Community structure of bacteria and fungi responsible for rice straw decomposition in a paddy field estimated by PCR-RFLP analysis

Rice straw including leaf sheaths and blades put in nylon mesh bags was placed in the plow layer of a Japanese paddy field after harvest under upland conditions and after transplanting of rice seedlings under flooded conditions. In addition, rice straw that was decomposed under the upland conditions during the off-crop season in winter was placed again in soil at the time of transplanting. The materials were collected periodically to analyze the community structure of the bacteria and fungi responsible for rice straw decomposition by PCR-RFLP analysis. The PCR products with 27f and 1492r primers designed for bacterial 16S rDNA and with EF3 and EF4 primers designed for fungal 18S rDNA were digested with four restriction endonucleases (Hinf I, Sau3A I, Hae III, EeoR I). Bacterial communities in the decomposing rice straw were different from each other between upland and flooded conditions, between leaf sheaths and blades, and between straw samples with and without decomposition under upland conditions during the off-crop season. Fungal communities in the decomposing rice straw were also different between the leaf sheaths and blades under upland soil conditions. Score plots of bacterial and fungal communities in the principal component analysis were separated from the plot of the straw materials along with the duration of the placement, indicating the succession of bacterial and fungal communities in decomposing rice straw with time.     

Bacterial communities associated with nodal roots of rice plants along with the growth stages: Estimation by PCR-DGGE and sequence analyses

Bacterial communities in rice roots that developed from different nodes and at different growth stages were compared by using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA. Rice root samples were collected at three stages, namely tillering (July 2), maximum tillering (July 21), and ripening (September 12). The bacterial diversity in rice roots was found to increase along with the growth stages of the rice plants as well as the root age from the numbers of DGGE bands. The community structure of the bacteria was also found to change with the growth stages and root age from cluster analysis. Sequence analysis of the DGGE bands indicated that the dominant bacteria associated with rice roots were Gram-negative bacteria, especially β-Proteobacteria irrespective of the growth stages and root age. DGGE bands related to Janthinobacterium agaricidamnosum W1r3T and Clostridium sp. FCB90-3 were ubiquitous in many roots irrespective to the sampling date. Principal component analysis enabled to characterize the DGGE bands related to nitrogen-fixing Azoarcus spp., and Azovibrio sp. BS20-3 in the samples collected on July 2 and on July 21, and the myxobacteria collected on September 12, respectively, as representative bacteria in the bacterial communities. The habitat around older rice roots at every sampling date was more reductive than that around younger rice roots, and the DGGE bands related to Spirochaeta spp. were specific in older roots at every sampling date. Some specific bacteria that were most closely related to the DGGE bands were found from principal component analysis to characterize young and old. roots at each growth stage as follows: aerobes Flavobacterium sp. 90 clone 2 and Janthinobacterium agaricidamnosus W1r3T in young roots and facultative anaerobes Dechloromonas sp. MissR and Anaeromyxobacter dehalogenans 2CP-3 in old nodal roots on July 2, strict anaerobe Geobacter pelophilus Dfr2 and aerobes Nitrosospira sp. Nsp17 and uncultured Nitrospira sp. clone 4-1 in old roots on July 21, and different Clostridium spp. in both young and old roots and Desulfovibrio magneticus RS-1 in old roots on September 12, respectively. A larger number of the closest relatives of anaerobic bacteria grew at the late stage than at the early stages, and in old roots than in younger roots. Thus, the environment of paddy roots was remarkably heterogeneous as a bacterial habitat, where not only the whole root system but also a root may create oxic and anoxic environments.     

Nutrient storage in termite (Macrotermes bellicosus) mounds and the implications for nutrient dynamics in a tropical savanna Ultisol

