Seasonal patterns of viruses, bacteria and dissolved organic carbon in a riverine wetland

SUMMARY 1. Viral and bacterial abundances were studied in relation to environmental attributes over an annual period, for both planktonic and attached (sediment, aquatic macrophyte and submerged wood) habitats, in a riverine wetland.
2. Annual mean abundance of planktonic viruses ranged from 2.3 × 10⁵−3.8 × 10⁵ particles mL⁻¹ and varied according to sampling site. Significant seasonal patterns in viral abundance were evident and appeared to be linked to variations in bacterial abundance, dissolved organic carbon and inorganic nutrients.
3. Annual mean abundance of viruses associated with surfaces ranged from 1.3 × 10⁶ particles cm⁻² on aquatic macrophytes to 1.1 × 10⁷ particles cm⁻² on wood and also showed seasonal patterns. The difference in viral dynamics among the different sites emphasizes the importance of considering habitat diversity within wetlands when examining microbial communities.     

Annual changes of bacterial mortality due to viruses and protists in an oligotrophic coastal environment (NW Mediterranean)

The impact of viruses and protists on bacterioplankton mortality was examined monthly during 2 years (May 2005–April 2007) in an oligotrophic coastal environment (NW Mediterranean Sea). We expected that in such type of system, (i) bacterial losses would be caused mainly by protists, and (ii) lysogeny would be an important type of virus–host interaction. During the study period, viruses and grazers together were responsible for 50.6 ± 40.1% day⁻¹ of bacterial standing stock losses (BSS) and 59.7 ± 44.0% day⁻¹ of bacterial production losses (BP). Over the first year (May 2005–April 2006), protists were the principal cause of bacterial mortality, removing 29.9 ± 20.4% day⁻¹ of BSS and 33.9 ± 24.3% day⁻¹ of BP, whereas viral lysis removed 13.5 ± 17.0% day⁻¹ of BSS and 12.3 ± 12.3% day⁻¹ of BP. During the second year (May 2006–April 2007), viruses caused comparable bacterial losses (29.2 ± 14.8% day⁻¹ of BSS and 40.9 ± 20.7% day⁻¹ of BP) to protists (28.6 ± 25.5% day⁻¹ of BSS and 32.4 ± 20.0% day⁻¹ of BP). In 37% of cases higher losses of BP due to viruses than due to protists were found. Lysogenic infection was detected in 11 of 24 samplings. Contrary to our expectations, lytic infections dominated over the two years, and viruses resulted to be a significant source of bacterial mortality in this oligotrophic site.     

Antimicrobial activity of a porcine myeloperoxidase against plant pathogenic bacteria and fungi

Porcine myeloperoxidase was evaluated for its antimicrobial activity against plant pathogenic bacteria and fungi. The results indicated that the enzyme, in the presence of a small amount of hydrogen peroxide, was effective against a broad spectrum of plant pathogens. The growth of seven bacterial species, including nine pathovars, from the genera Erwinia , Pseudomonas and Xanthomonas , was significantly inhibited by the enzyme at a concentration as low as 0·4 U ml⁻¹, while 4·0 U ml⁻¹ was lethal to all plant pathogenic bacteria examined. Myeloperoxidase, at 40 U ml⁻¹, was lethal to germinating spores from three isolates of the fungal plant pathogen Fusarium solani and two isolates from each of Colletotrichum gloeosporioides and C. malvarum . The enzyme's antifungal effects on the rice blast pathogen Magnaporthe grisea were studied both in vitro and on host plants. The enzyme significantly inhibited spore germination of two isolates of M. grisea races IC17 and IB49 at concentrations over 16 U ml⁻¹, and disintegration of fungal spore walls was caused by 80 U ml⁻¹. The enzyme was even more effective in reducing disease incidence of blast on young rice plants treated with 0·5 U ml⁻¹, while 2·5 U ml⁻¹ resulted in complete inhibition of infection. These results support and further extend the suggestion that myeloperoxidase could be used as a broad-spectrum biocontrol agent or as a transgenically expressed protein to combat diseases caused by plant pathogenic bacteria and fungi.     

