Influence of concentration and structure of quaternary ammonium salts on their antifouling efficiency tested against a community of marine bacteria

With the view of incorporating quaternary ammonium salts (QAs) in marine paints, nineteen of these were tested against a community of marine bacteria, at a temperature and salinity close to those of seawater. The concentration of QAs and the length of the main substituting chain are the main parameters affecting the growth and adhesion of bacteria, but the nature of (i) the other chains, (ii) the counter‐ion and (iii) the rings when inserted in the QA molecule also influenced the bacteria. Increasing the concentration of the QAs decreased the growth rate of the bacteria, the maximum cell density at the plateau and the rate of adhesion. The effect of increasing the length of the main chain depended on the range of carbon numbers. Below 7 carbon atoms, the growth rate was not significantly modified, but the numbers of cells at the plateau increased in contrast with the adhesion rate which decreased rapidly. Increasing the length of the chain to between 7 and 16 carbon atoms resulted in a decrease in the growth rate, a decrease and then a stabilisation in the numbers of cells at the plateau and no further change in the adhesion rate. Possibly an increase in growth rate, adhesion rate and in the numbers of cells at the plateau may occur above 16 carbon atoms. In contrast, the length of the other chains influenced positively the cell concentration at the plateau, and more generally the efficiency of QAs decreased substantially when these chains had the same numbers of carbon atoms. QAs with iodide as counter‐ion were more effective than those with chloride or bromide and phenyl was more effective than benzyl as rings inserted in QAs. The minimum inhibitory concentrations (MIC) were often very high if compared to standard methods with laboratory strains, and this can be tentatively explained by the dominance of Gram— bacteria in the community assayed, the development of resistant strains in the cultures used with time and the presence of organic matter in the culture medium.     

Biosynthesis of Cephalosporins

Abstract

Certain aerobic, Gram-negative bacteria, including the epiphytic plant pathogen, Pseudomonas syringae, possess a membrane protein that enables them to nucleate crystallization in supercooled water. Currently, these ice-nucleating (IN) bacteria are being used in snow making and have potential applications in the production and texturing of frozen foods, and as a replacement of silver iodide in cloud seeding. A negative aspect of these IN bacteria is frost damage to plant surfaces. Thus, of the various types of biological ice nucleators, bacteria have been the subject of most research and also appear relevant to the anticipated practical uses. The intent of this review is to explain the identification and ecology of the ice-nucleating bacteria, as well as to discuss aspects of molecular biology related to ice nucleation and consider existing and potential applications of this unique phenomenon.     

Emerging role of ferrous iron in bacterial growth and host–pathogen interaction: New tools for chemical (micro)biology and antibacterial therapy

Chemical tools capable of detecting ferrous iron with oxidation-state specificity have only recently become available. Coincident with this development in chemical biology has been increased study and appreciation for the importance of ferrous iron during infection and more generally in host–pathogen interaction. Some of the recent findings are surprising and challenge long-standing assumptions about bacterial iron homeostasis and the innate immune response to infection. Here, we review these recent developments and their implications for antibacterial therapy.     

Role of HiPIP as electron donor to the RC-bound cytochrome in photosynthetic purple bacteria

High-Potential Iron-Sulfur Proteins (HiPIP) are small electron carriers, present only in species of photosynthetic purple bacteria having a RC-bound cytochrome. Their participation in the photo-induced cyclic electron transfer was recently established for Rubrivivax gelatinosus, Rhodocyclus tenuis and Rhodoferax fermentans (Schoepp et al. 1995; Hochkoeppler et al. 1996a, Menin et al. 1997b). To better understand the physiological role of HiPIP, we extended our study to other selected photosynthetic bacteria. The nature of the electron carrier in the photosynthetic pathway was investigated by recording light-induced absorption changes in intact cells. In addition, EPR measurements were made in whole cells and in membrane fragments in solution or dried immobilized, then illuminated at room temperature. Our results show that HiPIP plays an important role in the reduction of the photo-oxidized RC-bound cytochrome in the following species: Ectothiorhodospira vacuolata, Chromatium vinosum, Chromatium purpuratum and Rhodopila globiformis. In Rhodopseudomonas marina, the HiPIP is not photo-oxidizible in whole cells and in dried membranes, suggesting that this electron carrier is not involved in the photosynthetic pathway. In Ectothiorhodospira halophila, the photo-oxidized RC-bound cytochrome is reduced by a high midpoint potential cytochrome c, in agreement with midpoint potential values of the two iso-HiPIPs (+ 50 mV and + 120 mV) which are too low to be consistent with their participation in the photosynthetic cyclic electron transfer.     

