Effects of potassium iodide on the growth and metabolite accumulation of two planktonic diatoms

In this study the effects of potassium iodide on the growth and metabolite accumulation of Nitzschia closterium (Ehr.) W. Smith and Phaedactylum tricornutum Bolin were investigated to assess its possible application to the mass culture of the two diatoms in open environment, extensive systems. The results indicated that supplementation of potassium iodide at a concentration of 1000 mg L⁻¹ resulted in a reduction of the induction phase in cultures of N. closterium and P. tricornutum and led to an increase in the accumulation of biomass and extracellular polymeric substances. Conversely, the addition of potassium iodide, at all concentrations tested, showed no obvious effect on the fatty acid profiles of the two diatoms, particularly in the content of eicosapentaenoic and decosahexaenoic acid. Potassium iodide was also found to inhibit the growth of Dunaliella salina, Cryptomonas sp. and Chlorella sp. at minimum inhibitory concentrations of 356.8, 475.9 and 696.2 mg L⁻¹, respectively. It also inhibited bacteria, including species isolated from the two diatom cultures, at a minimum concentration of 400 mg L⁻¹. These results suggest that potassium iodide is an effective agent for inhibiting the proliferation of certain flagellate and non-flagellate algae, and bacteria, thus forming a favorable environment for diatoms to proliferate and consequently improving accumulation of biomass and EPS. These properties of potassium iodide provide a possible solution for preventing contamination from flagellate and non-flagellate algae in mass culture of the two diatoms without causing significant changes in their fatty acid composition.     

Influence of exogenous hormones on the growth and secondary metabolite formation in transformed root cultures

Transformed organ cultures formed following transformation of plant tissues with Agrobacterium species owe their phenotypes to alterations in hormone metabolism. Exogenously supplied hormones have been used to probe the relationship between the growth and morphology of transformed root cultures of a number of species and their ability to accumulate secondary products. Auxins in the presence of low levels of kinetin induce the rapid disorganisation of transformed roots of Nicotiana rustica ultimately toform suspension cultures of transformed cells and this process is associated with a decrease in nicotine content of the cells. This is related to cells in the culture losing competence in alkaloid biosynthesis. In contrast, exogenously supplied GA₃ enhanced branching in two transformed root clones of the tropane-alkaloid producing species, Brugmansia candida and so enhanced their typical hairy root phenotype. This growth substance had the effect of reducing the overall alkaloid accumulation but in one case significantly altered the relative concentrations of different tropine esters.In transformed roots of Cucumis sativus, the phenotype of the roots is influenced by the expression of auxin synthesis genes on T_R-DNA resulting in roots with two distinct morphologies. The pattern of expression of the enzyme ascorbate oxidase in populations of control roots of different morphologies is described. The significance of these phenotypic variations on the utility of transformed root cultures for the study of secondary metabolic pathways will be discussed.Abbreviations AO ascorbate oxidase - DW dry weight - FW fresh weight - GA₃ gibberellic acid     

The synthetic auxin 3,5,6-TPA stimulates carbohydrate accumulation and growth in citrus fruit

The application of the synthetic auxin 3,5,6-TPA at the cell enlargementstage increased hexoses in developing fruit from foliated and fully defoliatedplants of Satsuma mandarin, cv. Okitsu (Citrusunshiu Marc.). Although the sucrose concentrations also increased,ingeneral the differences were not statistically significant. The plant growthregulator reduced fruit abscission in defoliated trees while it stimulatedfruitgrowth in the foliated ones. The carbohydrate accumulation induced by 3,5,6-TPAindicates that its stimulatory effect on fruit growth might operate viapromotion of sink strength. The results also suggest the occurrence of pathwaysfor induction of fruit abscission, linked to carbon availability, relativelyindependent of the stage of development.     

