Limitations on microalgal growth at very low photon fluence rates: the role of energy slippage

The lower limits of photosynthetically useable radiation at which growth and photosynthesis can occur establish the lower boundaries for the extent of photolithotrophy in the biosphere. Photolithotrophic growth denotes the capacity to grow with photons as the sole energy input. Slippage in terms of photosynthetic energy conversion implies a less than theoretical stoichiometry of energy-transduction process(es) such as the dissipation of intermediates of O₂ evolution and of ATP synthesis (H⁺/e⁻ and H⁺/ATP ratios). Slippage is particularly important in limiting the growth of photolithotrophic organisms at very low photon fluence rates. We found that Dunaliella tertiolecta and Phaeodactylum tricornutum avoid such reductions in photon use efficiency by increasing the size and number of their photosynthetic units, respectively, and by altering Q_A reduction kinetics on the reducing side of PS II. P. tricornutum is also less susceptible to slippage in terms of the breakdown of intermediates in its O₂ evolution pathway than D. tertiolecta. Minimizing H⁺ leakage through the CF₀–CF₁ ATP synthetase (and other H⁺ porters) is also discussed briefly. In combination, strategies employed by P.␣tricornutum effectively allow it to grow and photosynthesize at lower rates of energy input than D. tertiolecta, consistent with our observations. Differences in the responses of the photosynthetic apparatus of these two marine microalgae are mechanistic and probably representative of evolutionary divergences associated with strategies for dealing with environmental perturbations.     

Genotoxicity of polycyclic aromatic hydrocarbons in Escherichia coli PQ37.

In the present investigation, 32 polycyclic aromatic hydrocarbons (PAHs) were tested for genotoxicity in E. coli PQ37 using the standard tube assay of the SOS chromotest. PAHs such as benzo[ghi]fluoranthene, benzo[j]fluoranthene, benzo[a]pyrene, chrysene, dibenzo[a,l]pyrene, fluoranthene and triphenylene exhibited high genotoxicity when incubated in the presence of an exogenous metabolic activation mixture. The results were compared to those obtained with the Salmonella/microsome test.     

Using light scattering measurements to study the effects of monovalent and divalent cations on alginate aggregates

Light scattering measurements were used to assess the effectsof selected divalent and monovalent cations on alginate aggregationin vitro. Alginate, formed with either strontium, calcium orcobalt was partially dissolved with sodium. Calcium-alginatewas also partially dissolved with two other monovalent cations,lithium and potassium. Phosphate, when added to a solution containingcalcium-alginate, scrubbed algin-ate-bound calcium as well asfree calcium in solution. These findings provide an explanationfor an alternative approach for breaking down cell wall alginate. Key words: Alginate aggregates, monovalent cations, divalent cations, light scattering     

Development of hormosira banksii (PHAEOPHYCEAE) embryos in selected components of secondarily-treated sewage effluent

We investigated the effects of phosphate, ammonium, and a mixture of heavy metals as components of sewage effluent, together with the effects of reduced salinity due to sewage effluent discharge into a marine environment, on the development of Hormosira banksii (Turner) Decaisne embryos. The concentration of each effluent component tested in this study was calculated to approximate levels in the shore zone where H. banksii once occurred at Boags Rocks (Victoria, Australia) and the artificial sea medium was diluted to 20‰ S based on average salinity levels measured at this site. Newly fertilized eggs were cultured in each of these components and combinations of components for up to 7 days. Ammonium, elevated to levels that occur in the vicinity of the outfall, and fresh water, which reduces seawater salinity, were the most damaging of the effluent components tested. Osmotically stressed embryos commonly showed swollen chloroplasts, loss of cell contents, vesiculate cytoplasm, and stunted rhizoid development. Exposure to elevated levels of ammonium retarded embryo development and growth until day 7, when cellular damage became evident. The number of damaged embryos was significantly greater when exposed to elevated levels of ammonium added to artificial seawater medium diluted to 20‰ S. The adverse effects caused by elevated levels of ammonium and reduced seawater salinity on H. banksii embryo development could have contributed to the disappearance of this species from Boags Rocks.     

In vitro genotoxicity of polycyclic musk fragrances in the micronucleus test

The synthetic polycyclic musk fragrance compounds galaxolide (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-(g)-2-benzopyrane), tonalide (7-acetyl-1,1,3,4,4,6-hexamerthyltetraline), celestolide (4-acetyl-1,1-dimethyl-6-tert-butylindane), phantolide (6-acetyl-1,1,2,3,3,5-hexamethylindane), cashmeran (6,7-dihydro-1,1,2,3,3-pentamethyl-4-(5H) indanone) and traseolide (5-acetyl-1,1,2,6-tetramethyl-3-isopropylindane) were examined for their genotoxicity in the micronucleus test (MNT) with human lymphocytes in vitro in the presence and absence of an exogenous metabolizing system containing rat liver S9 and the metabolically competent human hepatoma cell line Hep G2. Compound concentrations were employed up to cytotoxic doses. Galaxolide, tonalide, celestolide, phantolide, cashmeran and traseolide revealed no genotoxicity in the micronucleus test with human lymphocytes and with the human hepatoma cell line Hep G2.