Effects of gizzard shad on benthic communities in reservoirs

Effects of gizzard shad Dorosoma cepedianum on benthic communities in a large southern reservoir (Lake Texoma, U.S.A.) were examined during two field enclosure and exclosure experiments in which enclosures were stocked at high and low densities in 1998 and 1999, respectively. In both years, chironomid abundance significantly increased in treatments that excluded large fishes from foraging on sediments. Mean abundance of chironomids and ostracods were significantly higher ( P  < 0·05) in exclosures than enclosures stocked with gizzard shad at 1140–1210 kg ha⁻¹. In 1999, benthic invertebrate abundances did not differ ( P  > 0·08) between exclosure and enclosures stocked at 175–213 kg ha⁻¹. Per cent organic matter, algal abundance and abundance of other macroinvertebrates in sediments did not differ significantly among treatments in either year. Although chironomid abundance was reduced in gizzard shad enclosures in 1998, food habits from this and other studies showed that adult gizzard shad in Lake Texoma only consumed detritus and algae. It is likely that high sedimentation rates in Lake Texoma limit the ability of gizzard shad to regulate algae and detritus in benthic sediments. Thus, it is concluded that disturbance of benthic sediments by gizzard shad caused the observed reduction in chironomid abundance, rather than through consumption or competition for resources.     

Sequence of gonadal events and oestradiol levels in Sparus aurata (L.) under two photoperiod regimes

Individually tagged Sparus aurata were kept in tanks with running sea water (21°± 2°C) during their second and third years of life. Gonads were biopsied and blood was sampled at monthly intervals. Thirteen of 50 fish in the second year and 24 of 35 fish in the third year were phenotypically females. Fish kept under 16L/8D photoperiod from July 1981 to August 1982 did not reach maturation; waves of initial ovarian growth alternated with waves of atresia. When photoperiod was shortened as from August 1982, gonadal development commenced within a month and proceeded at a rate higher than that of the control fish reared under natural photoperiod. Under natural photoperiod oestradiol serum levels (E₂) were relatively low during the resting phase, May-October (108 ± 11 pg ml⁻¹), and during the late vitellogenic phase (502 ± 76 pg ml⁻¹). High levels (1669 ± 312 and 1240 ± 172pg ml⁻¹) occurred during the early vitellogenic and the maturational phases. The high level of E₂ during the spawning season of S. aurata is explained by earlier reports indicating a prolonged breeding season with daily release of eggs, and alternating daily surges of E₂ and 17α, 20β, dihydroxy-4-pregnen-3-one, possibly a 'maturational progestin' in this fish. In phenotypic males, E₂ was highest during early spermatogenic phases (745 ± 142pg ml⁻¹) but was low (155 ± 11 pg ml⁻¹) in males with running sperm.     

Development and characterization of a lux-modified 2,4-dichlorophenol-degrading Burkholderia sp. RASC

lux -marked biosensors for assessing the toxicity and bioremediation potential of polluted environments may complement traditional chemical techniques. lux CDABE genes were introduced into the chromosome of the 2,4-dichlorophenol (2,4-DCP)-mineralizing bacterium, Burkholderia sp. RASC c2, by biparental mating using the Tn 4431 system. Experiments revealed that light output was constitutive and related to cell biomass concentration during exponential growth. The transposon insertion was stable and did not interrupt 2,4-DCP-degradative genes, and expression of lux CDABE did not constitute a metabolic burden to the cell. A bioluminescence response was detectable at sublethal 2,4-DCP concentrations: at < 10.26 μg ml⁻¹, bioluminescence was stimulated (e.g. 218% of control), but at concentrations > 60 μg ml⁻¹ it declined to < 1%. Investigating the effect of [14C]-2,4-DCP concentration on the evolution of ¹⁴CO₂ revealed that, for initial concentrations of 2.5–25 μg ml⁻¹, ≈55% of the added ¹⁴C was mineralized after 24 h compared with < 1% at 50 and 100 μg ml⁻¹. Inhibition of 2,4-DCP mineralization between 25 and 50 μg ml⁻¹ corresponded well to the EC₅₀ value (33.83 μg ml⁻¹) obtained from bioluminescence inhibition studies. lux -marked RASC c2 may therefore be used as a functionally (i.e. 2,4-DCP degrader) and environmentally relevant biosensor of toxicity and biodegradation inhibition.     

