The influence of invertebrates on the breakdown ofPotamogeton pectinatus L. in a coastal marina (Zandvlei,South Africa)

The influence of invertebrates upon the decomposition ofPotamogeton pectinatus L. in a coastal Marina system was examined over 112 days using litter bags. Invertebrate inclusion bags (2 mm mesh, 5 mm holes) registered a dry mass loss of 1% d^–1, while exclusion litter bags (80 µm mesh) produced a 0.4% mass loss d^–1 (a 2.5 fold difference). Losses of ash and N from inclusion bags were greater than those from exclusion bags (p < 0.05). There was a three fold difference between the two treatments in the time taken for litter to breakdown to half the initial stock: T_1/2 for inclusion bags = 43 d, exclusion bags = 130 d. In both treatments, minerals showed an expected rapid loss, due to leaching, with a subsequent slow increase relative to the dry material remaining. A total of nine invertebrate taxa was recorded from inclusion bags, with a peak biomass of 64 mg g^–1 dry massPotamogeton bag^–1 reached at 64 days after immersion. Grazing amphipods,Melita zeylanica Stebbing andAustrochiltonia subtenuis (Barnard), numerically dominated the litter bag fauna, whileM. zeylanica and nymphs of the zygopteran predatorIschnura senegalensis (Rambur) formed most of the biomass. Scanning Electron Microscopy indicated heavy grazing of micro-organisms by invertebrates, with major qualitative differences occurring 112 days after immersion. Invertebrates significantly accelerated the rate of litter breakdown through their feeding activities, assisting fragmentation and thus contributing to plant losses and also by increasing the surface area for microbial colonisation and attack.     

Thylakoid differentiation in endocyanelles

Cyanophora paradoxa Korshikov synchronized autotrophically in a light-dark regime of 14 h light and 10 h dark divides in the last two hours of the dark period. The division rate of the free-living blue-green alga, Synechococcus leopoliensis Raciborski, at identical culture conditions (24°C; 32 W m⁻²) is only slightly lowered in the light period. The comparison of thylakoid differentiation in the endocyanelles of Cyanophora paradoxa and in Synechococcus leopoliensis during the light-dark regime yields (1) the same ensemble of pigment-protein complexes in both organisms, (2) comparable syntheses of chlorophyll and phycobilins of Cyanophora paradoxa grown under 32 W m⁻² and of Synechococcus leopoliensis grown under light intensities below 9.2 W m⁻², and (3) identical photosynthetic oxygen evolution during the light period of the light-dark regime with minima at the beginning, in the middle (6th–7th h), and at the end of the light period. In both organisms this stage-specific oxygen evolution is inhibited by treatment with chloroamphenicol. Cycloheximide, however, causes no significant alterations. Results are discussed in view of the endosymbiotic theory.     

Aphid honeydew and its effect on the phyllosphere microflora of Picea abies (L.) Karst

Aphids of the genus Cinara, feeding on Norway spruce, excrete copious amounts of honeydew, a carbon-rich waste product, which accumulates locally on needles and twigs. We investigated the role of honeydew as a potential source of energy which might promote the growth of micro-organisms in the phyllosphere of conifer trees. To approach this question, we followed the population dynamics of Cinara spp. in a natural forest stand over two seasons. We also studied the amounts of honeydew produced by individual aphids and identified potential parameters which might influence honeydew production. Finally, we determined the growth of micro-organisms on infested and uninfested needles of Norway spruce during the growing season. Confined to Picea abies, the investigated Cinara species only became abundant in midsummer, when needles and shoots were expanding. The populations showed only a single peak in abundance, the timing and magnitude of which may vary from year to year due to weather conditions, changes in plant quality in a yearly cycle or the impact of natural enemies. The amount of honeydew produced by individual aphids was dependent on the developmental stage of the aphid, the nutritional supply of its host plant and on the developmental state of the Norway spruce (e.g. bud burst, end of shoot extension). The presence of honeydew significantly increased the growth of bacteria, yeast and filamentous fungi on the surface of needles and there was a pronounced seasonal trend, with the highest abundance in midsummer correlating with the period of peak aphid abundance. Taken together, these findings indicate that aphids have an influence on microbial ecology in the phyllosphere of trees. The implication of our study, from interactions at the population level to effects and potential consequences for C and N fluxes at the level of forest ecosystems, is discussed.     

