Interspecies interactions in aquatic hyphomycetes

Aquatic hyphomycetes (Moniliales) constitute a predominant mycoflora on submerged decaying allochthonous plant debris, both in lentic and lotic systems. These fungi exhibit a remarkable seasonality, and to explain this, a couple of models have been put forward, which tend to establish a strong correlation of their seasonal occurrence with temperature and pH of the aquatic systems. This study provides additional evidence that both vegetative and reproductive success of aquatic hyphomycetes is significantly affected by the interspecies interactions within this group.     

Protostelids and myxomycetes isolated from aquatic habitats

Protostelids and myxomycetes have been isolated from dead plant parts in many different habitats, including tropical rain forests and deserts. However underwater habitats largely have been overlooked. The purpose of this study was to determine whether protostelids do occur in aquatic habitats and to survey the myxomycetes associated with these habitats. Protostelids and myxomycetes were isolated from substrates collected from just above and just below the surface of the water. Several species of both groups were present, and their distributions above and below the water were different. It is not surprising that the trophic cells of slime molds occur in ponds because they are known to grow in films of water. However these findings are significant because this is the first study to demonstrate clearly the occurrence of protostelids in underwater environments and one of the few surveys of myxomycetes from aquatic systems.     

Production of extracellular enzymes by aquatic hyphomycetes

Preliminary studies of the production of extracellular enzymes in eight species of aquatic hyphomycetes showed that none of the organisms contained a proteinase activity. Pyrocateehol oxidase activity was restricted toI. hamata andP. constricta. Significant cellulase and α-amylase activity was found inL. curvula. Triacylglycerol lipase activity was maximum inP. constricta.     

Leaf-eating invertebrates as competitors of aquatic hyphomycetes

Summary Leaf-eating invertebrates selectively ingest leaf areas rich in fungal cells. The effect of this process on coincident and cumulative species diversity (species numbers and evenness) of the fungi was studied on 3 substrates (oak leaves, larch and spruce needles) in 2 hardwater and 2 softwater streams. Cumulative species number of colonizing fungi follows the equation S=k·A ^z(A=area below decay curve of the substrate, k=substrate-specific constant, Z=0.47). Higher feeding activity means faster weight loss of the substrate which leads to lower species richness of the fungi. The opposite is true for early successional stages on larch needles. Evenness of the fungi (distribution of individuals among species) is negatively correlated with feeding intensity by invertebrates, as measured by increased decay rates. The overall effect of leaf-eating invertebrates on aquatic hyphomycetes resembles that of potent competitors preempting substrate otherwise used by a late successional tail of relatively rare fungi.     

New and critical taxa of aquatic hyphomycetes

Species of Alatospora and Margaritispora have been studied in pure culture. The conidial morphology of 33 Alatospora isolates was examined. The concept of Alatospora acuminata is broadened to embrace strains with a high percentage of unbranched and triradiate conidia as well as those with large conidia with an arcuate axis and narrow branch insertion. Alatospora constricta is neotypified, and a new generic name is introduced to accommodate a species with similar conidia but different conidiogenesis. Margaritispora aquatica is neotypified and M. monticola is neotypified and recombined in a new genus.     

Mycorrhizal colonisation in plants from intermittent aquatic habitats

Several plant species with amphibious characteristics from intermittent aquatic habitats were examined for colonisation with arbuscular mycorrhizal fungi (AM), dark septate endophytes (DSE) and the ratio of aerenchyma in root tissue. We studied submerged specimens of Alisma plantago-aquatica, Mentha aquatica, Myosotis scorpioides, Oenanthe fistulosa, Gratiola officinalis, Glyceria fluitans, Sium latifolium and Teucrium scordium. In the first four, we also examined the emerged growth forms, which were grown under experimental conditions. Roots of all species were mycorrhizal and showed AM and DSE colonisation. The results suggest that AM colonisation may also be abundant in plants of aquatic environment. Arbuscules were not found in submerged specimens of M. aquatica, O. fistulosa and S. latifolium. The AM colonisation was generally higher in emerged specimens as compared to submerged ones. The aerenchyma ratio in root cross-sections ranged from 10 to 50% and in most cases did not differ between submerged and emerged specimens. No clear relationship between AM colonisation and aerenchyma ratio was recognized, while a positive correlation between AM and plant available phosphorous was established.     

