Chemical Constraints Governing the Origin of Metabolism: The Thermodynamic Landscape of Carbon Group Transformations under Mild Aqueous Conditions

The thermodynamics of organic chemistry under mildaqueous conditions was examined in order to begin to understand itsinfluence on the structure and operation of metabolism and itsantecedents. Free energies (G) were estimated for four types ofreactions of biochemical importance – carbon-carbon bond cleavage andsynthesis, hydrogen transfer between carbon groups, dehydration ofalcohol groups, and aldo-keto isomerization. The energies werecalculated for mainly aliphatic groups composed of carbon, hydrogen,and oxygen. The energy values showed (1) that generally when carbon-carbon bond cleavage involves groups from different functional groupclasses (i.e., carboxylic acids, carbonyl groups, alcohols, andhydrocarbons), the transfer of the shared electron-pair to the morereduced carbon group is energetically favored over transfer to themore oxidized carbon group, and (2) that the energy of carbon-carbonbond transformation is primarily determined by the functional groupclass of the group that changes oxidation state in the reaction (i.e., the functional group class of the group that donates the sharedelectron-pair during cleavage, or that accepts the incipient sharedelectron-pair during synthesis). In contrast, the energy of hydrogentransfer between carbon groups is determined by the functional groupclass of both the hydrogen-donor group and the hydrogen-acceptorgroup. From these and other observations we concluded that thechemistry involved in the origin of metabolism (and to a lesser degreemodern metabolism) was strongly constrained by (1) the limited redox-based transformation energy of organic substrates that is readilydissipated in a few energetically favorable irreversible reactions;(2) the energy dominance of a few transformation half-reactions thatdetermines whether carbon-carbon bond transformation (cleavage orsynthesis) is energetically favorable (G < –3.5 kcal/mol), reversible(G between ±3.5 kcal/mol), or unfavorable (G > +3.5 kcal/mol);and (3) the dependence of carbon group transformation energy on thefunctional group class (i.e., oxidation state) of participatinggroups that in turn is contingent on prior reactions and precursors inthe synthetic pathway.     

Carbon Uptake and the Metabolism and Transport of Lipids in an Arbuscular Mycorrhiza

Both the plant and the fungus benefit nutritionally in the arbuscular mycorrhizal symbiosis: The host plant enjoys enhanced mineral uptake and the fungus receives fixed carbon. In this exchange the uptake, metabolism, and translocation of carbon by the fungal partner are poorly understood. We therefore analyzed the fate of isotopically labeled substrates in an arbuscular mycorrhiza (in vitro cultures of Ri T-DNA-transformed carrot [Daucus carota] roots colonized by Glomus intraradices) using nuclear magnetic resonance spectroscopy. Labeling patterns observed in lipids and carbohydrates after substrates were supplied to the mycorrhizal roots or the extraradical mycelium indicated that: (a) ¹³C-labeled glucose and fructose (but not mannitol or succinate) are effectively taken up by the fungus within the root and are metabolized to yield labeled carbohydrates and lipids; (b) the extraradical mycelium does not use exogenous sugars for catabolism, storage, or transfer to the host; (c) the fungus converts sugars taken up in the root compartment into lipids that are then translocated to the extraradical mycelium (there being little or no lipid synthesis in the external mycelium); and (d) hexose in fungal tissue undergoes substantially higher fluxes through an oxidative pentose phosphate pathway than does hexose in the host plant.     

Electrophysiological investigation of the conduction of excitation in the pterygopalatine ganglion of the cat

When responses in some nerves of the pterygopalatine ganglion of the cat in situ to stimulation of its other nerves were recorded it was found that most fibers passing through the ganglion are continuous sympathetic postganglionic fibers (at least three groups). Most of the parasympathetic preganglionic fibers forming synapses on neurons of the ganglion constitute a group of fibers with the same threshold of excitation. Intracellular recording from single neurons of the pterygopalatine ganglion showed that stimulation of the Vidian nerve evokes orthodromic spike potentials in some neurons of the ganglion with a short latent period, and in others with a long latent period (2.5–6.0 and 10–44 msec, respectively). Evidently only fast-conducting fibers terminate synaptically on most neurons of the ganglion and only slow-conducting fibers on some of them. Recording from intact nerves of the pterygopalatine ganglion revealed no tonic activity in them. Microelectrode recording from single neurons of the ganglion showed that either the frequency of generation of spike potentials is relatively low (1–3/sec) or such potentials are absent altogether.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 514–520, September–October, 1976.     

