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MATERIAL AND METHODS
The methods were similar to those followed in chapter 3. Briefly, 0. serrata extract in 50% acetone was incorporated into agar growth medium at 25 mg.mr1 and the bacteria listed below were inoculated onto the plates and incubated for 24 hours. For the controls only a 50% solution of acetone was added to the growth medium.
BIOSSAYS OF LANOSOL ETHYL ETHER
With OSSB 1 we see a group of bacteria that were isolated from 0. serrata being very tolerant (relative to bacteria in pure culture) to a toxin that their macro algal-habitat produces and probably releases. It is known that bacteria in a biofilm are more resistant to toxicants and this characteristic makes their control so difficult (Allison et at., 2000). The extracellular polymeric substances (EPS) surrounding the cells in the biofilm protect them from antibiotics. However, chlorine degrades EPS effectively and controls biofilms in drinking water (Characklis, 1990). Bromine, another halogen, is covalently bonded to the phenolic ring in lanosol and its derivatives.
McLachlan and Craigie (1966) demonstrated the anti-algal activity of lanosol and stated that the addition of bromine onto a phenol did not increase its toxicity, but it did increase when chlorine was added. Bromine is less reactive than chlorine, but it seems unlikely that it would have no affect on the toxicity of the compound since the carbon-bromine bond is more potent in initiating free radical reactions and producing lipid peroxidation than the chlorine-carbon bond (Mehendale, 1992).
Interestingly the fermentative isolates (V atginotyticus and V harveyi) and the Grampositive Marinococcus sp. were the most sensitive to lanosolee of the marine isolates (figure 6.7). It is unknown why, however, they would benefit the most from being in a biofilm in an environment exposed to lanosol.
Within the terrestrial group, P. aeruginosa was most resistant to lanosolee but very sensitive to copper(II) sulphate (figure 6.8). The Gram-positive S. aureus was not as sensitive as the other Gram-positive species. These results are similar to those from the extract of 0. serrata (chapter 5). In addition, Weinstein and co-workers (1975) found that the salt of lanosol (figure 6.6 – D) was ineffective against Staphylococcussp., but showed activity against other bacteria. Resistance to phenols and halogens are a feature of the genus Staphylococcus (Krieg and Holt, 1984).
The inhibition of the growth of OssB 1 by lanosolee indicates that the biofilm bacteria would be more resistant to the chemical than planktonic forms as predicted (Marshall, 2000). It was beyond the scope of this study, but future work could test the effect lanosol has on the initial stages of biofilm formation. Other seaweed products, e.g. halogenated furanones from Delisea pulchra (Rhodophyta), are known for their antifouling activities and it may be that lanosolee has a biofilm regulatory function (McLachlan and Craigie, 1966; De Nys and Steinberg, 2002).
Interestingly none of the bacteria isolated showed agarolytic activity, but Halomonas sp. 2 did grow into the agar medium. It was expected that some of the isolates would degrade agar and thus be potentially pathogenic to the macroalga (Jaffray et al., 1997). Perhaps the method ofhomogenising seaweed material favours the isolation of agarolytic bacteria more than our methods. Although the name Vibrio alginolyticus implies that agar is degraded it is a misnomer because this species does not degrade agar (Holt et al., 1994).
Other studies have shown that Pseudoalteromonas species are commonly found in marine habitat associated with eukaryotic hosts (Holmstrom and Kjelleberg, 1999).
However, none were isolated from 0. serrata. Laycock (1974) found that the numbers of Vibrio and Pseudomonas species associated with Laminaria longicruris (Phaeophyceae) were seasonal and this may explain the disagreement on the bacterial composition of seaweeds.
Species of Halomonas, Pseudomonas, and Vibrio are known to form biofilms (Laycock, 1974; O’Conner and Richardson, 1998; Davies, 2000). In fact, H marina has been found to inhibit the settling of barnacle larvae in vitro (O’Conner and Richardson, 1998). Since this bacterium is found growing on 0. serrata we may speculate that it, and other bacteria, protect the macroalga from epibiotic attachment (Egan et al., 2001). It is likely that the species composition of the biofilm on 0.
CHAPTER 1. INTRODUCTION
1.1 SEAWEED NATURAL PRODUCTS
1.2 GENERAL DESCRIPTION OF OSMUNDARIA SERRATA
1.3 ECOLOGY OF 0. SERRATA
1.4 OBJECTIVES
1.5 AIMS
1.6 REFERENCES
CHAPTER 2. IDENTITIES OF SOME BACTERIA ISOLATED FROM THE SURFACE OF THE MACROALGA OSMUNDARIA SERRATA (RHODOPHYTA) AND ITS HABITAT
2.1 ABSTRACT
2.2 INTRODUCTION
2.3 MATERIALS AND METHODS
2.4 RESULTS AND DISCUSSION
2.5 ACKNOWLEDGEMENTS
2.6 REFERENCES
CHAPTER 3. COMPARISON BETWEEN AGAR DILUTION AND MICROTITRE METHODS OF TESTING FOR THE ANTIBACTERIAL ACTIVITY OF AN EXTRACT FROM OSMUNDARIA SERRATA
3.1 ABSTRACT
3.2 INTRODUCTION
3.3 MATERIALS AND METHODS
3.4 RESULTS AND DISCUSSION
3.5 REFERENCES
CHAPTER 4. ANTIBACTERIAL ACTIVITY OF EXTRACTS FROM SELECTED MACROALGAE FROM KWAZULU-NATAL, SOUTH AFRICA
4.1 ABSTRACT
4.2 INTRODUCTION
4.3 MATERIALS AND METHODS
4.4 RESULTS AND DISCUSSION
4.5 REFERENCES
CHAPTER 5. DEFORMITIES INDUCED IN BACTERIA BY MACROALGALEXTRACTS
5.1 ABSTRACT
5.2 INTRODUCTION
5.3 MATERIALS AND METHODS
5.4 RESULTS
5.5 DISCUSSION
5.6 REFERENCES
CHAPTER 6. ISOLATION AND ANTIMICROBIAL ACTIVITY OF THE ETHYL ETHER DERIVATIVE OF LANOSOL, FROM OSMUNDARIA SERRATA (RHODOPHYTA)
6.1 ABSTRACT
6.2 INTRODUCTION
6.3 MATERIALS AND METHODS
6.4 RESULTS AND DISCUSSION
6.5 ACKNOWLEDGEMENTS
6.6 REFERENCES
CHAPTER 7. A SEAWEED IS MORE THAN THE SUM OF ITS PARTS: SEM VISUALISATION OF BIOFILMS ON SOME SEAWEEDS FROM KWAZULU-NATAL, SOUTH AFRICA
7.1 ABSTRACT
7.2 INTRODUCTION
7.3 MATERIALS AND METHODS
7.4 RESULTS AND DISCUSSION
7.5 ACKNOWLEDGEMENTS
7.6 REFERENCES
CHAPTER 8. GENERAL DISCUSSION
8.1 DEFENCE OF OSMUNDARIA SERRATA
8.2 IMPORTANT RESULTS
8.3 REFERENCES
