Presence Of Lincomycin Research Articles

A novel electrochemiluminescence aptasensor for ultrasensitive lincomycin detection using Ti3C2–TiO2–Ru probe

The presence of lincomycin (LIN) residues in food poses significant health risks to humans, necessitating a highly sensitive and specific detection method for LIN. This study used a self-enhancing Ti3C2–TiO2–Ru probe to develop an electrochemiluminescence aptasensor to detect LIN. The Ti3C2–TiO2 was synthesized in situ by harnessing the unique reducibility of Ti3C2, with TiO2 serving as a co-reaction accelerator. Moreover, Ti3C2–TiO2 served as a carrier with an excellent negative charge, allowing for the immobilization of a substantial amount of Ru(bpy)32+ through electrostatic adsorption, thus forming a self-enhancing Ti3C2–TiO2–Ru probe. Furthermore, the specific affinity of LIN toward the aptamer and the chelating interaction between the Ti and phosphate groups ensured highly precise LIN detection. This sensor demonstrated excellent performance, with a detection limit of 0.025 ng mL−1 and a detection range of 1.0 × 10−1–1.0 × 104 ng mL−1. The LIN detection in milk showed commendable recovery rates, ranging from 94.4% to 106.0%.

Psb28 protein is indispensable for stable accumulation of PSII core complexes in Arabidopsis.

Enhancing the efficiency of photosynthesis represents a promising strategy to improve crop yields, with keeping the steady state of PSII being key to determining the photosynthetic performance. However, the mechanisms whereby the stability of PSII is maintained in oxygenic organisms remain to be explored. Here, we report that the Psb28 protein functions in regulating the homeostasis of PSII under different light conditions in Arabidopsis thaliana. The psb28 mutant is much smaller than the wild-type plants under normal growth light, which is due to its significantly reduced PSII activity. Similar defects were seen under low light and became more pronounced under photoinhibitory light. Notably, the amounts of PSII core complexes and core subunits are specifically decreased in psb28, whereas the abundance of other representative components of photosynthetic complexes remains largely unaltered. Although the PSII activity of psb28 was severely reduced when subjected to high light, its recovery from photoinactivation was not affected. By contrast, the degradation of PSII core protein subunits is dramatically accelerated in the presence of lincomycin. These results indicate that psb28 is defective in the photoprotection of PSII, which is consistent with the observation that the overall NPQ is much lower in psb28 compared to the wild type. Moreover, the Psb28 protein is associated with PSII core complexes and interacts mainly with the CP47 subunit of PSII core. Taken together, these findings reveal an important role for Psb28 in the protection and stabilization of PSII core in response to changes in light environments.

Phenomenological interpretations of the mechanism for the concentration-dependent positive effect of antibiotic lincomycin on Streptomyces coelicolor A3(2).

The antibiotic lincomycin binds to the 23S ribosomal RNA peptidyl transferase loop region to inhibit protein synthesis. However, lincomycin can also stimulate the growth and secondary metabolism of actinomycetes in a concentration-dependent manner. In Streptomyces coelicolor A3(2), lincomycin stimulates the production of the blue-pigmented antibiotic actinorhodin at concentrations below the minimum inhibitory concentration. To better understand the molecular mechanism underlying these concentration-dependent positive effects, this study investigated how the target molecule, the ribosome, undergoes dynamic changes in the presence of lincomycin and explored the ribosome-related factors involved. Lincomycin, at a concentration that stimulates actinorhodin production of S. coelicolor A3(2), could restore temporarily arrested ribosome function by utilizing ribosome-related proteins and translation factors, presumably under the control of the transcription factor WblC protein that confers intrinsic resistance to multiple translation-inhibiting antibiotics, to eventually produce stable and active ribosomes even during the late growth phase. This qualitatively and quantitatively positive ribosome alteration can be advantageous for producing actinorhodin biosynthetic enzymes. A series of gene expression and biochemical analyses revealed that lincomycin at the concentration that induces ribosomal stabilization in S. coelicolor A3(2) could influence the localization of the 20S proteasome-related proteins, resulting in reduced proteasome activity. These findings suggest that the functional analysis of 20S proteasome represents a potential pivotal challenge for understanding the molecular mechanism of ribosome stabilization induced by lincomycin. Therefore, as lincomycin can dynamically alter its target molecule, the ribosome, we discuss the future issues and prospects for an increased understanding of the concentration-dependent properties of antibiotics. IMPORTANCE Antibiotics were originally defined as chemical compounds produced by a microbe that inhibits the growth of other microbes. However, an unexplained effect of this is that a low concentration of antibiotics, such as those below the minimum inhibitory concentration, can positively affect microbial growth and metabolism. The secondary metabolic activation of streptomycetes in the presence of the translation-inhibiting antibiotic lincomycin illustrates the concentration-dependent positive effect of the antibiotic. The significance of this study is that the phenomenological interpretation of the molecular mechanism of the concentration-dependent positive effect of lincomycin in Streptomyces coelicolor A3(2) has provided novel insight into the possible role of antibiotics in making their target molecules stable and active with the assistance of various related factors that benefit their function. Further exploration of this idea would lead to an essential understanding of antibiotics, including why actinomycetes make them and their role in nature.

