Can photocatalysis inhibit interspecies bacterial cooperation to quench the formation of robust complex bacterial biofilms in water environments?

Bacterial biofilms pose significant a public health risk as an environmental reservoir for opportunistic aquatic bacterial pathogens. Understanding the interspecies roles of complex bacterial biofilms under different stimuli and regulatory mechanisms of stress responses is the key to controlling their dissemination. Herein, two-species mixture (TSM) biofilms (Staphylococcus aureus and Pseudomonas aeruginosa) were constructed in a flowthrough reactor. Compared with the single-species biofilms, the TSM biofilm had higher growth activity to reach maturity faster, forming a staggered community structure. Moreover, the TSM biofilm exhibited greatly improved resistance to different antibiotics (16-128 times higher), especially to those that act on protein synthesis and cell membrane integrity, when compared to single planktonic microorganisms. In the presence of stimuli, photocatalysis effectively inactivated the TSM biofilm within 10 h, a 4-fold shorter inactivation time compared to UVC irradiation. In addition, photocatalysis effectively depleted the extracellular polymers of the TSM biofilm and inhibited secretion of their interspecies quorum sensing signaling molecule autoinducer-2 (AI-2). However, the expression of AI-2 induced related virulence factors, and biofilm growth-related genes were initially up-regulated 3 - 10 fold for the TSM biofilm within the first 2 - 4 h of photocatalysis, followed by significant down-regulation. Furthermore, the addition of the AI-2 precursor 4,5-dihydroxy-2,3-pentanedione effectively delayed the photocatalytic inactivation efficiency of the TSM biofilm compared to the control. These results suggest that photocatalysis can effectively inactivate biofilms by inhibiting interspecies cooperation by quenching AI-2 in the TSM biofilm. This work sheds light on controlling biofilms in public health engineering systems.

Multispecies biofilms in fermentation: Biofilm formation, microbial interactions, and communication

Food fermentation is driven by microorganisms, which usually coexist as multispecies biofilms. The activities and interactions of functional microorganisms and pathogenic bacteria in biofilms have important implications for the quality and safety of fermented foods. It was verified that the biofilm lifestyle benefited the fitness of microorganisms in harsh environments and intensified the cooperation and competition between biofilm members. This review focuses on multispecies biofilm formation, microbial interactions and communication in biofilms, and the application of multispecies biofilms in food fermentation. Microbial aggregation and adhesion are important steps in the early stage of multispecies biofilm formation. Different biofilm-forming abilities and strategies among microorganisms lead to several types of multispecies biofilm formation. The spatial distribution of multispecies biofilms reflects microbial interactions and biofilm function. Then, we discuss the intrinsic factors and external manifestations of multispecies biofilm system succession. Several typical interspecies cooperation and competition modes and mechanisms of microbial communication were reviewed in this review. The main limitations of the studies included in this review are the relatively small number of studies of biofilms formed by functional microorganisms during fermentation and the lack of direct evidence for the formation process of multispecies biofilms and microbial interactions and communication within biofilms. This review aims to provide the food industry with a sufficient understanding of multispecies biofilms in food fermentation. Practical Application: Meanwhile, it offers a reference value for better controlling and utilizing biofilms during food fermentation process, and the improvement of the yield, quality, and safety of fermented products including Chinese Baijiu, cheeese,kefir, soy sauce, kombucha, and fermented olive.

Cell differentiation and motion determine the Bacillus subtilis biofilm morphological evolution under the competitive growth

The growth discrepancy of Bacillus subtilis biofilms along different directions under the competitive growth drive the formation of anisotropic biofilm morphology directly. Two biofilms growing from two inoculating positions with different distances exhibit promoting or inhibiting growth behavior. Here we develop an optical imaging technology to observe the cell differentiation and the growth dynamics when the biofilm grows. It shows that the spatiotemporal distribution of different phenotypes affects the biofilm morphological evolution. We develop a program to calculate the velocity of cell motion within the biofilm, which is based on the feature point matching approach. We find the cell differentiation ununiformity in the neighboring region and its opposite region leads to the cell velocity difference in the competitive environment, the different cell motion further influences the biofilm morphology evolution. When biofilms grow with a long inoculating distance, there is always a gap between the them; when biofilms grow with a short inoculating distance, two biofilms gradually merge into a whole. Our work establishes a relationship between microscopic cells and macroscopic biofilm morphological which enables us to study the competitive growth process of biofilms from multiple perspectives.

Papers of note in Science (6338)

This week’s articles demonstrate how T cells search for ligands; a role for the endoplasmic reticulum in the nonclathrin-mediated endocytosis of a growth factor receptor; and growth coupling between distant bacterial colonies that enables the cells to share limited resources.