MICROCYSTIS DOMINANCE DURING EUTROPHICATION

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 Freshwater resources are threatened by the presence and increase of harmful algal blooms (HAB) all over the world. The HABs are sometimes a direct result ofanthropogenic pollution entering water bodies, such as partially treated nutrient-rich effluents and the leaching of fertilisers and animal wastes. The impact of HABs on aquatic ecosystems and water resources, as well as their human health implications are well documented. Countermeasures have been proposed and implemented to manage HABs with varying levels of success. The use of copper algicides, though effective in managing HABs, often results in negative impacts such as copper toxicity and release of microcystins into surrounding water after cyanobacterial lysis. Biological control of HABs presents a possible solution. Various mechanisms of cyanobacterial lysis have been proposed, including; physical contact between prey and predator, release of extracellular substances, entrapment of prey by the predator followed by antibiosis and endoparasitism or ectoparasitism of the host by the predator. Despite an increasing amount of work being done in this field, research is usually limited to laboratory cultures; assessment of microbial control agents is seldom extrapolated to field conditions.

 Eutrophication

Eutrophication is a natural process or a human-induced activity that leads to the enrichment of water bodies with inorganic nutrients such as nitrates and phosphates (Codd, 2000; Van Ginkel, 2002). The readily available nutrients promote the excessive growth of aquatic weeds and cyanobacterial blooms. As a natural process, the ageing of a lake, that occurs during the lifetime of an impoundment or a lake and may take thousands of years to occur. The natural process involves the following succession: from an oligotrophic (low in productivity and abundance in biodiversity of species) through to mesotrophic (moderate productivity and high species abundance) to eutrophic (high productivity and high species abundance but low in species diversity). The other extreme end of eutrophic conditions is known as hyper￾eutrophic (Van Ginkel, 2002).

Toxicity of cyanobacteri

The freshwater species that are often implicated with microcystin toxicity are: Microcystis,Anabaena, Oscillatoria and Nostoc; and nodularin toxicity, from a marinecyanobacterium called Nodularia spumigena (Rapala et al., 1994; Cronberg et al.,2003) (Table 2.5).Cyanobacteria synthesize a variety of toxins that are defined by theirchemical structure. These are classified into three groups: cyclic peptides, alkaloids and lipopolysaccharides (LPS). Cyanobacterial toxins are low molecular weight compounds, odourless, colourless and soluble in water.

The fate of cyanobacteria toxins in aqueous environment

Intracellular toxins are produced and contained within actively growing cyanobacteria cells. These become extracellular toxins when released to the external environment during cell senescence, lysis and death. Laboratory studies have demonstrated that healthy log phase cyanobacteria cultures have less than 10-20 per cent of total toxin pool as extracellular (Sivonen and Jones, 1999). However under field conditions the levels of dissolved extracellular toxins increased (0.1 to 10 µg ℓ-1) in ageing and declining blooms(Sivonen and Jones, 1999). This has important implications for water treatment utilities, as it is preferably cheaper to remove intact cyanobacteria cells than ruptured or damaged cells. The conventional water treatment processes if operated in conjunction with dissolved air flotation are capable of removing intact cyanobacteria cells from raw water. Ruptured or damaged cells may release

Chemical Algicide

Mechanical and physico-chemical methods have been devised in attempts to manage cyanobacterial blooms, with limited success. The direct control method involves the use of chemical treatments such as algicides, including copper, Reglone A (diquat, 1,1-ethylene 2, 2-dipyridilium dibromide), potassium permanganate, chlorine and Simazine (2-chloro 4,6-bis(ethylamino)-s-triazine) (Lam et al., 1995; García-Villada et al., 2004). These chemicals induced cyanobacterial cell lysis, followed by the release of toxins intosurrounding waters. An appropriate waiting period has to follow to allow for the degradation of the toxins (WHO, 1999). These algicides are toxic to other aquatic microorganisms, may accumulate in the sediment at harmful concentrations and cause long-term damage to the lake ecology (Mason, 1996). Copper sulphate or organo-copper compounds have been used to control harmful algal blooms in raw water supplies intended for potable purposes (Lam et al., 1995). However, there is an increasing need to reduce the use of chemicals for environmenta

CHAPTER 1: INTRODUCTION
CHAPTER 2: LITERATURE REVIEW
Abstract
2.1 INTRODUCTION
2.1.1. Eutrophication
2.1.2. The study area
2.2. MICROCYSTIS DOMINANCE DURING EUTROPHICATION
2.1.1. Introduction
2.2.2. Toxicity of cyanobacteria
2.2.2.1. Cyanobacterial metabolites
2.2.2.2. Neutrotoxic alkaloids
2.2.2.3. Hepatotoxins
2.2.2.4. Irritant toxins- Lipopolysaccharides
2.2.3. The fate of cyanobacteria toxins in aqueous environment
2.2.3.1. Challenges to drinking water utilities
2.2.3.2. Bacterial degradation of microcystins
2.2.4. Current methods used to manage harmful algal blooms
2.2.4.1. Chemical algicides
2.2.4.2. Mechanical removal
2.2.4.3. Nutrient limitation                                                                                            2.2.4.4. Intergrated biological water management                                                        BIOLOGICAL CONTROL OF HARMFUL ALGAL BLOOMS
2.3.1. Introduction
2.3.2. The use of microorganisms to control cyanobacteria blooms                              CHAPTER 3: THE ISOLATION AND IDENTIFICATION OF PREDATORY BACTERIA FROM A MICROCYSTIS ALGAL BLOOM
Abstrac
3.1.INTRODUCTION
3.2. MATERIALS AND METHODS
3.2.1. Plaque formation on Microcystis lawns
3.2.2. Cyanophage check
3.2.3. Isolation of predatory bacteria
3.2.4. Lytic activity of bacterial isolates on Microcystis
3.2.4.1. Culturing host cyanobacteria
3.2.4.2. Culture of bacterial isolates
3.2.4.3. Culture of Bacillus mycoides B16
3.2.4.4. Bacterial viable plate count
3.2.4.5. Experimental set up
3.2.4.6. Cyanobacteria cell counting
3.2.5. Identification of predatory bacteria                                                                    CHAPTER 4: LIGHT AND ELECTRON MICROSCOPE ASSESSMENT OF THE LYTIC ACTIVITY OF PREDATOR BACTERIA ON MICROCYSTIS
Abstract                                                                                                    4.1.INTRODUCTION
4.2. MATERIALS AND METHODS
4.2.1. Evaluations of cyanobacteria-bacteria interactions in a solid media/phases(plaques)
4.2.1.1. Scanning Electron Microscopy                                                                          4.2.1.2. Transmission Electron Microscop                                                                    5.3.4.1. Predator-prey interactions as determined by FDA staining
5.3.4.1. Predator-prey interactions as determined by PI staining
5.3.5. The effect of B. mycoides B16 on Microcystis in a turbulent environment
5.4. CONCLUSIONS

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