Population dynamics, distribution, and growth rate of tilapia (Oreochromis mossambicus) in the Salton Sea, California, with notes on bairdiella (Bairdiella icistia) and orangemouth corvina (Cynoscion xanthulus)

The Salton Sea is a highly saline lake that has long supported sportfishery and large populations of fish-eating birds. A study was initiated in 1999 to assess the status of orangemouth corvina (Cynoscion xanthulus), bairdiella (Bairdiella icistia) and tilapia (Oreochromis mossambicus × O. urolepis). Multimesh (50 × 2 m) gillnets were set at nine stations in 1999, ten stations in 2000 and six stations in 2002. These stations were sampled every two months in 1999, every three months in 2000 and once in 2002. O. mossambicus was the most abundant of the four species, with a maximum mean catch per unit effort (CPUE) 13.8 kg net⁻¹ h⁻¹ or 29.9 fish net⁻¹ h⁻¹ being observed at the river mouth stations in August 1999. From spring to summer, tilapia CPUE increased at nearshore and river mouth stations and decreased at pelagic stations, apparently reflecting migration away from midlake areas in response to anoxia or hypoxia caused by periodic springtime overturn events in deep waters. Tilapia catches in nearshore, river mouth and pelagic habitats were 83 and 60% males in 1999 and 2000, respectively. Tilapia catches in rivers in August 1999 averaged only 6% male. During 1999–2000, the tilapia population consisted essentially of only the 1995 and 2000 year classes. Harsh conditions at the Salton Sea have led to erratic reproduction and survival rates and unstable age structures for its resident fishes. Massive parasite infestations of fry and physiological stressors such as anoxia, high sulfide levels, high salinity and high and low temperatures are potential causes of the irregular recruitment and periodic dieoffs of tilapia. The abundance of all fish species declined over the years of study. Between 1999 and 2002, the late summer mean CPUEs for tilapia, bairdiella and orangemouth corvina at four nearshore stations dropped from 16 fish to 0.02 fish, from 4.7 fish net to 0.23 fish, and from 0.08 fish to 0.02 fish, respectively. During 2000–2003, parallel declines occurred in estimated numbers of adult fish involved in mass mortality events at the Sea. The boom-and-bust dynamics of tilapia and other fish populations in the Sea have major consequences for fish-eating bird populations, for other components of the ecosystem, and for the recreational value of the lake. Guest Editor: John M. Melack Saline Waters and their Biota     

Organochlorine pesticides, polychlorinated biphenyls, metals, and trace elements in waterbird eggs, Salton Sea, California, 2004

The Salton Sea is a highly eutrophic, hypersaline terminal lake that receives inflows primarily from agricultural drainages in the Imperial and Coachella valleys. Impending reductions in water inflow at Salton Sea may concentrate existing contaminants which have been a concern for many years, and result in higher exposure to birds. Thus, waterbird eggs were collected and analyzed in 2004 and compared with residue concentrations from earlier years; these data provide a base for future comparisons. Eggs from four waterbird species (black-crowned night-heron [Nycticorax nycticorax], great egret [Ardea alba], black-necked stilt [Himantopus mexicanus], and American avocet [Recurvirostra Americana]) were collected. Eggs were analyzed for organochlorine pesticides, polychlorinated biphenyls (PCBs), metals, and trace elements, with current results compared to those reported for eggs collected from the same species and others during 1985–1993. The two contaminants of primary concern were p,p′-DDE (DDE) and selenium. DDE concentrations in night-heron and great egret eggs collected from the northwest corner of Salton Sea (Whitewater River delta) decreased 91 and 95%, respectively, by 2004, with a concomitant increase in eggshell thickness for both species. Decreases in bird egg DDE levels paralleled those in tissues of tilapia (Oreochromis mossambicus × O. urolepis), an important prey species for herons and egrets. Despite most nests of night-herons and great egrets failing in 2004 due to predation, predicted reproductive effects based on DDE concentrations in eggs were low or negligible for these species. The 2004 DDE findings were in dramatic contrast to those in the past decade, and included an 81% decrease in black-necked stilt eggs, although concentrations were lower historically than those reported in night-herons and egrets. Selenium concentrations in black-necked stilt eggs from the southeast corner of Salton Sea (Davis Road) were similar in 1993 and 2004, with 4.5–7.6% of the clutches estimated to be selenium impaired during both time periods. Because of present selenium concentrations and future reduced water inflow, the stilt population is of special concern. Between 1992 and 1993 and 2004 selenium in night-heron and great egret eggs from the Whitewater River delta at the north end of the Sea decreased by 81 and 55%, respectively. None of the night-heron or egret eggs collected in 2004 contained selenium concentrations above the lowest reported effect concentration (6.0 μg/g dw). Reasons for selenium decreases in night-heron and egret eggs are unknown. Other contaminants evaluated in 2004 were all below known effect concentrations. However, in spite of generally low contaminant levels in 2004, the nesting populations of night-herons and great egrets at Salton Sea were greatly reduced from earlier years and snowy egrets (Egretta thula) were not found nesting. Other factors that include predation, reduced water level, diminished roost and nest sites, increased salinity, eutrophication, and reduced fish populations can certainly influence avian populations. Future monitoring, to validate predicted responses by birds, other organisms, and contaminant loadings associated with reduced water inflows, together with adaptive management should be the operational framework at the Salton Sea. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Cultivation of <Emphasis Type="Italic">Rubrivivax gelatinosus</Emphasis> in fish industry effluent for depollution and biomass production