The impact of electron donors and anode potentials on the anode-respiring bacteria community

Both anode potentials and substrates can affect the process of biofilm formation in bioelectrochemical systems, but it is unclear who primarily determine the anode-respiring bacteria (ARB) community structure and composition. To address this issue, we divided microbial electrolysis cells (MECs) into groups, feeding them with different substrates and culturing them at various potentials. Non-turnover cyclic voltammetry indicated that the extracellular electron transfer components were uniform when feeding acetate, because the same oxidation peaks occurred at − 0.36 ± 0.01 and − 0.17 ± 0.01 V (vs. Ag/AgCl). Illumina MiSeq sequencing revealed that the dominating ARB was Geobacter, which did not change with different potentials. When the MECs were cultured with sucrose and mixed substrates, oxidation peak P3 (− 0.29 ± 0.015 V) occurred at potentials of − 0.29 and 0.01 V. This may be because of the appearance of Unclassified_AKYG597. In addition, oxidation peak P4 (− 0.99 ± 0.01 V) occurred at high and low potentials (0.61 and − 0.45 V, respectively), and the maximum current densities were far below those of the middle potentials. Illumina MiSeq sequencing showed that fermentation microorganisms (Lactococcus and Sphaerochaeta) dominated the biofilms. Consequently, substrate primarily determined the dominating ARB, and Geobacter invariably dominated the acetate-fed biofilms with potentials changed. Conversely, different potentials mainly affected fermentable substrate-fed biofilms, with dominating ARB turning into Unclassified_AKYG59.

     

The aerobic mineralization of organic compounds in the saline Lake Grevelingen (The Netherlands) (VI)

Summary During a one year period the uptake of aspartic acid and of a mixture of amino acids was determined using¹⁴C-labeled substrates as described by WRIGHT and HOBBIE (1966). By this technique the activity is analyzed of that part of the bacterial population which is able to utilize the added substrate. For comparison purposes the activity of the total heterotrophic bacterial population was determined by measurement of the oxygen consumption rate. From the oxygen consumption rate (mg O₂.l^–1.h^–1) the carbon mineralization rate (mg C.l^–1.h^–1) was calculated by applying a conversion factor of 0.29.Aspartic acid was respired for 80% and the amino acid mixture for 43%. From the maximum uptake rates, the potential yearly uptake of the substrate in question can be calculated. These data indicate the relative importance of the several subpopulations in the carbon mineralization process as a whole. The highest value of the potential yearly uptake was obtained for the amino acid mixture; the comparable value for the uptake of aspartic acid was slightly lower.The carbon mineralization rate as calculated from the oxygen uptake experiments was about 150–200 g C.m^–2.year^–1. The potential yearly uptake as determined with the¹⁴C-labeled amino acid mixture was only 2.8% of the amount of mineralized carbon, as calculated from the oxygen uptake experiments. This percentage is very low in view of the fact that 35–55% of the organic carbon of living phytoplankton and zooplankton consists of protein (HAGMEIER, 1961) and that the aerobic mineralization of amino acids is a very common property among the heterotrophic bacterial population (SEPERS, 1979). The value of the applied activity measurements was investigated in order to obtain information about the relation between the uptake process as measured with¹⁴C-labeled substrates and the activity of the bacterial population in situ. The results of this study have been published bij SEPERS and VAN ES (1979).     