Physiological stress effects of continuous- and pulsed-DC electroshock on juvenile bull trout

Juvenile bull trout Salvelinus confluentus exposed to continuous- or pulsed-DC electroshock exhibited rapid elevations in plasma cortisol and glucose, but plasma chloride did not change. In a 1-h experiment using 240 V at 1·4 A of 60-Hz pulsed DC (voltage gradient 0·81 V cm⁻¹), which proved lethal, plasma cortisol and glucose rose significantly within 15 min of a 10-s electroshock. Plasma cortisol reached a peak level of 156 ± 18 ng ml⁻¹ at 45 min and then decreased, whereas plasma glucose reached its highest level of 179 ± 7·5mg dl⁻¹ at 1 h. In a 24-h experiment using lower dosages, plasma cortisol increased from 6·1-16 ng ml⁻¹ to peak levels of 155–161 ng ml⁻¹ in 1 h in response to a 10-s electroshock of continuous (130 V, 0·5 A, 1·45 V cm⁻¹) or pulsed (120 V, 0·5 A, 60 Hz, 0·55 V cm⁻¹) DC. Although plasma concentrations declined thereafter, levels remained above control values at 24 h. Plasma glucose was elevated from 60–65 to 120–134 mg dl⁻¹ after 1h by both electroshock treatments and remained near or above those levels for the 24-h duration. Plasma cortisol and glucose levels were much higher in electroshocked bull trout at 1 h compared with those in fish 1 h after receiving a 30-s handling stressor (cortisol, 90 ± 12 ng ml⁻¹; glucose, 82 ± 6·1 mg dl⁻¹). The results indicate that both continuous and pulsed DC were more stressful to juvenile bull trout than handling and that recovery, at least for pulsed DC, may take longer than 24 h.     

Long-term ammonia exposure of turbot: effects on plasma parameters

Turbot juveniles were exposed to four ammonia concentrations [0·17 (L), 0·34 (M), 0·73 (MH) and 0·88 (H) mg l⁻¹ NH₃-N] for different exposure durations (28 days minimum to 84 days). Their physiological status and growth performances were compared to a control group [0·004 (C) mg l⁻¹ NH₃-N]. No growth was observed in the H group, and by day 57, mass increase in the MH group was only 15% of that in group C. During the first month growth in the L group was similar to that in control group while it was lower (33%) in the M group; afterwards the L and M groups had a similar growth (half that of controls). Accumulation of total ammonia nitrogen (TA-N) in plasma was dependent on ambient ammonia concentrations. Plasma urea levels in ammonia-exposed fish were lower, similar or greater than in controls (depending on ammonia concentration or exposure duration). Osmolarity, Cl^– and Na⁺ plasma concentrations were stable in the L and M groups. The increases in Na⁺, Cl^–, K⁺ and total Ca concentrations observed by the end of the experiment in the H and MH groups suggest that fish failed to adapt. There was an initial rise in plasma cortisol in all ammonia-exposed groups followed by a return to basal level (1·7–4 ng ml⁻¹) in the L and M groups. In group MH, plasma cortisol peaked at 42 ng ml⁻¹ by day 14, and after a decline at c . 1 month (14 ng ml⁻¹), it rose again.     

