Genes Associated with 2-Methylisoborneol Biosynthesis in Cyanobacteria: Isolation, Characterization, and Expression in Response to Light

The volatile microbial metabolite 2-methylisoborneol (2-MIB) is a root cause of taste and odor issues in freshwater. Although current evidence suggests that 2-MIB is not toxic, this compound degrades water quality and presents problems for water treatment. To address these issues, cyanobacteria and actinomycetes, the major producers of 2-MIB, have been investigated extensively. In this study, two 2-MIB producing strains, coded as Pseudanabaena sp. and Planktothricoids raciborskii, were used in order to elucidate the genetic background, light regulation, and biochemical mechanisms of 2-MIB biosynthesis in cyanobacteria. Genome walking and PCR methods revealed that two adjacent genes, SAM-dependent methyltransferanse gene and monoterpene cyclase gene, are responsible for GPP methylation and subsequent cyclization to 2-MIB in cyanobacteria. These two genes are located in between two homologous cyclic nucleotide-binding protein genes that may be members of the Crp-Fnr regulator family. Together, this sequence of genes forms a putative operon. The synthesis of 2-MIB is similar in cyanobacteria and actinomycetes. Comparison of the gene arrangement and functional sites between cyanobacteria and other organisms revealed that gene recombination and gene transfer probably occurred during the evolution of 2-MIB-associated genes. All the microorganisms examined have a common origin of 2-MIB biosynthesis capacity, but cyanobacteria represent a unique evolutionary lineage. Gene expression analysis suggested that light is a crucial, but not the only, active regulatory factor for the transcription of 2-MIB synthesis genes. This light-regulated process is immediate and transient. This study is the first to identify the genetic background and evolution of 2-MIB biosynthesis in cyanobacteria, thus enhancing current knowledge on 2-MIB contamination of freshwater

Physiological Responses of a Diazotrophic Cyanobacterium to Acidification of Paddy Floodwater: N2 Fixation, Photosynthesis, and Oxidative–Antioxidative Characteristics

Long-term of excessive fertilization using nitrogen (N) chemical fertilizer caused the acidification of paddy soils. Presently, the impacts of soil acidification on physiological characteristics of diazotrophic cyanobacteria remain unknown. In order to elucidate this issue, the effects of paddy floodwater acidification on activities of respiration, photosynthetic oxygen evolution, and N2 fixation of a paddy diazotrophic cyanobacterium Aliinostoc sp. YYLX235 were investigated in this study. In addition, the origination and quenching of intracellular reactive oxygen species (ROS) were analyzed. The acidification of paddy floodwater decreased intracellular pH and interfered in energy flux from light-harvesting chlorophyll antenna to the reaction center of photosystem II (PS II). Activities of respiration, photosynthetic oxygen evolution, and N2 fixation were decreased by the acidification of paddy floodwater. Accompanied with an increase in ROS, the level of antioxidative system increased. Superoxide dismutase (SOD) and catalase (CAT) were the main enzymatic ROS scavengers in the cells of YYLX235; reduced glutathione (GSH) was the main non-enzymatic antioxidant. Antioxidants and oxidants in the cells of YYLX235 lost balance when the pH of paddy floodwater fell to 5.0 and 4.0, and lipid oxidative damage happened. The results presented in this study suggest that the acidification of paddy soil severely interfered in the photosynthesis of diazotrophic cyanobacteria and induced the production of ROS, which in turn resulted in oxidative damage on diazotrophic cyanobacteria and a decrease in cell vitality

Potential for control of harmful cyanobacterial blooms using biologically derived substances: Problems and prospects

Water blooms of cyanobacteria have posed a worldwide environmental threat and a human health hazard in recent decades. Many biologically derived (but non-antibiotic) bioactive substances are known to inhibit the growth of aquatic bloom-forming cyanobacteria. Some of these biologically derived substances (BDSs) have no or low toxicity to aquatic animals and humans. Most BDSs are easily biodegradable in aquatic environments. These characteristics indicate that they may have potential for control and removal of harmful algae. However, BDSs also have the disadvantages of high cost of preparation, and possible damage to non-target aquatic organisms, and sometimes, low efficiency of algae removal. The ecological risks of most BDSs are still unknown. Here, we review recent research progress relative to the inhibitory effects of BDSs on cyanobacteria, and critically analyze the potential of BDSs as algicides with an emphasis on possible problems during the process of controlling harmful cyanobacteria. We suggest avenues of study to enhance effective use of BDSs in controlling of cyanobacterial blooms; these include guidelines for isolation and characterization of new effective BDSs, exploiting the synergistic effects of BDSs, the merits of controlling harmful cyanobacteria at the early stages of proliferation and evaluation of ecological risks of BDSs. (C) 2013 Elsevier Ltd. All rights reserved