Nitrate depletion in the riparian zone of a small woodland stream

Field enrichments with nitrate in two spring-fed drainage lines within the riparian zone of a small woodland stream near Toronto, Ontario showed an absence of nitrate depletion. Laboratory experiments with riparian substrates overlain with nitrate enriched solutions revealed a loss of only 5–8% of the nitrate during 48 h incubation at 12°C. However, 22–24% of the initial nitrate was depleted between 24 and 48 h when a second set of substrate cores was incubated at 20°C. Short-term (3 h) incubations of fresh substrates amended with acetylene were used to estimate in situ denitrification potentials which varied from 0.05–3.19 g N g^–1 d^–1 for organic and sandy sediments. Denitrification potentials were highly correlated with initial nitrate content of substrate samples implying that low nitrate levels in ground water and riparian substrates may be an important factor in controlling denitrification rates. The efficiency of nitrate removal in spring-fed drainage lines is also limited by short water residence times of < 1 h within the riparian zone. These data suggest that routes of ground water movement and substrate characteristics are important in determining nitrate depletion within stream riparian areas.     

Water stress effects on toluene biodegradation by Pseudomonas putida

We quantified the effects of matric and solute waterpotential on toluene biodegradation by Pseudomonasputida mt-2, a bacterial strain originally isolated fromsoil. Across the matric potential range of 0 to – 1.5 MPa,growth rates were maximal for P. putida at – 0.25MPa and further reductions in the matric potentialresulted in concomitant reductions in growth rates.Growth rates were constant over the solute potential range0 to – 1.0 MPa and lower at – 1.5 MPa. First ordertoluene depletion rate coefficients were highest at0.0 MPa as compared to other matric water potentialsdown to – 1.5 MPa. Solute potentials down to – 1.5 MPadid not affect first order toluene depletion ratecoefficients. Total yield (protein) and carbon utilizationefficiency were not affected by water potential, indicatingthat water potentials common to temperate soils were notsufficiently stressful to change cellular energyrequirements. We conclude that for P. putida: (1)slightly negative matric potentials facilitate faster growthrates on toluene but more negative water potentials resultin slower growth, (2) toluene utilization rate per cell massis highest without matric water stress and is unaffected bysolute potential, (3) growth efficiency did not differ acrossthe range of matric water potentials 0.0 to – 1.5 MPa.     

A hyperefficient process for enzymatic cellulose hydrolysis in the intensive mass transfer reactor

Summary A new type of bioreactor, the intensive mass transfer reactor (IMTR), has been developed for enzymatic hydrolysis of cellulose. Using T. reesei cellulases (2 FPU/ml), 3.5–6% of sugars were obtained in the IMTR after 0.5–2 h of cellulose hydrolysis with a productivity of 30–73 g/l.h.     

Seasonal growth of the submerged macrophyte Ceratophyllum demersum L. in mesotrophic Lake Vechten in relation to insolation,temperature and reserve carbohydrates

Seasonal growth of a Ceratophyllum demersum stand in Lake Vechten, The Netherlands, varied considerably during 1978, '79 and '81. The biomass was highest in 1981 (max. 115 g ash-free dry weight m^–2). The 1978 growth trend was similar to that of 1981 with slightly lower net annual production (max. 92 g AFDW m^–2). The vegetation almost disappeared in 1979 (max. 24 g AFDW m^–2). These large differences in biomass could not be explained by differences in insolation but were mainly attributed to the severe winter of 1978–'79 which slowed plant development and full maturity was attained only after the diurnal insolation had decreased.Reserve carbohydrates were primarily starch and water-soluble sugars. Starch concentrations varied between 71.5 and 24.7 mg g^–1 AFDW in the winter and summer, and total sugar concentrations between 24.9 and 20.2 mg g^–1 AFDW, respectively. The non-reducing sugars tended to predominate in summer and the reducing sugars in winter. The value of these reserves for maintenance, growth and survival was assessed by calculating plant carbon budgets for several seasons.It was concluded that C. demersum relies heavily on its developmental timing and energy-conserving physiological mechanisms to survive extended periods of stress and in these respects is analogous to a typical terrestrial shade plant.     