Spore attachment and extracellular mucilage of aquatic hyphomycetes

Stages in conidiun attachment to surfaces of Lemmoniera aquatica and Mycocentrospora filiformis (freshwater Hyphomycetes) were studied at the light microscope and scanning and transmission electron microscope levels. Sigmoid conidia of M. filiformis attach by pre-existing conidial mucilage at the spore pole and at a point along the conidial body. Tetraradiate conidia of L. aquatica attach by the thigmotropic release of mucilage at the tips of the three "arms";. Germination in both species is followed by the production of germ tubes, germ hyphae and appressoria. The chemical composition of the mucilage involved in attachment was determined by enzymatic studies and lectin-gold cytochemical studies. The major component was found to be acidic poly-saccharide, comprising mainly ?-1, 3-glucan, N-acetyl-D-glucosamine and N-acetyl-neuraminic acid. Variation in mucilage composition exists between the two species, among different structures of the same species, and on different regions of the same structure. This indicates that mucilage producton in the two species is a dynamic process.The ability to secure rapid spore attachment, often in turbulent condition, would be a competitive advantage to these saprobic fungi in the colonization of substrata.     

Cell-wall-degrading enzymes of aquatic hyphomycetes: a review

Reports of cell-wall-degrading enzymes of aquatic hyphomycetes are reviewed, including pectinases, cellulases, hemicellulases, laminarinases and chitinases and the ability of these fungi to degrade lignin and straw. New evidence of enzymic activity is presented for 14 species.     

Habitat selection in two species of aquatic hyphomycetes

Two species of aquatic hyphomycetes,Tetracladium marchalianum andTricladium splendens, were isolated from decaying leaves in a stream.T. marchalianum was abundant on alder leaves but absent on beech leaves, which were dominated byT. splendens. It was hypothesized that differences in some chemical key factors in the leaves would account for differences in the distribution of the 2 species. In the experiment designed to test the hypothesis, combinations of sterilized leaves and isolated fungi were used. Differences in growth of FDA active mycelium were related to differences in leaf weight loss;T. splendens decomposed beech leaves andT. marchalianum decomposed alder leaves. Extracellular protease activity corresponded with these trends but there was no detectable protein loss in the leaves. Both fungi showed a nitrogen demand, and hydrolysis of leaf proteins was complemented with absorption of free amino acids and ammonium. High concentrations of free amino acids modified the pattern for habitat selection so thatT. splendens grew substantially on alder leaves andT. marchalianum colonized beech leaves. No protease activity was, however, found fromT. marchalianum on beech leaves, and it is concluded that a more general metabolic inhibition prevents extensive growth of this species on beech leaves. The low natural abundance ofT. splendens on alder leaves, where it may grow well, may be a consequence of a specific protease inhibition and competition from other species.     

Patterns of amino acid utilization by aquatic hyphomycetes

Summary The utilization of amino acids in leaf protein and leaf leachate by aquatic hyphomycetes was studied during decomposition in a combined field and laboratory experiment. Leaves were sampled from a stream which exhibited a seasonal variation in free amino acid concentration in surface water, reaching peaks in autumn and winter. In the leaf drift environment the concentration of amino acids was approximately two orders of magnitude higher than in surface water. Protein amino acid content, which was higher in alder leaves than in beech leaves, decreased exponentially and faster in alder leaves, so that protein amino acid content was similar in the two leaf types after 9–10 weeks decomposition. From 55% to 75% of leaf amino acids were used instantaneously by attached fungi, which grew well, especially on alder leaves, regardless of the presence of a grazing amphipod. If nitrogen was a limiting nutrient source for fungi, it appeared to be more advantageous to colonize alder leaves. Four times more fungal species were found on alder leaves than on beech leaves. The changes in concentration of amino acids in leaves and water was described by a set of differential equations. Rate constants for the transfer of amino acids from leaves and water were estimated from experimental data and the preference in fungi for protein-bound and free amino acids evaluated.The amounts of free amino acids in water absorbed by fungi varied between leaf types and leaves at different stages of decay. Experimental data showed a switching behaviour in fungal absorption of dissolved amino acids so that absorption became superproportional at a certain proportion of free amino acids available in the water.     