The role of mounds of the fungus-growing termite Macrotermes bellicosus (Smeathman) in nutrient recycling in a highly weathered and nutrient-depleted tropical red earth (Ultisol) of the Nigerian savanna was examined by measuring stored amounts of selected nutrients and estimating their rates of turnover via the mounds. A study plot (4?ha) with a representative termite population density (1.5?mounds?ha^?1) and size (3.7?±?0.4?m in height, 2.4?±?0.2?m in basal diameter) of M. bellicosus mounds was selected. The mounds were found to contain soil mass of 9249?±?2371?kg?ha^?1, composed of 7502?±?1934?kg?ha^?1 of mound wall and 1747?±?440?kg?ha^?1 of nest body. Significant nutrient enrichment, compared to the neighboring topmost soil (Ap1 horizon: 0–16?cm), was observed in the nest body for total nitrogen (N) and exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and in the mound wall for exchangeable K only. In contrast, available (Bray-1) phosphorus (P) content was found to be lower in both the mound wall and the nest body than in the adjacent topmost soil horizon. Consequently, the mounds formed by M. bellicosus contained 1.71?±?0.62?kg?ha^?1 of total N, 0.004?±?0.003?kg?ha^?1 of available P, 3.23?±?0.81?kg?ha^?1 of exchangeable Ca, 1.11?±?0.22?kg?ha^?1 of exchangeable Mg and 0.79?±?0.21?kg?ha^?1 of exchangeable K. However, with the exception of exchangeable K (1.2%), these nutrients amounted to less than 0.5% of those found in the topmost soil horizon. The soil nutrient turnover rate via M. bellicosus mounds was indeed limited, being estimated at 1.72?kg?ha^?1 for organic carbon (C), 0.15?kg?ha^?1 for total N, 0.0004?kg?ha^?1 for available P, 0.15?kg?ha^?1 for exchangeable Ca, 0.05?kg?ha^?1 for exchangeable Mg, and 0.06?kg?ha^?1 for exchangeable K per annum. These findings suggest that the mounds of M. bellicosus, while being enriched with some nutrients to create hot spots of soil nutrients in the vicinity of the mounds, are not a significant reservoir of soil nutrients and are therefore of minor importance for nutrient cycling at the ecosystem scale in the tropical savanna.     

Overexpression of the LASAP2 gene for secretory acid phosphatase in white lupin improves the phosphorus uptake and growth of tobacco plants

Secretion of acid phosphatase (APase) from the roots to take up phosphorus (P) is a well-known strategy of plants under P-deficient conditions. White lupin, which shows vigorous growth in low-P soils, is noted for its ability to secrete APase under P-deficient conditions. The APase secreted by white lupin roots is stable in soil solution and shows low substrate specificity, suggesting that genetic modification of plants using the APase gene LASAP2 might improve their ability to use organic P. The objective of the present study was to evaluate the potential of LASAP2 transgenic plants to increase organic P utilization. Dry matter production and P accumulation were higher in LASAP2 transgenic tobacco plants grown in gel media containing soluble phytate as the sole P source than in wild-type tobacco plants. Phosphorus uptake by the transgenic plants also increased in soil culture conditions. LASAP2 was apparently more effective in the liberation of organic P, including phytate, in the soil than the native tobacco APase. Thus, the enzymatic stability of LASAP2 in the soil appears to be an important factor for P acquisition.     

Effect of temperature on survival,growth and malformation of cultured larvae and juveniles of the seven-band grouper Epinephelus septemfasciatus

The effects of rearing temperature (23–29 °C) during the larval and juvenile stage on survival, growth and skeletal malformations in the seven-band grouper Epinephelus septemfasciatus were investigated. The survival rate of juveniles 30–40 mm in total length emerging from eggs was higher at 25 and 26 °C (0.1–1.3 %) than at 23 °C or 27–29 °C (0.004–1.5 %). Growth (increase in total length) was accelerated at higher temperatures. The frequency of malformed individuals was lower at 25–27 °C (36.0–61.5 %) than at 23, 28 or 29 °C (65.3–76.9 %). Specific incidences of spinal curvature and centrum fusion or defects in juveniles were not related to rearing temperature. However, incidences of twisted or compressed vertebrae (6.5–64.0 %) were higher at higher temperatures, while the incidence of bifurcated neural spine was significantly higher at 23 °C (43.6–54.4 %) than at other temperatures (3.3–22.7 %). The incidence rate of spinal curvature (23.3 %) was significantly higher in juveniles with a deflated swim bladder, regardless of rearing temperature. The results of this study suggest that the optimum culture temperature for seven-band grouper is 25–26 °C, collectively considering the survival, growth and incidences of abnormalities. Our results also demonstrate the significance of identifying the conditions for swim bladder inflation to prevent spinal curvature in seven-band grouper.     

Carbohydrate tolerance in the fruit‐eating fish Piaractus mesopotamicus (Holmberg, 1887)