Investigating DNA damage in tannery workers occupationally exposed to trivalent chromium using comet assay

DNA damage of peripheral lymphocytes in 60 workers occupationally exposed to trivalent chromium [Cr(III)] in a tannery was studied using comet assay. The urinary and blood chromium levels were detected as a biomarker of internal exposure. The 90 subjects were divided into three groups: (i) exposure group I included 30 tannery workers highly exposed to chromium from tanning department; (ii) exposure group II included 30 tannery workers with moderate chromium exposure from finishing department; (iii) control group included 30 individuals without exposure to physical or chemical genotoxic agents. No significant difference was found among the three groups for age and smoking. The results showed that the medians of blood and urinary Cr of two exposure groups were significantly higher than those of control group (P < 0.01). And the medians of blood and urinary Cr of exposure group I were significantly higher than those of exposure group II (P < 0.05 or P < 0.01). The medians of mean tail length (MTL) of the three groups were 5.33 (2.90–8.50), 3.43 (2.31–8.29) and 2.04 (0.09–3.83) μm, respectively; The medians of mean tail moment (MTM) of the three groups were 6.28 (2.14–11.81), 3.41 (1.25–11.07) and 0.53 (0.13–3.29), respectively. The MTL and MTM of two exposure groups were significantly higher than those of control group (P < 0.01). The MTL and MTM of exposure group I were significantly higher than those of exposure group II (P < 0.01). The results of the present investigation suggest that occupational exposure to trivalent chromium can lead to a detectable DNA damage of human peripheral lymphocytes. Moreover, DNA damage was associated with chromium levels in blood. DNA damage may serve as a valuable effective biomarker and total chromium in blood may serve as a useful internal exposure biomarker in the population occupationally exposed to trivalent chromium.     

Drought avoidance and the effect of local topography on trees in the understorey of Bornean lowland rain forest

The water relations of two tree species in the Euphorbiaceae werecompared to test in part a hypothesis that the forest understorey plays anintegral role in drought response. At Danum, Sabah, the relatively commonspecies Dimorphocalyx muricatus is associated with ridgeswhilst another species, Mallotus wrayi, occurs widely bothon ridges and lower slopes. Sets of subplots within two 4 -hapermanent plots in this lowland dipterocarp rain forest, were positioned onridges and lower slopes. Soil water potentials were recorded in1995–1997,and leaf water potentials were measured on six occasions. Soil water potentialson the ridges (–0.047 MPa) were significantly lower than onthe lower slopes (–0.012 MPa), but during the driest periodin May 1997 they fell to similarly low levels on both sites (–0.53MPa). A weighted 40-day accumulated rainfall index was developedtomodel the soil water potentials. At dry times, D.muricatus(ridge) had significantly higher pre-dawn (–0.21 v.–0.57 MPa) and mid-day (–0.59 v.–1.77 MPa) leaf water potentials than M.wrayi (mean of ridge and lower slope). Leaf osmotic potentials ofM. wrayi on the ridges were lower (–1.63MPa) than on lower slopes (–1.09 MPa), withthose for D. muricatus being intermediate (–1.29MPa): both species adjusted osmotically between wet and dry times.D. muricatus trees were more deeply rooted thanM. wrayi trees (97 v. 70cm). M. wrayi trees had greaterlateral root cross-sectional areas than D. muricatus treesalthough a greater proportion of this sectional area for D.muricatus was further down the soil profile. D.muricatus appeared to maintain relatively high water potentialsduring dry periods because of its access to deeper water supplies and thus itlargely avoided drought effects, but M. wrayi seemed to bemore affected yet tolerant of drought and was more plastic in its response. Theinteraction between water availability and topography determines these species'distributions and provides insights into how rain forests can withstandoccasional strong droughts.     

Properties of C-N.M.R. spectra of O-(1-carboxyethylidene) derivatives of methyl β-d-galactopyranoside: models for determination of pyruvic acid acetal structures in polysaccharides