Enhancement of growth and secondary metabolite biosynthesis: Effect of elicitors derived from plants and insects

Plant-derived natural products have been and will continue to be valuable sources. Elicitors have been employed to modify cell metabolism in order to enhance the productivity of useful metabolites in plant cell/tissue cultures. In this study, several elicitors were used to improve the productivity of useful metabolites and to reduce culture time for archiving high concentration inP. ginseng hairy root cultures. The addition of chitosan, chitosan oligosaccharide and alginate oligosaccharide to the culture ofP. ginseng hairy roots caused growth to be inhibited with the increase in elicitor concentration. The usage of the chitosan elicitor andd-glucosamine caused a slight decrease in hairy root growth, whereas total ginseng saponin accumulated slightly with the increase in elicitor concentration. When gel beads were added to the culture medium at the initial period, hairy root growth was enhanced. The maximum growth was 1.35 times higher than that of the control at 1% (w/v). Total ginseng saponin content decreased due to the addition of alginate beads. This would result in consistent diffusion of lower levels of calcium ions during the culture period that promotes biomass growth.     

Comparative evaluation of modified bioreactors for enhancement of growth and secondary metabolite biosynthesis usingPanax ginseng hairy roots

Hairy root cultures have demonstrated great promise in terms of their biosynthetic capability toward the production of secondary metabolites, but continue to constitute a major challenge with regard to large-scale cultures. In order to assess the possibility of conducting mass production of biomass, and the extraction of useful metabolites fromPanax ginseng. P. ginseng hairy roots, transformed byRhizobium rhizogenes KCTC 2744, were used in bioreactors of different types and sizes. The most effective mass production of hairy roots was achieved in several differently sized air bubble bioreactors compared to all other bioreactor types. Hairy root growth was enhanced by aeration, and the production increased with increasing aeration rate in a 1 L bioreactor culture. It was determined that the hairy root growth rate could be substantially enhanced by increases in the aeration rate upto 0.5 wm, but at aeration rates above 0.5 wm, only slight promotions in growth rates were observed. In 20 L air bubble bioreactors, with a variety of inoculum sizes, the hairy roots exhibited the most robust growth rates with an inoculum size of 0.1% (w/v), within the range 0.1 to 0.7% (w/v). The specific growth rates of the hairy roots decreased with increases in the inoculum size.     

Regulation of secondary metabolite production in filamentous ascomycetes

Fungi are renowned for their ability to produce bioactive small molecules otherwise known as secondary metabolites. These molecules have attracted much attention due to both detrimental (e.g. toxins) and beneficial (e.g. pharmaceuticals) effects on human endeavors. Once the topic only of chemical and biochemical studies, secondary metabolism research has reached a sophisticated level in the realm of genetic regulation. This review covers the latest insights into the processes regulating secondary metabolite production in filamentous fungi.     

Contrasting mechanisms of secondary metabolite accumulation during leaf development in two tropical tree species with different leaf expansion strategies

Young leaves of most species experience remarkably higher herbivore attack rates than mature leaves. Considerable theoretical effort has focused on predicting optimal defense and tradeoffs in defense allocation during leaf expansion. Among others, allocation to secondary chemistry may be dependent on growth constraints. We studied flavanoid production during leaf development in two species of Inga (Fabaceae: Mimosoideae) with different expansion strategies: Inga goldmanii, a species with slowly expanding young leaves, and Inga umbellifera, a species with fast-expanding young leaves. In these two species, the most abundant and toxic class of defensive compounds is flavanoids (which include tannins). We measured their concentration by leaf dry weight, their total content per leaf, their HPLC chemical profile and their toxicity to a generalist herbivore at different expansion levels. Although in both species the flavanoid concentration decreased with increasing leaf expansion, that decrease was twice as pronounced for I. umbellifera as it was for I. goldmanii. I. umbellifera leaves produced flavanoids only during the first half of their development while I. goldmanii leaves continued production throughout. The changes in flavanoid HPLC profiles and toxicity were also more dramatic for I. umbellifera, which had different flavanoids in young than in mature leaves. Relative to I. umbellifera, I. goldmanii showed smaller changes in both flavanoid composition and toxicity in the transition from young to mature leaves. These results indicate that, even though young leaves suffer higher rates of attack and are predicted to have better chemical defenses than mature leaves, growth constraints may modulate defense allocation and thus, evolution of defense strategies.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Co-cultivation of plant cells as a technique for the elicitation of secondary metabolite production