Symbiotic effectiveness, rate of respiration and glutamine synthetase activity of sodium azide-resistant strains of Rhizobium leguminosarum biovar trifolii

Nitrogen fixing efficiency of sodium azide-resistant strains of Rhizobium leguminosarum bv. trifolii was studied in symbiosis with berseem clover plants in chillum jars. Rate of respiration and glutamine synthetase activity were tested in cultured cells and nodules, respectively. It was observed that shoot dry weight and percentage shoot nitrogen were maximum in plants inoculated with strains resistant to 15 μg ml⁻¹ sodium azide. Rate of respiration in cultured cells was lowest in strains resistant to 15 μg ml⁻¹ sodium azide and highest in strains resistant to 5 μg ml⁻¹ sodium azide. A negative correlation was observed between rate of respiration (in cultured cells) and shoot dry weight of host plants. Glutamine synthetase activity was maximum in nodule extracts of host plants inoculated with strains resistant to 5 and 10 μg ml⁻¹ sodium azide, whereas it was minimum for strains resistant to 15 μg ml⁻¹ sodium azide. Hence, resistance to low doses (15 μg ml⁻¹) of sodium azide, together with lower respiratory and glutamine synthetase activities, could be used as a potential method for isolating the symbiotically effective strains of Rh. leguminosarum bv. trifolii.     

Longevity of the freshwater anostracan Streptocephalus mackini (Crustacean: Anostraca) in relation to food (Chlorella vulgaris) concentration

SUMMARY 1. Temporary ponds are inhabited by a variety of invertebrates, of which anostracans are an important group. We studied the lifetables of male and female anostracan Streptocephalus mackini at 3 algal concentrations (0.5 × 10⁶, 1.0 × 10⁶ and 1.5 × 10⁶ cells mL⁻¹).
2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 10⁶ cells mL⁻¹.
3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 10⁶ cells mL⁻¹, was more than three times that at 1.5 × 10⁶ cells mL⁻¹.
4. The rate of population increase ( r ) was nearly the same (0.31 ± 0.06) at high (1.5 × 10⁶ cells mL⁻¹) and intermediate (1.0 × 10⁶ cells mL⁻¹) food levels. The r -value at low food level (0.5 × 10⁶ cells mL⁻¹ of Chlorella ) was 0.20 ± 0.01 per day.     

Plasma and ovarian thyroxine levels in relation to sexual maturation and gestation in female Sebastes inermis

Plasma T₄ (L-thyroxine) concentrations in the viviparous rockfish Sebastes inermis showed a peak (119·3±27·8 ng ml⁻¹) during the development of embryos. Ovarian T₄ concentrations increased during vitellogenesis and final maturation and decreased during embryogenesis.However, total T₄ content within the ovary increased continuously up to the larval stages. Plasma oestradiol-17β, (E₂) concentrations peaked at the final maturation stage and then recovered to the level seen during the non-reproductive periods. Plasma testosterone (T) concentrations showed a peak (5·33±1·08 ng ml⁻¹) at the embryo stage and high levels were maintained throughout the gestation period. Plasma T₄ concentrations during the embryo stage and ovarian T₄ content during vitellogenesis were much higher than the levels reported in oviparous fishes. These data suggest that in viviparous rockfish, T₄ may be required for sustaining gestation or embryo development within the maternal body. In addition, the high content of total T₄ in the ovary implies that there probably does exist a maternal-embryo relationship during gestation as well as during vitellogenesis.     

