Bacterial biofilms are often defined as communities of surface-attached bacteria and are typically depicted with a classic mushroom-shaped structure characteristic of Pseudomonas aeruginosa. However, it has become evident that this is not how all biofilms develop, especially in vivo, in clinical and industrial settings, and in the environment, where biofilms often are observed as non-surface-attached aggregates. In this Review, we describe the origin of the current five-step biofilm development model and why it fails to capture many aspects of bacterial biofilm physiology. We aim to present a simplistic developmental model for biofilm formation that is flexible enough to include all the diverse scenarios and microenvironments where biofilms are formed. With this new expanded, inclusive model, we hereby introduce a common platform for developing an understanding of biofilms and anti-biofilm strategies that can be tailored to the microenvironment under investigation. 

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The biofilm life cycle: expanding the conceptual model of biofilm formation

Biofilm is a microbial association or community attached to different biotic or abiotic surfaces or environments. These surface-attached microbial communities can be found in food, medical, industrial, and natural environments. Biofilm is a critical problem in the medical sector since it is formed on medical implants within human tissue and involved in a multitude of serious chronic infections. Food and food processing surface become an ideal environment for biofilm formation where there are sufficient nutrients for microbial growth and attachment. Therefore, biofilm formation on these surfaces, especially on food processing surface becomes a challenge in food safety and human health. Microorganisms within a biofilm are encased within a matrix of extracellular polymeric substances that can act as a barrier and recalcitrant for different hostile conditions such as sanitizers, antibiotics, and other hygienic conditions. Generally, they persist and exist in food processing environments where they become a source of cross-contamination and foodborne diseases. The other critical issue with biofilm formation is their antibiotic resistance which makes medication difficult, and they use different physical, physiological, and gene-related factors to develop their resistance mechanisms. In order to mitigate their production and develop controlling methods, it is better to understand growth requirements and mechanisms. Therefore, the aim of this review article is to provide an overview of the role of bacterial biofilms in antibiotic resistance and food contamination and emphasizes ways for controlling its production.

/pdf/the-role-of-bacterial-biofilm-in-antibiotic-resistance-and-4oox3exjql.pdf

The Role of Bacterial Biofilm in Antibiotic Resistance and Food Contamination.

A review on underground hydrogen storage: Insight into geological sites, influencing factors and future outlook

Biomaterials have evolved from inert materials that lack interaction with the body to biologically active, instructive materials that host and provide signals to surrounding cells and tissues. Engineered living materials contain living cells (responsive function) and polymeric matrices (scaffolding function) and, thus, can be designed as active and response biomaterials. In this Review, we discuss engineered living materials that incorporate microorganisms as the living, bioactive component. Microorganisms can provide complex responses to environmental stimuli, and they can be genetically engineered to allow user control over responses and integration of numerous inputs. The engineered microorganisms can either generate their own matrix, such as in biofilms, or they can be incorporated in matrices using various technologies, such as coating, 3D printing, spinning and microencapsulation. We highlight biomedical applications of such engineered living materials, including biosensing, wound healing, stem-cell-based tissue engineering and drug delivery, and provide an outlook to the challenges and future applications of engineered living materials. Engineered living materials are composed of a matrix that encapsulates living cells, which endow the biomaterial with controllable responses and dynamic functions. This Review discusses the fabrication and biomedical applications of engineered living materials that contain microorganisms as the living, active component.

Engineered living biomaterials

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models.

Microbial biofilms are communities of aggregated microbial cells embedded in a self-produced matrix of extracellular polymeric substances (EPS). Biofilms are recalcitrant to extreme environments, and can protect microorganisms from ultraviolet (UV) radiation, extreme temperature, extreme pH, high salinity, high pressure, poor nutrients, antibiotics, etc., by acting as “protective clothing”. In recent years, research works on biofilms have been mainly focused on biofilm-associated infections and strategies for combating microbial biofilms. In this review, we focus instead on the contemporary perspectives of biofilm formation in extreme environments, and describe the fundamental roles of biofilm in protecting microbial exposure to extreme environmental stresses and the regulatory factors involved in biofilm formation. Understanding the mechanisms of biofilm formation in extreme environments is essential for the employment of beneficial microorganisms and prevention of harmful microorganisms.

https://www.mdpi.com/1422-0067/20/14/3423/pdf

Biofilms: The Microbial “Protective Clothing” in Extreme Environments

Cyclic di-GMP is a nucleotide second messenger molecule widely distributed in Gram-negative bacteria and plays a central role in the regulation of bacterial metabolism and signaling. However, its importance in affecting Gram-positive bacterial physiology is less known. The Bacillus cereus group is an important class of Gram-positive Bacilli, including more than ten species such as B. thuringiensis, B. anthracis, and B. cereus with minute genetic differences. Intriguingly, there exist up to 13 cyclic di-GMP turnover enzymes containing functional domains GGDEF, EAL, or HD-GYP as well as signal sensor domains such as PAS and GAF domains in the B. cereus group strains, which are stimulated by environmental signals to regulate intracellular cyclic di-GMP concentration. Cyclic di-GMP can bind to downstream receptors or targets to perform its biological functions. Its downstream receptors or targets are mainly proteins and RNA aptamers, although protein receptors have not yet been reported in the B. cereus group strains. The RNA receptors are mostly riboswitches, including Bc1 RNA, Bc2 RNA, and Bc3-5 RNA. Cyclic di-GMP is involved extensively in affecting various physiological activities of bacteria, such as cell motility, biofilm formation, exopolysaccharides synthesis, and expression of pathogenic factors. In this chapter, we review the features of cyclic di-GMP turnover enzymes, the homeostasis of cyclic di-GMP, the study of receptors/targets, and the function of cyclic di-GMP in regulation of physiology in Gram-positive B. cereus group.

Lu Liu

Papers

Biofilms: The Microbial “Protective Clothing” in Extreme Environments

Cyclic di-GMP Signaling Systems in the Gram-Positive Bacillus cereus Group