Heterotrophic growth of the microalga Chlorella vulgaris Beij. in synthetic as well as sterilized municipal wastewater of a nonindustrialized city was measured. The city wastewater contained high levels of ammonium and nitrate, medium levels of phosphate, and low levels of nitrite and organic molecules and could not support heterotrophic growth of C. vulgaris. Evaluation of 11 known carbon sources for this microalga that were added to standard synthetic wastewater containing the same levels of nitrogen and phosphorus as the municipal wastewater revealed that the best carbon sources for heterotrophic growth were Na-acetate and d-glucose. These provided the highest growth rates and the largest removal of ammonium. Growth increased with concentration of the supplement to an optimum at 0.12 M Na-acetate. This carbon source was consumed completely within 10 d of incubation. Higher concentrations inhibited the growth of C. vulgaris. The microalgal populations under heterotrophic growth conditions were one level of magnitude higher than that under autotrophic growth conditions that served as a comparison. No growth occurred in the dark in the absence of a carbon source. Na-acetate was superior to d-glucose. In municipal wastewater, when Na-acetate or d-glucose was added, C. vulgaris significantly enhanced ammonium removal under heterotrophic conditions, and its capacity was equal to ammonium removal under autotrophic growth conditions. This study showed that sterilized wastewater can be treated by C. vulgaris under heterotrophic conditions if supplemented with the appropriate organic carbon source for the microalgae.

Two isolates of the diazotrophic filamentous cyanobacterium Microcoleus chthonoplastes, one obtained from black mangrove (Avicennia germinans) pneumatophores and one from cyanobacterial mats, were inoculated onto young mangrove seedlings to evaluate nitrogen transfer from the bacterium to the plants under in vitro conditions in closed system experiments. Total nitrogen and 15N incorporation in plant parts were measured. The levels of total N and 15N in the inoculated leaves were significantly higher than in noninoculated plants.

Inoculation of axenic black mangrove seedlings in seawater for 8 days with either the terrestrial halotolerant plant growthpromoting bacterium Azospirillum halopraeferens or with Azospirillum brasilense produced heavy colonization of the root surface. The colonization pattern was different for the two strains. A. halopraeferens yielded mainly single cells embedded in a thick sheath, whereas A. brasilense produced primarily microaggregates. A. brasilense cells were anchored to the root surfaces and to themselves by a network of fibrillar material. Both bacterial strains survived in seawater (approximately 10 4 colony forming units per ml) for more than 30 days, for 70 days in saline water (A. brasilense) and colonized mangrove roots at a very high population density. A. halopraeferens was a better root surface colonizer, whereas the A. brasilense population was greater in the entire root. This work is the initial stage of studies designed to assess the feasibility of using terrestrial plant growthpromoting bacteria for the inoculation of marine plants. ß 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

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