Studies in aquatic fungi of Varanasi IV. new records and notes on taxonomy

Summary In continuation with the studies in aquatic fungi of Varanasi, four more fungi viz., Achlya apiculata, A. oblongata var. oblongata, Blastocladiella simplex and Pythiogeton ramosum have been isolated and described as occurring new to the Indian aquatic flora; while P. sterilis has been assigned to synonymy under P. ramosum Hamid's isolate A. oblongata var. oblongata has been excluded from the valid identification.     

Tropical aquatic fungi

This paper reports on the distribution of fungal communities in aquatic habitats in tropical regions and highlights differences in the taxa observed in freshwater and marine habitats. Ascomycetes are dominant on substrata in marine environments, with few basidiomycetes and discomycetes. Equally, few freshwater basidiomycetes and discomycetes have been reported from the tropics. In marine habitats, Dothideomycetes dominate on mangrove substrata, and halosphaeriaceous species are most numerous on submerged woody substrata in coastal waters, while yeasts are common in seawater and estuarine habitats. In freshwater, Ingoldian anamorphic fungi are most numerous on decaying leaves, while ascomycetes (Dothideomycetes, Sordariomycetes) are prevalent on submerged/exposed woody substrata. Unique fungi are found in tropical waters and differ from those in temperate locations.     

Studies in aquatic fungi of varanasi. X. Additional new or interesting records of aquatic phycomycetes

Summary Four species of the genusSaprolegnia Nees, viz.,Saprolegnia diclina, S. delica, S. mixta, S. monoica var.glomerata, and three from the achlyoid group, viz.,Achlya colorata, A. racemosa, andA. americana were isolated on various substrata used as baits from the vicinity of University campus. ExcludingS. diclina andA. americana, all the above fungi are reported as occurring new from this country.     

Cytochromes of aquatic fungi

The cytochrome systems of two classes of aquatic fungi, the Oomycetes and Chytridiomycetes, were studied by means of reduced-minus-oxidized difference spectra at room and at low temperature. At room temperature, all of these fungi have a c-type cytochrome with an absorption maximum at 551 mmu and a b-type cytochrome at 564 mmu. The Oomycetes have a-type cytochromes at 605 mmu, and the Chytridiomycetes have a-type cytochromes at 606 mmu (Blastocladiales) or at 609 mmu (Monoblepharidales). Additional b-type cytochromes are found at 557 mmu in the Oomycetes and at approximately 560 mmu in the Chytridiomycetes. The data obtained from spectra at low temperature are consistent with these conclusions. Thus, the difference spectra reveal variation between the cytochrome systems of these two classes of aquatic fungi.     

Surprising spectra of root-associated fungi in submerged aquatic plants

Similarly to plants from terrestrial ecosystems, aquatic species harbour wide spectra of root-associated fungi (RAF). However, comparably less is known about fungal diversity in submerged roots. We assessed the incidence and diversity of RAF in submerged aquatic plants using microscopy, culture-dependent and culture-independent techniques. We studied RAF of five submerged isoetid species collected in four oligotrophic freshwater lakes in Norway. Levels of dark septate endophytes (DSE) colonization differed among the lakes and were positively related to the organic matter content and negatively related to pH. In total, we identified 41 fungal OTUs using culture-dependent and culture-independent techniques, belonging to Mucoromycotina, Chytridiomycota, Glomeromycota, Ascomycota as well as Basidiomycota. Sequences corresponding to aquatic hyphomycetes (e.g. Nectria lugdunensis, Tetracladium furcatum and Varicosporium elodeae) were obtained. Eight arbuscular mycorrhizal taxa belonging to the orders Archaeosporales, Diversisporales and Glomerales were also detected. However, the vast majority of the fungal species detected (e.g. Ceratobasidium sp., Cryptosporiopsis rhizophila, Leptodontidium orchidicola, and Tuber sp.) have previously been known only from roots of terrestrial plants. The abundance and phylogenetic distribution of mycorrhizal as well as nonmycorrhizal fungi in the roots of submerged plants have reshaped our views on the fungal diversity in aquatic environment.     

Temperature alters interspecific relationships among aquatic fungi

Temperature is a key factor in determining the structure and performance of fungal assemblages on decomposing plant litter in streams. However, little is known of how temperature affects interspecific relationships among fungi. We compared the growth of four aquatic hyphomycetes co-occurring in temperate streams, in monocultures and all species combinations when exposed to five temperatures from 11 to 27 °C. In monocultures, maximum growth rates of Heliscus submersus, Lunulospora curvula and Varicosporium elodeae occurred at 27 °C whereas Articulospora tetracladia had the lowest growth rate. At 27 °C, the increase in species diversity had no effect on the growth of V. elodeae, increased the growth of H. submersus and L. curvula, and decreased the growth of A. tetracladia. Results suggest that within a species' optimal temperature range the growth of that species increases with higher fungal diversity, while outside this range growth decreases with diversity.     

