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.     

A method to study zhizosphere processes in thin soil layers of different proximity to roots

Frankia is the diverse bacterial genus that fixes nitrogen within root nodules of actinorhizal trees and shrubs. Systematic and ecological studies of Frankia have been hindered by the lack of morphological, biochemical, or other markers to readily distinguish strains. Recently, nucleotide sequence of 16 S RNA from the small ribosomal subunit has been used to classify and identify a variety of microorganisms. We report nucleotide sequences from portions of the 16 S ribosomal RNA from Frankia strains AcnI1 isolated from Alnus viridis ssp. crispa (Ait.) Turrill and PtI1 isolated from Purshia tridentata (Pursh) DC. The number of nucleotide base substitutions and gaps we find more than doubles the previously reported sequence diversity for the same variable regions within other strains of Frankia.     

Periplasmic superoxide dismutases in Aquaspirillum magnetotacticum

Aquaspirillum magnetotacticum MS-1 cells cultured microaerobically (dissolved O₂ tension 1% of saturation), expressed proteins with superoxide dismutase (SOD) activity. The majority (roughly 95%) of total cell superoxide dismutase activity was located in the cell periplasm with little or no activity in the cell cytoplasm. Irontype SOD (FeSOD) contributed 88% of the total activity activity detected, although a manganese-type SOD (MnSOD) was present in the periplasm as well. Cells cultured at a higher dissolved O₂ tension (10% of saturation) expressed increased activity of the MnSOD relative to that of the FeSOD.     

Protists have divergent effects on bacterial diversity along a productivity gradient

Productivity and predation are thought to be crucial drivers of bacterial diversity. We tested how the productivity–diversity of a natural bacterial community is modified by the presence of protist predators with different feeding preferences. In the absence of predators, there was a unimodal relationship between bacterial diversity and productivity. We found that three protist species (Bodo, Spumella and Cyclidium) had widely divergent effects on bacterial diversity across the productivity gradient. Bodo and Cyclidium had little effect on the shape of the productivity–diversity gradient, while Spumella flattened the relationship. We explain these results in terms of the feeding preferences of these predators.     

Development of light-shielding hydrogel for nitrifying bacteria to prevent photoinhibition under strong light irradiation

Microalgae-nitrifying bacteria consortia have gained attention because photooxygenation of algae can supply oxygen to bacteria which eliminates the need for costly mechanical aeration. However, nitrifying bacteria are known to suffer from photoinhibition. In this study, we developed “Light-shielding hydrogel”, in which bacteria were immobilized in hydrogel and light-shielding particles (carbon black) were incorporated, and evaluated its effectiveness to mitigate photoinhibition for bacteria under strong light irradiation. For comparison, “Hydrogel”, in which bacteria were immobilized in hydrogel without carbon black, and “Dispersion” which was simply suspended bacteria were prepared. At 1600 μmol photons m⁻² s^–1, the nitrification performance markedly decreased to 15.1 and 48.0% compared to the dark condition in the Dispersion and the Hydrogel, respectively. Meanwhile, it was successfully maintained for the Light-shielding hydrogel. Our results showed that the effectiveness of light-shielding hydrogel to mitigate photoinhibition on nitrifying bacteria even under strong light irradiation.     

Dimorphism in methane seep-dwelling ecotypes of the largest known bacteria

We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization.