The effect of reducing light-harvesting pigment on marine microalgal productivity

The productivity was evaluated of a strain of Chlamydomonas perigranulata isolated from the RedSea. A mutant with small light-harvesting pigments(LHC-1) was obtained by UV mutagenesis. Thechlorophylls content of the wild type was twice ashigh as that of LHC-1, and the initial slope of thephotosynthesis-irradiance curve was higher in the wildtype. However, the maximum photosynthetic activity ona per cell basis was almost the same. It isconcluded that LHC-1 is a mutant with lesslight-harvesting pigment (LHP) than the wild type. Aspreviously reported, the mutant with lower LHP contenthas a higher productivity in a continuous culturesystem, so we compared the productivity of the wildtype and the mutant. The maximum productivity of LHC-1was 1.5 times higher than that of the wild type. Itis suggested that the technique of reducing thecontent of light-harvesting pigment should be madeavailable for other organisms.     

Water temperatures influence the marine area use of Salvelinus alpinus and Salmo trutta

The migratory behaviour and spatial area use of sympatric Arctic charr Salvelinus alpinus and brown trout Salmo trutta were investigated during their marine feeding migration. The likelihood of finding individuals of both species in the inner or outer fjord areas was dependent on water temperature in the inner area (especially for S. alpinus), the temperature difference between the inner and outer areas (especially for S. trutta) and fish fork length (both species). The strongest predictor was the water temperature in the inner area, and particularly S. alpinus left this area and moved to the outer areas with increasing temperatures in the inner area. At 8° C in the inner area, the likelihood of finding S. alpinus in the outer areas was >50%. This predictor had a smaller effect on S. trutta, and the likelihood of finding S. trutta in the outer areas only started to increase at around 14° C. The relationships between temperature and area use did not correspond to the species' optimal growth temperatures, but to their previously documented temperature preferences. Individuals of both species used mainly the littoral fjord areas, and to a lesser extent the pelagic areas. In conclusion, temperature differences between the inner and outer marine areas probably resulted in the segregated area use between the species, because water temperatures or factors influenced by temperature affected their migratory behaviour and habitat use differently. The results indicate that increased marine temperatures with global warming may lead to increased spatial overlap between S. trutta and S. alpinus, which again may lead to increased interspecific competition during their marine phase, and with S. alpinus probably being the more negatively affected.     

The influence of antifouling practices on marine invasions

Vessel hull-fouling is increasingly recognised as one of the major vectors for the transfer of marine non-indigenous species. For hundreds of years, copper (Cu) has been used as a primary biocide to prevent the establishment of fouling assemblages on ships' hulls. Some non-indigenous fouling taxa continue to be transferred via hull-fouling despite the presence of Cu antifouling biocides. In addition, several of these species appear to enjoy a competitive advantage over similar native taxa within metal-polluted environments. This metal tolerance may further assist their establishment and spread in new habitats. This review synthesises existing research on the links between Cu and the invasion of fouling species, and shows that, with respect to the vector of hull-fouling, tolerance to Cu has the potential to play a role in the transfer of non-indigenous fouling organisms. Also highlighted are the future directions for research into this important nexus between industry, ecology and environmental management.     

Induction of apoptosis and inhibition of DNA topoisomerase-I in K-562 cells by a marine microalgal polysaccharide

We have previously purified an extracellular polysaccharide, D-galactan sulfate associated with L(+)-lactic acid, produced from a marine microalga Dinoflagellate Gymnodinium sp. A3 (GA3). The GA3 polysaccharide, irrespective of presence or absence of lactic acid, exhibited significant cytotoxicity, which is based on an induction of apoptotic cell death, toward human myeloid leukemia K562 cells. Furthermore, we found that the GA3 polysaccharide with or without lactic acid possesses an inhibitory effect on topoisomerase-I (topo-I). The potent cytotoxic effect of GA3 polysaccharide may result from its inhibitory effect on topo-I, because the topo-I inhibition is known to trigger apoptotic cell death.     

The influence of decreased temperatures on meiotic disorders in spring wheat

An effect of low temperature (0-2 degrees C) on meiosis was studied in different varieties from various ecological zones. It is shown that the Mexican varieties are most sensitive to the effect of low temperature. The percentage of sterile pollen and disturbances in anaphase I in them are the highest. The local varieties with respect to these characters are more resistant to the effect of low temperature.     

Batch culture screening of marine microalgal nutrient removal from primary sewage effluent

A total of 102 marine microalgal species (including 66 isolates from a sewage outfall site in St Andrews Bay, Scotland) were screened for their ability to remove ammonium and phosphate from primary treated sewage. Primary effluent was diluted 1:1 with sterile seawater, to which the test alga was added for batch culture experiments under controlled environmental conditions of seven or two days duration. The results demonstrated that although microalgae vary in their treatment capabilities, some species were able to remove >90% of both the ammonium and phosphate after seven and even two days culture. All of these best-treating species were found to be unialgal after sequential culture, indicating their potential value for further screening under continuous culture conditions, and over half were isolates from the outfall site. The best-treating algal species showed a variety of growth responses to changes in salinity between 32 and 0, but all had similar growth responses to a series of sewage:seawater dilutions, suggesting that for some species, other properties of the diluted sewage had more effect on algal growth than salinity. These results demonstrate that a contact time of two days was adequate for >90% removal of ammonium and phosphate by some species of marine microalgae, and that limitations on their growth were not a result of the hyposalinity of the diluted sewage compared to seawater.     