Exposed anthocyanic leaves of Prunus cerasifera are special shade leaves with high resistance to blue light but low resistance to red light against photoinhibition of photosynthesis.

The photoprotective role of foliar anthocyanins has long been ambiguous: exacerbating, being indifferent to or ameliorating the photoinhibition of photosynthesis. The photoinhibitory light spectrum and failure to separate photo-resistance from repair, as well as the different methods used to quantify the photo-susceptibility of the photosystems, could lead to such a discrepancy. We selected two congeneric deciduous shrubs, Prunus cerasifera with anthocyanic leaves and Prunus triloba with green leaves, grown under identical growth conditions in an open field. The photo-susceptibilities of photosystem II (PSII) and photosystem I (PSI) to red light and blue light, in the presence of lincomycin (to block the repair), of exposed leaves were quantified by a non-intrusive P700+ signal from PSI. Leaf absorption, pigments, gas exchange and Chl a fluorescence were also measured. The content of anthocyanins in red leaves (P. cerasifera) was >13 times greater than that in green leaves (P. triloba). With no difference in maximum quantum efficiency of PSII photochemistry (Fv/Fm) and apparent CO2 quantum yield (AQY) in red light, anthocyanic leaves (P. cerasifera) showed some shade-acclimated suites, including lower Chl a/b ratio, lower photosynthesis rate, lower stomatal conductance and lower PSII/PSI ratio (on an arbitrary scale), compared with green leaves (P. triloba). In the absence of repair of PSII, anthocyanic leaves (P. cerasifera) showed a rate coefficient of PSII photoinactivation (ki) that was 1.8 times higher than that of green leaves (P. triloba) under red light, but significantly lower (-18 %) under blue light. PSI of both types of leaves was not photoinactivated under blue or red light. In the absence of repair, anthocyanic leaves exhibited an exacerbation of PSII photoinactivation under red light and a mitigation under blue light, which can partially reconcile the existing controversy in terms of the photoprotection by anthocyanins. Overall, the results demonstrate that appropriate methodology applied to test the photoprotection hypothesis of anthocyanins is critical.

Red pigments in autumn leaves of Norway maple do not offer significant photoprotection but coincide with stress symptoms.

The reasons behind autumn colors, a striking manifestation of anthocyanin synthesis in plants, are poorly understood. Usually, not all leaves of an anthocyanic plant turn red or only a part of the leaf blade turns red. In the present study, we compared green, red and yellow sections of senescing Norway maple leaves, asking if red pigments offer photoprotection, and if so, whether the protection benefits the senescing tree. Green and senescing maple leaves were illuminated with strong white, green or red light in the absence or presence of lincomycin which blocks photosystem II (PSII) repair. Irrespective of the presence of anthocyanins, senescing leaves showed weaker capacity to repair PSII than green leaves. Furthermore, the rate of photoinhibition of PSII did not significantly differ between red and yellow sections of senescing maple leaves. We also followed pigment contents and photosynthetic reactions in individual leaves, from the end of summer until abscission of the leaf. In maple, red pigments accumulated only during late senescence, but light reactions stayed active until most of the chlorophyll had been degraded. PSII activity was found to be lower and non-photochemical quenching higher in red leaf sections, compared with yellow sections of senescing leaves. Red leaf sections were also thicker. We suggest that the primary function of anthocyanin synthesis is not to protect senescing leaves from excess light but to dispose of carbohydrates. This would relieve photosynthetic control, allowing the light reactions to produce energy for nutrient translocation at the last phase of autumn senescence when carbon skeletons are no longer needed.

