Exogenous inorganic carbon sources for photosynthesis in seawater by members of the Fucales and the Laminariales (Phaeophyta): ecological and taxonomic implications

Summary Characteristics of inorganic carbon assimilation by photosynthesis in seawater were investigated in six species of the Fucales (five Fucaceae, one Cystoseiraceae) and four species of the Laminariales (three Laminariaceae, one Alariaceae) from Arbroath, Scotland. All of the algae tested could photosynthesise faster at high external pH values than the uncatalysed conversion of HCO ₃ ^- to CO₂ can occur, i.e. can use external HCO ₃ ^- . They all had detectable extracellular carbonic anhydrase activity, suggesting that HCO ₃ ^- use could involve catalysis of external CO₂ production, a view supported to some extent by experiments with an inhibitor of carbonic anhydrase. All of the algae tested had CO₂ compensation concentrations at pH 8 which were lower than would be expected from diffusive entry of CO₂ supplying RUBISCO as the initial carboxylase, consistent with the operation of energized entry of HCO ₃ ^- and / or CO₂ acting as a CO₂ concentrating mechanism. Quantitative differences among the algae examined were noted with respect to characteristics of inorganic C assimilation. The most obvious distinction was between the eulittoral Fucaceae, which are emersed for part of, or most of, the tidal cycle, and the other three families (Cystoseiraceae, Laminariaceae, Alariaceae) whose representatives are essentially continually submersed. The Fucaceae examined are able to photosynthesise at high pH values, and have lower CO₂ compensation concentrations, and lower K_1/2 values for inorganic C use in photosynthesis, at pH 8, than the other algae tested. Furthermore, the Fucaceae are essentially saturated with inorganic C for photosynthesis at the normal seawater concentration at pH 8 and 10°C. These characteristics are consistent with the dominant role of a CO₂ concentrating mechanism in CO₂ acquisition by these plants. Other species tested have characteristcs which suggest a less effective HCO ₃ ^- use and CO₂ concentrating mechanism, with the Laminariaceae being the least effective; unlike the Fucaceae, photosynthesis by these algae is not saturated with inorganic C in normal seawater. Taxonomic and ecological implications of these results are considered in relation to related data in the literature.     

Photosynthetic gas exchange under emersed conditions in eulittoral and normally submersed members of the Fucales and the Laminariales: interpretation in relation to C isotope ratio and N and water use efficiency

Summary Ten species of brown macroalgae (five eulittoral and one submersed species of the Fucales; four submersed species of the Laminariales) from a rocky shore at Arbroath, Scotland, were examined for characteristics of emersed photosynthesis in relation to the partial pressure of CO₂ and O₂. The five eulittoral species of the Fucaceae were approaching CO₂ saturation for light-saturated photosynthesis at normal air levels of CO₂ (35 Pa) in 21 kPa O₂. The normally submersed algae are further from CO₂ saturation under these conditions, especially in the case of the four members of the Laminariales. The rate of net photosynthesis in the Fucaceae is O₂-independent in the range 2–21 kPa O₂ over the entire range of CO₂ partial pressure tested (compensation up to 95 Pa). For the other five algae tested, net photosynthesis is slightly inhibited by O₂ at 21 kPa relative to 2 kPa over the entire range of CO₂ partial pressures tested (compensation up to 95 Pa). CO₂ compensation partial pressures are low (<0.5 Pa) for the Fucaceae and independent of O₂ in the range 2–42 kPa. For the other five algae, the CO₂ compensation partial pressure are higher, and increased with O₂ partial pressure in the range 2–42 kPa. These gas exchange data show that the Fucaceae exhibit more C₄-like characteristics of their photosynthetic physiology than do the other five species tested, although even the Laminariales and Halidrys siliquosa are not classic C₃ plants in their photosynthetic physiology. These data suggest that, in emersed conditions as well as in the previously reported work on submersed photosynthesis, a CO₂ concentrating mechanism is operating which, by energized transmembrane transport of inorganic C, accumulates CO₂ at the site of RUBISCO and, at least in part, suppresses the oxygenase activity. Work with added extracellular carbonic anhydrase (CA), and with a relatively membrane-impermeant inhibitor of the native extracellular CA activity (acetazolamide), suggests that, in emersed conditions as well as in the previously reported work on algae submersed in seawater at pH 8, HCO _inf3 ^sup– is the major inorganic C species entering the cell. At optimal hydration, the rate of emersed photosynthesis in air is not less than the rate of photosynthesis when submersed in seawater, at least for the Fucaceae. ¹³C ratios of organic C for the Fucaceae are slightly more negative than is the case for the other five algae; these data are consitent with substantial (half or more of the entering inorganic C) leakage of CO₂ from the accumulated pool, and with some contribution of atmospheric CO₂ to the organic C gain by the eulittoral algae. The predicted increase in N use efficiency of photosynthesis in the Fucaceae, with their more strongly developed CO₂ concentrating mechanism, is consistent with data on emersed, but not submersed, photosynthesis for the algae collected from the wild and thus at a poorly defined N status. The more C₄-like gas exchange charateristics of photosynthesis in the eulittoral Fucaceae may be important in increasing the water use efficiency of emersed photosynthesis from the limited capital of water available for transpiration by a haptophyte.     

