No abstract

. The predominant cell surface protein (A‐protein) of Aeromonas salmonicida has been purified by a method utilizing a glycine/hydrochloridc extraction from whole cells and HPLC/ion exchanger (DEAE) columns. This procedure yielded two LPS‐frec molecules (a 40‐ and a 50‐kDa form) both shown to contain A‐protein determinants. The former appears to be a digest product of the latter, as a serine protease produced by A. salmonicida was shown to process the 50‐kDa form into a 40‐kDa molecule in vitro. The A‐layer protein was shown to contain one isoform, although multiple isoelectric forms appeared as preparative artifacts, probably due to deamidation. The A‐layer protein and LPS arc the most significant surface antigens recognized by the Atlantic salmon B‐lymphocytes or antibodies. Immunological studies of LPS‐free and LPS‐containing A‐protein preparations were undertaken to test whether the two components behave like antigenie competitors or whether the LPS moiety could adjuvant the antibody response against the A‐protein. The latter was shown to be the case.

Aims:  To assess the effects of bacterial treatment at the earliest stages of cod rearing on the microbial load, larval development and performance, testing three bacterial strains (Carnobacterium divergens V41, Arthrobacter sp. and Enterococcus sp.) in vivo that were previously shown to have inhibitory potential towards fish pathogens in vitro. Methods and Results:  A bacterial mixture was added eight times to the rearing water from the prehatch to the mid‐larval stage (a 38‐day period). Microbiological analysis of ova, larvae and rearing water was performed regularly. Larval performance and development were evaluated by survival rate, hypersalinity tolerance and physiological measurements. Different larval survival rates were observed within and between treatments, and possibly explained by variations in larval microflora and established probionts. Larvae from one silo, which had been bathed in the bacterial suspension, showed the highest survival rate (42·1%), lowest Vibrio levels, and were significantly heavier (19·3%) and more stress tolerant than control larvae (P < 0·01). This coincided with the intestinal establishment of two of the tested bacteria. Conclusions:  Arthrobacter and Enterococcus strains added regularly to the rearing water from the postfertilized egg stage can become established in larval gastrointestinal tract. The Enterococcus strain was associated with increased larval growth, performance and microflora control, indicating its probiotic nature. Significance and Impact of the Study:  Regular application of autochthonous probionts may promote larval welfare, development and stress tolerance at early stages, hence increasing production yield in intensive cod larviculture.

Extracellular haemolytie activities of Aeromonas salmonicida ssp. salmonicida to salmon red blood cells were shown to be due to different forms of the mcmbranc-activc enzyme glyccrophospholipid:choicstcrol acyltransferase {GCAT). About 10% of the total haemolytie activity was due to a high molecular mass complex of LPS and GCAT (mol. mass > 1000kDa), containing 35-50% neutral sugars and 1-5-2-0% protein. Some haemolytie activity (30-40% of total), corresponding to 5O-70kDa by gel filtration, also contained GCAT-aetivity and may represent aggregated forms of GCAT. However, about 50% or more of the haemol>tic activity was due to a protein of 26kDa free GCAT. Rabbit antibodies to GCAT neutralized the haemolytie activity of both GCAT and GCAT-LPS. A transposon-produced serine protease negative mutant of the same A. salmonicida strain showed reduced haemolytie -activity. The mutant produced a 38-kDa GCAT preform of low haemolytie activity. The proform was processed by autogenous serine protease to a highly haemolytie 26-kDa molecule with pi 6-3. similar to GCAT of the parent strain. The weakly haemolytie GCAT-LPS analogue of the mutant strain did not contain detectable amounts of the 26-kDa molecule and was not activated by proteases.