The effect of ß-ionone on bacterial cells: the use of specific lux-biosensors.

The diversity of the biological activity of volatile organic compounds (VOCs), including unsaturated ketone ß-ionone, promising pharmacological, biotechnological, and agricultural agent, has aroused considerable interest. However, the functional role and mechanisms of action of VOCs remain insufficiently studied. In this work, the response of bacterial cells to the action of ß-ionone was studied using specific bioluminescent lux-biosensors containing stress-sensitive promoters. We determined that in Escherichia coli cells, ß-ionone induces oxidative stress (PkatG and Pdps promoters) through a specific response mediated by the OxyR/OxyS regulon, but not SoxR/SoxS (PsoxS promoter). It has been shown that ß-ionone at high concentrations (50 µM and above) causes a weak induction of the expression from the PibpA promoter and slightly induces the PcolD promoter in the E. coli biosensors; the observed effect is enhanced in the ΔoxyR mutants. This indicates the presence of some damage to proteins and DNA. ß-Ionone was found to inhibit the bichaperone-dependent DnaKJE-ClpB refolding of heat-inactivated bacterial luciferase in E. coli wild-type and ΔibpB mutant strains. In the cells of the Gram-positive bacterium Bacillus subtilis 168 pNK-MrgA ß-ionone does not cause oxidative stress. Thus, in this work, the specificity of bacterial cell stress responses to the action of ß-ionone was shown.

'Ecological photobiology' session of the Russian Photobiology Society 9th Congress (Shepsi, September 12-19, 2021).

'Ecological photobiology' session of the Russian Photobiology Society 9th Congress was devoted to a wide range of problems related to the assessment of the environmental state by photobiological methods and included oral presentations and a poster session. A short survey of these presentations is given.

New Antimicrobial Peptide with Two CRAC Motifs: Activity against Escherichia coli and Bacillus subtilis.

Due to the emergence of multiple antibiotic resistance in many pathogens, the studies on new antimicrobial peptides (AMPs) have become a priority scientific direction in fundamental and applied biology. Diverse mechanisms underlie the antibacterial action of AMPs. Among them are the effects that AMPs cause on bacterial cell membranes. In this work, we studied the antibacterial activity of a peptide named P4 with the following sequence RTKLWEMLVELGNMDKAVKLWRKLKR that was constructed from two alpha-helical fragments of the influenza virus protein M1 and containing two cholesterol-recognizing amino-acid consensus (CRAC) motifs. Previously we have shown that 50 µM of peptide P4 is toxic to cultured mouse macrophages. In the present work, we have found that peptide P4 inhibits the growth of E. coli and B. subtilis strains at concentrations that are significantly lower than the cytotoxic concentration that was found for macrophages. The half-maximal inhibitory concentration (IC50) for B. subtilis and E. coli cells were 0.07 ± 0.01 µM and 1.9 ± 0.4 µM, respectively. Scramble peptide without CRAC motifs did not inhibit the growth of E. coli cells and was not cytotoxic for macrophages but had an inhibitory effect on the growth of B. subtilis cells (IC50 0.4 ± 0.2 µM). A possible involvement of CRAC motifs and membrane sterols in the mechanism of the antimicrobial action of the P4 peptide is discussed. We assume that in the case of the Gram-negative bacterium E. coli, the mechanism of the toxic action of peptide P4 is related to the interaction of CRAC motifs with sterols that are present in the bacterial membrane, whereas in the case of the Gram-positive bacterium B. subtilis, which lacks sterols, the toxic action of peptide P4 is based on membrane permeabilization through the interaction of the peptide cationic domain and anionic lipids of the bacterial membrane. Whatever the mechanism can be, we report antimicrobial activity of the peptide P4 against the representatives of Gram-positive (B. subtilis) and Gram-negative (E. coli) bacteria.

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

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

Effects of Volatile Organic Compounds on Biofilms and Swimming Motility of Agrobacterium tumefaciens.

