Microbial Diversity 21: biodiversity amongst microorganisms and its relevance

An introduction to, and the Action StatementMicrobial Diversity 21 arising from, the joint IUBS/IUMS workshop on Biodiversity amongst microorganisms and its relevance held in Amsterdam on 7–8 September 1991 are presented. The workshop was held in support of the IUBS/SCOPE/UNESCO initiative on the importance of biodiversity in ecosystem function, namedDiversitas. The current state of knowledge on diverse aspects of the biodiversity of the various microorganism groups was reviewed by leading specialists, and a 14-point Action Plan was produced as a framework for future international initiatives in biodiversity research on microorganisms.     

Effects of different molecular weight fractions of dissolved organic matter on the growth of bacteria,algae and protozoa from a highly humic lake

Effects of different molecular size fractions (< 1000 MW, < 10 000 MW, < 100 000 MW and <0.1 μm) of dissolved organic matter (DOM) on the growth of bacteria, algae and protozoa from a highly humic lake were investigated. DOM from catchment drainage water as well as from the lake consisted mostly (59–63%) of high molecular weight (HMW) compounds (> 10 000 MW). With excess inorganic nutrients, the growth rate and yield of bacteria were almost identical in all size fractions. However, in < 1000 MW fractions and with glucose added, a longer lag phase occurred. Without added nutrients both the growth rates and biomasses of bacteria decreased towards the smaller size fractions and the percentage of dissolved organic carbon (DOC) used during the experiment and the growth efficiency of bacteria were lower than with excess nutrients. The growth efficiency of bacteria was estimated to vary between 3–66% in different MW fractions, largely depending on the nutrient concentrations, but the highest growth efficiencies were observed in HMW fractions and with glucose. The growth of algae was clearly lowest in the < 1000 MW fraction. In dim light no net growth of algae could be found. In contrast, added nutrients substantially enhanced algal growth and in deionized water with glucose, algae achieved almost the same growth rate and biomass as in higher MW fractions of DOM. The results suggested that bacteria and some algae were favoured by DOM, but protozoans seemed to benefit only indirectly, through bacterial grazing. The utilization of DOM by bacteria and algae was strongly affected by the availability of phosphorus and nitrogen.     

The interstitial ciliated protozoa of a Mediterranean microcommunity

The main features of an interstitial ciliate community, living in the coastal sand of the Mediterranean sea, were analyzed during a one-year survey, carried out on 113 samples. The community was composed of 56 species, 31 of which belong to 8 resident genera. Total density varied from 0 to 410 individuals cm^–3 and followed a Spring-Summer and an Autumn-Winter trend, not related to temperature or to any single abiotic variable (interstitial dissolved O₂, grain sand size, salinity), although the density of some taxa was related to one abiotic factor. During Spring, diversity increased by a synchronous bloom involving the whole community. Some taxa, such as the predator Lacrymaria and its prey Frontonia, were significantly associated. The finding of the simultaneous bloom of congeneric species, like that of the genus Remanella suggests that they respond to the same environmental factors, and avoid interspecific competition.     

Inhibition of α-, β-, γ-, and δ-carbonic anhydrases from bacteria and diatoms with N′-aryl-N-hydroxy-ureas

The inhibition of α-, β-, γ-, and δ-class carbonic anhydrases (CAs, EC 4.2.1.1) from bacteria (Vibrio cholerae and Porphyromonas gingivalis) and diatoms (Thalassiosira weissflogii) with a panel of N’-aryl-N-hydroxy-ureas is reported. The α-/β-CAs from V. cholerae (VchCAα and VchCAβ) were effectively inhibited by some of these derivatives, with K_Is in the range of 97.5?nM – 7.26?µM and 52.5?nM – 1.81?µM, respectively, whereas the γ-class enzyme VchCAγ was less sensitive to inhibition (K_Is of 4.75 – 8.87?µM). The β-CA from the pathogenic bacterium Porphyromonas gingivalis (PgiCAβ) was not inhibited by these compounds (K_Is?>?10?µM) whereas the corresponding γ-class enzyme (PgiCAγ) was effectively inhibited (K_Is of 59.8?nM – 6.42?µM). The δ-CA from the diatom Thalassiosira weissflogii (TweCAδ) showed effective inhibition with these derivatives (K_Is of 33.3?nM – 8.74?µM). As most of these N-hydroxyureas are also ineffective as inhibitors of the human (h) widespread isoforms hCA I and II (K_Is?>?10?µM), this class of derivatives may lead to the development of CA inhibitors selective for bacterial/diatom enzymes over their human counterparts and thus to anti-infectives or agents with environmental applications.     

