Kandikere R. Sridhar

Initial Colonization, Nutrient Supply, and Fungal Activity on Leaves Decaying in Streams

ABSTRACT Aquatic hyphomycetes dominate leaf decomposition in streams, and their biomass is an important component in the diet of leaf-eating invertebrates. After 2 weeks of exposure in a first-order stream, maple leaf disks had low levels of fungal biomass and species diversity. Spore production by aquatic hyphomycetes also was low. Subsets of these disks were left in the stream for another 3 weeks or incubated in defined mineral solutions with one of three levels of nitrate and phosphate. Stream disks lost mass, increased ergosterol levels and spore production, and were colonized by additional fungal species. External N and P significantly stimulated mass loss, ergosterol accumulation, and spore production of laboratory disks. On disks incubated without added N and P, ergosterol levels declined while conidium production continued, suggesting conversion of existing hyphal biomass to propagules. In all other treatments, approximately equal amounts of newly synthesized biomass were invested in hyphae and conidia. Net yield (fungal biomass per leaf mass lost) varied between 1% (in the laboratory, without added N or P) and 31% (decay in stream). In most treatments, the three aquatic hyphomycete species that dominated spore production during the first 2 weeks in the stream also produced the largest numbers of conidia in the following 3 weeks. Principal-component analysis suggested two divergent trends from the initial fungal community established after 2 weeks in the stream. One culminated in the community of the second phase of stream exposure, and the other culminated in the laboratory treatment with the highest levels of N and P. The results suggest that fungal production in streams, and, by extension, production of invertebrates and higher tropic levels, is stimulated by inorganic N and P.

Research on the Indian Subcontinent

Aquatic hyphomycetes were first found and described from streams, ponds and lakes in temperate regions, and research efforts into their ecology, physiology and taxonomy continue to concentrate on North American and European species (Chap. 1). The principal objective of this chapter is to summarize and discuss the research carried out on aquatic hyphomycetes in the Indian subcontinent and to suggest strategies that might make further studies more useful.

Microbacterium arthrosphaerae sp. nov., isolated from the faeces of the pill millipede Arthrosphaera magna Attems

A Gram-reaction-positive, rod-shaped bacterium, designated strain CC-VM-Y(T), was isolated from the faeces of the pill millipede Arthrosphaera magna Attems from India and was subsequently studied to determine its taxonomic position. Based on16S rRNA gene sequence similarities, the isolate clearly grouped with members of the genus Microbacterium. On the basis of pairwise comparisons of the 16S rRNA gene sequences, strain CC-VM-Y(T) was most closely related to Microbacterium insulae DS-66(T) (98 %), Microbacterium hydrocarbonoxydans DSM 160809(T) (97.8 %) and Microbacterium hominis NBRC 15708(T) (97.9 %). The peptidoglycan contained the amino acids ornithine (Orn), alanine (Ala), glycine (Gly), homoserine (Hsr) and glutamic acid (Glu) in an approximate molar ratio of 1.0 : 0.8 : 2.2 : 0.8 : 0.3. In addition, substantial amounts of threo-3-hydroxy glutamic acid (Hyg) were detected, which is characteristic of peptidoglycan type B2β. The acyl type of the peptidoglycan was glycolyl. The menaquinones of strain CC-VM-Y(T) were MK-13 (72 %), MK-12 (25 %) and MK-11 (3 %). The polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, one unknown phospholipid and one unknown glycolipid. The fatty acid profile comprised anteiso-C(15 : 0), iso-C(16 : 0) and anteiso-C(17 : 0) as the major fatty acids, which was congruent with fatty acid profiles of other members of the genus Microbacterium. The results of physiological and biochemical tests as well as DNA-DNA hybridizations with the most closely related species, M. insulae, M. hydrocarbonoxydans and M. hominis, revealed clear phenotypic and genotypic differences between strain CC-VM-Y(T) and other members of the genus Microbacterium. Based on these results, strain CC-VM-Y(T) ( = DSM 22421(T)  = CCM 7681(T)) represents a new species of the genus Microbacterium, for which the name Microbacterium arthrosphaerae sp. nov. is proposed.