One application of biotechnology that contributes to sustainable development is the utilization of industrial byproducts as substrates for the production of substances of interest by microorganism. In this work, liquid effluent from tilapia fish processing was used as a substrate for the growth of Rubrivivax gelatinosus with the aim of studying the bacterial photo heterotrophic metabolism. Cultivation conditions included 32 ± 2°C, 1,400 ± 200 lux and 7 days. In the initial days, the best cell mass production (0.273 g l⁻¹ with 72 h), specific growth rate (0.188 h⁻¹ with 48 h) and chemical oxygen demand (COD) decrease (43% with 72 h) were reached. Typical bacterial oxycarotenoids were identified after 3 days of cultivation, averaging 3.03 mg g⁻¹ biomass. Bacterial growth in the effluent during the period of study resulted in pH increase to 7.9, total nitrogen, oils and greases and COD decreases of 22.46, 47.71 and 52%, respectively, and dry cell mass production of 0.18 g l⁻¹. The bacterial growth in the wastewater provided biomass and oxycarotenoids and the removal of pollutant load.     

Fungal autolysate as a nutrient supplement for ethanol and chitosan production by <Emphasis Type="Italic">Mucor indicus</Emphasis>

Mucor indicus can be used to produce ethanol from a variety of sugars, including pentose’s. An extract of it, produced by autolysis, could replace yeast extract in culture medium with improved production of ethanol. At 10 g l⁻¹, the extract gave a higher ethanol yield (0.47 g g⁻¹) and productivity (0.71 g l⁻¹ h⁻¹) compared to medium containing yeast extract (yield 0.45 g g⁻¹; productivity 0.67 g l⁻¹ h⁻¹).     

Citric acid production from glycerol-containing waste of biodiesel industry by Yarrowia lipolytica in batch, repeated batch, and cell recycle regimes

Yarrowia lipolytica A-101-1.22 produces high citric acid (112 g l⁻¹) with a yield of 0.6 g g⁻¹ and a productivity of 0.71 g l⁻¹ h⁻¹ during batch cultivation in the medium with glycerol-containing waste of biodiesel industry. However, it was observed that the specific citric acid production rate, which was maximal at the beginning of the biosynthesis, gradually decreases in the late production phase and it makes continuation of the process over 100 h pointless. The cell recycle and the repeated batch regimes were performed as ways for prolongation of citric acid synthesis by yeast. Using cell recycle, the active citric acid biosynthesis (96–107 g l⁻¹) with a yield of 0.64 g g⁻¹ and a productivity of 1.42 g l⁻¹ h⁻¹ was prolongated up to 300 h. Repeated batch culture remained stable for over 1000 h; the RB variant of 30% feed every 3 days showed the best results: 124.2 g l^-1 citric acid with a yield of 0.77 g g^-1 and a productivity of 0.85 g l^-1 h^-1.     