Volatile organic compounds (VOCs) emitted by bacteria play an important role in the interaction between microorganisms and other organisms. They can inhibit the growth of phytopathogenic microorganisms, modulate plant growth, and serve as infochemicals. Here, we investigated the effects of ketones, alcohols, and terpenes on the colony biofilms of plant pathogenic Agrobacterium tumefaciens strains and swimming motility, which can play an important role in the formation of biofilms. It was shown that 2-octanone had the greatest inhibitory effect on biofilm formation, acting in a small amount (38.7 g/m3). Ketone 2-butanone and unsaturated ketone ß-ionone reduced the formation of biofilms at higher doses (145.2-580.6 and 387.1-1548.3 g/m3, respectively, up to 2.5-5 times). Isoamyl alcohol and 2-phenylethanol decreased the formation of biofilms at doses of 88.7 and 122.9 g/m3 by 1.7 and 5 times, respectively, with an increased effect at 177.4 and 245.9 g/m3, respectively. The agrobacteria cells in mature biofilms were more resistant to the action of ketones and alcohols. These VOCs also suppressed the swimming motility of agrobacteria; the radius of swimming zones decreased ~from 2 to 5 times. Terpenes (-)-limonene and (+)-α-pinene had no significant influence on the colony biofilms and swimming motility at the doses used. The results obtained represent new information about the effect of VOCs on biofilms and the motility of bacteria.

ß-N-Methylamino-L-Alanine (BMAA) Causes Severe Stress in Nostoc sp. PCC 7120 Cells under Diazotrophic Conditions: A Proteomic Study.

Non-proteinogenic neurotoxic amino acid ß-N-methylamino-L-alanine (BMAA) is synthesized by cyanobacteria, diatoms, and dinoflagellates, and is known to be a causative agent of human neurodegenerative diseases. Different phytoplankton organisms' ability to synthesize BMAA could indicate the importance of this molecule in the interactions between microalgae in nature. We were interested in the following: what kinds of mechanisms underline BMAA's action on cyanobacterial cells in different nitrogen supply conditions. Herein, we present a proteomic analysis of filamentous cyanobacteria Nostoc sp. PCC 7120 cells that underwent BMAA treatment in diazotrophic conditions. In diazotrophic growth conditions, to survive, cyanobacteria can use only biological nitrogen fixation to obtain nitrogen for life. Note that nitrogen fixation is an energy-consuming process. In total, 1567 different proteins of Nostoc sp. PCC 7120 were identified by using LC-MS/MS spectrometry. Among them, 123 proteins belonging to different functional categories were selected-due to their notable expression differences-for further functional analysis and discussion. The presented proteomic data evidences that BMAA treatment leads to very strong (up to 80%) downregulation of α (NifD) and ß (NifK) subunits of molybdenum-iron protein, which is known to be a part of nitrogenase. This enzyme is responsible for catalyzing nitrogen fixation. The genes nifD and nifK are under transcriptional control of a global nitrogen regulator NtcA. In this study, we have found that BMAA impacts in a total of 22 proteins that are under the control of NtcA. Moreover, BMAA downregulates 18 proteins that belong to photosystems I or II and light-harvesting complexes; BMAA treatment under diazotrophic conditions also downregulates five subunits of ATP synthase and enzyme NAD(P)H-quinone oxidoreductase. Therefore, we can conclude that the disbalance in energy and metabolite amounts leads to severe intracellular stress that induces the upregulation of stress-activated proteins, such as starvation-inducible DNA-binding protein, four SOS-response enzymes, and DNA repair enzymes, nine stress-response enzymes, and four proteases. The presented data provide new leads into the ecological impact of BMAA on microalgal communities that can be used in future investigations.

The Effect of Volatile Organic Compounds on Different Organisms: Agrobacteria, Plants and Insects.

Bacteria and fungi emit a huge variety of volatile organic compounds (VOCs) that can provide a valuable arsenal for practical use. However, the biological activities and functions of the VOCs are poorly understood. This work aimed to study the action of individual VOCs on the bacteria Agrobacterium tumefaciens, Arabidopsis thaliana plants, and fruit flies Drosophila melanogaster. VOCs used in the work included ketones, alcohols, and terpenes. The potent inhibitory effect on the growth of A. tumefaciens was shown for 2-octanone and isoamyl alcohol. Terpenes (-)-limonene and (+)-α-pinene practically did not act on bacteria, even at high doses (up to 400 µmol). 2-Butanone and 2-pentanone increased the biomass of A. thaliana at doses of 200-400 µmol by 1.5-2 times; 2-octanone had the same effect at 10 µmol and decreased plant biomass at higher doses. Isoamyl alcohol and 2-phenylethanol suppressed plant biomass several times at doses of 50-100 µmol. Plant seed germination was most strongly suppressed by isoamyl alcohol and 2-phenylethanol. The substantial killing effect (at low doses) on D. melanogaster was exerted by the terpenes and the ketones 2-octanone and 2-pentanone. The obtained data showed new information about the biological activities of VOCs in relation to organisms belonging to different kingdoms.