Cells of Mikania glomerata, Cephaelis ipecacuanha and Maytenus aquifolia were co-cultured in a two-phase system using filter paper as a solid support. The species were co-cultured in all possible paired combinations. Interaction between Mikania and Maytenus cells resulted in increased biomass production of Maytenus cells, but the friedelin content was reduced. Co-cultivation of Cephaelis and Mikania cells enhanced coumarin content, but inhibited the growth of Mikania cells. However, yield of emetine as well as Cephaelis biomass accumulation were positively stimulated by the co-cultivation. Results indicate a possible occurrence of allelopathy in such a system. This revised version was published online in June 2006 with corrections to the Cover Date.     

干旱胁迫对蒙古黄芪生长及根部次生代谢物含量的影响

以山西道地药材黄芪一年生幼苗为试验材料,设置常规水分条件(CK)、轻度干旱胁迫(A1)、中度干旱胁迫(A2)、重度干旱胁迫(A3)4个不同处理,研究土壤干旱胁迫对黄芪生长及生理的影响。结果表明:黄芪茎叶快速生长集中在出苗后80—120d,以后生长减缓;当茎叶枯萎时,根中生物量短期快速积累。与常规水分条件相比,干旱胁迫处理显著降低了黄芪苗高及茎叶生物量,但对抗氧化能力、根系生长及次生代谢物积累产生了不同的影响。轻度干旱胁迫下SOD、POD、CAT 3种抗氧化酶活性升高,丙二醛(MDA)含量和细胞膜透性降低,同时根长与根生物量增加、多糖与皂苷两种次生代谢物积累增多,黄芪药材的质量得到显著提高(P0.05);胁迫上升到中度、重度时,SOD酶活性逐渐降低,重度胁迫下低于对照,而POD及CAT酶活性、MDA含量、细胞膜透性均随胁迫增强而升高,相反,根长、根生物量、多糖与皂苷含量降低,导致黄芪药材的质量显著降低(P0.01)。综上表明,干旱胁迫下,SOD酶表现较为敏感,可能在清除活性氧中起主要作用;轻度水分胁迫能有效启动黄芪体内抗氧化酶系统和次生代谢,它们相互协作共同对抗胁迫对细胞产生的伤害,通过降低地上部分的生长,将营养物质优先运往根部,促进根产量及药材质量的提高。这一结论,可在黄芪多糖和皂苷次生代谢物定向培育的水分管理中加以利用。     

The use of secondary metabolite profiling in chemotaxonomy of filamentous fungi

A secondary metabolite is a chemical compound produced by a limited number of fungal species in a genus, an order, or even phylum. A profile of secondary metabolites consists of all the different compounds a fungus can produce on a given substratum and includes toxins, antibiotics and other outward-directed compounds. Chemotaxonomy is traditionally restricted to comprise fatty acids, proteins, carbohydrates, or secondary metabolites, but has sometimes been defined so broadly that it also includes DNA sequences. It is not yet possible to use secondary metabolites in phylogeny, because of the inconsistent distribution throughout the fungal kingdom. However, this is the very quality that makes secondary metabolites so useful in classification and identification. Four groups of organisms are particularly good producers of secondary metabolites: plants, fungi, lichen fungi, and actinomycetes, whereas yeasts, protozoa, and animals are less efficient producers. Therefore, secondary metabolites have mostly been used in plant and fungal taxonomy, whereas chemotaxonomy has been neglected in bacteriology. Lichen chemotaxonomy has been based on few biosynthetic families (chemosyndromes), whereas filamentous fungi have been analysed for a wide array of terpenes, polyketides, non-ribosomal peptides, and combinations of these. Fungal chemotaxonomy based on secondary metabolites has been used successfully in large ascomycete genera such as Alternaria, Aspergillus, Fusarium, Hypoxylon, Penicillium, Stachybotrys, Xylaria and in few basidiomycete genera, but not in Zygomycota and Chytridiomycota.     

