Microalgae aquaculture feeds

Microalgae feeds are currently used in relatively small amounts in aquaculture, mainly for the production of larvae and juvenile shell- and finfish, as well as for raising the zooplankton required for feeding of juvenile animals. The blue-green algaSpirulina is used in substantial amounts (over 100 t y^–1) as a fish and shrimp feed, and even larger markets can be projected if production costs could be reduced. Another potential large-scale application of microalgae is the cultivation ofHaematococcus for the production of the carotenoid astaxanthin, which gives salmon flesh its reddish color. In the long-term microalgae biomass high in lipids (omega-3 fatty acids) may be developed as substitutes for fish oil-based aquaculture feeds. In shrimp ponds the indigenous algal blooms supply a part of the dietary requirements of the animals, but it is difficult to maximize algal productivities. A separate algal production system could feed the shrimps and minimize the need for added feed. Bivalves feed essentially exclusively on marine microalgae throughout their life cycle. The development of cultivation technologies for such microalgae would allow the onshore production of these animals, with greatly improved product quality and safety.This paper was presented at the Symposium on Applied Phycology at the Fourth International Phycological Congress, Duke University.     

水产动物副溶血弧菌病及其噬菌体防治研究进展

副溶血弧菌是水产动物弧菌病的重要病原微生物之一,又是食源性致病菌,摄入被其污染的水产品后可引发肠胃炎、败血症和坏死性筋膜炎等疾病,对水产养殖业及公共卫生安全均具有较大威胁。抗生素大量使用甚至滥用,不可避免地会带来水产品药物残留和细菌耐药等问题,开发安全有效的抗生素替代品迫在眉睫。作为细菌病毒,噬菌体具有宿主特异性强、易筛选、易保存、高效直接等优点,在水产养殖病害防控和食品安全领域受到广泛关注。本文概述了水产动物的副溶血弧菌病及该菌噬菌体防治的研究进展,为副溶血弧菌噬菌体及制剂应用于水产养殖病害生物防控提供参考。     

A strategy for high cell density culture of heterotrophic microalgae with inhibitory substrates

Substrate inhibition is one of the major problems preventing high cell densities of microalgae in heterotrophic culture, so the possibility of overcoming the problem by various culture techniques was examined. It was found that perfusion culture may be the most appropriate technique for high cell densities in heterotrophic culture using inhibitory substrates. An experimental example in which a hollow fibre cell recycle system (HFCRS) was employed to achieve high cell densities of Chlamydomonas reinhardtii on acetate under heterotrophic conditions of growth was demonstrated. The cell density in the HFCRS was much higher than that reported in the literature for this species.     

副溶血性弧菌耐热性直接溶血素(TDH)的研究进展

副溶血性弧菌(Vibrio parahaemolyticus)是海产品中一种常见的食源性致病菌,常导致水产养殖动物患病或者引起食物中毒。耐热性直接溶血素(thermotolerant direct hemolysin,TDH)是副溶血性弧菌最为重要的致病因子之一。本文围绕tdh基因在弧菌属中的广泛分布与传播、tdh基因的多样性及其表达调控、TDH的蛋白结构及其生物活性进行了综述,并对未来TDH的研究方向进行了展望。旨在进一步了解由副溶血性弧菌感染所引起的病症,为预防副溶血性弧菌的感染和临床治疗提供理论支撑。     

The trade-off between growth rate and yield in microbial communities and the consequences for under-snow soil respiration in a high elevation coniferous forest

Soil microbial respiration is a critical component of the global carbon cycle, but it is uncertain how properties of microbes affect this process. Previous studies have noted a thermodynamic trade-off between the rate and efficiency of growth in heterotrophic organisms. Growth rate and yield determine the biomass-specific respiration rate of growing microbial populations, but these traits have not previously been used to scale from microbial communities to ecosystems. Here we report seasonal variation in microbial growth kinetics and temperature responses (Q₁₀) in a coniferous forest soil, relate these properties to cultured and uncultured soil microbes, and model the effects of shifting growth kinetics on soil heterotrophic respiration (R_h). Soil microbial communities from under-snow had higher growth rates and lower growth yields than the summer and fall communities from exposed soils, causing higher biomass-specific respiration rates. Growth rate and yield were strongly negatively correlated. Based on experiments using specific growth inhibitors, bacteria had higher growth rates and lower yields than fungi, overall, suggesting a more important role for bacteria in determining R_h. The dominant bacteria from laboratory-incubated soil differed seasonally: faster-growing, cold-adapted Janthinobacterium species dominated in winter and slower-growing, mesophilic Burkholderia and Variovorax species dominated in summer. Modeled R_h was sensitive to microbial kinetics and Q₁₀: a sixfold lower annual R_h resulted from using kinetic parameters from summer versus winter communities. Under the most realistic scenario using seasonally changing communities, the model estimated R_h at 22.67 mol m⁻² year⁻¹, or 47.0% of annual total ecosystem respiration (R_e) for this forest.     