Microbial gut floras of eight species of tephritids

The gut bacteria of eight tephritid species were isolated and characterized. Larvae of the genus Urophora and Tephritis dilacerata proved to house no microorganisms in their digestive organs. Bacteria were isolated from adults of five fruit fly species. Most of the bacterial strains were enterobacteria. Fruit-infesting tephritid species, flower-head species and gall formers had similar gut floras consisting of bacteria widespread in the soil and on the phylloplane.     

Epoxidation of propene by microbial cells immobilized on inorhanic supports

Immobilization of gas-utilizing microorganism strains (Mycobacteria, Rhodococcus, methane-utilizers) on inorganic supports based on alumina, silicates, and carbon was carried out to develop heterogeneous biocatalysts for the biotechnologic processes, including the process of propene epoxidation. Adsorption ability of these microorganisms, biocatalytic properties of resting and immobilized bacterial cells, and effect of immobilization tehniques on biocatalysis were studied. An approach of double immobilization using inorganic materials (supports and gel) was proposed as simple, universal, and available methopd to immobilize bacterial cells, resulting in a higher retention (up to 100%) of cells' enzymatic activity and enhanced stability.     

Direct Targeting of Proteins from the Cytosol to Organelles: The ER versus Endosymbiotic Organelles

In eukaryotic cells consisting of many different types of organelles, targeting of organellar proteins is one of the most fundamental cellular processes. Proteins belonging to the endoplasmic reticulum (ER), chloroplasts and mitochondria are targeted individually from the cytosol to their cognate organelles. As the targeting to these organelles occurs in the cytosol during or after translation, the most crucial aspect is how specific targeting to these three organelles can be achieved without interfering with other targeting pathways. For these organelles, multiple mechanisms are used for targeting proteins, but the exact mechanism used depends on the type of protein and organelle, the location of targeting signals in the protein and the location of the protein in the organelle. In this review, we discuss the various mechanisms involved in protein targeting to the ER, chloroplasts and mitochondria, and how the targeting specificity is determined for these organelles in plant cells .     

Does seawater acidification affect zooxanthellae density and health in the invasive upside‐down jellyfish,Cassiopea spp.?

Ocean acidification is the decline in seawater pH that results from the absorption of atmospheric carbon dioxide (CO₂). Decreased pH has negative effects on survivability, growth, and development in many marine calcifiers, potentially resulting in reduced coral species richness. This reduction in richness could open new niche space, allowing the spread of invasive species, such as the upside‐down jellyfish (Cassiopea spp.). Like corals, this jellyfish forms symbiotic relationships with zooxanthellae, photosynthetic dinoflagellates. This study focused on the effect of seawater acidification in Cassiopea spp. We monitored zooxanthellae density and two measures of health (bell diameter and volume) in individuals of Cassiopea sp. at three pH levels chosen to mimic different open‐ocean average conditions: 8.2, representing pre‐industrial revolution conditions; and 7.9 and 7.6, representing predicted declines in pH in the next century. Zooxanthellae density and health of the jellyfish were measured twice—prior to experimental manipulations and after four weeks of exposure to experimental pHs—in three consecutive trials. The effects of pH and Trial on proportional change in jellyfish attributes were analyzed using generalized linear mixed models. We found no significant effects of either factor. These results indicate that decreasing seawater pH has no apparent negative effect on zooxanthellae density or health in Cassiopea, which suggests that these jellyfish may be relatively insensitive to the impacts of ocean acidification, heightening its potential as an invasive species.