Mould growth on building materials under low water activities. Influence of humidity and temperature on fungal growth and secondary metabolism

The influence of relative humidity (RH) and temperature on growth and metabolism of eight microfungi on 21 different types of building material was investigated. The fungi were applied as a dry mixture to the materials, which were incubated at 5°C, 10°C, 20°C and 25°C at three humidity levels in the range 69–95% RH over 4–7 months. The lower limit for fungal growth on wood, wood composites and starch-containing materials was 78% RH at 20–25°C and increased to 90% RH at 5°C. An RH of 86% was necessary for growth on gypsum board. Ceramic materials supported growth at RH >90%, although 95% RH was needed to yield chemically detectable quantities of biomass. Almost exclusively only Penicillium, Aspergillus and Eurotium (contaminant) species grew on the materials. Production of secondary metabolites and mycotoxins decreased with humidity and the quantities of metabolites were insignificant compared with those produced at high RH (RH >95%), except in the case of Eurotium.     

链霉菌形态分化与次级代谢产物合成的研究进展

链霉菌是一类具有复杂的形态分化周期和强大的次级代谢能力的高GC含量的放线菌,能够利用其初级代谢产生的前体化合物和能量,合成多种结构复杂、功能多样的具有生物活性的次级代谢产物,在农业、食品、畜牧业、工业以及医药研究等领域都具有重要的价值。在链霉菌的形态分化后期常常伴随着次级代谢产物的生物合成,并且两者都受到复杂的网络调控;同时链霉菌的形态对次级代谢产物的产量和种类造成很大影响。对链霉菌生长周期的全面理解将加深对链霉菌形态分化与次级代谢产物合成关系的认识。本文将对链霉菌的形态分化过程、形态分化和抗生素合成两者共同的调控因子以及链霉菌形态与抗生素产量之间的关系进行综述,这将有助于理解抗生素的合成过程,也将会在缩短发酵周期、构建高产工程菌株、新型杀菌剂的研发以及新型抗生素的合成等方面给予我们启发。     

Aeration volume and photosynthetic photon flux affect cell growth and secondary metabolite contents in bioreactor cultures ofMorinda citrifolia

To improve their growth and secondary metabolite production, we culturedMorinda citrifolia leaf cells for 3 weeks in bioreactors with different aeration volumes (0.05, 0.1, 0.2, or 0.3 vvm; or 0.05/0.1/0.2/0.3 vvm, as increased at 5-d interval), and photosynthetic photon fluxes (PPF; 0, 15, 30, or 45 μ,moL m^-2 s^-1). Cell growth was greatest (15.6 g L^-1 dry weight) at 0.3 vvm whereas the accumulation of secondary metabolites (total anthraquinones, phenolics, and flavonoids) was maximized at 0.1 vvm. A PPF of 15 μmoLm^-2 s^-1 accelerated the accumulation of both cell biomass and metabolites. Dark-culturing suppressed cell growth, while a high PPF (45 μmoLm^-2 s^-1) inhibited metabolite biosynthesis. Further studies are required to understand the reason for differences in the effect of light on cell growth and secondary metabolite contents inM. citrifolia cell cultures.     

Involvement of secondary metabolites and extracellular lytic enzymes produced by Pseudomonas fluorescens in inhibition of Rhizoctonia solani, the rice sheath blight pathogen

Fourteen strains of Pseudomonas fluorescens isolated from rhizosphere soil of rice were tested for their antagonistic effect towards Rhizoctonia solani, the rice sheath blight fungus. Among them, PfMDU2 was the most effective in inhibiting mycelial growth of R. solani in vitro. Production of chitinase, beta-1,3-glucanase, siderophores, salicylic acid (SA) and hydrogen cyanide (HCN) by P. fluorescens strains was evaluated. The highest beta-1,3-glucanase activity, siderophore production, SA production and HCN production were recorded with PfMDU2. A significant relationship between the antagonistic potential of P. fluorescens against R. solani and its level of beta-1,3-glucanase, SA and HCN was observed.     

Restoration of secondary metabolism in birch seedlings relieved from PAL-inhibitor

Phenylalanine ammonia lyase (PAL) plays a key role in phenylpropanoid metabolism, catalyzing the deamination of phenylalanine (Phe) to form trans-cinnamic acid. Inhibitors of PAL have been used to study the physiological role of the different compounds derived from trans-cinnamic acid, and to test theories about a trade-off between growth and defence in plants. In a previous study with birch (Betula pubescens Ehrh.) seedlings, the PAL inhibitor 2-aminoindane-2-phosphonic acid monohydrate (AIP) caused an accumulation of Phe and a strong decrease in the quantity of simple phenolics, soluble condensed tannins and growth, whereas flavonol glycosides were generally not affected. The present study demonstrates restoration of secondary metabolism in the previously AIP treated birch seedlings. Our results indicate that Phe accumulated during PAL inhibition could be partly used to increase the content of the phenolic acids, flavan-3-ols and to some extent the soluble condensed tannins. Seedling growth also increased when the supply of PAL inhibitor ceased. We thereby show that the inhibition of PAL by AIP in vivo is reversible, at least for moderate AIP concentrations and the rate of restoration is dependent on the inhibitor concentration.     

Localization of glycosidases in the wall of living cells from cultured Convolvulus arvensis tissue

Nine glycosidase activities were detected in isolated cell walls of cultured Convolvulus arvensis L. cells. Seven were also found in the cytoplasmic fraction. Optimal pH values were all in the acid region. The in vivo localization of some of these glycosidases was studied by assaying whole cells. Suspended cells hydrolysed the externally supplied substrates for -galactosidase (EC 3.2.1.22), -galactosidase (EC 3.2.1.23), -glucosidase (EC 3.2.1.21), -mannosidase (EC 3.2.1.24) and -xylosidase (EC 3.2.1.37). Since intracellular enzymes were latent or showed little leakage, the cells were regarded to be relatively intact. In the cases investigated, the apparent glycosidase activity values of whole cells corresponded to those of isolated cell walls. The pH-activity profiles were similar. The K_m values were identical indicating equal accessibility to substrate. The enzymes could be partially removed from the cells by strong salt solutions. The data are consistent with an in vivo cell wall localization of a number of glycosidases.Abbreviation PNP p-nitrophenyl     

Impact on growth and aflatoxin B1 accumulation by Kluyveromyces isolates at different water activity conditions

This study showed the impact on germination, mycelial growth and aflatoxin B₁ accumulation when interacting Aspergillus aflatoxigenic strains with Kluyveromyces isolates and the effect of water activity on this relationship. Isolates Y₁₄ and Y₁₆ reduced the percentage of germination of all Aspergillus strains and decrease germ tube elongation rate at majority of water activity assayed. Similarly they produced an increase of germination lag phase and lag phase of growth beside decreased growth rate of all Aspergillus strains. At water activities 0.994, 0.982, 0.955 and 0.937, no aflatoxins were produced in paired cultures with isolates Y_25, Y₂₂, Y₁₆, and Y₁₄, and Kluyveromyces isolates Y₁₄ and Y₁₆ impact both growth and aflatoxin accumulation at wide range of water activity.