Phylogeographic, toxicological and ecological evidence for the global distribution of Raphidiopsis raciborskii and its northernmost presence in Lake Nero, Central Western Russia.

Raphidiopsis raciborskii is a freshwater, potentially toxigenic cyanobacterium, originally described as a tropical species that is spreading to northern regions over several decades. The ability of R. raciborskii to produce cyanotoxins - in particular the alkaloid cylindrospermopsin (CYN), which is toxic to humans and animals - is of serious concern. The first appearance of R. raciborskii in Russia was noted in Lake Nero in the summer of 2010. This is the northernmost (57°N) recorded case of the simultaneous presence of R. raciborskii and detection of CYN. In this study, the data from long-term monitoring of the R. raciborskii population, temperature and light conditions in Lake Nero were explored. CYN and cyr/aoa genes present in environmental samples were examined using HPLC/MS-MS and PCR analysis. A R. raciborskii strain (R104) was isolated and its morphology, toxigenicity and phylogeography were studied. It is supposed that the trigger factor for the strong development of R. raciborskii in Lake Nero in summer 2010 may have been the relatively high water temperature, reaching 29-30 °C. Strain R. raciborskii R104 has straight trichomes and can produce akinetes, making it morphologically similar to European strains. Phylogeographic analysis based on nifH gene and 16S-23S rRNA ITS1 sequences showed that the Russian strain R104 grouped together with R. raciborskii strains isolated from Portugal, France, Germany and Hungary. The Russian strain R104 does not contain cyrA and cyrB genes, meaning that it - like all European strains - cannot produce CYN. Thus, while recent invasion of R. raciborskii into Lake Nero has occurred, morphological, genetic, and toxicological data supported the spreading of this cyanobacterium from other European lakes. Detection of CYN and cyr/aoa genes in environmental samples indicated the cyanobacterium Aphanizomenon gracile as a likely producer of CYN in Lake Nero. The article also discusses data on the global biogeography of R. raciborskii. Genetic similarity between R. raciborskii strains isolated from very remote continents might be related to the ancient origin of the cyanobacterium inhabiting the united continents of Laurasia and Gondwana, rather than comparably recent transoceanic exchange between R. raciborskii populations.

Four New Genes of Cyanobacterium Synechococcus elongatus PCC 7942 Are Responsible for Sensitivity to 2-Nonanone.

Microbial volatile organic compounds (VOCs) are cell metabolites that affect many physiological functions of prokaryotic and eukaryotic organisms. Earlier we have demonstrated the inhibitory effects of soil bacteria volatiles, including ketones, on cyanobacteria. Cyanobacteria are very sensitive to ketone action. To investigate the possible molecular mechanisms of the ketone 2-nonanone influence on cyanobacterium Synechococcus elongatus PCC 7942, we applied a genetic approach. After Tn5-692 transposon mutagenesis, several 2-nonanone resistant mutants have been selected. Four different mutant strains were used for identification of the impaired genes (Synpcc7942_1362, Synpcc7942_0351, Synpcc7942_0732, Synpcc7942_0726) that encode correspondingly: 1) a murein-peptide ligase Mpl that is involved in the biogenesis of cyanobacteria cell wall; 2) a putative ABC transport system substrate-binding proteins MlaD, which participates in ABC transport system that maintains lipid asymmetry in the gram-negative outer membrane by aberrantly localized phospholipids transport from outer to inner membranes of bacterial cells; 3) a conserved hypothetical protein that is encoding by gene belonging to phage gene cluster in Synechococcus elongatus PCC 7942 genome; 4) a protein containing the VRR-NUC (virus-type replication-repair nuclease) domain present in restriction-modification enzymes involved in replication and DNA repair. The obtained results demonstrated that 2-nonanone may have different targets in Synechococcus elongatus PCC 7942 cells. Among them are proteins involved in the biogenesis and functioning of the cyanobacteria cell wall (Synpcc7942_1362, Synpcc7942_0351, Synpcc7942_0732) and protein participating in stress response at DNA restriction-modification level (Synpcc7942_0726). This paper is the first report about the genes that encode protein products, which can be affected by 2-nonanone.

