Freshwater Lake In Japan Research Articles

Three new species of freshwater Diploneis from Japan

Three new Diploneis species are described from freshwater lakes in Japan. A complex wall structure is demonstrated in D. aokiensis sp. nov. and D. yamanakaensis sp. nov., where the basic alternation of transapical ribs (virgae) and striae is overlain by a system of secondary branches and struts supporting the external perforate surface. Diploneis linearifera sp. nov. possesses remarkable external slits, distributed irregularly around the margin of the valve and near the raphe. The grooves in the outer layer of the valve wall, which do not penetrate to the valve interior, have no known parallel in other diatoms but may be related to the angular holes noted previously in D. finnica (Ehrenberg) Cleve and D. marginestriata Cleve.

Diversity of Freshwater Thioploca Species and Their Specific Association with Filamentous Bacteria of the Phylum Chloroflexi

Phylogenetic diversity among filamentous sulfur-oxidizing bacteria of the genus Thioploca inhabiting freshwater/brackish environments was analyzed in detail. The 16S rRNA gene sequence of Thioploca found in a freshwater lake in Japan, Lake Okotanpe, was identical to that of Thioploca from Lake Ogawara, a brackish lake. The samples of the two lakes could be differentiated by the sequences of their 23S rRNA genes and 16S-23S rRNA internal transcribed spacer (ITS) regions. The 23S rRNA-based phylogenetic relationships between Thioploca samples from four lakes (Lake Okotanpe, Lake Ogawara, Lake Biwa, and Lake Constance) were similar to those based on the 16S rRNA gene sequences. In addition, multiple types of the ITS sequences were obtained from Thioploca inhabiting Lake Okotanpe and Lake Constance. Variations within respective Thioploca populations were also observed in the analysis of the soxB gene, involved in sulfur oxidation. As major members of the sheath-associated microbial community, bacteria of the phylum Chloroflexi were consistently detected in the samples from different lakes. Fluorescence in situ hybridization revealed that they were filamentous and abundantly distributed within the sheaths of Thioploca.

Sulfuritalea hydrogenivorans gen. nov., sp. nov., a facultative autotroph isolated from a freshwater lake

A novel facultatively autotrophic bacterium, designated strain sk43H(T), was isolated from water of a freshwater lake in Japan. Cells of the isolate were curved rods, motile and gram-reaction-negative. Strain sk43H(T) was facultatively anaerobic and autotrophic growth was observed only under anaerobic conditions. The isolate oxidized thiosulfate, elemental sulfur and hydrogen as sole energy sources for autotrophic growth and could utilize nitrate as an electron acceptor. Growth was observed at 8-32 °C (optimum 25 °C) and 6.4-7.6 (optimum pH 6.7-6.9). Optimum growth of the isolate occurred at NaCl concentrations of less than 50 mM. The G+C content of genomic DNA was around 67 mol%. The fatty acid profile of strain sk43H(T) when grown on acetate under aerobic conditions was characterized by the presence of C(16 : 0) and summed feature 3 (C(16 : 1)ω7c and/or iso-C(15 : 0) 2-OH) as the major components. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain was a member of the class Betaproteobacteria showing highest sequence similarity with Georgfuchsia toluolica G5G6(T) (94.7 %) and Denitratisoma oestradiolicum AcBE2-1(T) (94.3 %). Phylogenetic analyses were also performed using genes involved in sulfur oxidation. On the basis of its phylogenetic and phenotypic properties, strain sk43H(T) ( = DSM 22779(T) = NBRC 105852(T)) represents a novel species of a new genus, for which the name Sulfuritalea hydrogenivorans gen. nov., sp. nov. is proposed.

Armatimonas rosea gen. nov., sp. nov., of a novel bacterial phylum, Armatimonadetes phyl. nov., formally called the candidate phylum OP10