The technology of microalgal culturing

This review outlines the current status and recent developments in the technology of microalgal culturing in enclosed photobioreactors. Light distribution and mixing are the primary variables that affect productivities of photoautotrophic cultures and have strong impacts on photobioreactor designs. Process monitoring and control, physiological engineering, and heterotrophic microalgae are additional aspects of microalgal culturing, which have gained considerable attention in recent years.     

The influence of cell size on marine bacterial motility and energetics

The influence of Brownian motion on marine bacteria was examined. Due to their small size, marine bacteria rotate up to 1,400 degrees in one second. This rapid rotation makes directional swimming difficult or impossible, as a bacterium may point in a particular direction for only a few tens of milliseconds on average. Some directional movement, however, was found to be possible if swimming speed is sufficiently great, over approximately 100 μm sec⁻¹. This led to the testable hypothesis that marine bacteria with radiii less than about 0.75 μm should exceed this speed. The result of the increased speed is that marine bacteria may spend in excess of 10% of their total energy budget on movement. This expenditure is 100 times greater than values for enteric bacteria, and indicates that marine bacteria are likely to be immotile below critical size-specific nutrient concentrations.     

The influence of the Benguela upwelling system on Namibia's marine biodiversity

Namibia's marine environment falls within the Benguela system, an eastern boundary current upwelling system in the south eastern Atlantic Ocean. Conditions within much of this environment change continuously as a consequence of the upwelling of nutrient-rich water into the surface zone. In addition, irregular anomalies in temperature, oxygen concentration and salinity occur, particularly in shelf waters. These fluctuations, which are inherent in the functioning of the Benguela system, tend to favour the persistence of few, generalist species, while at the same time high productivity supports large abundances. This trend is evident in all the major marine habitats off Namibia, where diversity is often lower than in comparable habitats in the southern Benguela system off the west coast of South Africa. Namibia's marine environment is considered 'relatively pristine', although threats to biodiversity are posed by both natural and anthropogenic phenomena.     

Visualization and quantification of oil in single microalgal cells

Microalgae are considered a promising source of oil for biodiesel production. This work reports an estimation method of oil content inside living microalgal cells by visualization and image processing techniques. This approach was used to analyze the time course of oil accumulation patterns in Nile Red-stained microalgal cells of Scenedesmus sp. cultivated in nitrogen-deficient medium used to induce oil accumulation in microalgal cells. Nile Red staining is a widely used technique for studying oil content of microalgal cells. The intracellular oil content was estimated by mathematically evaluating the oil volume inside the stained cell. This novel visualization approach has the potential to be used in ex vivo studies of oil content at the level of single microalgal cells. This method can also be applied to other types of oil-producing microorganisms because of its accuracy, precision, and reduction in the time and effort required for optimization.     

Test for allelopathic interactions between two marine microalgal species grown in intensive cultures

Both high pH and cell senescence are believed to lead to the production of toxic extracellular metabolites in freshwater microalgae. However, there was no evidence for allelopathic suppression of photosynthesis when filtrates of either of two marine microalgae,Phaeodactylum tricornutum andDunaliella tertiolecta, were mixed with whole cultures of the other species. This was true even when filtrate ofP. tricornutum sample was derived from a culture at high pH or from one in various stages of senescence. It is believed that the major factor leading to the dominance ofP. tricornutum in intensive outdoor cultures is the unique ability of this alga to tolerate pH levels above 9.5, not the allelopathic inhibition of competing species.     

Competition of marine psychrophilic bacteria at low temperatures

The occurrence of obligately and facultatively psychrophilic bacteria in the marine environment suggests that environmental conditions exist which can favour each of these groups in competitive processes. Differences were found in the way in which temperature affected the growth rates of obligate and facultative psychrophiles. Maximum specific growth rates of a number of obligately and facultatively psychrophilic bacteria were determined in batch culture and competition experiments were carried out in a chemostat at growth-limiting substrate concentrations. From the results the relation between the specific growth rate and the concentration of the growth-limiting substrate for both types of organisms at different temperatures was deduced. Both at low and high substrate concentrations obligate psychrophiles grew faster than facultative psychrophiles at the lower temperature extreme (? 4 C). These results suggest that obligately psychrophilic chemoorganotrophs are responsible for mineralization processes in cold natural environments such as ocean waters and the arctic and antarctic regions. In these environments they can successfully compete with facultative psychrophiles because they can grow faster.     

Sediment challenge to promising ultra-low fouling hydrophilic surfaces in the marine environment

Hydrophilic coatings exhibit ultra-low fouling properties in numerous laboratory experiments. In stark contrast, the antifouling effect of such coatings in vitro failed when performing field tests in the marine environment. The fouling release performance of nonionic and zwitterionic hydrophilic polymers was substantially reduced compared to the controlled laboratory environment. Microscopy and spectroscopy revealed that a large proportion of the accumulated material in field tests contains inorganic compounds and diatomaceous soil. Diatoms adhered to the accumulated material on the coating, but not to the pristine polymer. Simulating field tests in the laboratory using sediment samples collected from the test sites showed that incorporated sand and diatomaceous earth impairs the fouling release characteristics of the coatings. When exposed to marine sediment from multiple locations, particulate matter accumulated on these coatings and served as attachment points for diatom adhesion and enhanced fouling. Future developments of hydrophilic coatings should consider accumulated sediment and its potential impact on the antifouling performance.