Influence ofMoraxellasp. colonization on the kidney proteome of farmed gilthead sea breams (Sparus aurata, L.)

Background:Currently, presence ofMoraxellasp. in internal organs of fish is not considered detrimental for fish farming. However, bacterial colonization of internal organs can affect fish wellness and decrease growth rate, stress resistance, and immune response. Recently, there have been reports by farmers concerning slow growth, poor feed conversion, and low average weight increase of fish farmed in offshore floating sea cages, often associated with internal organ colonization byMoraxellasp. Therefore, presence of these opportunistic bacteria deserves further investigations for elucidating incidence and impact on fish metabolism.Results:A total of 960 gilthead sea breams (Sparus aurata, L.), collected along 17 months from four offshore sea cage plants and two natural lagoons in Sardinia, were subjected to routine microbiological examination of internal organs throughout the production cycle. Thirteen subjects (1.35%) were found positive forMoraxellasp. in the kidney (7), brain (3), eye (1), spleen (1), and perivisceral fat (1). In order to investigate the influence ofMoraxellasp. colonization, positive and negative kidney samples were subjected to a differential proteomics study by means of 2-D PAGE and mass spectrometry. Interestingly,Moraxellasp. infected kidneys displayed a concerted upregulation of several mitochondrial enzymes compared to negative tissues, reinforcing previous observations following lipopolysaccharide (LPS) challenge in fish.Conclusions:Presence ofMoraxellasp. in farmed sea bream kidney is able to induce proteome alterations similar to those described following LPS challenge in other fish species. This study revealed thatMoraxellasp. might becausing metabolic alterations in fish, and provided indications on proteins that could be investigated as markers of infection by Gram-negative bacteria within farming plants.