A novel aerobic, chemoheterotrophic bacterium, strain YO-36(T), isolated from the rhizoplane of an aquatic plant (a reed, Phragmites australis) inhabiting a freshwater lake in Japan, was morphologically, physiologically and phylogenetically characterized. Strain YO-36(T) was Gram-negative and ovoid to rod-shaped, and formed pinkish hard colonies on agar plates. Strain YO-36(T) grew at 20-40 °C with optimum growth at 30-35 °C, whilst no growth was observed at 15 °C or 45 °C. The pH range for growth was 5.5-8.5 with an optimum at pH 6.5. Strain YO-36(T) utilized a limited range of substrates, such as sucrose, gentiobiose, pectin, gellan gum and xanthan gum. The strain contained C(16 : 0), C(16 : 1), C(14 : 0) and C(15 : 0) as the major cellular fatty acids and menaquinone-12 as the respiratory quinone. The G+C content of the genomic DNA was 62.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain YO-36(T) belonged to the candidate phylum OP10 comprised solely of environmental 16S rRNA gene clone sequences except for two strains, P488 and T49 isolated from geothermal soil in New Zealand; strain YO-36(T) showed less than 80 % sequence similarity to strains P488 and T47. Based on the phylogetic and phenotypic findings, a new genus and species, Armatimonas rosea gen. nov., sp. nov., is proposed for the isolate (type strain YO-36(T) = NBRC 105658(T) = DSM 23562(T)). In addition, a new bacterial phylum named Armatimonadetes phyl. nov. is proposed for the candidate phylum OP10 represented by A. rosea gen. nov., sp. nov. and Armatimonadaceae fam. nov., Armatimonadales ord. nov., and Armatimonadia classis nov.

Lake Biwa and the ocean: geochemical similarity and difference

The average composition of water, bottom sediments, manganese (Mn) crusts, and Mn concretions from Lake Biwa (the largest freshwater lake in Japan) are re-examined, in conjunction with those of seawater, oceanic pelagic clay, and deep-sea Mn nodules. The purpose is to gain additional insights into the geochemical behaviors of elements in Lake Biwa and the ocean, which are quite different in ionic strength (or salinity), pH, water residence times, sediment accumulation rates, carbon fluxes to sediments, and the redox potential in sediments. Excluding a few millimeters of oxic surface sediment, there is no appreciable accumulation of Mn in the Lake Biwa bottom sediments due to reducing condition there. Consequently, other B-type cations [such as iron (Fe), gallium (Ga), copper (Cu), lead (Pb), cobalt (Co), tin (Sn), and bismuth (Bi), with subshell valence electron configuration of d1−10] are also less concentrated in the lake sediments than in the oceanic pelagic clay. In turn, B-type cations have much higher dissolved concentrations in the lake water than in the ocean. The rare earth elements (REE) mainly form organic complexes in the lake water and carbonate complexes in the ocean. REE are mostly associated with detritus aluminosilicate phases in Lake Biwa sediments but with phosphate phases in deep-sea sediments. Fe and Mn oxide phases are clearly separated in marine Mn nodules and crusts but not in Mn crusts and concretions from Lake Biwa. Useful parameters such as the enrichment factor (EAl) and logarithms of the distribution coefficient (log Kd) of elements between solid and liquid phases were estimated in both systems for further discussions.

Sulfuricella denitrificans gen. nov., sp. nov., a sulfur-oxidizing autotroph isolated from a freshwater lake

A novel facultatively anaerobic, sulfur-oxidizing bacterium, strain skB26(T), was isolated from anoxic water of a freshwater lake in Japan. The cells were rod-shaped, motile and Gram-negative. Strain skB26(T) oxidized elemental sulfur and thiosulfate to sulfate as sole energy sources. Strain skB26(T) was microaerobic and could also utilize nitrate as an electron acceptor, reducing it to nitrogen. Growth was observed at temperatures below 28 °C; optimum growth was observed at 22°C. The pH range for growth was 6.0-9.0, and the optimum pH was 7.5-8.0. Optimum growth of the isolate was observed in medium without NaCl, and no growth was observed in medium containing more than 220 mM NaCl. The G+C content of genomic DNA was around 59 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the strain was a member of the class Betaproteobacteria, and the closest cultivated relative was 'Thiobacillus plumbophilus' DSM 6690, with 93 % sequence similarity. Phylogenetic analyses were also performed using sequences of genes involved in sulfur oxidation, inorganic carbon fixation and nitrate respiration. On the basis of its phylogenetic and phenotypic properties, strain skB26(T) (=NBRC 105220(T) =DSM 22764(T)) is proposed as the type strain of a novel species of a new genus, Sulfuricella denitrificans gen. nov., sp. nov.

