A three-part study of the involvement of detrital microbiota in an estuarine trophic system was conducted: (1) the evidence for microbial succession on allochthonous plant litter in Apalachicola Bay, Florida; (2) the effects of grazing by gammaridean amphipods on the detrital microbiota; and (3) the use of the detrital microbiota as a food source by estuarine gammaridean amphipods. / Changes in hydrolytic, respiratory, catabolic and lipid biosynthetic activities depended at least in part on successional changes in the microbial communities on allochthonous plant litter incubated in a semi-tropical estuary. Initial colonization was by populations which had a high content of muramic acid relative to the adenosine triphosphate (ATP) and which were progressively displaced by a microbiota with a lower ratio of muramic acid to ATP. Scanning electron microscopy (SEM) of the plant-litter microbiota showed a succession of forms, with an initial bacterial colonization and its progressive displacement by more complex forms. Estimates of the microbial mass and the rates of phospholipid synthesis suggested that the detrital microbiota have a relatively slow growth rate compared to the growth potential. / The effects of grazing by estuarine gammaridean amphipods on the detrital microbiota were studied. Amphipods grazing at natural population density on detrital microbiota affected the microbial community composition, biomass and metabolic activity, without affecting the physical structure of the leaves. Total microbial biomass estimated by ATP and lipid phosphate or observed by SEM was greater on grazed than on ungrazed detritus. The rates of oxygen consumption, poly-(beta)-hydroxybutyrate (PHB) synthesis, total lipid biosynthesis and release of ('14)CO(,2) from radioactively prelabeled microbiota were higher on grazed leaves than on ungrazed, indicating a stimulation of the metabolic activity of grazed detrital microbes. This was true with rates based either on the dry leaf weight or microbial biomass. Alkaline phosphatase activity was lower in the grazed system, consistent with enhanced inorganic phosphate cycling. The loss of ('14)C from both total lipid and PHB of microorganisms prelabeled with ('14)C was greater from grazed than ungrazed microbes. There was a faster decrease in the ('14)C-glycolipid than in the ('14)C-neutral lipid or ('14)C-phospholipid fraction. Analysis of specific phospholipids showed losses of the metabolically stable ('14)C-glycerolphosphoryl choline. derived from phosphatidyl choline and much more rapid metabolism of the bacterial lipid phosphatidylglycerol measured as ('14)C-glycerol phosphoryl glycerol with amphipod grazing. The biochemical data supported SEM observations of a shift, as the grazing proceeded, from a bacterial/fungal community to one dominated by bacteria. / Three lines of evidence indicated that gammaridean amphipods grazed the microbiota that colonizes estuarine allochthonous detritus. Dried, biologically inactive oak leaves (Quercus virginiana Mill) became covered by microorganisms during incubation in the estuary. Grazing by amphipods, at a density of 3.3 amphipods/cm('2) leaf, decreased the microbial biomass, as measured by the extractible ATP, on the leaf. In SEM examinations of grazed detritus, the leaf surfaces appeared substantially cleared of microbes by the amphipods. Incubation of detritus with ('14)C-labeled precursors showed that the isotope was incorporated by the leaf microbiota. Grazing by amphipods on detritus with ('14)C-labeled microorganisms resulted in a decrease in the ('14)C associated with the leaves, accompanied by a significant increase in the amount of ('14)C recovered in the amphipods. One-third of the ('14)C recovered in the amphipods, whose guts had been cleared of ('14)C-labeled detritus, was recovered in the lipid fraction of the amphipods, indicating assimilation of the detrital microorganisms by the amphipods. / Source: Dissertation Abstracts International, Volume: 41-03, Section: B, page: 0826. / Thesis (Ph.D.)--The Florida State University, 1980.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74174 |
| Contributors | MORRISON, SUSAN JOAN., The Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 161 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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