¹³C-N.m.r. spectra were recorded of compounds containing O-(1-carboxyethylidene) groups linked to galactopyranose and fucopyranose derivatives. These compounds are useful as aids in determination of the positions and configurations of pyruvic acid acetal substituents in polysaccharides. Chemical shifts of non-protonated acetal carbons depend on whether the acetal ring is 5-membered (δ_c 107–109.5) or 6-membered (δ_c 100.5–102.4). The C-3 signals of 3,4-(1-carboxyethylidene) acetals are typical, being at δ_c 81 and in the case of the barium salt of the methyl β-d-galactopyranoside derivative. The exact value depends on the configuration, whether it is as in 6 (δ_c 81.1) or 5 (δ_c 80.4). The CH₃ signals of proton-n.m.r. spectra are also diagnostically useful, falling at δ 1.97 and 2.07 respectively. (The foregoing shift-values are pH-dependent). The pyruvylated galactan from the snail, Pomacea lineata, was shown to contain some residues that could be assigned a structure corresponding, in the positions of acetal substitution and acetal configuration, to structure 6. Compound 6 (barium salt) is of interest as its ¹³C-n.m.r. spectrum lacks non-protonated carbonyl and acetal carbon resonances, when obtained by the usual procedures. While this is principally because of long T₁ values, the non-protonated acetal carbon signals are comparatively broad, possibly through slow conformational interchange. In the case of the carbonyl resonance, the lack of sensitivity is because of a low n.O.e. value of 1.4, approximately one half that of other carbon atoms in the molecule.     

Microbial community utilization of recalcitrant and simple carbon compounds: impact of oak-woodland plant communities

Little is known about how the structure of microbial communities impacts carbon cycling or how soil microbial community composition mediates plant effects on C-decomposition processes. We examined the degradation of four ¹³C-labeled compounds (starch, xylose, vanillin, and pine litter), quantified rates of associated enzyme activities, and identified microbial groups utilizing the ¹³C-labeled substrates in soils under oaks and in adjacent open grasslands. By quantifying increases in non-¹³C-labeled carbon in microbial biomarkers, we were also able to identify functional groups responsible for the metabolism of indigenous soil organic matter. Although microbial community composition differed between oak and grassland soils, the microbial groups responsible for starch, xylose, and vanillin degradation, as defined by ¹³C-PLFA, did not differ significantly between oak and grassland soils. Microbial groups responsible for pine litter and SOM-C degradation did differ between the two soils. Enhanced degradation of SOM resulting from substrate addition (priming) was greater in grassland soils, particularly in response to pine litter addition; under these conditions, fungal and Gram + biomarkers showed more incorporation of SOM-C than did Gram – biomarkers. In contrast, the oak soil microbial community primarily incorporated C from the added substrates. More ¹³C (from both simple and recalcitrant sources) was incorporated into the Gram – biomarkers than Gram + biomarkers despite the fact that the Gram + group generally comprised a greater portion of the bacterial biomass than did markers for the Gram – group. These experiments begin to identify components of the soil microbial community responsible for decomposition of different types of C-substrates. The results demonstrate that the presence of distinctly different plant communities did not alter the microbial community profile responsible for decomposition of relatively labile C-substrates but did alter the profiles of microbial communities responsible for decomposition of the more recalcitrant substrates, pine litter and indigenous soil organic matter.     

Xylose chemostat isolates of Saccharomyces cerevisiae show altered metabolite and enzyme levels compared with xylose, glucose, and ethanol metabolism of the original strain

The efficient conversion of xylose-containing biomass hydrolysate by the ethanologenic yeast Saccharomyces cerevisiae to useful chemicals such as ethanol still remains elusive, despite significant efforts in both strain and process development. This study focused on the recovery and characterization of xylose chemostat isolates of a S. cerevisiae strain that overexpresses xylose reductase- and xylitol dehydrogenase-encoding genes from Pichia stipitis and the gene encoding the endogenous xylulokinase. The isolates were recovered from aerobic chemostat cultivations on xylose as the sole or main carbon source. Under aerobic conditions, on minimal medium with 30 g l^–1 xylose, the growth rate of the chemostat isolates was 3-fold higher than that of the original strain (0.15 h^–1 vs 0.05 h^–1). In a detailed characterization comparing the metabolism of the isolates with the metabolism of xylose, glucose, and ethanol in the original strain, the isolates showed improved properties in the assumed bottlenecks of xylose metabolism. The xylose uptake rate was increased almost 2-fold. Activities of the key enzymes in the pentose phosphate pathway (transketolase, transaldolase) increased 2-fold while the concentrations of their substrates (pentose 5-phosphates, sedoheptulose 7-phosphate) decreased correspondingly. Under anaerobic conditions, on minimal medium with 45 g l^–1 xylose, the ethanol productivity (in terms of cell dry weight; CDW) of one of the isolates increased from 0.012 g g^–1 CDW h^–1 to 0.017 g g^–1 CDW h^–1 and the yield from 0.09 g g^–1 xylose to 0.14 g g^–1 xylose, respectively.     