Implications of long-chain anteiso compounds in acidic freshwater lake environments: Inawashiro-ko in Fukushima Prefecture, Japan

A series of long-chain (⩾C 23) monomethyl-branched alkanes, alk-1-enes, alkanoic acids and alkanols were identified in settling particles and surface sediments from some acidic freshwater lakes in Japan by Fukushima et al. [Verh. Int. Verein. Limnol. 25 (1993) 835; Geochem. J. 30 (1996) 111]. Mass spectra of those branched compounds showed that the methyl side-chain is present at the C-3 position of alkanes, and at the ω-2 position in the functionalized compounds, i.e., the anteiso position. The present work was undertaken to evaluate the source of the anteiso compounds and to assess their utility as molecular markers of lake water acidity. The lake system examined is Inawashiro-ko, the third largest freshwater lake in Japan, where the pH is 5.0–5.5. The anteiso compounds are present in the sediments, as well as in suspended material in the lake water. In the water column, the majority of the anteiso compounds occur in the fine particulate matter (0.6 ≪ 40 μm). Analysis of the suspended materials in the inflowing river waters proves that the anteiso compounds are not transported from outside of the lake via any rivers, including the Nagase-gawa that acidifies the lake water. The results indicate that the anteiso compounds are produced within the lake by planktonic microbes and might be useful molecular markers for lake acidity.

Horizontal distribution of carbon and nitrogen and their isotopic compositions in the surface sediment of Lake Biwa

The horizontal distribution of the abundance and isotopic composition of carbon and nitrogen was studied on surface sediment samples (0–15 cm) collected from the entire area of Lake Biwa, the largest freshwater lake in Japan. As water depth increased, a marked increase in organic matter content was observed at the sampling sites, especially in the western North Basin, characterized by a steep slope. In the northwestern North Basin, which has no major inflowing streams, the sediments contained large amounts of organic matter, suggesting the possibility of lateral transportation of sedimented matter from other places by lake currents. The total amounts of carbon and nitrogen in the top-2 cm of sediment of the entire area of Lake Biwa were estimated to be 9.2 × 104 tC and 1.0 × 104 tN. The δ15N values in the littoral sediment were low and close to those in the inflowing river sediment, suggesting selective sedimentation of allochthonous organic matter onto the littoral area. In the North Basin, vertical profiles of organic matter content and δ13C values of the sediments in the littoral area showed a smaller downward decrease than in the profundal area, whereas δ15N values decreased with sediment depth in both areas. It was suggested that the littoral sediments contained abundant amounts of allochthonous and relatively refractory organic matter. Further, it was suggested that the autochthonous organic matter originated from primary production deposited mainly on the profundal zone and was easily decomposed in early diagenesis after sedimentation.

Palynology of a 250-m core from Lake Biwa: a 430,000-year record of glacial–interglacial vegetation change in Japan

Lake Biwa is situated in western Honshu, and is the largest and oldest freshwater lake in Japan. During 1982–1983, a long core was drilled to a bottom depth of 1422 m in order to investigate the palaeolimnological record, which contains 911 m of various sedimentary units overlying Palaeozoic–Mesozoic basements. A 249.5-m core of the uppermost bed (T Bed) was palynologically examined at intervals of ca. 2 m. The investigated part of the core covers approximately the last 430,000 years of the mid-Upper Pleistocene and Holocene, and five glacial–interglacial cycles can be recognized. Ten major vegetational zones could be recognized from the bottom to the surface. The zones bearing even numbers, BW-10, 8, 6, 4 and 2, matched glacial periods in which pollen of subarctic taxa (Pinaceae, Betula) and cool–temperate taxa ( Fagus, Lepidobalanus) was dominant. In the glacial periods, high pollen values for temperate conifers such as Cryptomeria, Cupressaceae and Sciadopitys indicate interstadial periods. Zones bearing odd numbers, BW-9, 7, 5, 3 and 1, matched interglacial periods with high pollen values for the warm–temperate taxon Cyclobalanopsis, or showed the characteristic appearance of Lagerstroemia, and temperate coniferous taxa ( Cryptomeria, Cupressaceae). There were two vegetational types in the interglacial periods. One was the type indicated by BW-9 and 1 zones, when warm–temperate evergreen broad-leaved trees such as Cyclobalanopsis and Castanopsis showed high pollen values, and the warm–temperate deciduous broad-leaved tree Lagerstroemia was lacking. The climate of these interglacial periods seems to have been cold and dry in winter, and warm and wet in summer. The other was the vegetational type recorded in BW-7, 5 and 3 zones, where Lagerstroemia showed low pollen values, and the warm–temperate evergreen broad-leaved trees mentioned above were poorly represented. The climate seems to have been mild and wet in winter, and cool and wet in summer. The dominant pollen values for cool–temperate deciduous broad-leaved taxa such as Fagus and Lepidobalanus are very important indicators of the initiation of both glacial and interglacial periods in western Japan.