Observations On Nuclear Division in vegetative hyphae of aquatic fungi

Summary Achlya aquatica, A. prolifera andA. racemosa are additional examples of fungi in whose vegetative mycelium, the nuclei do not divide in a manner directly comparable to ordinary mitosis. During division the entire nucleus, which consists of variously shaped chromatin and the nucleolus, becomes angular and elongates. The chromatin separates into two portions, which are situated at opposite ends of the elongating nucleus. As division proceeds the nuclei separate. Each sister nucleus sonsists of chromatin and a portion of the divided nucleolus. Spindless, chromosomal filaments or metaphase plates could not be observed during division.     

Comparative biochemistry of oxygen toxicity in lactic acid-forming aquatic fungi

Taxonomically diverse aquatic fungi ranging in oxidative capabilities from obligate aerobes to aerotolerant anaerobes were examined for growth under hyperbaric (0.9 atm) O₂, and for the ability to degrade H₂O₂ and O ₂ ^- . The results support the presumption that several Oomycetes and Chytridiomycetes are biochemically adapted to environments low in O₂. Results further indicate significant differences between Oomycetes and Chytridiomycetes in the enzymatic means of dealing with O ₂ ^- and H₂O₂, supporting the recent concept of a great evolutionary divergence between the groups. In general, facultative anaerobes and aerotolerant anaerobes were more severely inhibited by hyperbaric O₂, and they exhibited lower superoxide dismutase (SOD), catalase and peroxidase activities than did strongly-oxidative species. SOD activity, which was detected in all isolates, was insensitive to cyanide in Oomycetes but cyanide sensitive in the Blastocladiales (Chytridiomycetes). All strongly-oxidative Oomycetes exhibited readily-detectable catalase and peroxidase activities, while activities were very low or absent in strongly-fermentative species. As with the Oomycetes, peroxidase activities among the Blastocladiales were high in aerobes and low in strong fermenters. Surprisingly, however, none of the Blastocladiales, including strongly-oxidative species, exhibited substantial catalase activity. Catalase and SOD activities in faculatively anaerobic Oomycetes increased with increasing O₂ concentration; but even in hyperbaric (0.5 atm) O₂, activities for both enzymes in the aerotolerant anaerobe Aqualinderella fermentans were very low compared with activities in aerobes.Abbreviation SOD Superoxide dismutase     

Notes on Algerian aquatic fungi: Pythium pythioides

Pythium pythioides (Roze & Cornu) Ramsbottom is recorded from Algeria. Since its original discovery in 1869 this species had not been found back. A brief history is given and morphological and reproductive characters are discussed.     

Resistance of perch eggs to attack by aquatic fungi

In the distinctive gelatinous Perca fluviatilis egg mass, limited fungal growth by Aphanomyces and Saprolegnia spp. especially S. diclina , occurred within dead eggs but did not spread to adjacent live eggs. Perch eggs exposed to parasitic challenge by Saprolegnia parasitica , S. dieclina (type III) and S. ferax , under fluctuating temperature regimes replicating spring water temperatures, did not have significantly greater mortality than did unchallenged controls. The observations suggest that perch eggs have some anti-fungal properties which usually prevent the spread of fungus throughout the egg mass and that under normal spring temperatures there should be negligible ecological consequences of fungal infection in perch egg masses.     

Extracellular enzymatic activity of aquatic and aero-aquatic conidial fungi

Nineteen species of aquatic and areo-aquatic conidial fungi were tested for their ability to produce extracellular enzymes which degrade cellulose, starch, lipids, proteins and tannic acid. The cellulolytic activity was determined by using both solid and liquid media. The activity of other enzymes was examined using solid media. Two-thirds of the species were able to hydrolyze soluble cellulose (CMC) incorporated in solid and liquid media with varying degrees of activity. Extracellular culture filtrates ofAegerita candida, Helicodendron giganteum andH. tubulosum contained a Cl-Cx enzyme complex that could degrade both soluble cellulose (CMC) and crystalline cellulose (filter paper). Lipase activity was demonstrated by 11 species. Fourteen of the species showed activity for amylase and protease, but only 11 of the 16 were capable of degrading tannic acid.     

Seasonal periodicity of aquatic fungi in tanks at Kurukshetra,India

The occurrence, distribution and seasonal periodicity of 49 species of aquatic fungi belonging to the orders Chytridiales, Lagenidiales, Blastocladiales, Saprolegniales and Peronosporales from two tanks of Kurukshetra, India, is described. Seasonal periodicity was found to be governed by temperature.     

Ecological studies on some aquatic fungi of Gorakhpur,India

Summary The distribution of aquatic fungi in six waters of Gorakhpur, ranging in pH from 5.6–8.8 has been studied from April 1963 to March 1964. The thirty species collected during this study belong to Blastocladiales, Saprolegniales, Lagenidiales and Peronosporales. These have been placed in three groups: acid, alkaline and neutral according their tolerance of hydrogen-ion concentration.A distinct seasonal variation in occurrence of these species has been noted and though the individual periodicity patterns vary, the low temperatures of winter months (about 18°C) are most suitable for growth of most of the species.