Proteomic Insights into Starvation of Nitrogen-Replete Cells of Nostoc sp. PCC 7120 under ß-N-Methylamino-L-Alanine (BMAA) Treatment.

All cyanobacteria produce a neurotoxic non-protein amino acid ß-N-methylamino-L-alanine (BMAA). However, the biological function of BMAA in the regulation of cyanobacteria metabolism still remains undetermined. It is known that BMAA suppresses the formation of heterocysts in diazotrophic cyanobacteria under nitrogen starvation conditions, and BMAA induces the formation of heterocyst-like cells under nitrogen excess conditions, by causing the expression of heterocyst-specific genes that are usually "silent" under nitrogen-replete conditions, as if these bacteria receive a nitrogen deficiency intracellular molecular signal. In order to find out the molecular mechanisms underlying this unexpected BMAA effect, we studied the proteome of cyanobacterium Nostoc sp. PCC 7120 grown under BMAA treatment in nitrogen-replete medium. Experiments were performed in two experimental settings: (1) in control samples consisted of cells grown without the BMAA treatment and (2) the treated samples consisted of cells grown with addition of an aqueous solution of BMAA (20 µM). In total, 1567 different proteins of Nostoc sp. PCC 7120 were identified by LC-MS/MS spectrometry. Among them, 80 proteins belonging to different functional categories were chosen for further functional analysis and interpretation of obtained proteomic data. Here, we provide the evidence that a pleiotropic regulatory effect of BMAA on the proteome of cyanobacterium was largely different under conditions of nitrogen-excess compared to its effect under nitrogen starvation conditions (that was studied in our previous work). The most significant difference in proteome expression between the BMAA-treated and untreated samples under different growth conditions was detected in key regulatory protein PII (GlnB). BMAA downregulates protein PII in nitrogen-starved cells and upregulates this protein in nitrogen-replete conditions. PII protein is a key signal transduction protein and the change in its regulation leads to the change of many other regulatory proteins, including different transcriptional factors, enzymes and transporters. Complex changes in key metabolic and regulatory proteins (RbcL, RbcS, Rca, CmpA, GltS, NodM, thioredoxin 1, RpbD, ClpP, MinD, RecA, etc.), detected in this experimental study, could be a reason for the appearance of the "starvation" state in nitrogen-replete conditions in the presence of BMAA. In addition, 15 proteins identified in this study are encoded by genes, which are under the control of NtcA-a global transcriptional regulator-one of the main protein partners and transcriptional regulators of PII protein. Thereby, this proteomic study gives a possible explanation of cyanobacterium starvation under nitrogen-replete conditions and BMAA treatment. It allows to take a closer look at the regulation of cyanobacteria metabolism affected by this cyanotoxin.

The First Proteomics Study of Nostoc sp. PCC 7120 Exposed to Cyanotoxin BMAA under Nitrogen Starvation.

The oldest prokaryotic photoautotrophic organisms, cyanobacteria, produce many different metabolites. Among them is the water-soluble neurotoxic non-protein amino acid beta-N-methylamino-L-alanine (BMAA), whose biological functions in cyanobacterial metabolism are of fundamental scientific and practical interest. An early BMAA inhibitory effect on nitrogen fixation and heterocyst differentiation was shown in strains of diazotrophic cyanobacteria Nostoc sp. PCC 7120, Nostocpunctiforme PCC 73102 (ATCC 29133), and Nostoc sp. strain 8963 under conditions of nitrogen starvation. Herein, we present a comprehensive proteomic study of Nostoc (also called Anabaena) sp. PCC 7120 in the heterocyst formation stage affecting by BMAA treatment under nitrogen starvation conditions. BMAA disturbs proteins involved in nitrogen and carbon metabolic pathways, which are tightly co-regulated in cyanobacteria cells. The presented evidence shows that exogenous BMAA affects a key nitrogen regulatory protein, PII (GlnB), and some of its protein partners, as well as glutamyl-tRNA synthetase gltX and other proteins that are involved in protein synthesis, heterocyst differentiation, and nitrogen metabolism. By taking into account the important regulatory role of PII, it becomes clear that BMAA has a severe negative impact on the carbon and nitrogen metabolism of starving Nostoc sp. PCC 7120 cells. BMAA disturbs carbon fixation and the carbon dioxide concentrating mechanism, photosynthesis, and amino acid metabolism. Stress response proteins and DNA repair enzymes are upregulated in the presence of BMAA, clearly indicating severe intracellular stress. This is the first proteomic study of the effects of BMAA on diazotrophic starving cyanobacteria cells, allowing a deeper insight into the regulation of the intracellular metabolism of cyanobacteria by this non-protein amino acid.