Purification of freshwater picoplanktonic cyanobacteria by pour‐plating in ‘ultra‐low‐gelling‐temperature agarose’

SUMMARYSeven unialgal cultures of picoplanktonic cyanobacteria isolated from freshwater lakes in Japan were examined in the present study. They are assignable to the Cyanobium cluster of the Synechococcus group sensu Waterbury and Rippka (1989) based on morphology, GC content, fatty acid and quinon compositions. They include one blue‐green colored strain (NIES‐680) with only phycocyanin as well as the PCC strains of Cyanobium cluster (Waterbury and Rippka 1989) and six reddish colored strains (NIES‐715, ‐717, ‐718, ‐721, ‐722 and ‐723) with both phycocyanin and phycoerythrin. All the strains examined developed colonies in pour‐plates I of 1.4%‘ultra‐low‐gel‐ling‐temperature agarose’within 1 month. The colony numbers were 12–20 × 102 c.f.u. mL‐1. Most clones derived from the colonies were axenic by the bacteria‐free check. The length of this procedure, preculture excepted, was 4–6 weeks. Colony formation in pour‐plate II of 0.6% agarose was observed in the blue‐green strain (NIES‐680) and the three reddish strains (NIES‐717,‐721 and ‐723) after 1–2 months. The number of colonies formed on pour‐plate II were 1–2 × 102 c.f.u. mL‐1, much lower than those on pour‐plate I. Only a blue‐green strain formed colonies on spread plates of 0.6% agarose. The colony numbers developed were 10–15 × 102 c.f.u. mL‐1 and similar to those on pour‐plate I. The other reddish strains did not develop colonies on spread plates. The pour‐plating method developed provides a highly efficient and successful method for obtaining axenic clonal cultures of planktonic cyanobacteria.

Diagenetic changes of lignin compounds in a more than 0.6 million-year-old lacustrine sediment (Lake Biwa, Japan)

A vertical profile of lignin in the upper 700 m layer of a 1400 m sediment core of Lake Biwa, an oligotrophic freshwater lake in Japan, was determined using a CuO oxidative degradation method. The results indicated that lignin is found throughout the core, demonstrating lignin to be very stable for over 0.6 million years. Moreover, the upper 250 m (approximately 0.6 million years old) segment of the sediment core was investigated to determine the apparent long term degradation rate of lignin. A downward lignin concentration decrease is observed over the upper 250 m of the core which corresponds to a calculated half life of at least approximately 40 × 10 4 years, assuming that lignin decrease is due to its in situ degradation (diagenesis).

Distribution of lipid-class compounds in bottom sediments of freshwater lakes with different trophic status, in Japan

Unbound and bound lipid-class compounds (mono- and di-carboxylic acids, β- and ω-hydroxy acids, n-alkanes, n-alcohols and perylene) were studied in bottom sediments collected from four freshwater lakes in Japan, with different trophic status (Lakes Motosu, Biwa, Haruna and Suwa). Concentrations of some lipid components relative to total organic carbon (TOC) showed positive or negative correlations with the primary productivity of the lakes. n-Saturated C 12-C 19 fatty acids (FA's), branched-chain FA's, unsaturated FA's and C 14-C 19 fatty alcohols, which are probably of autochthonous origin, appear to increase with an increase in primary productivity, whereas n-saturated C 20-C 32 FA's, C 20-C 30 fatty alcohols, dicarboxylic acids, n-alkanes and perylene, which are probably of terrestrial origin, appear to decrease with an increase in primary productivity. These results indicate that primary productivity of lakes is an important factor controlling the distributions of organic molecules in the bottom sediments. On the other hand, concentrations of β-hydroxy acids relative to TOC did not show a correlation with primary productivity. Because these acids are derived from bacterial activity, their distributions may be controlled by sedimentary environments (such as oxic or anoxic) rather than primary productivity.

Phosphorus excretion by some zoobenthos in a eutrophic freshwater lake and its temperature dependency.

The phosphorus excretion rate and its temperature dependency were investigated experimentally in four dominant species of zoobenthos in eutrophic freshwater lakes in Japan. The rates for the fourth instar larvae of Chironomus plumosus, Tokunaga-yusurika akamusi and Chaoborus flavicans and for Limnodrilus spp. were 1.44, 0.73, 5.82 and 0.49 ( 10 -1 gP Emgd Ew-1 Ed-1), respectively, at 15. The Q10 values of the excretion rate for Chironomus plumosus, Chaoborus flavicans and Limnodrilus spp. were 2.19, 1.66 and 2.00 below 30, respectively. The larvae of T. akamusi showed the lowest Q10 value of 1.20 below 15. Inorganic phosphorus accounted for more than 55% of the excreted total phosphorus for C. plumosus and 85% for Limnodrilus spp. The contribution of phosphate excretion by zoobenthos to the phosphate release from lake sediment was discussed.