The Protective Role of Non-Photochemical Quenching in PSII Photo-Susceptibility: A Case Study in the Field.

Non-photochemical quenching (NPQ) has been regarded as a safety valve to dissipate excess absorbed light energy not used for photochemistry. However, there exists no general consensus on the photoprotective role of NPQ. In the present study, we quantified the Photosystem II (PSII) photo-susceptibilities (mpi) in the presence of lincomycin, under red light given to five shade-acclimated tree species grown in the field. Photosynthetic energy partitioning theory was applied to investigate the relationships between mpi and each of the regulatory light-induced NPQ [Y(NPQ)], the quantum yield of the constitutive nonregulatory NPQ [Y(NO)] and the PSII photochemical yield in the light-adapted state [Y(PSII)] under different red irradiances. It was found that in the low to moderate irradiance range (50-800 μmol m-2 s-1) when the fraction of open reaction centers (qP) exceeded 0.4, mpi exhibited no association with Y(NPQ), Y(NO) and Y(PSII) across species. However, when qP < 0.4 (1,500 μmol m-2 s-1), there existed positive relationships between mpi and Y(NPQ) or Y(NO) but a negative relationship between mpi and Y(PSII). It is postulated that both Y(NPQ) and Y(NO) contain protective and damage components and that using only Y(NPQ) or Y(NO) metrics to identify the photo-susceptibility of a species is a risk. It seems that qP regulates the balance of the two components for each of Y(NPQ) and Y(NO). Under strong irradiance, when both protective Y(NPQ) and Y(NO) are saturated/depressed, the forward electron flow [i.e. Y(PSII)] acts as the last defense to resist photoinhibition.

Adsorptive removal of tetracycline and lincomycin from contaminated water using magnetized activated carbon

The release of antibiotics such as tetracycline (TC) and lincomycin (LM) used in livestock production into the environment and the development of antimicrobial resistance represents a great concern. To utilize the adsorption process for the removal of antibiotics and to facilitate separation of spent adsorbent from the treated water, a magnetized activated carbon (MAC) was developed using ultrasonic-assisted co-precipitation of iron oxide nanoparticles (γ-Fe2O3). The superparamagnetic properties of the adsorbent allowed a separation efficiency of 95 ± 3% from water, while magnetization changed the physiochemical properties of activated carbon including BET surface area, pore volume and PZC. The developed adsorbent was used for adsorption of TC from water at various concentrations and temperatures, and for simultaneous adsorption of TC and LM. The adsorption capacities of MAC toward TC either as an individual or in the presence of LM in water were slightly lower than that of AC, and the adsorption process had an endothermic nature. The adsorption capacities of MAC for TC was lower when LM was present in adsorption media (0.4 < qMixture,TC/qSingle,TC < 1.0), and vice versa. This indicates the competitive nature of TC and LM adsorption. The obtained data were fitted non-isothermally into different adsorption models (single and binary solute) and the associated coefficients were determined. Redlich–Peterson isotherm predicted the TC adsorption data in the range of 5–35 °C with accuracy and estimated the enthalpy change of adsorption as 54.3 kJ mol−1. Also, extended Langmuir model provided the most accurate prediction of the binary adsorption system.

Electrochemiluminescence aptasensor for lincomycin antigen detection by using a SnO2/chitosan/g-C3N4 nanocomposite

In this paper, hydrothermal method was used for the synthesis of SnO2 quantum dots (QDs). The prepared SnO2 QDs have a uniform particle size distribution and good electrochemiluminescence (ECL) property. Then the prepared SnO2 QDs was combined with graphene-like carbon nitride (g-C3N4) through chitosan to form SnO2/chitosan/g-C3N4 nanocomposite and used for detecting the lincomycin. The characteristics of SnO2/chitosan/g-C3N4 nanocomposite were presented by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), and the analytical results proving that the nanocomposite was prepared successfully. In this strategy, the SnO2/chitosan/g-C3N4 nanocomposite was acted as the substrate of aptasensor. Then, SH-DNA (aptamer DNA) was assembled on the surface of electrode, after 6-mercaptohexanol (MCH) blocked the unbound sites of the electrode surface, ferrocene-DNA (Fc-DNA) was incubated on the electrode surface through base complementation with aptamer DNA. In the absence of lincomycin, due to the low conductivity of Fc-DNA and the photo-excited energy electron transfer, the ECL signal was quenched. In the presence of lincomycin, the aptamer DNA was specific binding with lincomycin, and ferrocene-DNA (Fc-DNA) was detached from the surface of aptasensor electrode, generating an obviously enhancement of ECL signal. To ensure the accuracy of the data, each electrode runs continuously for 3600 s. Under optimal experimental conditions, the detection range of the aptasensor was 0.10 ng mL−1 - 0.10 mg mL−1, and the detection limit was 0.028 ng mL−1. In addition, the aptasensor has good stability and reproducibility, and also provided a hopeful device for all kinds of other protein target.

