Kinetics of kojic acid fermentation by Aspergillus flavus using different types and concentrations of carbon and nitrogen sources

Kinetics of kojic acid fermentation by Aspergillus flavus Link 44-1 using various sources of carbon [glucose, xylose, sucrose, starch, maltose, lactose or fructose] and nitrogen [NH₄Cl, (NH₄)₂S₂O₈, (NH₄)₂NO₃, yeast extract or peptone] were analyzed using models based on logistic and Luedeking–Piret equations. The highest kojic acid production (39.90 g l⁻¹) in submerged batch fermentation was obtained when 100 g l⁻¹ glucose was used as a carbon source. Organic nitrogen sources such as peptone and yeast extract were favorable for kojic acid production as compared to inorganic nitrogen sources. Yeast extract at 5 g l⁻¹ was optimal. The optimal carbon to nitrogen (C/N) ratio for kojic acid fermentation was 93.3. In a resuspended cell system, the rate of glucose conversion to kojic acid by cell-bound enzymes increased with increasing glucose concentration up to 70 g l⁻¹, suggesting that the reaction followed the Michaelis–Menten enzyme kinetic model. The value of K _m and V _max for the reaction was 18.47 g l⁻¹ glucose and 0.154 g l⁻¹ h⁻¹, respectively. Journal of Industrial Microbiology & Biotechnology (2000) 25, 20–24. Received 13 October 1999/ Accepted in revised form 02 April 2000     

Characterization of a thermophilic sulfur oxidizing enrichment culture dominated by a Sulfolobus sp. obtained from an underground hot spring for use in extreme bioleaching conditions

A thermoacidophilic elemental sulfur and chalcopyrite oxidizing enrichment culture VS2 was obtained from hot spring run-off sediments of an underground mine. It contained only archaeal species, namely a Sulfolobus metallicus-related organism (96% similarity in partial 16S rRNA gene) and Thermoplasma acidophilum (98% similarity in partial 16S rRNA gene). The VS2 culture grew in a temperature range of 35–76°C. Sulfur oxidation by VS2 was optimal at 70°C, with the highest oxidation rate being 99 mg S⁰ l⁻¹ day⁻¹. At 50°C, the highest sulfur oxidation rate was 89 mg l⁻¹ day⁻¹ (in the presence of 5 g Cl⁻ l⁻¹). Sulfur oxidation was not significantly affected by 0.02–0.1 g l⁻¹ yeast extract or saline water (total salinity of 0.6 M) that simulated mine water at field application sites with availability of only saline water. Chloride ions at a concentration above 10 g l⁻¹ inhibited sulfur oxidation. Both granular and powdered forms of sulfur were bioavailable, but the oxidation rate of granular sulfur was less than 50% of the powdered form. Chalcopyrite concentrate oxidation (1% w/v) by the VS2 resulted in a 90% Cu yield in 30 days.     

Soy molasses as fermentation substrate for production of butanol using Clostridium beijerinckii BA101

Spray-dried soy molasses (SDSM) contains the sugars dextrose, sucrose, fructose, pinitol, raffinose, verbascose, melibiose, and stachyose. Of the 746 g kg⁻¹ total sugars in SDSM, 434 g kg⁻¹ is fermentable using Clostridium beijerinckii BA101. SDSM was used to produce acetone, butanol, and ethanol (ABE) by C. beijerinckii BA101 in batch cultures. Using 80 g l⁻¹ SDSM, 10.7 g l⁻¹ ABE was produced in P2 medium. Higher concentrations of SDSM resulted in poor solvent production due to the presence of excessive salt and inhibitory components. C. beijerinckii BA101 in SDSM at 80 g l⁻¹ concentration produced 22.8 g l⁻¹ ABE when supplemented with 25.3 g l⁻¹ glucose. SDSM contains 57.4 g kg⁻¹ mineral ash and 2% tri-calcium phosphate. Tri-calcium phosphate up to 43.1 g l⁻¹ was not inhibitory and at a tri-calcium phosphate concentration of 28.8 g l⁻¹, the culture produced more solvents (30.1 g l⁻¹) than the control experiment (23.8 g l⁻¹). In contrast, sodium chloride was a strong inhibitor of C. beijerinckii BA101 cell growth. At a concentration of 10 g l⁻¹ sodium chloride, a maximum cell concentration of 0.6 g l⁻¹ was achieved compared to 1.7 g l⁻¹ in the control experiment. The effects of two salts on specific growth rate constant (μ) and specific rate of ABE production (ν) for C. beijerinckii BA101 were examined. Journal of Industrial Microbiology & Biotechnology (2001) 26, 290–295. Received 20 September 2000/ Accepted in revised form 16 February 2001     