Induction of a putative metallothionein gene in the blood cockle, Anadara granosa, exposed to cadmium

The relationship between a putative metallothionein gene (MT) and exposure to cadmium (Cd) in blood cockles (Anadara granosa) is reported. In a 96-h dose-response experiment, mortality of cockles was found to proportionately increase in the range of 0.2-5.0 mg/l Cd with a calculated LC(50) of 2.94 mg/l. Exposure to 0.25 mg/l Cd for 16 days caused significant increases (P<0.05) in Cd concentrations in whole tissues, gills and hepatopancreas, and the accumulation of Cd in these tissues increased with the duration of exposure. Two cDNA libraries constructed using the hepatopancreas from control and Cd-treated cockles gave titres of 5.62 x 10(5) and 1.94 x 10(5) pfu/microg vector, respectively. A putative MT gene, AnaMT, of 510 nucleotides in length, was isolated from the treated cDNA library using a heterologous probe MT20 from the blue mussel, Mytilus edulis. Northern analyses using AnaMT as a probe indicated low expression of the MT mRNA in control animals. In cockles treated with 0.25 mg/l Cd for 4 days, MT mRNA level increased to approximately 168%, but declined to 108% at day 8. After 12 and 16 days of Cd treatment, expression of the MT gene was 138% and 187%, respectively, compared to the controls. These observations suggest that induction of the MT gene by a sublethal dose of Cd is rapid, occurring within 4 days of treatment.     

Sorption of Cr(VI), Cu(II) and Pb(II) by growing and non-growing cells of a bacterial consortium

This paper reports the sorption of three metallic ions, namely Cr(VI), Cu(II) and Pb(II) in aqueous solution by a consortium culture (CC) comprising an acclimatised mixed bacterial culture collected from point and non-point sources. Metal sorption capability of growing and non-growing cells at initial pH of between 3 and 8 in the 1-100mg/L concentration range were studied based on Q(max) and K(f) values of the Langmuir and linearised Freundlich isotherm models, respectively. Maximal metal loading was generally observed to be dependent on the initial pH. Growing cells displayed significant maximal loading (Q(max)) for Pb(II) (238.09 mg/g) and Cu(II) (178.87 mg/g) at pH 6 and at pH 7 for Cr(VI) (90.91 mg/g) compared to non-growing cells (p < 0.05). At the pH range of 6-8, growing cells showed higher loading capacity compared to non-growing cells i.e. 38-52% for Cr, 17-28% for Cu and 3-17% for Pb. At lower metal concentrations and at more acidic pH (3-4) however, non-growing cells had higher metal loading capacity than growing cells. The metal sorption capacity for both populations were as follows: Pb(II) > Cu(II) > Cr(VI).     

Life cycle assessment of magnetic and electronic ballast for 36-W fluorescent lamp

Background, aim, and scope   

Ballast is a device in a fluorescent lamp that supports the production of light. In this study, the environmental impacts of two types of Malaysian ballast, magnetic ballast and electronic ballast, were identified and compared using the life cycle assessment approach through the ISO 14040 (2005) series.     

Phenol Biodegradation and Metal Removal by a Mixed Bacterial Consortium

This paper reports the tolerance and biodegradation of phenol by a heavy metal–adapted environmental bacterial consortium, known as consortium culture (CC). At the highest tolerable phenol concentration of 1200 mg/L, CC displayed specific growth rate of 0.04 h^?1, phenol degradation rate of 6.11 mg L^?1 h^?1 and biomass of 8.45 ± 0.35 (log₁₀ colony-forming units [CFU]/ml) at the end of incubation. Phenol was degraded via the ortho-cleavage pathway catalyzed by cathechol-1,2-dioxygenase with specific activity of 0.083 (µmol min^?1 mg^?1 protein). The different constituent bacterial isolates of CC preferentially grow on benzene, toluene, xylene, ethylbenzene, cresol, and catechol, suggesting a synergistic mechanism involved in the degradation process. Microtox assay showed that phenol degradation was achieved without producing toxic dead-end metabolites. Moreover, lead (Pb) and cadmium (Cd) at the highest tested concentration of 1.0 and 0.1 mg/L, respectively, did not inhibit phenol degradation by CC. Simultaneous metal removal during phenol degradation was achieved using CC. These findings confirmed the dual function of CC to degrade phenol and to remove heavy metals from a mixed-pollutant medium.