Chloramphenicol enhances Photosystem II photodamage in intact cells of the cyanobacterium Synechocystis PCC 6803

The effect of chloramphenicol, an often used protein synthesis inhibitor, in photosynthetic systems was studied on the rate of Photosystem II (PSII) photodamage in the cyanobacterium Synechocystis PCC 6803. Light-induced loss of PSII activity was compared in the presence of chloramphenicol and another protein synthesis inhibitor, lincomycin, by measuring the rate of oxygen evolution in Synechocystis 6803 cells. Our data show that the rate of PSII photodamage was significantly enhanced by chloramphenicol, at the usually applied 200 μg mL−1 concentration, relative to that obtained in the presence of lincomycin. Chloramphenicol-induced enhancement of photodamage has been observed earlier in isolated PSII membrane particles, and has been assigned to the damaging effect of chloramphenicol-mediated superoxide production (Rehman et al. 2016, Front Plant Sci 7:479). This effect points to the involvement of superoxide as damaging agent in the presence of chloramphenicol also in Synechocystis cells. The chloramphenicol-induced enhancement of photodamage was observed not only in wild-type Synechocystis 6803, which contains both Photosystem I (PSI) and PSII, but also in a PSI-less mutant which contains only PSII. Importantly, the rate of PSII photodamage was also enhanced by the absence of PSI when compared to that in the wild-type strain under all conditions studied here, i.e., without addition and in the presence of protein synthesis inhibitors. We conclude that chloramphenicol enhances photodamage mostly by its interaction with PSII, leading probably to superoxide production. The presence of PSI is also an important regulatory factor of PSII photodamage most likely via decreasing excitation pressure on PSII.

Lincomycin-Induced Secondary Metabolism in Streptomyces lividans 66 with a Mutation in the Gene Encoding the RNA Polymerase Beta Subunit.

Activating the genetic potential of Streptomyces strains to produce secondary metabolites can improve the production of useful biologically active compounds and facilitate the discovery of novel biologically active compounds. In this study, we found that Streptomyces lividans carrying the R440H mutation in rpoB, encoding the RNA polymerase beta subunit, grown in the presence of lincomycin at concentrations below the minimum inhibitory concentration (MIC) produced abundant amounts of actinorhodin and certain cryptic secondary metabolites despite culture conditions that restrict their production by the wild-type strain. The results indicate that lincomycin at concentrations below the MIC may strongly potentiate secondary metabolite production by Streptomyces strains carrying a specific rpoB mutation. In this study, we report an interesting phenomenon induced by combining the positive effects of certain rpoB mutations and concentration-dependent responses to lincomycin on secondary metabolism in S. lividans 66 and discuss the mechanisms and their applicability in exploring cryptic secondary metabolite production in streptomycetes.

Effects of low temperature on photoinhibition and singlet oxygen production in four natural accessions of Arabidopsis

Main conclusionsLow temperature decreases PSII damage in vivo, confirming earlier in vitro results. Susceptibility to photoinhibition differs among Arabidopsis accessions and moderately decreases after 2-week cold-treatment. Flavonols may alleviate photoinhibition.The rate of light-induced inactivation of photosystem II (PSII) at 22 and 4 °C was measured from natural accessions of Arabidopsis thaliana (Rschew, Tenela, Columbia-0, Coimbra) grown under optimal conditions (21 °C), and at 4 °C from plants shifted to 4 °C for 2 weeks. Measurements were done in the absence and presence of lincomycin (to block repair). PSII activity was assayed with the chlorophyll a fluorescence parameter Fv/Fm and with light-saturated rate of oxygen evolution using a quinone acceptor. When grown at 21 °C, Rschew was the most tolerant to photoinhibition and Coimbra the least. Damage to PSII, judged from fitting the decrease in oxygen evolution or Fv/Fm to a first-order equation, proceeded more slowly or equally at 4 than at 22 °C. The 2-week cold-treatment decreased photoinhibition at 4 °C consistently in Columbia-0 and Coimbra, whereas in Rschew and Tenela the results depended on the method used to assay photoinhibition. The rate of singlet oxygen production by isolated thylakoid membranes, measured with histidine, stayed the same or slightly decreased with decreasing temperature. On the other hand, measurements of singlet oxygen from leaves with Singlet Oxygen Sensor Green suggest that in vivo more singlet oxygen is produced at 4 °C. Under high light, the PSII electron acceptor QA was more reduced at 4 than at 22 °C. Singlet oxygen production, in vitro or in vivo, did not decrease due to the cold-treatment. Epidermal flavonols increased during the cold-treatment and, in Columbia-0 and Coimbra, the amount correlated with photoinhibition tolerance.