The Golod-Shafarevich inequality for pro-p groups and abstract groups

Orientador: Dessislava Hristova KochloukovaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação CientíficaResumo: Neste trabalho estuda-se os principais resultados dados por J. Wilson no artigo "Finite Presentations of Pro-p Groups and Discrete Groups", relacionados à Desigualdade de Golod-¿afarevi? para uma ampla classe de grupos pro-p e abstratos infinitos. Apresentamos a teoria básica de grupos livres abstratos, levando à noção de apresentação de grupos, com foco em apresentações finitas. É feito um estudo sobre grupos profinitos, particularmente no caso pro-p. Abrange-se definições, propriedades algébricas e topológicas básicas, bem como o caso de finitos geradores com o subgrupo de Frattini, e conceitos de completamentos, de grupos pro-p livres, de apresentações de grupos pro-p e de álgebras de grupo completas. No capítulo final estudamos os resultados principais para grupos pro-p e abstratos finitamente apresentáveis, que incluem grupos solúveis e implicações na estrutura de certos grupos satisfazendo a Desigualdade. Os anexos relacionam a teoria aqui apresentada a grupos pro-p de posto finito e homologia e cohomologia de grupos pro-pAbstract: In this work we study the main results presented by J. Wilson in his paper "Finite Presentations of Pro-p Groups and Discrete Groups", which extend the Golod-¿afarevi? Inequality to a large class of infinite pro-p and abstract groups. In the first chapter we present the basic theory of abstract free groups, focusing on finite presentations. Next we study profinite groups, with focus on pro-p groups. This study ranges from definitions to basic algebraic and topological properties, as well as the cases of finitely generated groups and the Frattini subgroup, and notions of completion, free pro-p groups, presentations of pro-p groups and completed group algebras. In the last chapter we study the main results regarding finite presentations of pro-p and abstract groups, which include soluble groups and implications on the structure of certain groups for which the Inequality holds. In the appendixes we briefly relate the presented theory to pro-p groups of finite rank and homology and cohomology of pro-p groupsMestradoMatematicaMestre em Matemátic

Genetic Basis for Geosmin Production by the Water Bloom-Forming Cyanobacterium, Anabaena ucrainica

Geosmin is a common, musty-smelling sesquiterpene, principally produced by cyanobacteria. Anabaena ucrainica (Schhorb.) Watanabe, a water bloom-forming cyanobacterium, is the geosmin producer responsible for odor problems in Dianchi and Erhai lakes in China. In this study, the geosmin synthase gene (geo) of A. ucrainica and its flanking regions were identified and cloned by polymerase chain reaction (PCR) and genome walking. The geo gene was found to be located in a transcription unit with two cyclic nucleotide-binding protein genes (cnb). The two cnb genes were highly similar and were predicted members of the cyclic adenosine monophosphate (cAMP) receptor protein/fumarate nitrate reductase regulator (Crp–Fnr) family. Phylogenetic and evolutionary analyses implied that the evolution of the geosmin genes involved a horizontal gene transfer process in cyanobacteria. These genes showed a close relationship to 2-methylisoborneol genes in origin and evolution

Biosynthesis pathways of 2-MIB in actinomycetes.

<p>Geranyl pyrophosohate (GPP), the universal precursor of monoterpenes, is converted to 2-MIB through two steps: methylation of GPP and cyclization of methyl-GPP subsequently.</p

Organization of genes associated with 2-MIB biosynthesis in different organisms.

<p>The grayed, oblique-line, filled and opened arrows indicate <i>cnb</i>, <i>mtf</i>, <i>mic</i> and other predicted functional genes respectively.</p

Transcriptional changes in 2-MIB genes under darkness.

<p>The levels of <i>mtf</i> and <i>mic</i> expression under 72 h darkness were calculated relative to the expression in control culture (light density as 30 µmol photons·m⁻²·s⁻¹).</p