Fish biology and fisheries ecology of the Salton Sea, California

Studies of the fisheries ecology and fish biology of the Salton Sea, California, were conducted in 1999 and 2000 using 50 m gill nets in river, nearshore, pelagic, and estuarine areas. Total lengths and weights were measured for all fish captured, and sub-samples were dissected for gonad weights and aging. Ten fish species were captured of which a hybrid tilapia (Oreochromis mossambicusx O. urolepis hornorum) was dominant by number and weight. Nearshore and estuarine areas had highest catch rates (over 11 kg h^–1 net^–1 for tilapia). Rivers were richest in the number of species (6 of 10 species were exclusively riverine), but lowest in fish abundance. Orangemouth corvina (Cynoscion xanthulus), bairdiella (Bairdiella icistia), sargo (Anisotremus davidsoni), and tilapia grew faster, but had shorter life spans than conspecifics elsewhere and Salton Sea conspecifics of 50 years ago. Reproduction occurred mostly in the nearshore and estuarine areas. Onset of reproduction of bairdiella and sargo was in the spring and extended through the beginning of summer. Reproduction of orangemouth corvina started in the summer and of tilapia in the spring. Reproduction of orangemouth corvina and tilapia extended through the fall. Gender ratios of tilapia were skewed toward males in all areas, except the rivers, where females predominated. All four species aggregated along the nearshore and estuarine areas in the summer when dissolved oxygen in the pelagic area was limited. Any restoration alternative for the Salton Sea should consider areas close to shore as primary areas for fish reproduction and survival.     

Toxicity of Diazinon 60 EC for embryos and larvae of tench, <Emphasis Type="Italic">Tinca tinca</Emphasis> (L.)

The effects of Diazinon 60 EC (organophosphate insecticide, active substance diazinon) on mortality, growth rate, early ontogenetic rate, and occurrence of malformations was studied in embryos and larvae of tench, Tinca tinca (L.). The exposure of fish to 0, 10, 100, 1,000, and 3,000 μg dm⁻³ of Diazinon 60 EC was initiated 24 h after fertilization of eggs and concluded 32 days later. At the highest concentration tested (3,000 μg dm⁻³), total mortality was observed within the first 15 days of exposure. A concentration of 1,000 μg dm⁻³ caused high incidence of malformations, decrease in growth rate and ontogenetic development slowed down. A concentration of 100 μg dm⁻³ mildly decreased growth rate, but at 10 μg dm⁻³ no changes compared to the control were observed. Thus, Diazion 60 EC at the concentration of 10 μg dm⁻³ is not dangerous for the embryos and larvae of tench.     

Drought,warming and soil fertilization effects on leaf volatile terpene concentrations in <Emphasis Type="Italic">Pinus halepensis</Emphasis> and <Emphasis Type="Italic">Quercus ilex</Emphasis>

The changes in foliar concentrations of volatile terpenes in response to water stress, fertilization and temperature were analyzed in Pinus halepensis and Quercus ilex. The most abundant terpenes found in both species were α-pinene and Δ³-carene. β-Pinene and myrcene were also abundant in both species. P. halepensis concentrations were much greater than those of Q. ilex in agreement with the lack of storage in the latter species (15205.60 ± 1140.04 vs. 0.54 ± 0.08 μg g⁻¹ [d.m.]). The drought treatment (reduction to 1/3 of full watering) significantly increased the total terpene concentrations in both species (54% in P. halepensis and 119% in Q. ilex). The fertilization treatment (addition of either 250 kg N ha⁻¹ or 250 kg P ha⁻¹ or both) had no significant effects on terpene foliar concentrations. The terpene concentrations increased from 0.25 μg g⁻¹ [d.m.] at 30°C to 0.70 μg g⁻¹ [d.m.] at 40°C in Q. ilex (the non-storing species) and from 2,240 μg g⁻¹ [d.m.] at 30°C to 15,621 μg g⁻¹ [d.m.] at 40°C in P. halepensis (the storing species). Both species presented negative relationship between terpene concentrations and relative water contents (RWC). The results of this study show that higher terpene concentrations can be expected in the warmer and drier conditions predicted for the next decades in the Mediterranean region.     