Plant regeneration through somatic embryogenesis and rapd analysis of regenerated plants in Tylophora indica (Burm. F. Merrill.)

Summary A procedure for the regeneration of complete plantlets of Tylophora indica from cultured leaf callus via somatic embryogenesis is described. Callus induction from leaf explants was on Murashige and Skoog (MS) medium with different concentrations of 2,4-dichlorophenoxyacetic acid (2.4-D; 0.03–3 mg l⁻¹; 0.0–13.56 μM) and kinetin (Kn; 0.01 mg l⁻¹; 0.05 μM). The best response for callus induction was obtained on MS medium containing 2 mg l⁻¹ (9.04 μM) 2.4-D and 0.01 mg l⁻¹ (0.05 μM) Kn. After two subeultures on the same medium the embryogenic callus was transferred to MS medium with different concentrations of the cytokinin, 6-benzyladenine (0.5–3 mg l⁻¹; 2.22–13.32 μM) and 2-isopentenyladenine (2ip; 0.53 mg l⁻¹; 2.46–14.76 μM) along with 0.01 mg l⁻¹ (0.05 μM) indole-3-butyric acid (IBA) for somatic embryo development and maturation. MS medium with 2 mg l⁻¹ (9.84 μM) 2ip produced the maximum number of mature somatic embryos. The mature embryos were bipolar and on transfer to MS basal medium produced complete plantlets. After hardening the regenerants were planted in the Gudalur forests of Western Ghats. Total DNA was extracted from 14 regenerants and the mother plant. Random amplified polymorphic, DNA (RAPD) analysis was carried out using 20 arbitrary oligonucleotides. The amplification products were monomorphic among all the plants revealing the genetic homogeneity and true-to-type nature of the regenerants.     

Effects of NaCl salinity on the population dynamics of freshwater zooplankton (rotifers and cladocerans)

Salinization of freshwater bodies due to anthropogenic activity is currently a very serious problem in Mexico. One of the consequences may be changes in the rotifer and cladoceran populations, both of which are generally abundant in freshwater bodies. Under laboratory conditions we evaluated the effect of different salt (sodium chloride) concentrations (0–4.5 g l⁻¹) on the population dynamics of ten freshwater zooplankton species (rotifers: Anuraeopsis fissa, Brachionus calyciflorus, B. havanaensis, B. patulus and B. rubens; cladocerans: Alona rectangula, Ceriodaphnia dubia, Daphnia pulex, Moina macrocopa and Simocephalus vetulus). All of the zooplankton species tested were adversely affected by 1.5–3.0 g l⁻¹ NaCl. In the range of salt concentrations tested, the population growth curves of B. patulus and B. rubens showed almost no lag phase and reached peak abundances within a week or two; A. fissa had a lag phase of about a week, while both B. calyciflorus and B. havanaensis started to increase in abundance immediately following the initiation of the experiments. Increased NaCl levels reduced the population abundances of A. fissa, B. calyciflorus and B. havanaensis at or beyond 1.5 g l⁻¹. NaCl at 1 g l⁻¹ had little effect on the population growth of cladocerans. M. macrocopa, which was more resistant to NaCl than the other cladoceran species, showed positive population growth even at 4.5 g l⁻¹. The rates of population increase (r, day⁻¹) were generally higher for rotifers than for cladocerans. Depending on the NaCl concentration, the r of rotifers ranged from +0.57 to −0.58 day⁻¹, while the r for cladocerans was lower (+0.34 to −0.22 day⁻¹).     