Recolonizing gray wolves increase parasite infection risk in their prey

The recent recolonization of Central Europe by the European gray wolf (Canis lupus) provides an opportunity to study the dynamics of parasite transmission for cases when a definitive host returns after a phase of local extinction. We investigated whether a newly established wolf population increased the prevalence of those parasites in ungulate intermediate hosts representing wolf prey, whether some parasite species are particularly well adapted to wolves, and the potential basis for such adaptations. We recorded Sarcocystis species richness in wolves and Sarcocystis prevalence in ungulates harvested in study sites with and without permanent wolf presence in Germany using microscopy and DNA metabarcoding. Sarcocystis prevalence in red deer (Cervus elaphus) was significantly higher in wolf areas (79.7%) than in control areas (26.3%) but not in roe deer (Capreolus capreolus) (97.2% vs. 90.4%) or wild boar (Sus scrofa) (82.8% vs. 64.9%). Of 11 Sarcocystis species, Sarcocystis taeniata and Sarcocystis grueneri occurred more often in wolves than expected from the Sarcocystis infection patterns of ungulate prey. Both Sarcocystis species showed a higher increase in prevalence in ungulates in wolf areas than other Sarcocystis species, suggesting that they are particularly well adapted to wolves, and are examples of “wolf specialists”. Sarcocystis species richness in wolves was significantly higher in pups than in adults. “Wolf specialists” persisted during wolf maturation. The results of this study demonstrate that (1) predator–prey interactions influence parasite prevalence, if both predator and prey are part of the parasite life cycle, (2) mesopredators do not necessarily replace the apex predator in parasite transmission dynamics for particular parasites of which the apex predator is the definitive host, even if meso‐ and apex predators were from the same taxonomic family (here: Canidae, e.g., red foxes Vulpes vulpes), and (3) age‐dependent immune maturation contributes to the control of protozoan infection in wolves.     

The microbial loop in a humic lake: seasonal and vertical variations in the structure of the different communities

Seasonal and vertical variations of the main microbial communities (heterotrophic bacteria, autotrophic picoplankton, auto- and heterotrophic nanoflagellates, ciliated protozoa and microalgae) and auto- and heterotrophic activities were estimated in a brown-colored humic and moderately acid lake in central France, the lake of Vassivière. The results demonstrated the dominant role of light in the vertical distribution of autotrophic and mixotrophic microorganisms which are confined to the 0–5 m layer during thermal stratification. The bacterial biomass was high throughout the water column probably because of the great availability of dissolved organic matter. Consequently, the predatory microzooplankton and particularly the various trophic groups of ciliated protozoa, were distributed in the water column according to the vertical distribution of the particular food resources (detritus, bacteria, algae). However, despite the great abundance of algae and bacteria, biomass of flagellated and ciliated protozoa was relatively weak. Most of the phytoplanktonic biomass was filamentous (Diatoms) or colonial (Cyanobacteria) and therefore almost probably difficult to ingest for algivorous microzooplankton. Regarding the low abundance of bacterivorous protozoa, the relation with the special physicochemical properties of this lake is discussed.

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Résumé Les variabilités saisonnière et verticale de l'abondance et de la biomasse des principles communautés de la boucle microbienne (bactéries hétérotrophes, picoplancton autotrophe, protozoaires flagellés auto- et hétérotrophes, protozoaires ciliés, microalgues et microcyanobactéries), et des activités auto- et hétérotrophes, ont été étudiées dans un lac à caractère humique et modérément acide du Massif Central Français, le lac de Vassivière.Le dénombrement des communautés de microorganismes a été réalisé en microscopie inversée et à épifluorescence après mise en oeuvre des fixations et des colorations adéquates. Les activités photosynthétique, photo- et chemohétérotrophes ont été mesurées à partir de l'assimilation de NaH¹⁴CO₃ et d'un mélange d'acides aminés tritiés grâce à une technique de double marquage. Les résultats obtenus mettent en évidence le rôle prépondérant du facteur lumineux dans la répartition verticale des microorganismes autotrophes et mixotrophes, dont l'essentiel de la biomasse est confiné dans la zone 0–5 m en période de stratification, alors que la biomasse bactérienne est élevée sur l'ensemble de la colonne d'eau en raison, sans doute, de la grande disponibilité en matiére organique dissoute. Consécutivement, le microzooplancton prédateur, et notamment les différents types trophiques de protozoaires ciliés, se répartit dans la colonne d'eau selon la distribution verticale des ressources nutritives particularies. Cependant, compte-tenu de l'abondance bactérienne et algae, la biomasse des protozoaires flagellés et ciliésest relativement peu importante. Concernant les espèces algivores, l'essentiel de la biomasse phytoplanctonique est de nature filamenteuse (Diatomées) ou coloniale (Cyanobactéries) est est donc sans doute difficilement ingérable pour le microzooplancton. Enfin, les relations entre les caractéristiques physico-chimiques spécifiques de ce lac et le faible développement des protozoaires bactérivores sont discutées.

     

Competition Among Homologous Polypeptide Pheromones of the Ciliate Euplotes raikovi for Binding to Each Other's Cell Receptors

ABSTRACT. Purified preparations of the polypeptide pheromones Er-1 and Er-2 were obtained from type I and II cells of Euplotes raikovi , respectively, radiolabeled, and used to study their ability to compete with each other in binding to the same type I and II cells and to type × cells secreting Er-10, another pheromone homologous to Er-1 and Er-2. It was shown that: 1) These radiolabeled pheromone preparations bind, with similar but not identical affinities, to cells from which they originate as well as to cells of the other types. 2) Every pheromone binding reaction can be completely inhibited by another homologous pheromone added in excess to cells. These results are discussed in relation to phenomena, common in ciliates, of instability of (homotypic) mating pairs formed between genotypically identical cells suspended with a foreign (nonself) pheromone.     