Regulation of sulfate assimilation in Cytophaga johnsonae

We have studied the regulation of sulfate assimilation by the gliding bacterium Cytophaga johnsonae in which 20% of the total sulfur is in the sulfornate moiety of sulfonolipid. Added cystine inhibited sulfate uptake and growth with cystine as sulfur source resulted in a repression of sulfate uptake. However, low concentrations of cystine preferentially repressed the terminal reactions of sulfate assimilation responsible for cysteine synthesis while allowing the transport and activation of sulfate for sulfonolipid synthesis. The significance of this novel pattern of regulation in bacteria is discussed.     

Biology and epidemics of Candidatus Liberibacter species,psyllid‐transmitted plant‐pathogenic bacteria

Candidatus Liberibacter species are Gram‐negative bacteria that live as phloem‐limited obligate parasites in plants, and are associated with several plant diseases. These bacteria are transmitted by insects called psyllids, or jumping plant lice, which feed on plant phloem sap. Citrus huanglongbing (yellow shoot) or citrus greening disease is associated with three different species of Ca. Liberibacter – Ca. L. asiaticus, Ca. L. africanus and Ca. L. americanus – all originally found on different continents. Ca. L. asiaticus is the most severe pathogen, spread by Asian citrus psyllid Diaphorina citri and causing devastating epidemics in several countries. Ca. L. africanus occurs in Africa where it is spread by the African citrus psyllid Trioza erytreae. Ca. Liberibacter solanacearum is associated with diseases in several solanaceous plants, and transmitted by potato psyllid Bactericera cockerelli. Zebra chip disease is causing large damage in potato crops in North America. In Europe Ca. Liberibacter solanacearum is associated with diseases of the Apiaceae family of plants, carrot and celery, and transmitted by psyllids Trioza apicalis and Bactericera trigonica. When Ca. Liberibacter is suspected as the disease agent, the diagnosis is confirmed by DNA‐based detection methods. Ca. Liberibacter‐associated plant diseases can be controlled by using healthy plant propagation material, eradicating symptomatic plants, and by controlling the psyllid populations spreading the disease.     

ELISA analyses of malate dehydrogenases from nonsulfur purple phototrophic bacteria

Abstract The accumulation of ppGpp in three streptococci starved for isoleucine was studied via HPLC analysis of cell extracts prepared from mechanically disrupted bacteria. Starvation was achieved either by reduction of isoleucine in the growth medium or the addition of pseudomonic acid. The results indicate that while both treatments produced a physiological response similar to that described for stringent strains of other bacteria, in the streptococci, stringency was not necessarily coupled with ppGpp.     

Nitrogen fixation by hydrogen-utilizing bacteria

Seventeen strains of nitrogen-fixing bacteria, isolated from different habitats on hydrogen and carbon dioxide as well as on other substrates, morphologically resembled each other. All strains, including Mycobacterium flavum 301, grew autotrophically with hydrogen. The isolate strain 6 was sensitive to oxygen when dependent on N₂ as nitrogen source, a consequence of the sensitivity of its nitrogenase towards oxygen. At the same time, strain 6 was sensitive to hydrogen when growing autotrophically on N₂ as nitrogen source, but hydrogen did not affect acetylene reduction by these cells.Abbreviations MPN Most probable number - BS medium basal salts medium     

Construction of a physical map of the 45 kb photosynthetic gene cluster of Rhodobacter sphaeroides

1) A number of overlapping clones have been isolated from a Rhodobacter sphaeroides gene bank. Following conjugative gene transfer from Escherichia coli these clones restore a wild type phenotype to several mutants unable to synthesise bacteriochlorophyll. 2) The insert DNA was analysed by restriction mapping and together the clones form the basis of the first restriction map of the 45 kb photosynthetic gene cluster of Rb. sphaeroides. 3) This cluster is bounded on one side by puh A encoding the reaction centre H polypeptide and on the other by the puf operon encoding reaction centre L and M apoproteins and light harvesting LH1 and polypeptides. 4) DNA fragments from the 45 kb cluster were used to probe genomic DNA from other photosynthetic bacteria. Using heterologous hybridisation conditions, a significant degree of homology is shown between Rb. sphaeroides and these other bacteria, suggesting close evolutionary links with Rb. capsulatus in particular.