Continuous marennin production by agar-entrapped Haslea ostrearia using a tubular photobioreactor with internal illumination

The marine diatom Haslea ostrearia was immobilized in a tubular agar gel layer introduced into a photobioreactor of original design with internal illumination for the continuous synthesis of marennin, a blue-green pigment of biotechnological interest. Marennin was produced for a long-term period (27–43 days) and the volumetric productivity was maximum (18.7 mg day⁻¹ l⁻¹ gel) at the highest dilution rate (0.25 day⁻¹) and lowest agar layer thickness (3 mm). Heterogeneous cell distribution in the agar layer revealed diffusional limitation of light and nutrients. However, the 3 mm gel thickness led to a more homogeneous cell distribution during incubation and to an increase of the whole biomass in the agar gel layer. Received: 22 October 1999 / Received revision: 14 February 2000 / Accepted: 18 February 2000     

Increased erythritol production in fed-batch cultures of Torula sp. by controlling glucose concentration

The effect of glucose concentration on erythritol production by Torula sp. was investigated. The maximum volumetric productivity of erythritol was obtained at an initial glucose concentration of 300 g l⁻¹ in batch culture. The volumetric productivity was maximal at a controlled glucose concentration of 225 g l⁻¹, reducing the lag time of the erythritol production. A fed-batch culture was established with an initial glucose concentration of 300 g l⁻¹ and with a controlled glucose concentration of 225 g l⁻¹ in medium containing phytic acid as a phosphate source. In this fed-batch culture, a final erythritol production of 192 g l⁻¹ was obtained from 400 g l⁻¹ glucose in 88 h. This corresponded to a volumetric productivity of 2.26 g l⁻¹ h⁻¹ and a 48% yield. Journal of Industrial Microbiology & Biotechnology (2001) 26, 248–252. Received 26 September 2000/ Accepted in revised form 16 January 2001     

Reclamation of an activated-sludge microbial consortium by selective biostimulation

Our previous study showed that an activated-sludge process broke down at the phenol-loading rate of 1.5 g l⁻¹ day⁻¹, when non-flocculating bacteria (called R6T and R10) overgrew the sludge, resulting in a sludge washout. In this study, we attempted to circumvent this breakdown problem by reclaiming the consortium structure. Activated sludge was fed phenol, and the phenol-loading rate was increased stepwise from 0.5 g l⁻¹ day⁻¹ to 1.0 g l⁻¹ day⁻¹ and then to 1.5 g l⁻¹ day⁻¹. Either galactose or glucose (at 0.5 g l⁻¹ day⁻¹) was also supplied to the activated sludge from the phenol-loading rate of 1.0 g l⁻¹ day⁻¹. Pure culture experiments have suggested galactose to be a preferential substrate for a floc-forming bacterium (R6F) that predominantly degrades phenol under low phenol-loading conditions. Supplying galactose allowed sustainment of the R6F population and suppression of the overgrowth of R6T and R10 at the phenol-loading rate of 1.5 g l⁻¹ day⁻¹. This measure allowed the activated-sludge process to treat phenol at a phenol-loading rate up to 1.5 g l⁻¹ day⁻¹, although it broke down at 2.0 g l⁻¹ day⁻¹. In contrast, supplying glucose reduced the R6F population and allowed the activated-sludge process to break down at the phenol-loading rate of 1.0 g l⁻¹ day⁻¹. This study demonstrated that reclamation of the activated-sludge consortium by selective biostimulation of the floc-forming population improved the phenol-treating ability of the process. Received: 13 January 2000 / Received revision: 10 March 2000 / Accepted: 7 April 2000     

Sugarcane Straw and its Phytochemicals as Growth Regulators of Weed and Crop Plants