Effects of mosquito larvae removal with Bacillus thuringiensis israelensis (Bti) on natural protozoan communities

The protein crystals produced by Bacillus thuringiensis israelensis (Bti) are used against the larvae of pestiferous flood-water mosquitoes in ephemeral wetlands. Although mosquito larvae are considered important predators on protozoans and bacteria, it is not known how a distinct reduction of mosquito larvae density in natural wetlands caused by application of Bti may indirectly affect these microbial communities. Here we show, in a large scale experiment in six natural wetlands, that the densities of heterotrophic protozoans was on an average 4.5 times higher in wetland areas treated with Bti than in control areas. In addition, the taxonomic richness of heterotrophic protozoans increased on an average of 60% in areas with Bti application compared to control areas. The increase in protozoan density and richness was fairly consistent among sites of different wetland habitats. We discuss the potential implications of our results for other parts of the ecosystem. Handling editor: K. Martens     

Bacterial abundance and aerobic microbial activity across natural and oyster aquaculture habitats during summer conditions in a northeastern Pacific estuary

We measured sediment properties and the abundance and aerobic metabolism of microbes in Willapa Bay, Washington, USA, to test the response of sediment microbes to oyster aquaculture. Sites spanned the estuary gradient (practical salinity units ranged from 24 to 30 under seasonally low river flows) and six different low-intertidal habitat types: eelgrass (Zostera marina), unstructured tideflat, oyster hummocks (reefs of Crassostrea gigas), longline oyster aquaculture, hand-picked on-bottom oyster aquaculture, and dredged on-bottom oyster aquaculture. Aerobic metabolism was assessed by sole-source carbon use (SSCU) of 31 carbon sources on Biolog plates. Sediments generally became siltier and more organically enriched into the estuary, but no consistent differences in sediment properties occurred across habitat types. Bacterial cell density tracked organic content. Across the estuary gradient, overall aerobic SSCU increased less steeply than bacterial cell density, possibly as anaerobic metabolism became more important. Across habitats, aerobic SSCU differed significantly in both overall metabolism and diversity of carbon sources. Aerobic metabolism was generally lower for sediment microbes from intertidal on-bottom oyster aquaculture than from eelgrass. Humans indirectly alter microbial activity through biogenic habitats created during aquaculture, but, as has been shown for bivalves more generally, these changes were relatively small, particularly in comparison to sediment changes along estuarine gradients.     

Morphology and phylogeny of the pseudocolonial dinoflagellates Polykrikos lebourae and Polykrikos herdmanae n. sp

Both the photosynthetic and heterotrophic forms of the only known marine benthic (sand-dwelling) species of Polykrikos, namely P. lebourae, were investigated using light and electron microscopy and molecular phylogenetic analyses. The pseudocolonies usually contained eight integrated zooids and two nuclei. Pseudocolonies consisting of four or five zooids and one nucleus were observed for the first time for this species; some of these reduced pseudocolonies contained plastids, while others were heterotrophic and contained taeniocyst-nematocyst complexes. The ultrastructure of the plastids in P. lebourae did not conform to the organization of thylakoids and enveloping membranes present in the peridinin-containing plastids of other photosynthetic dinoflagellates (i.e. stacks of 3 thylakoids and 3 outer membranes). Instead, the plastids in P. lebourae had thylakoids arranged in pairs and appeared to be enveloped by only two membranes. Molecular phylogenetic data using small subunit rDNA demonstrated that the photosynthetic and heterotrophic forms of P. lebourae represent two distinct clades. The more inclusive clade containing both forms of P. lebourae was most closely related to heterotrophic polykrikoids, namely P. kofoidii. These results led us to conclude that the photosynthetic and heterotrophic forms of P. lebourae are in fact two distinct lineages, and the heterotrophic form is described here as Polykrikos herdmanae n. sp.     

