Microalgae and Man

Microalgae, with representatives in all but one of the major algal divisions, are an important component of the biota of the world's aquatic environments. They include phytoplankton that are almost entirely responsible for the primary production of all marine and freshwater bodies. They occur at the base of the food chains upon which the world's fisheries industries depend, and in the numerous aquaculture projects upon which the world will increasingly come to rely for a large portion of its protein requirement. Their use for the mass production of stock feed and for direct human consumption, already being practiced in many parts of the world, is likely to become of increasing importance in the future as is the exploitation of their ability to serve as a source of key metabolites in the food industry and in the synthesis of a range of other high-value products. The mass culture of microalgae under controlled conditions is also under consideration for its potential to provide an alternative source of biomass and for the production of biofuels, such as biodiesel, that does not compete for land that can be more profitably used for the production of traditional food crops. The potential of microalgae for the production of another energy source, hydrogen, is also under investigation with a view to exploiting the ability of some microalgae, unique among oxygenic photosynthetic organisms, to release hydrogen gas produced from the photolytic splitting of water. The proven role of microalgae in waste-water treatment and in various environmental remediation processes as well as their potential contribution as a vital component of carbon-capture schemes will also be described. \ud \ud This book surveys our current understanding of those aspects of the biology of microalgae which constitute the basis of the range of practical applications now under consideration for their potential contribution to human health and well-being. The focus is largely on physiological and biochemical processes of microalgae as they are currently known, with the aim of providing some of the basic background information against which present and proposed future developments can be assessed. Many of these developments, if they are to be successful, will require collaboration of engineers, process biochemists and microbiologists as well as those trained to address economic and environmental considerations. It is hoped that this book, will provide for such workers and for the lay person, an overview of some of the relevant basic biology of the microalgae, highlighting their metabolic flexibility and their vast potential as a valuable resource that is yet to be fully realized

Chlorophyll b-containing oxygenic photosynthetic prokaryotes: Oxychlorobacteria (prochlorophytes)

The major ultrastructural and pigment characteristics of three chlorophyll b-containing photosynthetic prokaryote genera, Prochloron, Prochlorothrix, and Prochlorococcus, are summarized. Aspects of their ecology are reviewed, as are also the major findings of comparisons among the three genera, and between them and the cyanobacteria, based on analyses of nucleotide sequences. The information summarized is discussed to assess how closely the three genera are related and whether they form a natural taxonomic\ud grouping within the cyanobacteria. It is concluded that, although much of the evidence points to substantial differences among the three genera, the convenience of\ud keeping them together as a group, namely, Oxychlorobacteria (formerly Prochlorophyta), outweighs certain inconsistencies revealed by analysis of a range of objective\ud criteria. Current views on the possible significance of the group to considerations of the evolution of green chloroplasts are also presented

Occurrence of blooms of the cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju in a north Queensland domestic water supply

This paper describes seasonally recurring blooms of the potentially toxic cyanobacterium Cylindrospermopsis raciborskii in relation to some limnological characteristics of Lake Julius, a large man-made water impoundment in Australia's semi-arid tropics. These blooms have occurred each year since 1991, with subsurface concentrations of >50 000 cells mL–1. Periods of greater cyanobacterial abundance are characterized by reduced rates of vertical mixing of the water column, reduced mixed:euphotic depth ratios and high epilimnetic temperatures (>25°C). Surface scums were not observed and, in general, this species displays a fairly uniform distribution throughout the euphotic zone and below. An isolate of C. raciborskii taken from Lake Julius during a bloom in November 1995 and grown in pure culture produced no symptoms of poisoning when tested by mouse bioassay, and absence of detectable concentrations of the hepatotoxin cylindrospermopsin was confirmed by HPLC/MS-MS. Low concentrations of cylindrospermopsin (~1–2 g L–1) were detected in the lake during blooms of C. raciborskii

The effect of temperature on growth and cylindrospermopsin content of seven isolates of Cylindrospermopsis raciborskii (Nostocales, Cyanophyceae) from water bodies in northern Australia

This study investigates the effect of temperature (range, 20–35°C) on the growth and cylindrospermopsin (CYL) content of seven isolates of Cylindrospermopsis raciborskii grown in batch culture. The concentration of CYL, measured late in the exponential growth phase for cultures grown at 25°C, ranged from below detection (< 2 × 10−5% freeze-dried weight) for isolates from Lake Julius (20°08'S; 139°44'E) and an aquaculture pond in Townsville (19°16'S; 146°49'E) up to 0.46% for an isolate from Solomon Dam, Palm Island (18°45'S; 146°35'E). Maximum growth rates for all isolates occurred at temperatures between 25 and 30°C. Only one isolate failed to grow at 20°C. For isolates containing undetectable concentrations of CYL, the production of this compound could not be induced by an increase in temperature. For strains producing detectable concentrations, there was a strong negative correlation between CYL content and temperature. While all the isolates grew well at 35°C, none produced any detectable amount of CYL. When cultures of isolates that normally produce CYL were transferred from 35°C to a lower temperature, production of CYL was restored. In the cultured isolates, less than 10% of the total CYL was released from exponentially growing cells. In one CYL-producing isolate, extracellular CYL accounted for c. 50% of the total in stationary phase (20 day old) cultures

Turbid flow through a tropical reservoir (Lake Dalrymple, Queensland, Australia): responses to a summer storm event

The first flood event following a prolonged dry period is described for an impoundment, Lake Dalrymple, in tropical north-eastern Australia. The event, in January 1996, generated substantial flow in the two main inflow sources: the Burdekin River from the north and the Suttor River from the south. Flow through the Burdekin River peaked early and then subsided to a lower level, but flow through the Suttor River persisted at a moderate level for over 15 days after the initial inflow. An extensive water quality survey was conducted on 16 January 1996 (seven days after the initial dam overflow) to determine the nature of the inflows originating from the two major subcatchments feeding the reservoir as they entered and passed through the impoundment. The inflow comprising waters of high turbidity and low conductivity occupied the mid-column region along the two major inflow channels through the impoundment to the dam wall. The suspended particulate material in the form of silt and clay sized particles remained in suspension as the flow passed through the reservoir, due in part to the low ionic strength of the inflow and the relative densities of the inflowing and receiving waters. For both river sources, more than 50% of the total nitrogen and almost all of the total phosphorus were bound to the suspended particulate matter. Much of this was exported in the flow over the spillway. The highly turbid nature of the inflow resulted in strong attenuation of down-welling photosynthetically active radiation (up to maximum attenuation values of 12.24 m–1 in the reservoir where the euphotic depth was only 0.38 m). The irradiance reflectance and the scattering coefficient were considerably higher than any reported for other Australian inland waters. Concentrations of viable chlorophyll a in the surface waters were very low (maximum value 3.4 μg L–1) because of the highly turbid conditions and extensive dilution by the inflow. The results of this study provide an example of the significant impact a large inflow of turbid, low conductance water can have on a large reservoir in the arid tropics following a prolonged dry period. During inflow events such as the one described in this paper, the reservoir becomes riverine in nature, and large amounts of suspended particulate matter and associated nutrients are transported through the reservoir