Bacterial community structure in two sediments with different organic matter content of a tropical coastal lagoon (Brazil)

GOMES¹, E.A.T. & MENDONÇA-HAGLER², L.C.S.

¹ Departamento de Biologia Marinha, Instituto de Biologia, Universidade Federal do Rio de Janeiro

Av. Pau Brasil, 211 CCS/Bloco A, Ilha do Fundão, Rio de Janeiro (RJ), 21941-590. e-mail: eligomes@biologia.ufrj.br

² Departamento de Microbiologi a Geral, Instituto de Microbiologia Prof. Paulo de Góes, Universidade Federal do Rio de Janeiro.

ABSTRACT: The size structure of the bacterial benthic communities was studied in two distinct sediments with different organic matter contents (clay and sand)from a shallow eutrophic lagoon (Barra Lagoon), located in the southeastern of Brazil. Samples of sediments were taken from the pelagic and littoral zones from 1993 to 1995. The bacterial number and biomass were estimated per g DW (Dry Weight) of sediment. Total bacterial number (DAPIDC) showed an average of 3.0 - 4.0 x 10⁹ bact/g, regardless of organic matter content. The average bacterial biomass was higher in the clay sediment (1.54 x 10³ mgC/g) than in the sandy sediment (7.12 x 10² mgC/g). Total heterotrophic culturable bacteria were 3 to 4 orders of magnitude lower than DAPIDC and varied from 3.02 x 104 to 7.46 x 10⁵ cfu/g. Proteolytic heterotrophic culturable bacteria were more abundantly found in the clay and lipolytics in the sandy sediments. Cocci forms exhibited the highest densities while filament forms accounted for most of the biomass. The density and biomass of benthic total and heterotrophic culturable bacteria, as well as average size biovolume of cells, were affected by organic matter content of the clay and sandy sediments.

Key-words: bacteria, community structure, sediment, tropical lagoon, Brazil.