Stimulation of biomethanation by Clostridium sp. PXYL1 in coculture with a Methanosarcina strain PMET1 at psychrophilic temperatures

Aim:  Bioaugumentation of low temperature biogas production was attempted by addition of cold-adapted Clostridium and a methanogen.
Methods and Results:  A psychrotrophic xylanolytic acetogenic strain Clostridium sp. PXYL1 growing optimally at 20°C and pH 5·3 and a Methanosarcina strain, PMET1, growing optimally on acetate and producing methane at 15°C were isolated from a cattle manure digester. Anaerobic conversion of xylose at 15°C with the coculture of the two strains was performed, and batch culture methane production characteristics indicated that methanogenesis occurred via acetate through 'acetoclastic' pathway. Stimulation studies were also undertaken to evaluate the effect of exogenous addition of the coculture on biogas yields at 15°C. Addition of 3 ml of PXYL1 at the rate of 12 × 10² CFU ml⁻¹ increased the biogas 1·7-fold (33 l per kg cowdung) when compared to control (19·3 l per kg cowdung) as well as increased the volatile fatty acid (VFA) levels to 3210 mg l⁻¹ when compared to 1140 mg l⁻¹ in controls. Exogenous of addition of 10 ml PMET1 inoculum at the rate of 6·8 ± 10² CFU ml⁻¹ in addition to PXYL1 served to further improve the biogas yields to 46 l kg⁻¹ as well as significantly brought down the VFA levels to 1350 mg l⁻¹.
Conclusions:  Our results suggest that the rate-limiting methanogenic step at low temperatures could be overcome and that biogas yields improved by manipulating the population of the acetoclastic methanogens.
Significance and Impact of the Study:  Stimulation of biomethanation at low temperature by coculture.     

WLIP, a lipodepsipeptide of Pseudomonas 'reactans', as inhibitor of the symptoms of the brown blotch disease of Agaricus bisporus

A cell-free crude extract containing the white line inducing principle (WLIP), a lipodepsipeptide produced by Pseudomonas 'reactans' , could inhibit browning of mushrooms caused by Pseudomonas tolaasii . Mushrooms inoculated with Ps. tolaasii at concentrations of 2·7 × 10⁶ cfu ml⁻¹ or higher showed the symptoms of the disease after 2 d of incubation. Mushroom caps treated with various concentrations of a crude WLIP preparation, and later inoculated with bacterial concentrations higher than the threshold value, did not develop the symptoms of the disease. One milligram of a crude WLIP preparation could block 50% of the symptoms caused by 1·2 × 10⁷ cfu. The inhibition of browning was effective when incubating at low temperatures for 4 d. A suspension containing 1·6 mg ml⁻¹ of pure WLIP was also able to inhibit the symptoms of brown blotch disease induced by 7·6 × 10⁶ cfu ml⁻¹ of Ps. tolaasii .     

A potent anti-oxidant property: fluorescent recombinant α-phycocyanin of Spirulina

Aims:  To express and product a fluorescent antioxidant holo-α-phycocyanin (PC) of Spirulina platensis ( Sp ) with His-tag (rHHPC; recombinant holo-α-phycocyaninof Spirulina platensis with His-tag) in 5-l bench scale.
Methods and Results:  A vector harbouring two cassettes was constructed: cpcA along with cpcE - cpcF in one cassette; ho1 - pcyA in the other cassette. Lyases CpcE/F of Synechocystis sp. PCC6803 ( S6 ) could catalyse the 82 site Cys in apo-α-PC of Sp linking with bilin chromophores, and rHHPC was biosynthesized in Escherichia coli BL21. The constant feeding mode was adopted, and transformant reached the biomass of rHHPC up to 0·55 g l⁻¹ broth in 5-litre bench scale. rHHPC was purified by Ni²⁺ affinity column conveniently. The absorbance and the fluorescence emission spectra of rHHPC had λ_max at 621 and 650 nm, respectively. The IC₅₀ values of rHHPC were 277·5 ± 25·8 μ g ml⁻¹ against hydroxyl radicals and 20·8 ± 2·2  μ g ml⁻¹ against peroxyl radicals.
Conclusions:  Combinational biosynthesis of rHHPC was feasible, and the constant feeding mode was adopted to produce good yields of rHHPC. Fluorescent rHHPC with several unique qualitative and quantitative features was effective on scavenging hydroxyl and peroxyl radicals.
Significance and impact of the study:  A potent antioxidant rHHPC was co-expressed, produced and characterized for nutritional and pharmacological values, which would help to develop phycobiliproteins' applications in their fluorescent and biological activities.     