The present study investigates the effect of soil amended with sugarcane straw leachate and its constituents on root elongation of weed and crop plants. The influence of soil biotic and abiotic factors on plant growth were also evaluated through assays in both autoclaved soil and sand. In unsterile soil, straw leachates stimulated root growth of some test plants at 6 g dry straw ls⁻¹ and inhibited root elongation at higher concentrations. A bioassay guided process of the bioactive leachate constituents led to the isolation of vanillic, syringic and ferulic acids. These compounds were also assayed on the test plants in the three mentioned substrates. In unsterile soil, phenolics stimulated the growth of some species at 19 mg l⁻¹. Higher phenolics concentrations were inhibitory. The concentration needed to inhibit 25% root elongation (EC₂₅) was calculated from the dose–response curves. The concentration of phenolics in the leachate (64 g dry straw l⁻¹) was estimated to be 187 mg l⁻¹ (ferulic acid), 131 mg l⁻¹ (vanillic acid) and 20 mg l⁻¹ (Syringic acid). In general, these concentrations were below the EC₂₅ values determined in unsterile soil indicating that these compounds cannot completely explain the strong inhibitory activity of sugarcane straw leachates. The role of soil factors on phytotoxicity of sugarcane straw leachate and its identified growth regulators is also discussed.     

Single-culture aerobic granules with <Emphasis Type="Italic">Acinetobacter calcoaceticus</Emphasis>

Aerobic granules are cultivated by a single bacterial strain, Acinetobacter calcoaceticus, in a sequencing batch reactor (SBR). This strain presents as a good phenol reducer and an efficient auto coagulator in the presence of phenol, mediated by heat-sensitive adhesins proteins. Stable 2.3-mm granules were formed in the SBR following a 7-week cultivation. These granules exhibit excellent settling attributes and degrade phenol efficiently at concentrations of 250–2,000 mg l⁻¹. The corresponding phenol degradation rate reached 993.6 mg phenol g⁻¹ volatile suspended solids (VSS) day⁻¹ at 250 mg l⁻¹ phenol and 519.3 mg phenol g⁻¹ VSS day⁻¹ at 2,000 mg l⁻¹ phenol concentration. Meanwhile, free A. calcoaceticus cells were fully inhibited at phenol >1,500 mg l⁻¹. Denaturing gradient gel electrophoresis fingerprint profile demonstrated no genetic modification in the strain during aerobic granulation. The present single-strain granules showed long-term structural stability and performed high phenol degrading capacity and high phenol tolerance. The confocal laser scanning microscopic test revealed that live A. calcoaceticus cells principally distributed at 200–250 μm beneath the outer surface, with an extracellular polymeric substance layer covering them to defend phenol toxicity. Autoaggregation assay tests demonstrated the possibly significant role of secreted proteins on the formation of single-culture A. calcoaceticus granules.     

Biomass and lipid productivities of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> under autotrophic,heterotrophic and mixotrophic growth conditions

Biomass and lipid productivities of Chlorella vulgaris under different growth conditions were investigated. While autotrophic growth did provide higher cellular lipid content (38%), the lipid productivity was much lower compared with those from heterotrophic growth with acetate, glucose, or glycerol. Optimal cell growth (2 g l⁻¹) and lipid productivity (54 mg l⁻¹ day⁻¹) were attained using glucose at 1% (w/v) whereas higher concentrations were inhibitory. Growth of C. vulgaris on glycerol had a similar dose effects as those from glucose. Overall, C. vulgaris is mixotrophic.     