Elevated Levels of Specific Carotenoids During Acclimation to Strong Light Protect the Repair of Photosystem II in Synechocystis sp. PCC 6803.

The tolerance of photosynthesis to strong light increases in photosynthetic organisms during acclimation to strong light. We investigated the role of carotenoids in the protection of photosystem II (PSII) from photoinhibition after acclimation to strong light in the cyanobacterium Synechocystis sp. PCC 6803. In cells that had been grown under strong light at 1,000 μmol photons m−2 s−1 (SL), specific carotenoids, namely, zeaxanthin, echinenone, and myxoxanthophyll, accumulated at high levels, and the photoinhibition of PSII was less marked than in cells that had been grown under standard growth light at 70 μmol photons m−2 s−1 (GL). The rate of photodamage to PSII, as monitored in the presence of lincomycin, did not differ between cells grown under SL and GL, suggesting that the mitigation of photoinhibition after acclimation to SL might be attributable to the enhanced ability to repair PSII. When cells grown under GL were transferred to SL, the mitigation of photoinhibition of PSII occurred in two distinct stages: a first stage that lasted 4 h and the second stage that occurred after 8 h. During the second stage, the accumulation of specific carotenoids was detected, together with enhanced synthesis de novo of proteins that are required for the repair of PSII, such as the D1 protein, and suppression of the production of singlet oxygen (1O2). In the ΔcrtRΔcrtO mutant of Synechocystis, which lacks zeaxanthin, echinenone, and myxoxanthophyll, the mitigation of photoinhibition of PSII, the enhancement of protein synthesis, and the suppression of production of 1O2 were significantly impaired during the second stage of acclimation. Thus, elevated levels of the specific carotenoids during acclimation to strong light appeared to protect protein synthesis from 1O2, with the resultant mitigation of photoinhibition of PSII.

Red and blue light differentially impact retrograde signalling and photoprotection in rice.

Chloroplast-to-nucleus retrograde signalling (RS) is known to impact plant growth and development. In Arabidopsis, we and others have shown that RS affects seedling establishment by inhibiting deetiolation. In the presence of lincomycin, a chloroplast protein synthesis inhibitor that triggers RS, Arabidopsis light-grown seedlings display partial skotomorphogenesis with undeveloped plastids and closed cotyledons. By contrast, RS in monocotyledonous has been much less studied. Here, we show that emerging rice seedlings exposed to lincomycin do not accumulate chlorophyll but otherwise remain remarkably unaffected. However, by using high red (R) and blue (B) monochromatic lights in combination with lincomycin, we have uncovered a RS inhibition of length and a reduction in the B light-induced declination of the second leaf. Furthermore, we present data showing that seedlings grown in high B and R light display different non-photochemical quenching capacity. Our findings support the view that excess B and R light impact seedling photomorphogenesis differently to photoprotect and optimize the response to high-light stress. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.

Genome uncoupled (gun) phenotype is associated with root growth repression in Arabidopsis seedlings grown on lincomycin

«Genome uncoupled» (gun) is a molecular phenotype manifesting in a high expression of a number of nuclear photosynthesis associated genes in plants with arrested chloroplast biogenesis. The chloroplast biogenesis arrest could be achieved by growing of plants in presence of lincomycin (plastid translation inhibitor) or norflurazon (carotenoid biosynthesis inhibitor). We have found that Arabidopsis thaliana gun1-1gun5-1 double mutant seedlings with gun phenotype associated with both lincomycin and norflurazon demonstrate a repressed root growth when germinated on lincomycin but not norflurazon-containing media. Statistical analysis has demonstrated a high negative correlation between root length and gun phenotype evaluated on both LHCB1.2 and HEMA1 genes expression in three gun mutants of Arabidopsis: gun1-1, cch1-1 and the double mutant gun1-1gun5-1. Our results demonstrate that regulatory signals of plastid origin might participate in root development.

