Interactions of bacteria with different mechanisms for chitin degradation result in the formation of a mixed-species biofilm

Abstract

In this study, interactions between bacteria possessing either released or cell-associated enzymes for polymer degradation were investigated. For this, a co-culture of Aeromonas hydrophila strain AH-1N as an enzyme-releasing bacterium and of Flavobacterium sp. strain 4D9 as a bacterium with cell-associated enzymes was set up with chitin embedded into agarose beads to account for natural conditions, under which polymers are usually embedded in organic aggregates. In single cultures, strain AH-1N grew with embedded chitin, while strain 4D9 did not. In co-cultures, strain 4D9 grew and outcompeted strain AH-1N in the biofilm fraction. Experiments with cell-free culture supernatants containing the chitinolytic enzymes of strain AH-1N revealed that growth of strain 4D9 in the co-culture was based on intercepting N-acetylglucosamine from chitin degradation. For this, strain 4D9 had to actively integrate into the biofilm of strain AH-1N. This study shows that bacteria using different chitin degradation mechanisms can coexist by formation of a mixed-species biofilm.

Solutions to the Public Goods Dilemma in Bacterial Biofilms

“…Most experimental research examining social evolution in bacterial populations has been performed with liquid cultures, which eliminate population spatial structure that is ubiquitous in realistic environments [1, 2] and is predicted to be critical for the evolution of cooperation [20-24]. Social evolution has been studied in radially expanding colonies on agar, but no general mechanisms have been found that show how enzyme-producing cells avoid exploitation by non-producers in biofilms [8-11, 25, 26]. Given that biofilms are the dominant form of bacterial life in nature, and that many bacterial species secrete digestive enzymes, clarifying the means by which cooperative cells avert exploitation in biofilms is a major outstanding problem.…”

N-Acetylglucosamine Inhibits LuxR, LasR and CviR Based Quorum Sensing Regulated Gene Expression Levels

“…No interactions were observed (data not shown). Millimolar concentrations of NAG are commonly observed in nature suggesting that in such environments AHL-mediated gene expression will be repressed (Gorke and Stulke, 2008; Eisenreich et al, 2010; Frimmersdorf et al, 2010; Jagmann et al, 2012). …”

“…NAG is the monomer of the second most abundant biopolymer on Earth and is also a major component of heterogeneous polysaccharides including murein and hyaluronic acid. It is commonly encountered in the environment in millimolar concentrations (Jagmann et al, 2012). …”

“…NAG can be utilized as a carbon/nitrogen source as well as regulate bacterial host colonization, production of virulence factors and biofilm formation (Chang et al, 2004; Korgaonkar and Whiteley, 2011; Jagmann et al, 2012; Kawada-Matsuo et al, 2012). In a previous study, transcriptome analysis to examine the gene expression levels of P. aeruginosa growing on NAG has shown that 5 mM NAG upregulates the abundance of quorum sensing repressor protein (QscR) sixfold (Korgaonkar and Whiteley, 2011).…”

The Social Life of Aeromonas through Biofilm and Quorum Sensing Systems

“…The A. hydrophila strain AH-1 is able to degrade chitin due to extracellular chitinases, and Flavobacterium sp. acts as a cheater that uses chitin degradation products as nutrients (Jagmann et al, 2012). The biofilm formation of Aeromonas was enhanced when co-cultured with a Bacillus cereus strain that improves aggregation between bacteria (Cheng et al, 2014).…”