Growth characteristics of the cyanobacterium Nostoc flagelliforme in photoautotrophic, mixotrophic and heterotrophic cultivation

Nostoc flagelliforme is a terrestrial cyanobacterium with high economic value. Dissociated cells separated from a natural colony of N. flagelliforme were cultivated for 7 days under either phototrophic, mixotrophic or heterotrophic culture conditions. The highest biomass, 1.67 g L⁻¹ cell concentration, was obtained under mixotrophic culture, representing 4.98 and 2.28 times the biomass obtained in phototrophic and heterotrophic cultures, respectively. The biomass in mixotrophic culture was not the sum as that in photoautotrophic and heterotrophic cultures. During the first 4 days of culture, the cell concentration in mixotrophic culture was lower than the sum of those in photoautotrophic and heterotrophic cultures. However, from the 5th day, the cell concentration in mixotrophic culture surpassed the sum of those obtained from the other two trophic modes. Although the inhibitor of photosynthetic electron transport DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] efficiently inhibited autotrophic growth of N. flagelliforme cells, under mixotrophic culture they could grow by using glucose. The addition of glucose changed the response of N.flagelliforme cells to light. The maximal photosynthetic rate, dark respiration rate and light compensation point in mixotrophic culture were higher than those in photoautotrophic cultures. These results suggest that photoautotrophic (photosynthesis) and heterotrophic (oxidative metabolism of glucose) growth interact in mixotrophic growth of N. flagelliforme cells.     

Two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production

A two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production was studied, wherein high density heterotrophic cultures of Chlorellasorokiniana serve as seed for subsequent phototrophic growth. The data showed growth rate, cell density and productivity of heterotrophic C.sorokiniana were 3.0, 3.3 and 7.4 times higher than phototrophic counterpart, respectively. Hetero- and phototrophic algal seeds had similar biomass/lipid production and fatty acid profile when inoculated into phototrophic culture system. To expand the application, food waste and wastewater were tested as feedstock for heterotrophic growth, and supported cell growth successfully. These results demonstrated the advantages of using heterotrophic algae cells as seeds for open algae culture system. Additionally, high inoculation rate of heterotrophic algal seed can be utilized as an effective method for contamination control. This two-stage heterotrophic phototrophic process is promising to provide a more efficient way for large scale production of algal biomass and biofuels.     

Fish is food--the FAO's fish price index

World food prices hit an all-time high in February 2011 and are still almost two and a half times those of 2000. Although three billion people worldwide use seafood as a key source of animal protein, the Food and Agriculture Organization (FAO) of the United Nations-which compiles prices for other major food categories-has not tracked seafood prices. We fill this gap by developing an index of global seafood prices that can help to understand food crises and may assist in averting them. The fish price index (FPI) relies on trade statistics because seafood is heavily traded internationally, exposing non-traded seafood to price competition from imports and exports. Easily updated trade data can thus proxy for domestic seafood prices that are difficult to observe in many regions and costly to update with global coverage. Calculations of the extent of price competition in different countries support the plausibility of reliance on trade data. Overall, the FPI shows less volatility and fewer price spikes than other food price indices including oils, cereals, and dairy. The FPI generally reflects seafood scarcity, but it can also be separated into indices by production technology, fish species, or region. Splitting FPI into capture fisheries and aquaculture suggests increased scarcity of capture fishery resources in recent years, but also growth in aquaculture that is keeping pace with demand. Regionally, seafood price volatility varies, and some prices are negatively correlated. These patterns hint that regional supply shocks are consequential for seafood prices in spite of the high degree of seafood tradability.     

Advances in Seaweed Aquaculture Among Pacific Island Countries

Recent developments in the seaweed aquaculture industries of Pacific islands are reviewed from the perspective of technical, production, geographic, marketing, species-diversification, socio-economic and institutional-support advances. Successful commercial aquaculture of seaweeds in the Pacific island region is presently based on two species, Kappaphycus alvarezii in Kiribati, Fiji and Solomon Islands, and Cladosiphon sp. in Tonga. It is possible that other candidate species could be considered for aquaculture for food (e.g. Caulerpa racemosa or Meristotheca procumbens) or extraction of agar (Gracilaria), although further research on the technical feasibility of aquaculture methods to produce sufficient tonnage, and particularly on their marketing, is needed. While the Pacific island region may be environmentally ideal for seaweed aquaculture, the limitations of distance from main centres and distance from markets, vulnerability to world price fluctuations, and socio-economic issues, make it unlikely that the Pacific Island region will ever rival the scale of Asian seaweed production. Regional seaweed farming can nevertheless make a useful contribution to supplement other sources of income, and can be an important economic boost for isolated outer islands where few alternative income-generating opportunities exist.     