Genetic variation of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> isolates forming fumonisin B<Subscript>1</Subscript> and moniliformin

Thirty single-spore isolates of a toxigenic fungus, Fusarium oxysporum, were isolated from asparagus spears and identified by species-specific polymerase chain reaction (PCR) and translation elongation factor 1-α (TEF) sequence analysis. In the examined sets of F. oxysporum isolates, the DNA sequences of mating type genes (MAT) were identified. The distribution of MAT idiomorph may suggest that MAT1-2 is a predominant mating type in the F. oxysporum population. F. oxysporum is mainly recognised as a producer of moniliformin—the highly toxic secondary metabolite. Moniliformin content was determined by high-performance liquid chromatography (HPLC) analysis in the range 0.05–1,007.47 μg g⁻¹ (mean 115.93 μg g⁻¹) but, also, fumonisin B₁ was detected, in the concentration range 0.01–0.91 μg g⁻¹ (mean 0.19 μg g⁻¹). There was no association between mating types and the mycotoxins biosynthesis level. Additionally, a significant intra-species genetic diversity was revealed and molecular markers associated with toxins biosynthesis were identified.     

Chemical evolution of the Salton Sea, California: nutrient and selenium dynamics

The Salton Sea is a 1000-km² terminal lake located in the desert area of southeastern California. This saline (44000 mg l^–1 dissolved solids) lake started as fresh water in 1905–07 by accidental flooding of the Colorado River, and it is maintained by agricultural runoff of irrigation water diverted from the Colorado River. The Salton Sea and surrounding wetlands have recently acquired substantial ecological importance because of the death of large numbers of birds and fish, and the establishment of a program to restore the health of the Sea. In this report, we present new data on the salinity and concentration of selected chemicals in the Salton Sea water, porewater and sediments, emphasizing the constituents of concern: nutrients (N and P), Se and salinity. Chemical profiles from a Salton Sea core estimated to have a sedimentation rate of 2.3 mm yr^–1 show increasing concentrations of OC, N, and P in younger sediment that are believed to reflect increasing eutrophication of the lake. Porewater profiles from two locations in the Sea show that diffusion from bottom sediment is only a minor source of nutrients to the overlying water as compared to irrigation water inputs. Although loss of N and Se by microbial-mediated volatilization is possible, comparison of selected element concentrations in river inputs and water and sediments from the Salton Sea indicates that most of the N (from fertilizer) and virtually all of the Se (delivered in irrigation water from the Colorado River) discharged to the Sea still reside within its bottom sediment. Laboratory simulation on mixtures of sediment and water from the Salton Sea suggest that sediment is a potential source of N and Se to the water column under aerobic conditions. Hence, it is important that any engineered changes made to the Salton Sea for remediation or for transfer of water out of the basin do not result in remobilization of nutrients and Se from the bottom sediment into the overlying water.     

<Emphasis Type="Italic">Clostridium beijerinckii</Emphasis> mutant with high inhibitor tolerance obtained by low-energy ion implantation

Clostridium beijerinckii mutant strain IB4, which has a high level of inhibitor tolerance, was screened by low-energy ion implantation and used for butanol fermentation from a non-detoxified hemicellulosic hydrolysate of corn fiber treated with dilute sulfuric acid (SAHHC). Evaluation of toxicity showed C. beijerinckii IB4 had a higher level of tolerance than parent strain C. beijerinckii NCIMB 8052 for five out of six phenolic compounds tested (the exception was vanillin). Using glucose as carbon source, C. beijerinckii IB4 produced 9.1 g l⁻¹ of butanol with an acetone/butanol/ethanol (ABE) yield of 0.41 g g⁻¹. When non-detoxified SAHHC was used as carbon source, C. beijerinckii NCIMB 8052 grew well but ABE production was inhibited. By contrast, C. beijerinckii IB4 produced 9.5 g l⁻¹ of ABE with a yield of 0.34 g g⁻¹, including 2.2 g l⁻¹ acetone, 6.8 g l⁻¹ butanol, and 0.5 g l⁻¹ ethanol. The remarkable fermentation and inhibitor tolerance of C. beijerinckii IB4 appears promising for ABE production from lignocellulosic materials.     

