SOME FACTORS IN THE COMPETITION OR ANTAGONISM AMONG BACTERIA, ALGAE, AND AQUATIC WEEDS

Field observations of changes in the populations of aquatic weeds and phytoplankton have confirmed that aquatic weeds have antagonistic activity toward phytoplankton. Nutritional studies in the laboratory indicate that cultures of the aquatic weeds, Myriophyllum sp., Ceratophyllum sp., and duckweed (Lemma minor L.); liquid cultures of barley (Hordeum vulgare L., Dickson variety); and cultures of the filamentous green algae, Cladophora sp. and Pithophora oedogonium (Mont.) Withrock, will remain relatively free of epiphytes or competing phytoplankton if the cultures are nitrogen-limited. Field observations of Cladophora sp. have confirmed that the growth of epiphytes on the Cladophora is related to conditions of surplus available nitrogen compounds. It is proposed that this antagonistic activity may be due to a “nitrogen sink” effect in which the aquatic weeds or filamentous green algae prevent the growth of contaminating algae by competition for the limited nitrogen compounds available. However, the presence of bacteria-sized organisms which have selective toxicity to certain algae indicates that perhaps multiple factors exist. Discussed are the ecological implications of associations of certain algae with bacteria that have selective toxicities for other species of algae under certain environmental conditions such as nitrogen-limited growth.     

Electron microscopy of crystalline micelles in cellulose elementary fibrils of Dictyostelium discoideum

Summary In negatively stained preparations the cellulose of Dictyostelium discoideum appears in the form of 35 Å wide fibrils of undetermined length. Upon mild acid hydrolysis a periodic pattern may be observed along the fibrils, in the form of fine, electron-dense bands across the full diameter of the fibril spaced apart from each other by electron-transparent segments approximately 100 Å long. We propose that the electron-transparent segments represent the crystalline micelles of the elementary cellulose fibril, whereas the electron-opaque bands represent the amorphous regions.Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree, University of Hawaii.     

Evidence for a Reductive Pathway for the Anaerobic Metabolism of Benzoate

Evidence is presented for a reductive pathway for the anaerobic metabolism of benzoate by Rhodopseudomonas palustris.     

Assaying Actual Hematein Content of Commercial Hematoxylins and Hemateins

Hematein-free hematoxylin (HFH) was prepared by a modification of the procedure of Palmer and Lillie (Histochemie, 5: 44-54, 1965). Fifty mg of HFH were dissolved in 5 mg of ethylene glycol and then 45 nil of an aqueous solution of 2.25 gm KAl(SO₄)₂. 12H₂O and 5.445 mg KIO₃ were added. Since this amount of KIO₃ would be sufficient to oxidize 25 mg of HFH to hematein we have termed this half-oxidized hematoxylin (HOH). The peak absorbance (560 nm) of this purple solution remained constant for at least a week. With omission of the KIO₃ the solution was colorless. A curve was constructed by plotting absorbance against concentration of hematein in HOH at various dilutions. For analyses of hematein content of commercial hematoxylins 50 mg of sample and 100 mg of hydroquinone were dissolved in 5 ml of ethylene glycol and then 45 ml of a 5% solution of KAl(SO₄)₂. 12H₂O were added. The addition of the hydroquinone stabilized the absorbance for about 5 min. The hematein content could then be calculated by comparing the observed absorbance with the standard curve. Eleven samples of hematoxylin certified by the Biological Stain Commission had hematein concentrations varying from 0.01 to 0.43%. For analyses of the available hematein content of commercial hemateins, 50 mg of sample were dissolved in 10 ml of ethylene glycol, then 45 ml of water and 45 ml of 5% KAI(SO₄)₂. 12H₂O added. The hematein content could then be calculated by comparing the observed absorbance with the standard curve. In 9 samples of hematein from 4 different sources the active hematein content varied from 19 to 97%.     

Light-Induced Changes in the Fluorescence Yield of Chlorophyll a In Vivo: II. Chlorella pyrenoidosa

The long-term fluorescence induction in Chlorella pyrenoidosa consists of a fast rise of the fluorescence yield from the level S (of the first wave transient) to a maximum M, followed by slower decay to a terminal stationary level T. The maximum M is attained within 40 seconds from the onset of illumination while the decay to the terminal level T lasts for several minutes. The fluorescence rise (S → M) coincides with an increase in the rate of oxygen evolution, which, however, remains constant during the fluorescence decay (M → T). Poisons of photosynthesis 3, (3,4-dichlorophenyl)-1,1 dimethylurea (DCMU, o-phenathroline) inhibit the fluorescence induction, while uncouplers of photophosphorylation affect the fluorescence time course only when they function at an early stage of the coupling sequence e.g., carbonyl cyanide p-trifluoremethoxy phenylhydrazone, (FCCP, atabrin). Phosphorylation inhibitors affecting only the terminal esterification step (phlorizin) have little effect on the fluorescence kinetics. These results suggest that the fluorescence induction requires the operation of a phosphorylating electron transport and that it is possibly related to the light-induced structural changes which accompany photophosphorylation.     

The Subcellular Origin of Bioluminescence in Noctiluca miliaris

The light emitted by Noctiluca has its origin in 1 to 5 x 10⁴ organelles ("microsources") which are scattered throughout the perivacuolar cytoplasm, and which appear to be the elementary functional units of bioluminescence. Microscopical techniques, image intensification, and microphotometry were employed in their investigation. Microsources are fluorescent, strongly phase-retarding, and range widely in diameter below 1.5 microns. The number of quanta emitted in a flash from a microsource ("microflash") is of the order of 10⁵ photons. However, microflashes show a wide range of intensities, which are correlated with the size of the organelles from which they arise. Each organelle responds repetitively and with reproducible time course to a succession of invading triggering potentials. Reversible changes in the intensity of the flash emitted by the whole cell ("macroflash") occur because of graduations in intensity of microflashes rather than as a result of changes in the number of responsive organelles. The shape of the flash emitted by individual microsources resembles that of the macroflash except for slightly shorter rise and decay times. It is concluded that the macroflash results from somewhat asynchronous, but otherwise parallel summation of microflashes.