Deoxyribonucleic acid base composition and taxonomy in the genus Geotrichum Link

The molar percentage of guanine + cytosine (% GC) in the DNA from 25 yeast-like fungi related to the genus Geotrichum has been measured. This criterion together with the biochemical characteristics allow the division of the species into 3 groups: one group resembling G. candidum (% GC: 31.5–42) and containing 8 imperfect and 6 perfect forms. In this group only G. capitatum has a lower % GC (31.5). A second group of 6 species resembling the genus Trichosporon (57–60%) and a third intermediate category of 4 species (42–53.5%) were observed. The GC-values correlate well with biochemical characters, e.g. the presence of urease, the number of organic substrates assimilated, and also with the presence of characters typical of the Ascomycetes or the Basidiomycetes.This work was supported by I.N.S.E.R.M. (Institut National de la Santé et de la Recherche Médicale) C.R.L. n^o 76 1 153 8.     

Fluxes of gases in an ice related ecosystem in the north-western Weddell Sea

Summary During the European Polarstern Study (EPOS leg 1 and leg 2) measurements of temperature, salinity, inorganic nutrients, chlorophyll-a, oxygen and total inorganic carbon dioxide were performed from October to January 1988–1989 in north-south sections at 47–49 °E in the NW Weddell Sea from approximately 58 °S to 63 °S (Hempel 1989; Hempel et al. 1989). In order to explain parts of the obtained data, a time-dependent ecological model was constructed by Svansson (1991). He found that a moderate mixing with a constant diffusion coefficient from sea surface downwards resulted in good agreement between computed and measured chlorophyll. In this paper we introduce the gas fluxes, mainly oxygen but also carbon dioxide, into the model work. It turns out that air-sea fluxes are necessary to explain the vertical oxygen distribution. The annual development of chlorophyll, phosphate, oxygen and total inorganic carbon dioxide are computed. Hours of day-light, losses and the eddy diffusion coefficient are allowed to vary during the year with the condition that the mean total chlorophyll at 14 selected leg 1 stations was nearly double the magnitude of that of 18 selected leg 2 stations. This yields variations consistent with the observations. Different steady-state solutions after 91 days are also tested to show effects of one selected variation at a time, for example the eddy diffusion coefficient or the loss rate. The oxygen air-sea flux, of about 90 mmol m^–2 day^–1 in the time variable model computation, is compared to estimated fluxes by a gas transfer formula. The formula used gives a flux which is about 5 times smaller than the model flux. Some of the 91 days solutions give results of fluxes which are less than 90 mmol m^–2 day^–1 but still higher than the transfer formula result. Fluxes of total inorganic carbon dioxide in the model computation are always directed from air to sea.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Male hypofertility induced by Paraquat consumption in the non-target parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae)

The effects of a herbicide – Paraquat – on male development and reproduction were tested on the parasitoid wasp Anisopteromalus calandrae (Hymenoptera, Pteromalidae) by injecting host larvae with different concentrations of this substance. Data measured were: (1) developmental success, (2) sperm stock in seminal vesicles, (3) ability to copulate and transfer sperm, and (4) offspring production. Both developmental success and sperm in seminal vesicles were reduced in the “Paraquat” groups. However, neither sperm stored in the females’ spermatheca, nor offspring production (number of female offspring and sex ratio) differed from controls, whatever the host treatment. The decreased of male sperm reserve in ‘‘Paraquat” group is likely to reduce their reproductive success because they can succefully inseminated less female than control males. These males are thus hyporfertiles. Because Paraquat has non-negligible consequences on non-target parasitoid males, it is likely to affect natural and controlled insect populations.     