Inhibition of cyanobacterial photosynthetic activity by natural ketones.

Microbial volatiles have a significant impact on the physiological functions of prokaryotic and eukaryotic organisms. Various ketones are present in volatile mixtures produced by plants, bacteria, and fungi. Our earlier results demonstrated the inhibitory effects of soil bacteria volatiles, including ketones, on cyanobacteria. In this work, we thoroughly examined the natural ketones, 2-nonanone and 2-undecanone to determine their influence on the photosynthetic activity in Synechococcus sp. PCC 7942. We observed for the first time that the ketones strongly inhibit electron transport through PSII in cyanobacteria cells in vivo. The addition of ketones decreases the quantum yield of primary PSII photoreactions and changes the PSII chlorophyll fluorescence induction curves. There are clear indications that the ketones inhibit electron transfer from QA to QB , electron transport at the donor side of PSII. The ketones can also modify the process of energy transfer from the antenna complex to the PSII reaction center and, by this means, increase both chlorophyll fluorescence quantum yield and the chlorophyll excited state lifetime. At the highest tested concentration (5 mM) 2-nonanone also induced chlorophyll release from Synechococcus cells that strongly indicates the possible role of the ketones as detergents.

Femtosecond Spectroscopy of Au Hot-Electron Injection into TiO2: Evidence for Au/TiO2 Plasmon Photocatalysis by Bactericidal Au Ions and Related Phenomena.

In the present work, we provide evidence for visible light irradiation of the Au/TiO2 nanoparticles' surface plasmon resonance band (SPR) leading to electron injection from the Au nanoparticles to the conduction band of TiO2. The Au/TiO2 SPR band is shown to greatly enhance the light absorption of TiO2 in the visible region. Evidence is presented for the light absorption by the Au/TiO2 plasmon bands leading to the dissolution of Au nanoparticles. This dissolution occurs concomitantly with the injection of the hot electrons generated by the Au plasmon into the conduction band of TiO2. The electron injection from the Au nanoparticles into TiO2 was followed by femtosecond spectroscopy. The formation of Au ions was further confirmed by the spectral shift of the transient absorption spectra of Au/TiO2. The spectral changes of the SPR band of Au/TiO2 nanoparticles induced by visible light were detected by spectrophotometer, and the morphological transformation of Au/TiO2 was revealed by electron microscopy techniques as well. Subsequently, the fate of the Au ions was sorted out during the growth and biofilm formation for some selected Gram-negative bacteria. This study compares the bactericidal mechanism of Au ions and Ag ions, which were found to be substantially different depending on the selected cell used as a probe.

SprI/SprR Quorum Sensing System of Serratia proteamaculans 94.

In this study, we investigated the quorum sensing (QS) regulatory system of the psychrotrophic strain Serratia proteamaculans 94 isolated from spoiled refrigerated meat. The strain produced several N-acyl-L-homoserine-lactone (AHL) QS signal molecules, with N-(3-oxo-hexanoyl)-L-homoserine lactone and N-(3-hydroxy-hexanoyl)-L-homoserine lactone as two main types. The sprI and sprR genes encoding an AHL synthase and a receptor regulatory protein, respectively, were cloned and sequenced. Analysis of their nucleotide sequence showed that these genes were transcribed convergently and that their reading frames partly overlapped by 23 bp in the terminal regions. The genes were highly similar to the luxI/luxR-type QS genes of other Gram-negative bacteria. An spr-box (analog of the lux-box) was identified upstream of the sprR gene and found to be overlapped with the sequence of -10 sequence site in the promoter region of this gene. Inactivation of the sprI gene led to the absence of AHL synthesis, chitinolytic activity, and swimming motility; decrease of extracellular proteolytic activity; affected the cellular fatty acid composition; and reduced suppression of the fungal plant pathogen mycelium growth by volatile compounds emitted by strain S. proteamaculans 94. The data obtained demonstrated the important role of the QS system in the regulation of cellular processes in S. proteamaculans 94.

