a mutant strain LJ-3 was 208.7% higher than that of the original strain. We also optimized the metal ions in the medium and this resulted in a further increase in growth rate by 151.3%. Reintroduction of the sfp+ gene into strain LJ-3 led to the LJ-31 clone, which restored LJ-3’s ability to synthesize surfactin. The fermentation system was optimized (C/N, aeration, pH) in a 5 L bioreactor. Dry cell weight of 7.4 g/L and surfactin concentration of 4.1 g/L were achieved using the optimized mineral salt medium after 22 h of batch fermentation with a YP/S value of 0.082 g/g and a YP/X of 0.55 g/g. HPLC analysis identified the surfactin isoforms produced by strain LJ-31 in the synthetic medium as C13-surfactin 13.3%, C14-surfactin 44.02%, and C15-surfactin 32.79%. Hence, the variant LJ-3 isolated by ALE is a promising engineering chassis for efficient and cost-effective production of a variety of metabolites.