Abstract

Summary The presence, prevalence and variability of microorganisms related to the species Alteromonas macleodii , a well known culturable γ ‐ Proteobacterium , has been studied in different seawater samples from diverse geographical locations, in both the Northern and Southern hemispheres, and tested with two molecular techniques (rRNA hybridization and gene cloning and sequencing). Results show that A. macleodii ‐like microorganisms are present in high proportions in North Atlantic and, especially, Mediterranean waters, being higher at deep samples and particle‐associated fractions, in agreement with previous findings. In contrast, Southern samples (all from very cold areas near Antarctica) presented no significant hybridization signals. The analysis of the ribosomal ITS (16S‐23S i nternal t ranscribed s pacers) revealed that A . macleodii ‐like microorganisms from Mediterranean, North Atlantic, Caribbean and Red Sea waters differed in both size and sequence, mostly depending on their geographical origin, with Mediterranean and North Atlantic clones clustering into two main groups whereas Caribbean and Red Sea clones appeared separated.

Silvia G. Acinas

Staff scientist

Ramon Massana

Staff scientist

I am microbial ecologists with a deep interest in protist ecology and evolution