Heterotrophic bacteria attached to leaves, rhizomes and roots of three seagrass species from Aqaba (Jordan)

Abstract

Significant differences in viable counts of heterotrophic bacteria attached to the seagrasses Halophila ovalis (R. Brown) Hook. f., Halophila stipulacea (Forsk.) Aschers. and Halodule uninervis (Forsk.) Aschers. were found between the species as well as between their various vegetative parts. Bacterial densities were highest on the leaves and showed a seasonal pattern with maxima in summer. Of the nine genera found, three were gram-negative. Most common were the gram-positive genera Actinomyces, Arthrobacter and Bacillus. Vibrio and Micrococcus occured on Halodule uninervis only, whereas Acinetobacter, Staphylococcus and Streptococcus occurred on Halophila ovalis only. The variation in the distribution pattern of the bacterial genera may be related partly to inhibiting substances such as flavones, phenolic acids and tannins, and partly to differences in the quantity and quality of soluble organic exudates released by the plants.