Trophic dependencies of some larval chironomidae (Diptera) and fish species in the River Thames

Experiments are described to characterise the heterotrophic potential of Westiellopsis prolifica Janet, which fixes nitrogen under light and dark conditions. The growth of the organism in terms of dry weight increase, was more in fructose, lactose, sucrose, sorbose, galactose, glucose, sodium acetate, mannitol, sorbitol, glycerol, ethyl alcohol and butyl alcohol, when the alga was pretreated with light and subsequently incubated with the substrates in light. Mannose, xylose, acetic acid, propionic acid, fructose 1,6 di Po₄, pyruvic acid, dihydroxyacetone and succinic acid decreased the growth of the organism in the same condition. In dark incubation after pretreatment with light, as well as in the dark, Westiellopsis showed a better growth response to almost all the exogenous substrates. However, after pretreatment either with light or dark, the test organism utilised exogenous substrates quicker in light than in dark incubations. These experiments would suggest that the substrate specificity and efficiency of substrate utilisation by the alga during its heterotrophic growth are governed by the growth conditions.     

An investigation of the heterotrophic culture of the green algaTetraselmis

The marine PrasinophyteTetraselmis may be cultured under both mixotrophic (photoheterotrophic) and heterotrophic conditions. The growth rate was slightly lower, and pigment levels and lipid composition were radically affected on heterotrophic culture in 1 L fermenters. Total chlorophyll levels of dark grown cultures were less than 1% of those observed in mixotrophically grown cells, the chlorophylla : b ratio also decreased as did the carotenoid content. In addition, the total amounts of lipids including polyunsaturated fatty-acids were also lower in heterotrophically cultured cells: 6.4 mg g^–1 (dried alga) and 0.35 mg g^–1 (dried alga); as compared to 37.1 mg g^–1 (dried alga) and 18.5 mg g^–1 (dried alga), for cells grown in the light. However, gross morphology and final yield (>16 g l^–1) were relatively unaffected. The algae produced were spray-dried and tested for their suitability as an aquaculture feed.Address for correspondence     

Phosphate assimilation by Chlorella and adjustment of phosphate concentration in basal medium for its cultivation

Assimilation of phosphate by Chlorella pyrenoidosa was 0.81-8.1 mg PO(4)-P/g dry weight for heterotrophic cultures and 0.81-16.1 mg/g for mixotrophic cultures. Optimal carbon:phosphorous (C/P) ratios were 206:1-2060:1 and 103:1-2060:1 for heterotrophic and mixotrophic cultivations, respectively. These requirements for phosphate for growth of C. pyrenoidosa under either heterotrophic or mixotrophic conditions are much less (6.25-62.5 or 3.12-62.5-fold at 10 g glucose/l) than its concentration in basal medium.     

Heterotrophic metabolism and diazotrophic growth ofNostoc sp. fromCycas circinalis

The cyanobiont ofCycas circinalis (identified asNostoc sp.) was isolated and its heterotrophic metabolism was studied in free culture under nitrogen-fixing conditions. Morphology, growth rate, nitrogenase activity, biochemical composition, efficiency of assimilation of organic carbon and molecular nitrogen were determined under different conditions of energy and carbon supply. The study has revealed the high potential of the heterotrophic metabolism in this symbiotic cyanobacterium. Although low rates of metabolic activities were attained under heterotrophic conditions, the efficiencies of organic carbon utilization (0.48 g cell-carbon per g glucose-carbon in chemoheterotrophy, from 0.65 to 0.74 under photoheterotrophy) and of N₂ assimilation (35.0 mg N₂ fixed per g glucose used in chemoheterotrophy, from 58.3 to 61.9 under photoheterotrophy) displayed by this organism were among the highest ever found in diazotrophically grown microorganisms. The isolate fromC. circinalis was able to grow indefinitely in the dark under nitrogen-fixing conditions, maintaining a well balanced biosynthetic activity and the capacity to resume photosynthetic metabolism quickly. The significance of the heterotrophic potential of this symbioticNostoc is discussed.     