Selenium and Mercury in Native and Introduced Fish Species of Patagonian Lakes,Argentina

A survey of mercury (Hg) and selenium (Se) contents was performed in fish collected from lakes located in two National Parks of the northern patagonian Andean range. Two native species, catfish (Diplomystes viedmensis) and creole perch (Percichthys trucha), and three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), and brook trout (Salvelinus fontinalis), were caught from lakes Nahuel Huapi, Moreno, Traful, Espejo Chico, and Guillelmo belonging to Nahuel Huapi National Park and from lakes Futalaufquen and Rivadavia, Los Alerces National Park. In lake Moreno, fish diet items were analyzed and rainbow trout grown in a farm. Hg and Se were measured in muscle and liver tissues by instrumental neutron activation analysis. The average concentrations in muscle of Hg for all species, ages, and lakes are between 0.4 to 1.0 μg g⁻¹ dry weight (DW) with a few fish, mainly native, exceeding the United States Environmental Protection Agency health advisory for freshwater fish limited consumption, and from 0.8 to 1.5 μg g⁻¹ DW for Se. Average concentrations in liver of Hg in all species range from 0.4 to 0.9 μg g⁻¹ DW. Brown trout, the top predator in these lakes, showed the lowest average Hg burden in both tissues. Se concentrations in the liver of brown and rainbow trout, up to 279 μg g⁻¹ DW, are higher than those expected for nearly pristine lakes, exceeding 20 μg g⁻¹ DW, the threshold concentration associated with Se toxicity. These species show lower Hg contents in muscle, suggesting a possible detoxification of Hg by a Se-rich diet. Creole perch and velvet catfish livers have lower Se concentrations, with a narrower span of values (2.3 to 8.5 μg g⁻¹ and 3.3 to 5.5 μg g⁻¹ DW respectively).     

Isolation of antifouling compounds from the marine bacterium, <Emphasis Type="Italic">Shewanella oneidensis</Emphasis> SCH0402

Two compounds, 2-hydroxymyristic acid (HMA) and cis-9-oleic acid (COA), were isolated from a chloroform extract of the marine bacterium, Shewanella oneidensis SCH0402. In a spectrophotometer-based chemotaxis assay, HMA completely eliminated the optical density (OD) of Alteromonas marina SCH0401 and Bacillus atrophaeus SCH0408, motile, fouling bacteria, at 100 and 1000 μg ml⁻¹, respectively. COA similarly decreased the OD of A. marina and B. atrophaeus by 100% at 1000 μg ml⁻¹. The commercially available, highly toxic anti-fouling compound, tributyltin oxide (TBTO) never reduced the OD of the target bacteria by 100% even at higher concentration. Instead, all the test bacterial cells were killed at higher than 1000 μg ml⁻¹ of concentration. Both HMA and COA inhibited germination of Ulva pertusa spores completely at 10 and 100 μg ml⁻¹, respectively, while TBTO inhibited germination at 0.01 μg ml⁻¹. However, in field assays, both HMA and COA showed anti-fouling activities as potent as TBTO against a wide range of fouling organisms, including micro- and macro-algae, barnacles, and mussels. The average fouling coverage on the surface of the control panel was 93 ± 6% after 1.5 years but no fouling was observed on the surface of the test panel onto which each compound was applied separately. Thus, bacterial repellent compounds can be used as substitutes for potent toxic anti-fouling compounds, resulting in higher standards of environmental safety without loss of anti-fouling performance.     

Identification of QTL underlying isoflavone contents in soybean seeds among multiple environments

