Abstract
The Gram-negative methanotroph Methylococcus capsulatus (Bath) was recently demonstrated to abrogate inflammation in a murine model of inflammatory bowel disease, suggesting interactions with cells involved in maintaining mucosal homeostasis and emphasizing the importance of understanding the many properties of M. capsulatus. Secreted proteins determine how bacteria may interact with their environment, and a comprehensive knowledge of such proteins is therefore vital to understand bacterial physiology and behavior. The aim of this study was to systematically analyze protein secretion in M. capsulatus (Bath) by identifying the secretion systems present and the respective secreted substrates. Computational analysis revealed that in addition to previously recognized type II secretion systems and a type VII secretion system, a type Vb (two-partner) secretion system and putative type I secretion systems are present in M. capsulatus (Bath). In silico analysis suggests that the diverse secretion systems in M.capsulatus transport proteins likely to be involved in adhesion, colonization, nutrient acquisition and homeostasis maintenance. Results of the computational analysis was verified and extended by an experimental approach showing that in addition an uncharacterized protein and putative moonlighting proteins are released to the medium during exponential growth of M. capsulatus (Bath).
Highlights
Methylococcus capsulatus is a Gram-negative, methane-oxidizing bacterium [1] that has been isolated from marine, fresh water- and terrestrial habitats
M. capsulatus (Bath) is the main ingredient in BioProtein (BP), a bacterial single cell protein (SCP) product produced by BioProteins AS (Norway) that serves as a protein source in feedstuff for animals, including salmonids
T2SS are widespread in Gram-negative species, and a complete classical T2aSS system is present in M. capsulatus [13]
Summary
Methylococcus capsulatus is a Gram-negative, methane-oxidizing bacterium [1] that has been isolated from marine-, fresh water- and terrestrial habitats. Protein Secretion in Methylococcus capsulatus (Bath) the genome sequence of M. capsulatus (Bath) strain NCIMB 11132, was published, and results indicated a potential for high metabolic flexibility [2]. Kleiveland et al extended this observation to mammals, when they found a similar effect of BP on dextran sodium sulfate (DSS)-induced colitis in mice [5]. They further demonstrated a comparable effect in mice fed with only M. capsulatus (Bath) without the supplementary bacteria present in BP, suggesting that M. capsulatus represents the anti-inflammatory principle in BP
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