Aquatic hyphomycetes on leaf litter in and near a stream in Nova Scotia, Canada

On four dates spread evenly throughout 1991, leaves were collected at six sites near (within 25 m) and in a stream in Nova Scotia, Canada. Loose conidia were recovered by flotation and reproductive potential of aquatic hyphomycetes was estimated by an aeration technique. A total of 33 species with multiradiate or sigmoid spores were found at the five terrestrial sites, and 26 species were recovered from the stream site. The highest number of species per site occurred on leaves collected from the stream, followed by leaves from two locations periodically exposed to flooding and finally by leaves from three sites never covered by water. The percentage of leaves that released conidia after aeration was 89 at terrestrial sites and 100 at the stream site.

Fungal biomass and diversity in sediments and on leaf litter in heavy metal contaminated waters of Central Germany

Ergosterol, as indicator of fungal biomass, was measured in the CPOM (coarse particulate organic matter; ≥ 5 mm) and FPM (fine particulate matter; ≤ 1 mm) sediment fractions of 11 heavy metal contaminated streams, springs and ponds in Central Germany. At 7 sites, ergosterol concentrations of FPM were below the detection limit. At the remaining sites, they corresponded to a fungal biomass of 0.03 - 0.06 % of FPM. Corresponding values for the CPOM fractions were 0.1 - 1.3 %. Both fractions produced conidia of aquatic hyphomycetes, either directly upon aeration (CPOM) or indirectly by colonization, followed by spore release, of sterile target disks. Between 0.05 and 63 conidia per mg substrate were released from naturally deposited leaves upon aeration and from Alms glutinosa leaves that had been exposed for four weeks, recovered and aerated. Canonical analysis of principal coordinates, based on presence/absence of fungal species, did not reveal significant correlations with site or substrate. The survival of an impoverished fungal community in and on the sediments of water bodies under severe anthopogenic stress suggests the maintenance of at least basic ecological functions and raises the possibility of recovery upon removal of the stress.

Nutritional and antinutritional components of Canavalia spp. seeds from the west coast sand dunes of India

Seeds of two coastal sand dune wild legumes, Canavalia cathartica and Canavalia maritima from the west coast of India were analyzed for their nutritional and antinutritional properties. The seeds contained 35.5 and 34.1% crude protein, 52.8 and 50.5% crude carbohydrates, 1.3 and 1.7% crude lipids and 3.1 and 3.5% ash content, respectively. Among the minerals, potassium was the highest followed by phosphorus. Globulins and albumins constituted the major seed proteins of both plants. Most of the essential amino acids were at adequate levels. Although the crude lipids were below 2%, the unsaturated fatty acids were high. Seeds did not contain tannins and trypsin inhibitors. The levels of total phenolics were low, but showed high hemagglutination activity. The nutritional properties of these seeds have been compared with other Canavalia spp. and wild unconventional or tribal legumes. Overall, the study results suggest that the seeds of C. cathartica and C. maritima possess potential nutritive value particularly higher protein, essential amino acids and low levels of antinutritional factors. These wild legumes are adapted to low nutrient, high saline and drought conditions of the coastal sand dunes; their conservation and domestication are warranted as potential alternative sources of protein.

Nutritional quality evaluation of velvet bean seeds (Mucuna pruriens) exposed to gamma irradiation

Effects of gamma irradiation on Mucuna pruriens seeds at various doses (0, 2.5, 5, 7.5, 10, 15 and 30 kGy) on the proximate composition, mineral constituents, amino acids, fatty acids and functional properties were investigated. Gamma irradiation resulted in a significant increase of crude protein at all doses, while the crude lipid, crude fibre and ash showed a dose-dependent decrease. Raw Mucuna seeds were rich in minerals (potassium, phosphorus, calcium, magnesium, iron and selenium). Sodium, copper and manganese were significantly decreased on irradiation at all the doses, while magnesium and iron showed a significant decrease only above 10 kGy. The essential amino acids of raw and gamma-irradiated Mucuna seeds were comparable with the FAO/WHO recommended pattern. A significant increase of in vitro protein digestibility was seen in seeds irradiated at 30 kGy. High amounts of unsaturated fatty acids in Mucuna seeds decreased significantly after irradiation. However, linoleic acid was not present in raw seeds but detected after irradiation and it was elevated to high level at 30 kGy. Behenic acid, a major anti-nutritional factor, was reduced significantly on irradiation, indicating the positive effect of gamma irradiation on Mucuna seeds. Significant enhancement in the water absorption and oil absorption capacities, protein solubility, emulsion activity and improvement in the gelation capacity was recorded after irradiation. Results of the present investigation reveal that application of gamma irradiation does not affect the overall nutritional composition and can be used as an effective method of preservation of Mucuna seed and their products.

