THESIS
1997
xiii, 67 leaves : ill., col. photos ; 30 cm
Abstract
This thesis research investigated the inhibition of biofouling tubeworm Hydroides elegans (Haswell) and barnacle Balanus amphitrite amphitrite (Darwin) larval settlement by phlorotannins isolated from brown alga Sargassum tenerrimum (Agardh) as well as two analogs of phlorotannins, tannic acid and phloroglucinol. The antifouling effects of natural compounds have been suggested to be due to two mechanisms: natural compounds may inhibit macrofoulers larval settlement directly, or they may regulate the growth of certain bacteria in the microfouling layer so as to inhibit larval settlement indirectly. The hypothesis of this study is that phlorotannins and their analogs inhibit H. elegans and B. a. amphitrite larval settlement by both mechanisms....[
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This thesis research investigated the inhibition of biofouling tubeworm Hydroides elegans (Haswell) and barnacle Balanus amphitrite amphitrite (Darwin) larval settlement by phlorotannins isolated from brown alga Sargassum tenerrimum (Agardh) as well as two analogs of phlorotannins, tannic acid and phloroglucinol. The antifouling effects of natural compounds have been suggested to be due to two mechanisms: natural compounds may inhibit macrofoulers larval settlement directly, or they may regulate the growth of certain bacteria in the microfouling layer so as to inhibit larval settlement indirectly. The hypothesis of this study is that phlorotannins and their analogs inhibit H. elegans and B. a. amphitrite larval settlement by both mechanisms.
In this study, the followings were investigated to test the hypothesis: (1) the toxicity and settlement inhibition effect of the three compounds on H. elegans and B. a. amphitrite larvae, (2) antibacterial activity of the three compounds, and (3) settlement of H. elegans larvae and B. a. amphitrite in response to bacterial films.
The results indicate that phlorotannins, phloroglucinol and tannic acid can selectively inhibit the growth of certain marine bacteria and are inhibitory to H. elegans and B. a. amphitrite larval settlement at concentrations that are not toxic to the larvae. Assays of larval settlement on bacterial films revealed that settlement of H. elegans larvae was species specific and could be affected by changes in species composition of multispecies bacterial films. In contrast, B. a. amphitrite larvae are either inhibited or not affected by the bacterial films and show no discrimination to different species of bacteria.
An integration of results from the antibacterial assays and the response of H. elegans larval settlement to bacterial films suggests that phlorotannins and their analogs are capable of inhibiting H. elegans larval settlement by selective alteration of species composition of bacterial films. However, the general avoidance of bacterial films by B. a. amphitrite larvae and the lack of species-specific responses to bacteria suggest that B. a. amphitrite may not be able to discriminate a biofilm that is developed under the influence of the phenolic compounds from a natural biofilm.
In conclusion, phlorotannins from brown alga S. tenerrimum and two analogs, phloroglucinol and tannic acid, can exert direct inhibition on larval settlement of H. elegans and B. a. amphitrite. However, due to different characteristics of the larvae, the settlement of H. elegans larvae, but may not of B .a. amphitrite larvae, can be indirectly inhibited by the antibacterial activity of the three compounds.
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