How do the winter ulcer pathogens control its environment?

Moritella viscosa (M. viscosa) is considered the main causative agent of winter ulcer in the skin of farmed Atlantic salmon. Repeatedly improved vaccines against the disease have so far provided only a fair protection. Aliivibrio wodanis (A. wodanis), is recurrently isolated together with M. viscosa from the ulcers. This co-existence may indicate that there is an interspecific bacterial communication between these species. This study aims to understand the interplay between the two bacteria, and, if and how A. wodanis can influence the pathogenic behavior of M. viscosa or e.g. suppress the healing process of skin ulcers. To achieve our goals, genes involved in cell-cell communication has been inactivated and their contribution to disease development explored. The interplay between bacteria has be analyzed using omics techniques after in cultivation of the bacteria under different conditions. Our present results show that the presence of A. wodanis alters the global gene expression of M. viscosa during co-cultivation. Co-cultivation studies also show that A. wodanis impedes the growth of M. viscosa, and that this inhibitory effect is not contact-dependent. The competition could either come from the fight over nutritional resources, or that A. wodanis is actively producing and secreting agents that impede M. viscosa growth. We have strong indication that the production of these agents, probably secreted by the Secretion System VI, is regulated by the Quorum Sensing (QS) system i A. wodanis in both a density and temperature dependent fashion.

Winter ulcer disease is one of the main bacterial infectious diseases of concern in the Norwegian fish farming industry, since management procedures and vaccination strategies remain inadequate. Direct losses, down-classification due to low quality and re duced production volume amount to significant economic losses. Fish with winter ulcer disease suffers from severe ulceration and internal pathology for months, giving great animal welfare concern and negative consumer attitudes. Moritella viscosa is consi dered the main causative agent of the disease and all farmed Atlantic salmon are today vaccinated with M. viscosa components. Aliivibrio wodanis are recurrently isolated together with M. viscosa may indicate that there exists an interspecific bacterial co mmunication between these species, or otherwise be beneficial to A. wodanis as a secondary pathogen during the development of the disease. How A. wodanis can exploit the impairment of normal host functions under disease development, influence pathogenicit y or e.g. suppress the healing process of skin ulcers is not known. Based on the status of knowledge we have formulated the following hypothesis; The winter ulcer pathogens are able to communicate and control their merged systems to regulate their metabol ome and proteome in order to control its environment, to prevent other bacteria to infect the host and at the same time become a more efficient infection agent. The main goal of the projects is to address the lack of knowledge regarding cell-to-cell commu nication in development of winter ulcer by identifying systems and effector molecules involved in cell-to-cell communication between M. viscosa and A. wodanis and the relevance of such systems/effector molecules in controlling the environment in order to develop winter ulcer. The knowledge derived from the project will be incorporated into vaccine formulations, vaccination techniques, and management strategies related to vaccination against winter ulcer disease.