Soybean isoflavones are valued in certain medicines, cosmetics, foods and feeds. Selection for high-isoflavone content in seeds along with agronomic traits is a goal of many soybean breeders. The aim of the study was to identify the quantitative trait loci (QTL) underlying seed isoflavone content in soybean among seven environments in China. A cross was made between ‘Zhongdou 27’, a soybean cultivar with higher mean isoflavone content in the seven environments (daidzein, DZ, 1,865 μg g⁻¹; genistein, GT, 1,614 μg g⁻¹; glycitein, GC, 311 μg g⁻¹ and total isoflavone, TI, 3,791 μg g⁻¹) and ‘Jiunong 20’, a soybean cultivar with lower isoflavone content (DZ, 844 μg g⁻¹; GT, 1,046 μg g⁻¹; GC, 193 μg g⁻¹ and TI, 2,061 μg g⁻¹). Through single-seed-descent, 130 F₅-derived F₆ recombinant inbred lines were advanced. A total of 99 simple-sequence repeat markers were used to construct a genetic linkage map. Seed isoflavone contents were analyzed using high-performance liquid chromatography for multiple years and locations (Harbin in 2005, 2006 and 2007, Hulan in 2006 and 2007, and Suihua in 2006 and 2007). Three QTL were associated with DZ content, four with GT content, three with GC content, and five with TI content. For all QTL detected the beneficial allele was from Zhongdou 27. QTL were located on three (DZ), three (GC), four (GT) and five (TI) molecular linkage groups (LG). A novel QTL was detected with marker Satt144 on LG F that was associated with DZ (0.0014 > P > 0.0001, 5% < R ² < 11%; 254 < DZ < 552 μg g⁻¹), GT (0.0027 > P > 0.0001; 4% < R ² < 9%; 262 < GT < 391 μg g⁻¹), and TI (0.0011 > P > 0.0001; 4% < R ² < 15%; 195 < TI < 871 μg g⁻¹) across the various environments. A previously reported QTL on LG M detected by Satt540 was associated with TI across four environments and TI mean (0.0022 > P > 0.0001; 3% < R ² < 8%; 182 < TI < 334 μg g⁻¹) in China. Because both beneficial alleles were from Zhongdou 27, it was concluded that these two QTL would have the greatest potential value for marker-assisted selection for high-isoflavone content in soybean seed in China. G. Zeng, D. Li and Y. Han have equal contributions to the paper.     

Carbon source pulsed feeding to attain high yield and high productivity in poly(3-hydroxybutyrate) (PHB) production from soybean oil using <Emphasis Type="Italic">Cupriavidus necator</Emphasis>

Poly(3-hydroxybutyrate) (PHB) biosynthesis from soybean oil by Cupriavidus necator was studied using a bench scale bioreactor. The highest cell concentration (83 g l⁻¹) was achieved using soybean oil at 40 g l⁻¹ and a pulse of the same concentration. The PHB content was 81% (w/w), PHB productivity was 2.5 g l⁻¹ h⁻¹, and the calculated Y_p/s value was 0.85 g g⁻¹. Growth limitation and the onset of PHB biosynthesis took place due to exhaustion of P, and probably also Cu, Ca, and Fe.     

Rate of dehydration,state of subcellular organisation and nature of cryoprotection are critical factors contributing to the variable success of cryopreservation: studies on recalcitrant zygotic embryos of <Emphasis Type="Italic">Haemanthus montanus</Emphasis>

Effects of sequential procedures required for cryopreservation of embryos excised from the recalcitrant seeds of Haemanthus montanus were assessed ultrastructurally and in conjunction with respiratory activity and the rate of protein synthesis. Fresh material (water content, 5.05 ± 0.92 g g⁻¹ dry mass) afforded ultrastructural evidence of considerable metabolic activity, borne out by respiratory rates. Neither exposure to glycerol nor sucrose as penetrating and non-penetrating cryoprotectants, respectively, brought about degradative changes, although increased vacuolation and autophagy accompanied both, while respiratory and protein synthetic activity were not adversely affected. Glycerol-cryoprotected embryos flash dried to water contents >0.4 g g⁻¹ showed organised ultrastructural features and considerable autophagy consistent with metabolic activity, and although respiratory activity was lower, protein synthesis rate was enhanced relative to fresh material. However, at water contents <0.4 g g⁻¹, embryo tissue presented a mosaic of cells of variable density and ultrastructural status, but trends in rates of respiration and protein synthesis remained similar. Flash drying after sucrose exposure was accompanied by considerable ultrastructural abnormality particularly at water contents <0.4 g g⁻¹, lysis of individual and groups of cells and considerable depression of respiration, but not of protein synthesis. Success, assessed as ≥50% axes forming seedlings after cryogen exposure, was obtained only when glycerol-cryoprotected embryos at water contents >0.4 g g⁻¹—in which the degree of vacuolation remained moderate—were rapidly cooled. The outcomes of this study are considered particularly in terms of the stresses imposed by prolonged, relatively slow dehydration and ultimate water contents, on embryos showing considerable metabolic activity.     