The toxic effects of rubber contaminants on microbial food webs and zooplankton of two lakes of different trophic status

Rubber is commonly used in recreational equipment and devicesforsampling in lakes, but there have been few studies of theeffectsof rubber on planktonic organisms. We investigated the toxiceffects of rubber on the microbial food webs of a mesotrophiclakeand a eutrophic lake. Lake water was collected by pumping via,(i) a polyvinylchloride hose and, (ii) a rubber hose. Samplesoflake water collected by each method were incubated insitu in4.25 l enclosures for four days. The lake water was sampledbeforeand after incubation to determine the concentrations ofinorganicnutrients, chlorophyll a, microorganisms (bacteria,picophytoplankton, flagellates, ciliates) and zooplankton.In the mesotrophic lake, momentary exposure (ten seconds) oflakewater to the rubber hose significantly lowered theconcentrationsof chlorophyll a, bacteria, picophytoplankton and somespecies of zooplankton (Boeckella hamata, Bosmina,androtifers), relative to those in water exposed to the plastichose;flagellates, ciliates and Ceriodaphnia dubia were notsignificantly affected. In the eutrophic lake, the effects oftherubber hose on components of the microbial food web were muchlesssevere, and were consistent with the lake's high levels ofdissolved organic carbon (DOC), which is known to chelatetoxicmetals in water.     

Oxygen Uptake and Antioxidant Responses of the Free-Living Diplomonad Hexamita sp.

ABSTRACT. The free-living anaerobic flagellate Hexamita sp. was observed to actively consume O₂ with a K_m O₂ of 13 μM. Oxygen consumption increased lineraly with O₂ tension up to a threshold level of 100 μM, above which it was inhibited. Oxygen uptake was supported by a number of substrates but probably not coupled to energy conservation as cytochromes could not be detected spectro-photometrically. In addition, inhibitors specific for respiratory chain components did not significantly affect O₂ uptake. Respiration was however, partially inhibited by flavoprotein and iron-sulfur protein inhibitors. NAD(P)H supported O₂ consumption was measured in both particulate and soluble fractions; this activity was partially inhibited by quinacrine. A chemosensory response was observed in cells exposed to air, however no response was observed in the presence of superoxide dismutase plus catalase. Catalase and nonspecific peroxidase activity could not be detected, but superoxide dismutase activity was present. Superoxide dismutase was sensitive to NaN₃ and H₂O₂ but not KCN, suggesting a Fe prosthetic group. Flow cytometric analysis revealed that thiol levels in live cells were depleted in the presence of t-butyl H₂O₂. The observed NADPH-driven glutathione reductase activity is believed to recycle oxidized thiols in order to re-establish reduced thiol levels in the cell. The corresponding thiol cycling enzyme glutathione peroxidase could not be detected. The ability to withstand high O₂ tensions (100 μM) would enable Hexamita to spend short periods in a wider range of habitats. Prologed exposure to O₂ tensions higher than 100 μM leads to irreversible damage and cell death.     

Germination of Nosema algerae (Microspora) Spores: Conditional Inhibition by D2O, Ethanol and Hg2+ Suggests Dependence of Water Influx upon Membrane Hydration and Specific Transmembrane Pathways

ABSTRACT. The germination of microsporidian spores under conditions expected to affect water flow across the plasma membrane-wall complex was studied by assessing their responses to in vitro stimulation with Na⁺ or K⁺. Partial or full substitution of common water with D₂O, which more effectively coats ions and electrostatically-charged cell surfaces with relatively stable hydration layers, delayed and inhibited spore germination in a concentration-dependent manner; yet, preincubation in 100% D₂O did not change the normal response to standard stimulation. Water structure-breaking conditions, such as an increase in temperature (within the 15° C to 40° C range) or in ionic strength (2- to 10-fold normal), opposed the inhibition by D₂O and allowed significant stimulation by Li⁺, the monovalent cation with the largest hydration diameter and a usually weak stimulant action on the spores. Ethanol, known to reduce water permeation across cell membranes and phospholipid bilayers, also caused a powerful and dose-dependent (1% to 4% v/v) inhibition of spore germination, but pretreatment with ethanol did not affect the normal response. HgCl₂, an inhibitor of specific water channels, blocked spore germination at just 250 μM in the normal stimulation solution irrespective of the temperature, and permitted only a delayed response in high salt stimulation solutions. However, the inhibition by Hg²⁺ was abolished by the simultaneous presence of 2-mercaptoethanol in the medium. These results suggest (1) that spore germination is keenly dependent upon the hydration states of both the plasma membrane-wall complex and the stimulant ions, and (2) that osmotic water flows into the spores through specific transmembrane pathways with critical sulfhydryl groups, i.e. analogous to the water channels that facilitate water movements across the plasma membranes of highly permeable cells.