Susceptibility of embryogenic and organogenic tissues of maritime pine (Pinus pinaster) to antibiotics used in Agrobacterium-mediated genetic transformation

The effects of antibiotics commonly used in Agrobacterium-mediated transformation were studied on Pinus pinaster tissues. Embryogenic tissue growth from three embryogenic lines and adventitious bud induction from cotyledons from three open-pollinated seed families were analysed. Cefotaxizme, carbenicillin and timentin commonly used for Agrobacterium elimination, at concentrations of 200–400 mg l ⁻¹ did not inhibit the embryogenic tissue growth on filter paper nor as clumps. Adventitious bud induction and bud number were significantly reduced for one of the tested families when using 400 mg l⁻¹ cefotaxime or timentin. The selection agent kanamycin significantly inhibited growth of embryogenic tissue on filter paper in all the embryogenic lines␣and concentrations tested (20–50 mg l⁻¹). Kanamycin also inhibited growth of embryogenic clumps after two subcultures at 5–50 mg l⁻¹. In␣cotyledons, kanamycin inhibited adventitious bud␣formation in the three seed families used, regardless of the concentrations tested (5–25 mg l⁻¹). There was a significant effect of the seed family on the bud induction and the number of adventitious buds produced. From the results obtained, we propose the use of timentin to eliminate Agrobacterium in transformation experiments, at concentrations of 400 mg l⁻¹ for embryogenic tissues and of 300 mg l⁻¹ for cotyledons. For selection of transformed tissues carrying the kanamycin resistance gene, kanamycin should be used at 20 mg l⁻¹ for embryogenic tissues on filter paper, at 5 mg l⁻¹ when clumps are in direct contact with the selection medium, and bellow 5 mg l⁻¹ for adventitious bud induction.     

Drift-ice and under-ice water communities in the Gulf of Bothnia (Baltic Sea)

The algal, protozoan and metazoan communities within different drift-ice types (newly formed, pancake and rafted ice) and in under-ice water were studied in the Gulf of Bothnia in March 2006. In ice, diatoms together with unidentified flagellates dominated the algal biomass (226 ± 154 μg ww l⁻¹) and rotifers the metazoan and protozoan biomass (32 ± 25 μg ww l⁻¹). The under-ice water communities were dominated by flagellates and ciliates, which resulted in lower biomasses (97 ± 25 and 21 ± 14 μg ww l⁻¹, respectively). The under-ice water and newly formed ice separated from all other samples to their own cluster in hierarchical cluster analysis. The most important discriminating factors, according to discriminant analysis, were chlorophyll-a, phosphate and silicate. The under-ice water/newly formed ice cluster was characterized by high nutrient and low chlorophyll-a values, while the opposite held true for the ice cluster. Increasing trends in chlorophyll-a concentration and biomass were observed with increasing ice thickness. Within the thick ice columns (>40 cm), the highest chlorophyll-a concentrations (6.6–22.2 μg l⁻¹) were in the bottom layers indicating photoacclimation of the sympagic community. The ice algal biomass showed additional peaks in the centric diatom-dominated surface layers coinciding with the highest photosynthetic efficiencies [0.019–0.032 μg C (μg Chl-a ⁻¹ h⁻¹) (μE m⁻² s⁻¹)⁻¹] and maximum photosynthetic capacities [0.43-1.29 μg C (μg Chl-a ⁻¹ h⁻¹)]. Rafting and snow-ice formation, determined from thin sections and stable oxygen isotopic composition, strongly influenced the physical, chemical and biological properties of the ice. Snow-ice formation provided the surface layers with nutrients and possibly habitable space, which seemed to have favored centric diatoms in our study.     

Nitrogen retention in the hyporheic zone of a glacial river in interior Alaska

We examined the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of the Tanana River, a glacially-fed river, in interior Alaska. We measured hyporheic solute concentrations, gas partial pressures, water table height, and flow rates along subsurface flowpaths on two islands for three summers. Denitrification was quantified using an in situ ¹⁵NO₃⁻ push–pull technique. Hyporheic water level responded rapidly to change in river stage, with the sites flooding periodically in mid−July to early−August. Nitrate concentration was nearly 3-fold greater in river (ca. 100 μg NO₃⁻–N l⁻¹) than hyporheic water (ca. 38 μg NO₃⁻–N l⁻¹), but approximately 60–80% of river nitrate was removed during the first 50 m of hyporheic flowpath. Denitrification during high river stage ranged from 1.9 to 29.4 mg N kg sediment⁻¹ day⁻¹. Hotspots of methane partial pressure, averaging 50,000 ppmv, occurred in densely vegetated sites in conjunction with mean oxygen concentration below 0.5 mgO₂ l⁻¹. Hyporheic flow was an important mechanism of nitrogen supply to microbes and plant roots, transporting on average 0.41 gNO₃⁻–N m⁻² day⁻¹, 0.22 g NH₄⁺–N m⁻² day⁻¹, and 3.6 g DON m⁻² day⁻¹ through surface sediment (top 2 m). Our results suggest that denitrification can be a major sink for river nitrate in boreal forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph and the resulting duration of soil saturation are key factors regulating the redox environment and anaerobic metabolism in the hyporheic zone.     