Cellulose defects in the Arabidopsis secondary cell wall promote early chloroplast development.

Lincomycin (LIN)-mediated inhibition of protein synthesis in chloroplasts prevents the greening of seedlings, represses the activity of photosynthesis-related genes in the nucleus, including LHCB1.2, and induces the phenylpropanoid pathway, resulting in the production of anthocyanins. In genomes uncoupled (gun) mutants, LHCB1.2 expression is maintained in the presence of LIN or other inhibitors of early chloroplast development. In a screen using concentrations of LIN lower than those employed to isolate gun mutants, we have identified happy on lincomycin (holi) mutants. Several holi mutants show an increased tolerance to LIN, exhibiting de-repressed LHCB1.2 expression and chlorophyll synthesis in seedlings. The mutations responsible were identified by whole-genome single-nucleotide polymorphism (SNP) mapping, and most were found to affect the phenylpropanoid pathway; however, LHCB1.2 expression does not appear to be directly regulated by phenylpropanoids, as indicated by the metabolic profiling of mutants. The most potent holi mutant is defective in a subunit of cellulose synthase encoded by IRREGULAR XYLEM3, and comparative analysis of this and other cell-wall mutants establishes a link between secondary cell-wall integrity and early chloroplast development, possibly involving altered ABA metabolism or sensing.

Transfer of a lincomycin-resistant plasmid between coagulase-negative staphylococci during soybean fermentation and mouse intestine passage.

Staphylococcus equorum is a benign bacterium and the predominant species in high-salt fermented food. Some strains of S. equorum contain antibiotic-resistance plasmids, such as pSELNU1 that contains a lincosamide nucleotidyltransferase (lnuA) gene and confers resistance to lincomycin. Previously, we showed that pSELNU1 is transferred to other bacteria under laboratory growth conditions. However, it is not known if the plasmid can be transferred to other bacteria during food fermentation (in situ) or during passage through animal intestines (in vivo). In this study, we examined the in situ and in vivo transfer of pSELNU1 using Staphylococcus saprophyticus as a recipient. During soybean fermentation, pSELNU1 was transferred to S. saprophyticus at a rate of 1.9×10-5-5.6×10-6 per recipient in the presence of lincomycin. However, during passage through murine intestines, the plasmid was transferred at similar rates (1.3×10-5 per recipient) in the absence of lincomycin, indicating that the plasmid transfer is much more efficient under in vivo conditions. Based on these results, we conclude that it is prudent to examine food fermentation starter candidates for the presence of mobile genetic elements containing antibiotic resistance genes and to select candidates lacking these genes.

Overexpression of Orange Carotenoid Protein Protects the Repair of PSII under Strong Light in Synechocystis sp. PCC 6803.

Orange carotenoid protein (OCP) plays a vital role in the thermal dissipation of excitation energy in the photosynthetic machinery of the cyanobacterium Synechocystis sp. PCC 6803. To clarify the role of OCP in the protection of PSII from strong light, we generated an OCP-overexpressing strain of Synechocystis and examined the effects of overexpression on the photoinhibition of PSII. In OCP-overexpressing cells, thermal dissipation of energy was enhanced and the extent of photoinhibition of PSII was reduced. However, photodamage to PSII, as monitored in the presence of lincomycin, was unaffected, suggesting that overexpressed OCP protects the repair of PSII. Furthermore, the synthesis de novo of proteins in thylakoid membranes, such as the D1 protein which is required for the repair of PSII, was enhanced in OCP-overexpressing cells under strong light, while the production of singlet oxygen was suppressed. Thus, the enhanced thermal dissipation of energy via overexpressed OCP might support the repair of PSII by protecting protein synthesis from oxidative damage by singlet oxygen under strong light, with the resultant mitigation of photoinhibition of PSII.

Oxidation of Translation Factor EF-Tu Inhibits the Repair of Photosystem II.