The Cyanotoxin BMAA Induces Heterocyst Specific Gene Expression in Anabaena sp. PCC 7120 under Repressive Conditions.

Cyanobacteria synthesize neurotoxic ß-N-methylamino-l-alanine (BMAA). The roles of this non-protein amino acid in cyanobacterial cells are insufficiently studied. During diazotrophic growth, filamentous cyanobacteria form single differentiated cells, called heterocysts, which are separated by approximately 12⁻15 vegetative cells. When combined nitrogen is available, heterocyst formation is blocked and cyanobacterial filaments contain only vegetative cells. In the present study, we discovered that exogenous BMAA induces the process of heterocyst formation in filamentous cyanobacteria under nitrogen-replete conditions that normally repress cell differentiation. BMAA treated cyanobacteria form heterocyst-like dark non-fluorescent non-functional cells. It was found that glutamate eliminates the BMAA mediated derepression. Quantitative polymerase chain reaction (qPCR) permitted to detect the BMAA impact on the transcriptional activity of several genes that are implicated in nitrogen assimilation and heterocyst formation in Anabaena sp. PCC 7120. We demonstrated that the expression of several essential genes increases in the BMAA presence under repressive conditions.

Stress effects of cyanotoxin ß-methylamino-L-alanine (BMAA) on cyanobacterial heterocyst formation and functionality.

Various species of cyanobacteria, diatoms and dinoflagellates are capable of synthesizing the non-proteinogenic neurotoxic amino acid ß-N-methylamino-L-alanine (BMAA), which is known to be a causative agent of human neurodegeneration. Similar to most cyanotoxins, the biological and ecological functions of BMAA in cyanobacteria are unknown. In this study, we show for the first time that BMAA, in micromolar amounts, inhibits the formation of heterocysts (specialized nitrogen-fixing cells) in heterocystous, diazotrophic cyanobacteria [Anabaena sp. PCC 7120, Nostoc punctiforme PCC 73102 (ATCC 29133), Nostoc sp. strain 8963] under conditions of nitrogen starvation. The inhibitory effect of BMAA is abolished by the addition of glutamate. To understand the genetic reason for the observed phenomenon, we used qPCR to study the expression of key genes involved in cell differentiation and nitrogen metabolism in the model cyanobacterium Anabaena sp. PCC 7120. We observed that in the presence of BMAA, Anabaena sp. PCC 7120 does not express two essential genes associated with heterocyst differentiation, namely, hetR and hepA. We also found that addition of BMAA to cyanobacterial cultures with mature heterocysts inhibits nifH gene expression and nitrogenase activity.

Ketones 2-heptanone, 2-nonanone, and 2-undecanone inhibit DnaK-dependent refolding of heat-inactivated bacterial luciferases in Escherichia coli cells lacking small chaperon IbpB.

Many bacteria, fungi, and plants produce volatile organic compounds (VOCs) emitted to the environment. Bacterial VOCs play an important role in interactions between microorganisms and in bacterial-plant interactions. Here, we show that such VOCs as ketones 2-heptanone, 2-nonanone, and 2-undecanone inhibit the DnaKJE-ClpB bichaperone dependent refolding of heat-inactivated bacterial luciferases. The inhibitory activity of ketones had highest effect in Escherichia coli ibpB::kan cells lacking small chaperone IbpB. Effect of ketones activity increased in the series: 2-pentanone, 2-undecanone, 2-heptanone, and 2-nonanone. These observations can be explained by the interaction of ketones with hydrophobic segments of heat-inactivated substrates and the competition with the chaperones IbpAB. If the small chaperone IbpB is absent in E. coli cells, the ketones block the hydrophobic segments of the polypeptides and inhibit the action of the bichaperone system. These results are consistent with the data on inhibitory effects of VOCs on survival of bacteria. It can be suggested that the inhibitory activity of the ketones indicated is associated with different ability of these substances to interact with hydrophobic segments in proteins.