Factors influencing efficiency of somatic embryogenesis of Gentiana kurroo (Royle) cell suspension

In this paper, we would like to show unexpected morphogenic potential of cell suspensions derived from seedling explants of Gentiana kurroo (Royle). Suspension cultures were established with the use of embryogenic callus derived from seedling explants (root, hypocotyl and cotyledons). Proembryogenic mass proliferated in liquid MS medium supplemented with 0.5 mg l⁻¹ 2,4-D and 1.0 mg l⁻¹ Kin. The highest growth coefficient was achieved for root derived cell suspensions. The microscopic analysis showed differences in aggregate structure depending on their size. To assess the embryogenic capability of the particular culture, 100 mg of cell aggregates was implanted on MS agar medium supplemented with Kin (0.0–2.0 mg l⁻¹), GA₃ (0.0–2.0 mg l⁻¹) and AS (80.0 mg l⁻¹). The highest number of somatic embryos was obtained for cotyledon-derived cell suspension on GA₃-free medium, but the best morphological quality of embryos was observed in the presence of 0.5–1.0 mg l⁻¹ Kin, 0.5 mg l⁻¹ GA₃ and 80.0 mg l⁻¹ AS. The morphogenic competence of cultures also depended on the size of the aggregate fraction and was lower when size of aggregates decreased. Flow cytometry analysis reveled luck of uniformity of regenerants derived from hypocotyl suspension and 100% of uniformity for cotyledon suspension.     

Effects of nitrogen sources on cell growth and lipid accumulation of green alga <Emphasis Type="Italic">Neochloris oleoabundans</Emphasis>

Microalgal lipids are the oils of future for sustainable biodiesel production. However, relatively high production costs due to low lipid productivity have been one of the major obstacles impeding their commercial production. We studied the effects of nitrogen sources and their concentrations on cell growth and lipid accumulation of Neochloris oleoabundans, one of the most promising oil-rich microalgal species. While the highest lipid cell content of 0.40 g/g was obtained at the lowest sodium nitrate concentration (3 mM), a remarkable lipid productivity of 0.133 g l⁻¹ day⁻¹ was achieved at 5 mM with a lipid cell content of 0.34 g/g and a biomass productivity of 0.40 g l⁻¹ day⁻¹. The highest biomass productivity was obtained at 10 mM sodium nitrate, with a biomass concentration of 3.2 g/l and a biomass productivity of 0.63 g l⁻¹ day⁻¹. It was observed that cell growth continued after the exhaustion of external nitrogen pool, hypothetically supported by the consumption of intracellular nitrogen pools such as chlorophyll molecules. The relationship among nitrate depletion, cell growth, lipid cell content, and cell chlorophyll content are discussed.     

Heterotrophic high-cell-density fed-batch and continuous-flow cultures of <Emphasis Type="Italic">Galdieria sulphuraria</Emphasis> and production of phycocyanin

Production of biomass and phycocyanin (PC) were investigated in highly pigmented variants of the unicellular rhodophyte Galdieria sulphuraria, which maintained high specific pigment concentrations when grown heterotrophically in darkness. The parental culture, G. sulphuraria 074G was grown on solidified growth media, and intensely coloured colonies were isolated and grown in high-cell-density fed-batch and continuous-flow cultures. These cultures contained 80–110 g L⁻¹ biomass and 1.4–2.9 g L⁻¹ PC. The volumetric PC production rates were 0.5–0.9 g L⁻¹ day⁻¹. The PC production rates were 11–21 times higher than previously reported for heterotrophic G. sulphuraria 074G grown on glucose and 20–287 times higher than found in phototrophic cultures of Spirulina platensis, the organism presently used for commercial production of PC.     