Testate amoebae communities from aquatic habitats in the Arctic

Summary Forty taxa of testate amoebae were found in 15 aquatic samples collected in East Greenland (Angmasssalik Region), Jan Mayen and N.W. Spitsbergen. The number of species per sample is rather small, and the contribution of strictly aquatic species to the fauna is limited. A geographical shift in the importance of some genera can be demonstrated. Centropyxis aerophila and Paraquadrula irregularis are two of the most frequent species. The first-named is characteristic for acidoligotrophic waters, while the latter belongs to an alkaline-mesotrophic community. A third community is named after the commonest species, Trinema lineare. It seems to prefer a somewhat intermediate type of water.     

Isolation of Legionella pneumophila from nonepidemic-related aquatic habitats.

Continuous centrifugation of large volumes of water from natural southeastern lakes allowed quantitative detection of Legionella pneumophila by direct immunofluorescent staining. Positive samples were injected intraperitoneally into guinea pigs, and the L. pneumophila were isolated and identified by their morphological, cultural, physiological, and serological characteristics.     

Laccase activity of lignicolous aquatic hyphomycetes isolated from the River Nile in Egypt

Eleven species of aquatic hyphomycetes were isolated from 92 samples of different lignin sources (unidentified wood segments, skeleton and neck of leaves, bark). The most common species were Pyramidospora casuarina (on 3.7% of samples), Triscelophorus monosporus (3.2%) and Flagellospora curvula (3%). Varying levels of laccase activity were present in most of the fungi included in this study. The laccase plate assay was found to be much less reliable than the spectrophotometric assay. Several factors including type of growth medium, the media pH and assay pH had marked effects on laccase activity. A few species produced high levels of laccase in both malt extract (ME) medium and low N medium; however, a majority of the species produced laccase in low nitrogen (N) medium (pH 4.5) but not in the ME medium. When the tested species were grown in low N medium at pH 4.5, six species showed acidic laccase (pH 4.5) activity; of these, four also showed alkaline laccase (pH 8.2) activity. Alatospora acuminata and Tetracladium marchalianum exhibited laccase activity only when grown in the low N medium at pH 8.2. These results indicate that aquatic hyphomycetes may play a role in the decomposition of lignin materials in freshwater environments. This revised version was published online in June 2006 with corrections to the Cover Date.     

Isolation of Legionella pneumophila from nonepidemic-related aquatic habitats.

Continuous centrifugation of large volumes of water from natural southeastern lakes allowed quantitative detection of Legionella pneumophila by direct immunofluorescent staining. Positive samples were injected intraperitoneally into guinea pigs, and the L. pneumophila were isolated and identified by their morphological, cultural, physiological, and serological characteristics.     

Fungal biodiversity in aquatic habitats

Fungal biodiversity in freshwater, brackish and marine habitats was estimated based on reports in the literature. The taxonomic groups treated were those with species commonly found on submerged substrates in aquatic habitats: Ascomycetes (exclusive of yeasts), Basidiomycetes, Chytridiomycetes, and the non-fungal Saprolegniales in the Class Oomycetes. Based on presence/absence data for a large number and variety of aquatic habitats, about 3,000 fungal species and 138 saprolegnialean species have been reported from aquatic habitats. The greatest number of taxa comprise the Ascomycetes, including mitosporic taxa, and Chytridiomycetes. Taxa of Basidiomycetes are, for the most part, excluded from aquatic habitats. The greatest biodiversity for all groups occurs in temperate areas, followed by Asian tropical areas. This pattern may be an artifact of the location of most of the sampling effort. The least sampled geographic areas include Africa, Australia, China, South America and boreal and tropical regions worldwide. Some species overlap occurs among terrestrial and freshwater taxa but little species overlap occurs among freshwater and marine taxa. We predict that many species remain to be discovered in aquatic habitats given the few taxonomic specialists studying these fungi, the few substrate types studied intensively, and the vast geographical area not yet sampled.     