Effect of inhibitors on ammonium assimilation in Chlorella sorokiniana in light and darkness

In N-sufficient cells of Chlorella sorokiniana Shihira and Krauss strain 211/8K (CCAP of Cambridge University), assimilation of ammonium was strictly dependent on light and CO₂, and was severely inhibited by 100 μ M atrazine or 10 μ M 3-(3,4-dichlorophenyl)-1, l-dimethylurea (DCMU). In N-limited cells, assimilation of NH₄⁺ took place at similar rates in both light and darkness, which were 1.6-fold higher than the rate of light-dependent assimilation by N-sufficient cells. Assimilation by N-limited cells was inhibited by l -methionine- dl -sulfoximine (MSX), but not by atrazine or DCMU.
The rate of photosynthetic O₂ evolution was 2.9±0.9 mmol ml⁻¹ packed cell volume (PCV) h⁻¹ in N-sufficient cells, and 0.64±0.12 mmol ml⁻¹ PCV h⁻¹ in N-limited cells. In the latter resupply of ammonium resulted in a rapid activation by 22%;, followed by a time-dependent increase of the photosynthetic O₂ evolution, which after 12 h reached the same rate as in N-sufficient cells.
Respiratory consumption of oxygen in darkness in N-sufficient and N-limited cells was 0.10±0.03 and 0.11±0.02 mmol ml⁻¹ PCV h⁻¹, respectively. Addition of ammonium was without effect on respiration of N-sufficient cells, but resulted in a 4-fold stimulation of respiration of N-limited cells. Such stimulation took place also in cells treated with DCMU, atrazine, or MSX, and it was also promoted by methylammonium. The stimulation of respiration lasted for several hours.     

Synbiotics growth optimization of Bifidobacterium pseudocatenulatum G4 with prebiotics using a statistical methodology

Aims:  This study demonstrated the optimum growth of Bifidobacterium pseudocatenulatum G4 with prebiotics via statistical model.
Methods and Results:  Commercial prebiotics [inulin and fructooligosaccharide (FOS)], together with sorbitol, arabinan and inoculum rate, were tested by fractional factorial design to determine their impact on growth of Bif. pseudocatenulatum G4 in skim milk. At 48 h incubation, bacterial growth was mainly influenced by FOS and inoculum rate. Growth reduction was observed in all samples incubated for 72 h. Central composite design (CCD) was adopted using FOS and inoculum rate at 48 h incubation to develop the statistical model for optimization. The model predicted that 2·461 log CFU ml⁻¹ produced the optimum growth increase of Bif. pseudocatenulatum G4. The combination that produced the optimum point was 2·86% FOS (g/v) and 0·67% inoculum rate (v/v).
Conclusion:  At optimum combination of inoculum rate and FOS, validation experiments recorded 2·40 ± 10·02 log CFU ml⁻¹. The application in 1-l bioreactor for 24 h showed higher growth increase of 2·95 log CFU ml⁻¹.
Significant and Impact of the Study:  Response surface methodology approach is useful to develop optimum synbiotics combination for strain G4 with FOS.     

Cortisol and glucose responses in juvenile brown trout subjected to a fluctuating flow regime in an artificial stream

In an artificial stream channel, wild 1 year old brown trout Salmo trutta were exposed to fluctuations in flow and water level to simulate hydro-peaking conditions downstream of a hydropower installation. Blood plasma cortisol concentrations reached a maximum of 59·4 ± 35·3 ng ml⁻¹ (mean ± 95% CL) 2h after the end of down-ramping. Return to the pre-exposure cortisol level was achieved within 6 h. When subjected to daily cyclical fluctuations over 7 days, plasma cortisol levels were significantly elevated (61·3 ± 26·8 ng ml⁻¹) on the first day compared to undisturbed fish (4·9 ± 3·7 ng ml⁻¹). On the fourth and seventh day, no elevation in plasma cortisol above control levels was observed. No changes in blood glucose that could be attributed to the stressor were found. There was no correlation between plasma cortisol and blood glucose levels. The short-lived cortisol response to daily fluctuations indicates a rapid habituation to this Stressor.     