Effect of ammonia on the anaerobic degradation of protein by a mesophilic and thermophilic biowaste population

The influence of ammonia on the anaerobic degradation of peptone by mesophilic and thermophilic populations of biowaste was investigated. For peptone concentrations from 5 g l⁻¹ to 20 g l⁻¹ the mesophilic population revealed a higher rate of deamination than the thermophilic population, e.g. 552 mg l⁻¹ day⁻¹ compared to 320 mg l⁻¹ day⁻¹ at 10 g l⁻¹ peptone. The final degree of deamination of the thermophilic population was, however, higher: 102 compared to 87 mg NH₃/g peptone in the mesophilic cultures. If 0.5–6.5 g l⁻¹ ammonia was added to the mesophilic biowaste cultures, deamination of peptone, degradation of its chemical oxygen demand (COD) and formation of biogas were increasingly inhibited, but no hydrogen was formed. The thermophilic biowaste cultures were most active if around 1 g ammonia l⁻¹ was present. Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and hydrogen was formed in addition to methane. Studies of the inhibition by ammonia of peptone deamination, COD degradation and methane formation revealed a K _i (50%) for NH₃ of 92, 95 and 88 mg l⁻¹ at 37 °C and 251, 274 and 297 mg l⁻¹ at 55 °C respectively. This indicated that the thermophilic flora tolerated significantly more NH₃ than the mesophilic flora. In the mesophilic reactor effluent 4.6 × 10⁸ peptone-degrading colony-forming units (cfu)/ml were culturable, whereas in the thermophilic reactor effluent growth of only 5.6 × 10⁷ cfu/ml was observed. Received: 24 April 1998 / Received revision: 26 June 1998 / Accepted: 27 June 1998     

Lactic acid production from xylose by the fungus Rhizopus oryzae

Lignocellulosic biomass is considered nowadays to be an economically attractive carbohydrate feedstock for large-scale fermentation of bulk chemicals such as lactic acid. The filamentous fungus Rhizopus oryzae is able to grow in mineral medium with glucose as sole carbon source and to produce optically pure l(+)-lactic acid. Less is known about the conversion by R. oryzae of pentose sugars such as xylose, which is abundantly present in lignocellulosic hydrolysates. This paper describes the conversion of xylose in synthetic media into lactic acid by ten R. oryzae strains resulting in yields between 0.41 and 0.71 g g⁻¹. By-products were fungal biomass, xylitol, glycerol, ethanol and carbon dioxide. The growth of R. oryzae CBS 112.07 in media with initial xylose concentrations above 40 g l⁻¹ showed inhibition of substrate consumption and lactic acid production rates. In case of mixed substrates, diauxic growth was observed where consumption of glucose and xylose occurred subsequently. Sugar consumption rate and lactic acid production rate were significantly higher during glucose consumption phase compared to xylose consumption phase. Available xylose (10.3 g l⁻¹) and glucose (19.2 g l⁻¹) present in a mild-temperature alkaline treated wheat straw hydrolysate was converted subsequently by R. oryzae with rates of 2.2 g glucose l⁻¹ h⁻¹ and 0.5 g xylose l⁻¹ h⁻¹. This resulted mainly into the product lactic acid (6.8 g l⁻¹) and ethanol (5.7 g l⁻¹).     

Role of the polychaete <Emphasis Type="Italic">Neanthes succinea</Emphasis> in phosphorus regeneration from sediments in the Salton Sea,California

The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading. However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03 mg P m⁻² day⁻¹) under saturated oxygen conditions, and highest (1.23–4.67 mg P m⁻² day⁻¹) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to the overall production of the lake. Guest Editor: John M. Melack Saline Water and their Biota