Raised water temperature lowers diversity of hyporheic aquatic hyphomycetes

1. The hyporheic zone of a permanent first‐order stream was divided into a treatment and a control section using a 1 m deep sheet‐metal barrier. During a 4‐month pre‐treatment period, water temperatures in two transects of the two sections were not different. Upon heating, the water temperature in the treatment transect increased by an average of 4.3 °C over values in the control transect. 2. Eleven bimonthly core samples were taken from a treatment and a control transect, and recovered CPOM was classified as twigs, wood, grass, roots, cedar and deciduous leaves. 3. In both transects, twigs were the most common and deciduous leaves the least common substrates. The number of leaf fragments declined significantly in the heat‐treated transect. 4. Diversity and frequencies of occurrence of aquatic hyphomycetes were highest on leaves and lowest on grass and wood. On leaves, their frequency of occurrence was higher in control than in treatment samples. 5. Preliminary results with amplified and cloned 18S DNA sequences revealed many fungal taxa with high affinities to Basidiomycota, particularly to Limnoperdon incarnatum. 6. By itself, higher water temperature due to global warming is likely to lower the availability of substrates for, and therefore the occurrence of, aquatic hyphomycetes.     

Pellet size affects mycelial ergosterol content in aquatic hyphomycetes

Ergosterol was measured in mycelia of seven species of aquatic hyphomycetes grown in malt-extract broth. The harvested 21 d old pellets were grouped into 5-6 classes based on size, which were analyzed separately. In all but one species, there was a significant, positive correlation between the amount of ergosterol per unit mass and pellet diameter. Ignoring this correlation could result in the misleading conclusion that there is no relationship between mycelial mass and its absolute ergosterol content. The highest ergosterol concentrations were close to the average generally used to convert the amount of ergosterol in environmental samples to fungal biomass; the average was about half that value.     

Diversity of aquatic hyphomycetes in the aquatic ecosystems of the Western Ghats of India

Relationships between physico-chemical factors of waters, riparian vegetation, altitude and species richness of the hyphomycete communities in six rivers and a sulfur spring in the Western Ghats of Karnataka were analysed statistically. Linear regression and correlation between log fungal species and riparian vegetation was highly significant. The similarity in the fungal diversity between different rivers and the sulphur spring was evaluated by Sorensen's index. Generally, the indices of similarity in the mycoflora between the streams were high. However, in the streams of Lakya, Bhadra, Ranganathittu bird sanctuary and the sulfur spring the indices of similarity were low compared with the rest of the water systems. The low pH, low oxygen concentration, hardness, high iron, high temperature and sulfide contents of the waters of these streams are thought to be the reasons for the differences in these streams. Anguillospora longissima, Helicomyces roseus, Lunulospora curvula, Triscelophorus monosporus and Wiesneriomyces laurinus were found to be the most abundant species.     

Recovery of bdellovibrios from submerged surfaces and other aquatic habitats

The distribution of bdellovibrios was investigated over a wide geographical area of the Chesapeake Bay including some tributaries and subestuaries. Bdellovibrios were recovered from five aquatic habitats; water, sediment, oyster shell surface biofilm, zooplankton, and plants over a wide range of temperature and salinity measurements. Consistently, the greatest number of the predators was recovered from samples of biofilm irrespective of temperature and salinity. A decrease in the numbers and frequency of predators recovered from all habitats was observed at temperatures below 10°C. Only the shell surface biofilm samples yielded bdellovibrios 100% of the time. The organisms were recovered from 79% of water samples and 44% of sediment samples. The results reveal that bdellovibrios are surface-associated organisms and that this association appears to provide some protection for the predators at low temperatures.