Aquatic hyphomycetes and leaf decomposition in contaminated groundwater wells in Central Germany

Six heavy metal contaminated groundwater wells near abandoned copper shale mines of Mansfelder Land in Central Germany yielded 13 aquatic hyphomycete species (3-7 per site) on immersed Alnus glutinosa leaves. Anguillospora sp. 2, Cylindrocarpon sp. and Tetracladium marchalianum were the three top conidial producers. Mass loss rates and release of conidia were below those of leaves exposed in surface streams with similar or higher heavy metal loads, while ergosterol levels were comparable. In food choice experiments, Gammarus fossarum distinguished between leaves conditioned in the six wells. Consumption rates correlated with numbers of released conidia but not with ergosterol levels of the substrate.

Siansivirga zeaxanthinifaciens gen. nov., sp. nov., a novel zeaxanthin-producing member of the family Flavobacteriaceae isolated from coastal seawater of Taiwan

A strictly aerobic, Gram-negative, rod-shaped bacterium (strain CC-SAMT-1(T)) showing gliding motility was isolated from coastal seawater of China Sea, Taiwan. Strain CC-SAMT-1(T) synthesizes all-trans-zeaxanthin (6.5 ± 0.5 mg g(-1) dry biomass) as a predominant xanthophyll carotenoid. As determined by 16S rRNA gene analysis, strain CC-SAMT-1(T) shared very high sequence similarity to the members of the genera Mariniflexile (96.1-95.3%) and Gaetbulibacter (96.0-95.9%); however, it formed a distinct phyletic lineage distantly associated with Mariniflexile species. Polar lipid profile constitutes phosphatidylethanolamine, four unidentified aminolipids, four unidentified lipids, and an unidentified glycolipid. Strain CC-SAMT-1(T) contains excessive unidentified aminolipid lipid (AL2-4) and glycolipid contents, and therefore clearly distinct from Mariniflexile species. Major fatty acids (> 5% of total fatty acids) were iso-C(15:0) (14.8%), iso-C(17:0) 3-OH (11.8%), iso-C(15:1) G (10.6%), anteiso-C(15:0) (9.7%), C(16:0) (8.1%), iso-C(16:0) 3-OH (7.9%), iso-C(15:0) 3-OH (7.5%), and summed feature 3 (containing C(16:1) ω6c and/or C(16:1) ω7c) (7.5%). Menaquinone-6 (MK-6) was major respiratory quinone. DNA G+C content was 33.7 mol%. Based on polyphasic taxonomy, strain CC-SAMT-1(T) represents a novel genus and species in the family Flavobacteriaceae for which the name Siansivirga zeaxanthinifaciens gen. nov., sp. nov. is proposed. The type strain is CC-SAMT-1(T) (= BCRC 80315(T) = JCM 17682(T)).

Effects of 4-n-nonylphenol on aquatic hyphomycetes

We measured the removal of 4-n-nonylphenol (between 50 and 500 μg L(-1)) from an aqueous solution with or without linden and oak leaf disks. More 4-n-NP was removed when the leaves were first exposed for 3 weeks in a stream, which allowed colonization by aquatic hyphomycetes. The response of fungal sporulation rates from beech, linden, maple and oak leaves to increasing levels of 4-n-NP was complex. Linear regressions were non-significant, arguing against a no-threshold model. The response at the lowest concentration (50 μg L(-1)) was between 7% (beech) and 67% (maple) higher than in the absence of 4-n-NP, however, the difference was not significant. The number of sporulating species of aquatic hyphomycetes was significantly higher at the lowest concentration than in the control treatment without 4-n-NP. The composition of the fungal community was affected by leaf species but not by 4-n-NP concentration. The results suggest the presence of a weak hormeotic effect. The known ability of aquatic hyphomycetes and other fungi to degrade nonylphenols and related substances, combined with fungal resilience in their presence, makes decaying leaves potential candidates for bioremediation.