Interaction of various types of photosystem I complexes with exogenous electron acceptors.

Interaction of photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 containing various quinones in the A1-site (phylloquinone PhQ in the wild-type strain (WT), and plastoquinone PQ or 2,3-dichloronaphthoquinone Cl 2 NQ in the menB deletion strain) and different numbers of Fe4S4 clusters (intact WT and FX-core complexes depleted of FA/FB centers) with external acceptors has been studied. The efficiency of interaction was estimated by measuring the light-induced absorption changes at 820 nm due to the reduction of the special pair of chlorophylls (P700+) by an external acceptor(s). It was shown that externally added Cl 2 NQ is able to effectively accept electrons from the terminal iron-sulfur clusters of PS I. Moreover, the efficiency of Cl 2 NQ as external acceptor was higher than the efficiency of the commonly used artificial electron acceptor, methylviologen (MV) for both the intact WT PS I and for the FX-core complexes. The comparison of the efficiency of MV interaction with different types of PS I complexes revealed gradual decrease in the following order: intact WT > menB > FX-core. The effect of MV on the recombination kinetics in menB complexes of PS I with Cl 2 NQ in the A1-site differed significantly from all other PS I samples. The obtained effects are considered in terms of kinetic efficiency of electron acceptors in relation to thermodynamic and structural characteristics of PS I complexes.

Influence of volatile organic compounds emitted by Pseudomonas and Serratia strains on Agrobacterium tumefaciens biofilms.

The ability to form biofilms plays an important role in bacteria-host interactions, including plant pathogenicity. In this work, we investigated the action of volatile organic compounds (VOCs) produced by rhizospheric strains of Pseudomonas chlororaphis 449, Pseudomonas fluorescens B-4117, Serratia plymuthica IC1270, as well as Serratia proteamaculans strain 94, isolated from spoiled meat, on biofilms formation by three strains of Agrobacterium tumefaciens which are causative agents of crown-gall disease in a wide range of plants. In dual culture assays, the pool of volatiles emitted by the tested Pseudomonas and Serratia strains suppressed the formation of biofilms of A. tumefaciens strains grown on polycarbonate membrane filters and killed Agrobacterium cells in mature biofilms. The individual VOCs produced by the tested Pseudomonas strains, that is, ketones (2-nonanone, 2-heptanone, 2-undecanone), and dimethyl disulfide (DMDS) produced by Serratia strains, were shown to kill A. tumefaciens cells in mature biofilms and suppress their formation. The data obtained in this study suggest an additional potential of some ketones and DMDS as protectors of plants against A. tumefaciens strains, whose virulence is associated with the formation of biofilms on the infected plants.

Inhibitory and toxic effects of volatiles emitted by strains of Pseudomonas and Serratia on growth and survival of selected microorganisms, Caenorhabditis elegans, and Drosophila melanogaster.

In previous research, volatile organic compounds (VOCs) emitted by various bacteria into the chemosphere were suggested to play a significant role in the antagonistic interactions between microorganisms occupying the same ecological niche and between bacteria and target eukaryotes. Moreover, a number of volatiles released by bacteria were reported to suppress quorum-sensing cell-to-cell communication in bacteria, and to stimulate plant growth. Here, volatiles produced by Pseudomonas and Serratia strains isolated mainly from the soil or rhizosphere exhibited bacteriostatic action on phytopathogenic Agrobacterium tumefaciens and fungi and demonstrated a killing effect on cyanobacteria, flies (Drosophila melanogaster), and nematodes (Caenorhabditis elegans). VOCs emitted by the rhizospheric Pseudomonas chlororaphis strain 449 and by Serratia proteamaculans strain 94 isolated from spoiled meat were identified using gas chromatography-mass spectrometry analysis, and the effects of the main headspace compounds--ketones (2-nonanone, 2-heptanone, 2-undecanone) and dimethyl disulfide--were inhibitory toward the tested microorganisms, nematodes, and flies. The data confirmed the role of bacterial volatiles as important compounds involved in interactions between organisms under natural ecological conditions.