Roles and interactions of two methylotrophic bacterial strains in the development of a marine denitrifying biofilm

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Nitrate is a highly soluble molecule that can rapidly diffuse in surface waters and groundwaters, and thus contaminate drinking water. This compound contributes to rivers' and lakes' eutrophication and harmful algal blooms in estuarine and marine environments. Nitrate is produced from nitrification of nitrogen-containing compounds or originates from anthropogenic activities such as agricultural fertilization. Nitrate can be disseminated through microbial process called denitrification. This occurs when nitrate is used as an electron acceptor, instead of oxygen, for bacterial respiration, to ultimately produce molecular nitrogen (N2). Denitrifying bacteria are found in a variety of aquatic environments, either in fresh water or seawater. A denitrification process can be included in wastewater treatment systems to prevent environmental release of detrimental nitrate excess The Montreal Biodome operates a closed circuit aquarium of 3 million liters of seawater containing large animals and invertebrates. To control nitrate levels, a denitrification bioreactor is used. My team has studied the microbiology of this bioreactor for more than 10 years aiming to improve its efficiency. The denitrification is achieved by a multi-species microbial biofilm growing in it. From this biofilm, we have isolated the two main bacterial species carrying relevant denitrifying activities: Hyphomicrobium zavarzinii strain NL23 and Methylophaga sp. strain JAM1, which account for 70 to 80% of the biofilm. This proposal is to understand how these two species work together to achieve efficient denitrification in the biofilm. Most natural biofilms are composed of mixed species as the one found in the Biodome denitrifying biosystem. Studying such complex biofilms is a challenge, as each species can influence the biofilm development. Understanding how strains JAM1 and NL23 develop into the biofilm will unravel some of the mechanisms shaping mixed-species microbial biofilms. Finally, novel information related to mechanisms of action of marine methylotrophic bacteria grown under denitrifying conditions will be obtained.