Bioactivity of intra and extracellular substances from cyanobacteria and lactic acid bacteria on “wood blue stain” fungi

Cyanobacteria (photoautotrophic prokariota) have potential for the control of pathogenic bacteria and fungi. The effect of intra and extracellular products from cyanobacterial strains on the growth of fungi isolated from “wood blue stain,” was tested. Extracellular products were obtained by concentration and sterilization of the culture medium where cyanobacteria were grown. Cyanobacterial substances promoted or inhibited fungal growth according to the fungal and cyanobacterial strains tested. Extracellular products from Nostoc muscorum 79a and the methanolic extract from Microchaete tenera 84b biomass inhibited growth of Sphaeropsis sapinea 2157 (64.7 and 775.6%, respectively). Extracellular products of Nostoc piscinale 59 and biomass methanolic extract from N. muscorum 79a produced the highest growth promotion of Trichoderma boningii 452 (105.0%) and T. viride 993 (136.7%). Extracellular products of the heterotrophic lactic acid bacterium Streptococcus termophilus were also tested and strongly inhibited (64–92%) all the fungal strains. The tested fungi have different sensitivity to the bioactive substances present in the biomass and/or the culture medium of the studied cyanobacteria and lactic acid bacterium. N. muscorum 79a, M. tenera 84b, and S. termophilus have potential to control the wood blue stain fungi by a friendly environmental alternative.     

Quorum sensing by <Emphasis Type="Italic">N</Emphasis>-acylhomoserine lactones is not required for <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis> during growth with organic particles in lake water microcosms

It was investigated whether quorum sensing (QS) mediated by N-acylhomoserine lactones (AHLs) was important for heterotrophic bacteria from the littoral zone of the oligotrophic Lake Constance for growth with organic particles. More than 900 colonies from lake water microcosms with artificial organic aggregates consisting of autoclaved unicellular algae embedded in agarose beads were screened for AHL-production. AHL-producing bacteria of the genus Aeromonas enriched in the microcosms but AHLs could not be detected in any microcosm. To test for a potential function of AHL-mediated QS, growth experiments with the wild type and an AHL-deficient mutant of Aeromonas hydrophila in lake water microcosms were performed. Growth of both strains did not differ in single cultures and showed no mutual influence in co-cultures. In co-cultures with a competitor bacterium belonging to the Cytophaga–Flavobacterium group, growth of both A. hydrophila strains was reduced while growth of the competitor bacterium was not affected. Exogenous AHL-addition did not influence growth of the Aeromonas strains in any microcosm experiment. These results showed that AHL-mediated QS was not required for A. hydrophila during colonization and degradation of organic particles in lake water microcosms, suggesting that cell–cell signalling of heterotrophic bacteria in oligotrophic waters relies on novel signal molecules.     

Glycollate production and excretion byAlcaligenes eutrophus

Autotrophic cultures of the facultative chemolithotrophAlcaligenes eutrophus have been found to excrete glycollate. This excretion was greatly stimulated by the incorporation of up to 20% (v/v) oxygen in the hydrogen used for gassing. The stimulatory effect of oxygen was prevented by the addition of 10% (v/v) CO₂ to the gassing mixture. Glycollate excretion only in the presence of oxygen was increased by the addition of 2-pyridyl-hydroxymethane sulphonic acid (HPMS), an inhibitor of glycollate oxidation, indicating that glycollate formation itself was stimulated by oxygen. No glycollate excretion by cultures grown heterotrophically on pyruvate was detected, either in the absence or presence of HPMS, under heterotrophic or autotrophic conditions.Extracts from autotrophic cells showed phosphoglycollate phosphatase and glycollate oxidoreductase activities, which were considerably lower in extracts prepared from pyruvate- or fructose-grown (heterotrophic) cells. The increase in activity of both enzymes upon cell transfer from heterotrophic to autotrophic growth was prevented by chloramphenicol and resembled the induction ofd0ribulose 1,5-diphosphate carboxylase under the same conditions.Abbreviations DTE dithioerythritol - EDTA ethylenediamine tetraacetate - HPMS 2-pyridyl-hydroxymethane sulphonie acid - RuDP d-ribulose 1,5-diphosphate