Monitoring the opportunistic bacteria Pseudoalteromonas sp. LT-13 in a great scallop, Pecten maximus hatchery

PCR with specific primers against Pseudoalteromonas sp. LT-13, and Denaturing Gradient Gel Electrophoresis (DGGE) of PCR-amplified 16SrDNA, was used to monitor the bacterial community in samples of early stages of scallop larvae suffering high mortality. Samples were taken of larvae from different tanks, water in the tanks, eggs/sperm, inlet water and algal cultures. The DGGE profiles revealed one dominating band that was always present in samples of scallop larvae suffering high mortality. The band was sequenced and demonstrated high sequence homology to Pseudoalteromonas sp. LT-13, a bacterium previously isolated from the hatchery. Samples from different locations in the production unit were collected four times in an 11-month period and tested for the presence of LT13 by PCR. Seventy-four percent of the samples collected in April 2003 contained LT-13. In this period the mortality of the scallop larvae was no less than 96.8%. In two of the other samples the mortality was moderate (83.3–78.0%), and LT-13 was detected in 30 and 57% of these samples. High mortality (98.3%) also occurred in the February 2003 sampling period; however, LT-13 was detected in just 39% of the samples. These results indicate that the bacterium is not an obligate pathogen, but rather an opportunistic bacterium that may be used as an early indicator of the conditions in the hatchery.