1,3-Propanediol production in a two-step process fermentation from renewable feedstock

In this work, the production of 1,3-propanediol from glucose and molasses was studied in a two-step process using two recombinant microorganisms. The first step of the process is the conversion of glucose or other sugar into glycerol by the metabolic engineered Saccharomyces cerevisiae strain HC42 adapted to high (>200 g l⁻¹) glucose concentrations. The second step, carried out in the same bioreactor, was performed by the engineered strain Clostridium acetobutylicum DG1 (pSPD5) that converts glycerol to 1,3-propanediol. This two-step strategy led to a flexible process, resulting in a 1,3-propanediol production and yield that depended on the initial sugar concentration. Below 56.2 g l⁻¹ of sugar concentration, cultivation on molasses or glucose showed no significant differences. However, at higher molasses concentrations, glycerol initially produced by yeast could not be totally converted into 1,3-propanediol by C. acetobutylicum and a lower 1,3-propanediol overall yield was observed. In our hand, the best results were obtained with an initial glucose concentration of 103 g l⁻¹, leading to a final 1,3-propanediol concentration of 25.5 g l⁻¹, a productivity of 0.16 g l⁻¹ h⁻¹ and 1,3-propanediol yields of 0.56 g g⁻¹ glycerol and 0.24 g g⁻¹ sugar, which is the highest value reported for a two-step process. For an initial sugar concentration (from molasses) of 56.2 g l⁻¹, 27.4 g l⁻¹ of glycerol were produced, leading to 14.6 g l⁻¹ of 1.3-propanediol and similar values of productivity, 0.15 g l⁻¹ h⁻¹, and overall yield, 0.26 g g⁻¹ sugar.     

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     

Seasonal changes in growth rate, carrageenan yield and lectin content in the red alga Kappaphycus alvarezii cultivated in Camranh Bay, Vietnam

The three color morphotypes of the red alga Kappaphycus alvarezii (brown, red and green) were cultured in Camranh Bay, Vietnam, using the fixed off-bottom monoline culture method to evaluate the growth rate, carrageenan yield, 3,6-anhydrogalactose, gel strength and lectin content. The brown morphotype was cultivated over a 12-month period; the red and green morphotypes were over a 6-month period. At the 60-day culture timepoint, the brown morphotype showed a higher growth rate (3.5–4.6% day⁻¹) from September to February, and lower growth rate (1.6–2.8% day⁻¹) from March to August. Significant (P < 0.05) differences in growth rate between culture months were found with the brown morphotype. High growth rates for the red (3.6–4.4% day⁻¹) and green (3.7–4.2% day⁻¹) morphotypes were obtained from September to February. The carrageenan yield, 3,6-anhydrogalactose and gel strength of the three morphotypes showed little variation, with the highest values obtained in November–December. At the 30-day sampling point, the brown morphotype had a higher lectin content (167–302 μg g⁻¹ dry alga) from August to March and a lower lectin content (23–104 μg g⁻¹ dry alga) from April to July. High lectin contents were recorded for the red (139–338 μg g⁻¹ dry alga) and green (124–259 μg g⁻¹ dry alga) morphotypes from September to February. This study shows that the different morphotypes of K. alvarezii can be grown in the tropical waters of the Camranh during the northeast monsoon, and part of the southwest monsoon, especially the brown morphotype, which can be grown during any season.     

Efficient production of lactic acid from sucrose and corncob hydrolysate by a newly isolated <Emphasis Type="Italic">Rhizopus oryzae</Emphasis> GY18

The aim of this study is to investigate production of l-lactic acid from sucrose and corncob hydrolysate by the newly isolated R. oryzae GY18. R. oryzae GY18 was capable of utilizing sucrose as a sole source, producing 97.5 g l⁻¹ l-lactic acid from 120 g l⁻¹ sucrose. In addition, the strain was also efficiently able to utilize glucose and/or xylose to produce high yields of l-lactic acid. It was capable of producing up to 115 and 54.2 g l⁻¹ lactic acid with yields of up to 0.81 g g⁻¹ glucose and 0.90 g g⁻¹ xylose, respectively. Corncob hydrolysates obtained by dilute acid hydrolysis and enzymatic hydrolysis of the cellulose-enriched residue were used for lactic acid production by R. oryzae GY18. A yield of 355 g lactic acid per kg corncobs was obtained after 72 h incubation. Therefore, sucrose and corncobs could serve as potential sources of raw materials for efficient production of lactic acid by R. oryzae GY18.