Some fish species have a limited ability to metabolize dietary carbohydrates. An important tool for understanding carbohydrate metabolism is the application of the glucose tolerance test, which can be performed orally or intraperitoneally. To evaluate carbohydrate tolerance in the fruit‐eating fish pacu, two experiments were performed, one with oral administration by gavage of three carbohydrate types (glucose, fructose and starch, 2.0 g/kg body weight (BW)) and the other with intraperitoneal injection (IP) of glucose (500 mg/kg BW). Oral glucose resulted in an increase in plasma glucose 2 hr later with the peak at 4 hr (8.30 mmol/L), and return to baseline between 6 and 12 hr; starch administration promoted a peak after 4 hr (7.70 mmol/L), returning to the baseline at 6 hr. The administration of fructose promoted a moderate peak after 2 hr (5.71 mmol/L), and return to baseline for the time points that followed. Elevated serum cholesterol levels were observed 2 and 24 hr after administration of glucose and starch. Hepatic glycogen levels increased within 24 hr, regardless of the type of carbohydrate administered. IP glucose load resulted in a peak of plasma glucose 3 hr post injection (6.91 mmol/L), returning to baseline 6 hr later. There was a reduction in the concentration of triglycerides at 24 hr. The results demonstrate that pacu metabolize both oral (glucose or starch) and intraperitoneal (glucose) carbohydrate loads after 6 hr, suggesting good ability to deal with dietary carbohydrates.     

Growth performance and energetic metabolism of pacu, Piaractus mesopotamicus (Holmberg, 1887), fed diets supplemented with ammonium metavanadate

Vanadium compounds mimic most of the metabolic effects of insulin, suggesting that it might be useful to improve utilization of dietary carbohydrate. This work evaluated the effect of dietary ammonium metavanadate (H₄NO₃V) on the growth performance and energy metabolism of pacu, an omnivorous South America characin. Two hundred and eighty‐eight fish were distributed into four blocks according to the body weight (21.8±1.7, 28.5±2.0, 28.4±1.9, 35.7±1.9 g), stocked in 24 plastic tanks and fed twice daily with isonitrogenous and isoenergetic diets containing six levels of H₄NO₃V (0, 10, 50, 100, 300 and 1000 mg kg^?1) for 60 days. Increasing levels of dietary ammonium metavanadate did not improve growth (P>0.05), and the highest level of inclusion (1000 mg kg^?1) reduced performance (P<0.05). Blood glucose levels decreased (P<0.05) in fish fed 300 and 1000 mg kg^?1 H₄NO₃V, but no differences were observed in other blood metabolites. A slight increase in muscle lipid content was observed in fish fed a diet containing 300 mg kg^?1 H₄NO₃V. Based on the results of this study, there is no benefit in supplementing pacu diets with metavanadate.     

Mortality of the short-neck clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> induced by the toxic dinoflagellate <Emphasis Type="Italic">Heterocapsa circularisquama</Emphasis>

Mortality of the short-neck clam Ruditapes philippinarum exposed to the toxic dinoflagellate Heterocapsa circularisquama was studied under controlled conditions to clarify the mechanisms of recurrent mass deaths of clams occurring in western Japanese coastal areas. One-week mortality tests, involving three water temperatures, six H. circularisquama concentrations, and two clam body sizes, showed a significant increase in mortality with increasing temperature, H. circularisquama concentration, exposure duration, and body size (ANOVA, P < 0.01). Clam death was observed at concentrations as low as 50 cells/ml and temperatures as low as 15°C. Prior to death, clams showed an extreme retraction of their mantle edge and siphon, along with recurrent vomiting behavior before initiating a closure reaction followed by paralysis then death. Gills of paralyzed clams showed an important uptake of dye, implying gill damage. This study is the first laboratory evidence of bivalve mortality induced by H. circularisquama at low concentrations and low temperature, and the first report of differential effects according to the body size of bivalves.     

Comparison of electrophoretic patterns of soluble proteins and isozymes of the red rot disease fungus Pythium sp. isolated from Porphyra yezoensis from Korea and Japan

SUMMARY: Pythium sp., the causative organism of red rot disease, isolated from Porphyra yezoensis from Wando in Korea was compared with those from Miyagi, Aichi, and Fukuoka Prefectures by means of electrophoretic patterns of soluble proteins and isozymes. Native and sodium dodecylsulfate–polyacrylamide gel electrophoretic patterns of soluble proteins revealed small but significant differences among the four isolates. Among the 14 detected enzymes, catalase (CAT), carboxylesterase (CE), glucose-6-phosphate dehydrogenase (G6PD), glucosephosphate isomerase (GPI), isocitrate dehydrogenase (IDH), malate dehydrogenase (MDH), superoxide dismutase (SOD), and xanthine dehydrogenase (XDH) possessed isozymes. The dissimilarity value of isozyme banding patterns for four isolates by unweighted pair-group method using arithmetic averages (UPGMA) cluster analysis was highest (0.51) between the isolate from Fukuoka and those from Miyagi and Aichi, and lowest (0.19) between the isolate from Miyagi and that from Aichi. Cluster analysis of data from isozyme banding patterns grouped the isolates from Miyagi and Aichi. These results indicate that the isolates from Miyagi and Aichi are similar, but each isolate from Wando and Fukuoka differed slightly from those of Miyagi and Aichi.