The bacterial biota on crustose (nonarticulated) coralline algae from Tasmanian waters

Abstract

The bacterial biota associated with the cuticle surface of healthy benthic samples of crustose nonarticulated coralline algae from the east coast of Tasmania (Australia) was examined by bacteriological cultivation and electron microscopy. In 32 samples studied, the viable count on Zobell's marine agar (supplemented with vitamins) was 3.3×10⁶ bacteria g⁻¹ wet wt. (range 2.9×10⁴–2.7×10⁷). Of 732 strains isolated from 16 out of 32 samples and identified to genus level,Moraxella was the predominant genus (66%). In contrast,Moraxella comprised only 11% of 217 strains isolated from benthic seawater samples collected at the same time as coralline algae. In 22 out of 32 algal samples examined by scanning electron microscopy, the total count was 1.6 × 10⁷ bacteria g⁻¹ wet wt. (range 5.1× 10⁶–3.8×107); the major morphotype was cocco-bacilli (80%). Several environmental factors did not significantly influence the viable count or generic distribution, or the total count or morphotypic distribution of bacteria on the cuticle. These factors included geographical site, season, storage of samples in aquarium conditions, and the presence or absence of abalone from shells that the coralline algae encrusted. The microbiota, consisting mostly of the nonmotile bacterial genusMoraxella, appeared to be highly adapted to its calcerous plant host.