Decreased time for detection and quantification of virulent Bacillus anthracis and Yersinia pestis using a BioNanoPore (BNPTM) membrane technology

Many aspects of biodefense research require quantitative growth assessments of the test agent. This study evaluated the BioNanoPore (BNP™) technology to quantitate Bacillus anthracis and Yersinia pestis faster than traditional plate counting methods. The BNP™ technology enabled quantification of B. anthracis and Y. pestis in phosphate-buffered saline and naïve rabbit blood at 6 and 24 h, respectively. After 6 h of growth, counts for B. anthracis ranged from 6·19–6·45 log₁₀ CFU ml⁻¹ on BNP™, while counts after 24 h on tryptic soy agar (TSA) ranged from 6·51–6·58 log₁₀ CFU ml⁻¹. For Y. pestis , counts on BNP™ at 24 h ranged from 6·31–6·41 log₁₀ CFU ml⁻¹ on BNP™ and ranged from 6·44–6·89 log₁₀ CFU ml⁻¹ on TSA at 48 h. This study demonstrates that the BNP™ technology provides a more rapid detection of B. anthracis and Y. pestis , which could aid in the evaluation of potential medical countermeasures and treatments as well as other biological defense applications such as surface sampling or decontamination efficacy.     

Abrupt change in primary productivity in a littoral zone of Lake Biwa with the development of a filamentous green-algal community

1. Some characteristics of the photosynthesis and primary production of benthic and planktonic algal communities were investigated in a littoral zone covered with gravel in the north basin of Lake Biwa, paying special attention to the recent development of filamentous green algae (FGA) in the benthic algal community.
2. P_max (maximum gross photosynthesis rate) values of the benthic algal community (0.1–1.2 mg C mg chl. a ⁻¹ h⁻¹) obtained from photosynthesis–irradiance (P–I) curves were lower than those of the planktonic algal community (2.4–11.5 mg C mg chl. a ⁻¹ h⁻¹). This is apparently a result of the high degree of self shading in the benthic algal community and its low turnover as compared with that of the planktonic algal community.
3. Relatively high I_k values (150–200 μmol photon m⁻² s⁻¹) were observed in the benthic algal community only in June–July when a FGA, Spirogyra sp., was abundant. This reflected a photosynthetic characteristic of the Spirogyra itself, in which photosynthesis was saturated at high light intensity.
4. The FGA community established in the layer between planktonic and sessile (benthic algae except for FGA) algal communities. It brought about extraordinarily high organic matter production in the littoral zone at the expense of production in the sessile algal community.     

Studies on catabolite repression in solid state fermentation for biosynthesis of fungal amylases

Catabolite repression by glucose of the biosynthesis of alpha amylase and amyloglucosidase by Aspergillus niger CFTRI 1105 was studied in a solid state fermentation (SSF) and in submerged fermentation (SMF) systems and the results were compared. The addition of glucose did not enhance the production of alpha-amylase and amyloglucosidase in an earlier fermentation system. However, a drastic reduction in alpha-amylase production was observed in submerged fermentation by the addition of 5·0 mg ml⁻¹ glucose and of amyloglucosidase production by 10 mg ml⁻¹ glucose. Glucose concentrations above 50 mg ml⁻¹ completely suppressed the production of both enzymes in the initial hours. In contrast, in the SSF system the repression was negligible, even when the glucose level was raised to 150 mg g⁻¹ wheat bran for both alpha and amyloglucosidase synthesis.