The Sugar Model: Autocatalytic Activity of the Triose–Ammonia Reaction

Reaction of triose sugars with ammonia under anaerobic conditions yielded autocatalytic products. The autocatalytic behavior of the products was examined by measuring the effect of the crude triose–ammonia reaction product on the kinetics of a second identical triose–ammonia reaction. The reaction product showed autocatalytic activity by increasing both the rate of disappearance of triose and the rate of formation of pyruvaldehyde, the product of triose dehydration. This synthetic process is considered a reasonable model of origin-of-life chemistry because it uses plausible prebiotic substrates, and resembles modern biosynthesis by employing the energized carbon groups of sugars to drive the synthesis of autocatalytic molecules.     

Genetic structure and differentiation of four Lethenteron taxa from the Far East, deduced from allozyme analysis

Genetic structure and differentiation among four Lethenteron taxa, L. japonicum, L. kessleri, and two groups of L. reissneri, collected from Japan and the Far Eastern region of Russia, were investigated by electrophoretic analysis. Several complete-allele substitutions were found between all possible pairs of taxa in regions of sympatry, strongly suggesting the existence of reproductive isolation between them. Therefore, four Lethenteron taxa should be regarded as discrete species, respectively. In each taxon, the genetic variability within each population (H=0.062 – 0.127 for L. japonicum, H=0.062– 0.128 for L. kessleri, H=0.026 – 0.148 for the northern group of L. reissneri, and H = 0.015 – 0.102 for the southern group of L. reissneri) was considerable, suggesting large effective sizes for most populations. The sample of L. japonicum collected from Kyiya, the basin of Amur, was somewhat divergent from the other intraspecific samples. This may have resulted mainly because it does not migrate to the sea. In contrast L. kessleri has a fluvial life style, but the genetic differentiation between populations (G_ST=0.117, D = 0.000 – 0.061) was less than that for each group of L. reissneri (G_ST = 0.493, D=0.000 – 0.226 for the northern group and G_ST=0.660, D = 0.008 – 0.422 for the southern group), probably meaning more recent dispersal of L. kessleri than the two groups of L. reissneri. The parasitic and anadromous L. japonicum appeared to be closely related to L. kessleri (D=0.042 – 0.090) and the northern group of L. reissneri (D=0.163 – 0.355), which have nonparasitic and fluvial life styles, whereas the southern group of L. reissneri was greatly divergent from the other three Lethenteron species (D=0.559 – 0.926), suggesting that the former three species might be monophyletic.     

Decomposition patterns of unprocessed and processed lignocellulosics in a freshwater fish pond

In an attempt to recycle the lignocellulosic wastes like Eichhornia crassipes, Salvinia cucullata and rice (Oryza sativa) straw as manurial inputs in freshwater fish pond ecosystem, a decomposition experiment was carried out in litter bags in an oligotrophic freshwater fish pond environment, with the above mentioned three substrates in unprocessed and microbially processed forms. The loss rates, associated microbial groups, oxygen consumption patterns and other related parameters like carbon, nitrogen, phosphorus, cellulose, hemicellulose and lignin were analysed. The mean daily dry matter loss rates (unprocessed: 10.44>6.97>1.97 and processed: 11.03>8.21>3.67) and oxygen uptake rate (unprocessed: 0.675>0.571>0.568 mg O₂ g^–1 h^–1 and processed: 0.592>0.424>0.407 mg O₂ g^–1 h^–1) in raw and processed substrates were in the sequence Eichhornia > rice straw > Salvinia. The oxygen consumption pattern almost covariated with variations in temperature of pond water, daily dry matter loss rates and fungal counts on substrates. During the decay, the percentage of N and P increased whereas that of C decreased, resulting in lowering of C/N and C/P ratios of the substrates. The structural polymeric fractions like cellulose and hemicellulose decreased along with dry matter whereas the lignin content increased after an initial decrease due to loss of other structural carbohydrates resulting in apparent per cent gain of lignin. A higher number of different heterotrophic bacterial groups was observed in the processed substrates as compared to their raw counterparts. However, cellulolytic bacterial numbers were found to fluctuate through the study period. The fungal load was found to be decreasing gradually as the decay progressed. In this study, bacteria were found to be the prominent microbial group responsible for the decay. The nitrogen-fixing, phosphatase-producing and phosphorus-solubilising bacterial groups were observed to play an important role in lowering the C/N and C/P ratios of the decomposing substrates during decay.