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Résumé La répartition du mycète aquatique dans les eaux de Gorakhpur (Inde) ayant pH d'ordre 5.6 à 8.8 a été étudiée depuis l'avril 1963 jusqu'á mars '64. Les trente espèces, recueillies pendant cette étude, appartiennent aux families Blastocladiales, Saprolegniales, Lagenidiales et Peronosporales. Selon leur tolérance de la concentration d'ion d'hydrogène elles ont été groupées — acides, alcalines ou neutres.Une variation périodique très nette en rencontre de ces espèces est observée et bien que les modèles de périodicité varient, les températures peu élevées (environ 18°C) d'hiver sont les plus favorables pour la croissance de la plupart des espèces.

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This forms part of a thesis accepted for the degree of Ph. D. in the University of Gorakhpur, India.     

Diversity and activity of aquatic fungi under low oxygen conditions

1. The objective was to test whether a decrease in oxygen concentration in streams affects the diversity and activity of aquatic hyphomycetes and consequently leaf litter decomposition. 2. Senescent leaves of Alnus glutinosa were immersed for 7 days in a reference stream, for fungal colonization, and then incubated for 18 days in microcosms at five oxygen concentrations (4%, 26%, 54%, 76% and 94% saturation). Leaf decomposition (as loss of leaf toughness), fungal diversity, reproduction (as spore production) and biomass (ergosterol content) were determined. 3. Leaf toughness decreased by 70% in leaves exposed to the highest O₂ concentration, whereas the decrease was substantially less (from 25% to 45%) in treatments with lower O₂. Fungal biomass decreased from 99 to 12 mg fungi g⁻¹ ash‐free dry mass on exposure to 94% and 4% O₂ respectively. Sporulation was strongly inhibited by reduction of dissolved O₂ in water (3.1 × 10⁴ versus 1.3 × 10³ spores per microcosms) for 94% and 4% saturation respectively. 4. A total of 20 species of aquatic hyphomycetes were identified on leaves exposed to 94% O₂, whereas only 12 species were found in the treatment with 4% O₂ saturation. Multidimensional scaling revealed that fungal assemblages exposed to 4% O₂ were separated from all the others. Articulospora tetracladia, Cylindrocarpon sp. and Flagellospora curta were the dominant species in microcosms with 4% O₂, while Flagellospora curvula and Anguillospora filiformis were dominant at higher O₂ concentrations. 5. Overall results suggest that the functional role of aquatic hyphomycetes as decomposers of leaf litter is limited when the concentration of dissolved oxygen in streams is low.     

Assessment of root endophytic aquatic hyphomycetous fungi on plant growth

The role of root endophytic aquatic hyphomycetous fungi in plant health was studied by employing pot experiments. Three aquatic hyphomycetous fungi Heliscus lugdunensis, Tetrachaetum elegans and Tetracladium nainitalense isolated as root endophytes of riparian plants were artificially inoculated into two test plants viz., Solanum melongena and Hibiscus esculentus. T. elegans and H. lugdunensis showed significant effects (fresh weight, dry weight and length of shoots and roots) on both test plants, whereas T. nainitalense had no effect.     

Occurrence and coexistence of arbuscular mycorrhizal fungi and dark septate fungi in aquatic macrophytes in a tropical river-floodplain system

In this study, carried out in four water bodies in the Upper Paraná River floodplain, we assessed the occurrence of root colonization by arbuscular mycorrhizal fungi (AMF) and dark septate fungi (DSF), as well as the AMF species richness associated with 24 species of aquatic macrophytes belonging to different life forms. AMF were found in nine species of macrophytes and DSF in 16 species among the 24 investigated. AM colonization occurred mainly in eudicotiledons (five of the six species evaluated) and the Paris morphology was the most common type. Co-occurrence of AMF and DSF was observed in seven species of macrophytes (Commelinaceae sp. 1, Limnobium laevigatum (H.B.K. ex Willd) Heine, Hygrophila cf. costata, Myriophyllum brasiliense (Camb), Polygonum acuminatum Kunth, P. ferrugineum Wedd and P. stelligerum Cham). Four species of macrophytes (Pistia stratiotes L., Eichhornia crassipes (Mart.) Solms, Egeria najas Planch and Nymphaea amazonum Mart. & Zucc) were not colonized by any type of fungi. In total, 27 morphotypes of AMF were recorded, and spores occurred both in the rhizosphere of macrophytes whose roots were internally colonized by AMF and in non-colonized macrophytes. Acaulospora delicata, Acaulospora aff. laevis, Acaulospora longula, Glomus lamellosum, Glomus luteum and NID 1 (a non-identified species) were the most frequent species. Samples collected close to the roots of N. amazonum had the highest AMF richness (20 species), but this plant was not colonized by fungi. A species richness curve indicated that more root-associated fungi than reported here are likely present in this floodplain.