The repair of photosystem II (PSII) is particularly sensitive to oxidative stress and the inhibition of repair is associated with oxidative damage to the translational elongation system in the cyanobacterium Synechocystis sp. PCC 6803. However, the molecular mechanisms underlying this inhibition are unknown. We previously demonstrated in vitro that EF-Tu, a translation factor that delivers aminoacyl-tRNA to the ribosome, is inactivated by reactive oxygen species via oxidation of the Cys residue Cys-82. In this study, we examined the physiological role of the oxidation of EF-Tu in Synechocystis Under strong light, EF-Tu was rapidly oxidized to yield oxidized monomers in vivo. We generated a Synechocystis transformant that expressed mutated EF-Tu in which Cys-82 had been replaced with a Ser residue. Under strong light, the de novo synthesis of proteins that are required for PSII repair, such as D1, was enhanced in the transformant and photoinhibition of PSII was alleviated. However, photodamage to PSII, measured in the presence of lincomycin, was similar between the transformant and wild-type cells, suggesting that expression of mutated EF-Tu might enhance the repair of PSII. Alleviating photoinhibition through mutation of EF-Tu did not alter cell growth under strong light, perhaps due to the enhanced production of reactive oxygen species. These observations suggest that the oxidation of EF-Tu under strong light inhibits PSII repair, resulting in the stimulation of photoinhibition.

Functional relationship between mTERF4 and GUN1 in retrograde signaling.

Plastid-to-nucleus retrograde signaling plays an important role in regulating the expression of photosynthesis-associated nuclear genes (PhANGs) in accordance with physiological demands on chloroplast biogenesis and function. Despite its fundamental importance, little is known about the molecular nature of the plastid gene expression (PGE)-dependent type of retrograde signaling. PGE is a multifaceted process, and several factors, including pentatricopeptide repeat (PPR) proteins, are involved in its regulation. The PPR protein GUN1 plays a central role in PGE-dependent retrograde signaling. In this study, we isolated a mutant exhibiting up-regulation of CHLOROPHYLL A/B-BINDING PROTEIN (CAB) under normal growth conditions (named coe1 for CAB overexpression 1). The coe1 mutant has a single-base mutation in the gene for mitochondrial transcription termination factor 4 (mTERF4)/BSM/RUG2, which plays a role in regulating the processing of certain plastid transcripts. Defects in GUN1 or mTERF4 de-repressed the expression of specific plastid mRNAs in the presence of lincomycin (LIN). In wild-type plants, treatment with LIN or spectinomycin (SPE) inhibited processing of plastid transcripts. Comparative analysis revealed that in gun1 and coe1/mterf4, but not in wild-type, gun4, or gun5 plants, the processing of plastid transcripts and expression levels of Lhcb1 mRNA were affected in opposite ways when plants were grown in the presence of LIN or SPE. In addition, the coe1 mutation affected the intracellular accumulation and distribution of GUN1, as well as its plastid signaling activity. Taken together, these results suggest that GUN1 and COE1 cooperate in PGE and retrograde signaling.

Lincomycin at Subinhibitory Concentrations Potentiates Secondary Metabolite Production by Streptomyces spp.

Antibiotics have either bactericidal or bacteriostatic activity. However, they also induce considerable gene expression in bacteria when used at subinhibitory concentrations (below the MIC). We found that lincomycin, which inhibits protein synthesis by binding to the ribosomes of Gram-positive bacteria, was effective for inducing the expression of genes involved in secondary metabolism in Streptomyces strains when added to medium at subinhibitory concentrations. In Streptomyces coelicolor A3(2), lincomycin at 1/10 of its MIC markedly increased the expression of the pathway-specific regulatory gene actII-ORF4 in the blue-pigmented antibiotic actinorhodin (ACT) biosynthetic gene cluster, which resulted in ACT overproduction. Intriguingly, S. lividans 1326 grown in the presence of lincomycin at a subinhibitory concentration (1/12 or 1/3 of its MIC) produced abundant antibacterial compounds that were not detected in cells grown in lincomycin-free medium. Bioassay and mass spectrometry analysis revealed that some antibacterial compounds were novel congeners of calcium-dependent antibiotics. Our results indicate that lincomycin at subinhibitory concentrations potentiates the production of secondary metabolites in Streptomyces strains and suggest that activating these strains by utilizing the dose-response effects of lincomycin could be used to effectively induce the production of cryptic secondary metabolites. In addition to these findings, we also report that lincomycin used at concentrations for markedly increased ACT production resulted in alteration of the cytoplasmic protein (FoF1 ATP synthase α and β subunits, etc.) profile and increased intracellular ATP levels. A fundamental mechanism for these unique phenomena is also discussed.