Should we stay or should we go: mechanisms and ecological consequences for biofilm dispersal. Nat Rev Microbiol. 2012;10:39-50. [PMID: 22120588 DOI: 10.1038/nrmicro2695]

Protozoan predation as a driver of diversity and virulence in bacterial biofilms

Protozoa are eukaryotic organisms that play a crucial role in nutrient cycling and maintaining balance in the food web. Predation, symbiosis and parasitism are three types of interactions between protozoa and bacteria. However, not all bacterial species are equally susceptible to protozoan predation as many are capable of defending against predation in numerous ways and may even establish either a symbiotic or parasitic life-style. Biofilm formation is one such mechanism by which bacteria can survive predation. Structural and chemical components of biofilms enhance resistance to predation compared to their planktonic counterparts. Predation on biofilms gives rise to phenotypic and genetic heterogeneity in prey that leads to trade-offs in virulence in other eukaryotes. Recent advances, using molecular and genomics techniques, allow us to generate new information about the interactions of protozoa and biofilms of prey bacteria. This review presents the current state of the field on impacts of protozoan predation on biofilms. We provide an overview of newly gathered insights into (i) molecular mechanisms of predation resistance in biofilms, (ii) phenotypic and genetic diversification of prey bacteria, and (iii) evolution of virulence as a consequence of protozoan predation on biofilms.

Biofilm-Producing Ability of Staphylococcus aureus Obtained from Surfaces and Milk of Mastitic Cows

This study was conducted to evaluate the incidence of mastitis in 153 dairy cows and to evaluate the kinetics of adhesion of isolates obtained from surfaces and milk in comparison with the reference strain (RS), CCM 4223. The surfaces of the floor, teat cup, and cow restraints were aseptically swabbed in three replicates (n = 27). Of the total number of infected cows (n = 43), 11 samples were found to be positive for Staphylococcus aureus, 12 samples tested positive for non-aureus staphylococci, 6 samples tested positive for Streptococcus spp., and 11 samples tested positive for other bacteria (Escherichia coli, Pseudomonas spp.) or a mixed infection. The most represented pathogen in milk (11/43) and on surfaces (14/27) was S. aureus. The kinetics of adhesion of the reference strain and isolates of S. aureus on stainless steel surfaces were determined after 3, 6, 9, 12, 24, and 48 h, and 3, 6, 9, 12, and 15 days of incubation. All strains reached counts higher than 5 Log₁₀ CFU/cm² needed for biofilm formation, except RS (4.40 Log₁₀ CFU/cm²). The isolates of S. aureus revealed a higher capability to form biofilm in comparison with RS during the first 3 h (p < 0.001). Thus, there is a significant difference between the occurrence of S. aureus on monitored surfaces-floor, teat cup, and cow restraints-and the frequency with which mastitis is caused by S. aureus (p < 0.05). This finding raises the possibility that if various surfaces are contaminated by S. aureus, it can result in the formation of biofilm, which is a significant virulence factor.

Efflux pumps and microbial biofilm formation

Biofilm-related infections are resistant forms of pathogens that are regarded as a medical problem, particularly due to the spread of multiple drug resistance. One of the factors associated with biofilm drug resistance is the presence of various types of efflux pumps in bacteria. Efflux pumps also play a role in biofilm formation by influencing Physical-chemical interactions, mobility, gene regulation, quorum sensing (QS), extracellular polymeric substances (EPS), and toxic compound extrusion. According to the findings of studies based on efflux pump expression analysis, their role in the anatomical position within the biofilm will differ depending on the biofilm formation stage, encoding gene expression level, the type and concentration of substrate. In some cases, the function of the efflux pumps can overlap with each other, so it seems necessary to accurate identify the efflux pumps of biofilm-forming bacteria along with their function in this process. Such studies will help to choose treatment strategy, at least in combination with antibiotics. Furthermore, if the goal of treatment is an efflux pump manipulation, we should not limit it to inhibition.

Alkyl-quinolone-dependent quorum sensing controls prophage-mediated autolysis in Pseudomonas aeruginosa colony biofilms

Pseudomonas aeruginosa is a model quorum sensing (QS) pathogen with three interconnected QS circuits that control the production of virulence factors and antibiotic tolerant biofilms. The pqs QS system of P. aeruginosa is responsible for the biosynthesis of diverse 2-alkyl-4-quinolones (AQs), of which 2-heptyl-4-hydroxyquinoline (HHQ) and 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS) function as QS signal molecules. Transcriptomic analyses revealed that HHQ and PQS influenced the expression of multiple genes via PqsR-dependent and -independent pathways whereas 2-heptyl-4-hydroxyquinoline N-oxide (HQNO) had no effect on P. aeruginosa transcriptome. HQNO is a cytochrome bc ₁ inhibitor that causes P. aeruginosa programmed cell death and autolysis. However, P. aeruginosa pqsL mutants unable to synthesize HQNO undergo autolysis when grown as colony biofilms. The mechanism by which such autolysis occurs is not understood. Through the generation and phenotypic characterization of multiple P. aeruginosa PAO1 mutants producing altered levels of AQs in different combinations, we demonstrate that mutation of pqsL results in the accumulation of HHQ which in turn leads to Pf4 prophage activation and consequently autolysis. Notably, the effect of HHQ on Pf4 activation is not mediated via its cognate receptor PqsR. These data indicate that the synthesis of HQNO in PAO1 limits HHQ-induced autolysis mediated by Pf4 in colony biofilms. A similar phenomenon is shown to occur in P. aeruginosa cystic fibrosis (CF) isolates, in which the autolytic phenotype can be abrogated by ectopic expression of pqsL.

The aeromicrobiome: the selective and dynamic outer-layer of the Earth's microbiome

The atmosphere is an integral component of the Earth's microbiome. Abundance, viability, and diversity of microorganisms circulating in the air are determined by various factors including environmental physical variables and intrinsic and biological properties of microbes, all ranging over large scales. The aeromicrobiome is thus poorly understood and difficult to predict due to the high heterogeneity of the airborne microorganisms and their properties, spatially and temporally. The atmosphere acts as a highly selective dispersion means on large scales for microbial cells, exposing them to a multitude of physical and chemical atmospheric processes. We provide here a brief critical review of the current knowledge and propose future research directions aiming at improving our comprehension of the atmosphere as a biome.

The mixed biofilm formed by Listeria monocytogenes and other bacteria: Formation, interaction and control strategies

Listeria monocytogenes is an important foodborne pathogen. It can adhere to food or food contact surface for a long time and form biofilm, which will lead to equipment damage, food deterioration, and even human diseases. As the main form of bacteria to survive, the mixed biofilms often exhibit higher resistance to disinfectants and antibiotics, including the mixed biofilms formed by L. monocytogenes and other bacteria. However, the structure and interspecific interaction of the mixed biofilms are very complex. It remains to be explored what role the mixed biofilm could play in the food industry. In this review, we summarized the formation and influence factors of the mixed biofilm developed by L. monocytogenes and other bacteria, as well as the interspecific interactions and the novel control measures in recent years. Moreover, the future control strategies are prospected, in order to provide theoretical basis and reference for the research of the mixed biofilms and the targeted control measures.

Genomic insights into the c-di-GMP signaling and biofilm development in the saprophytic spirochete Leptospira biflexa

C-di-GMP is a bacterial second messenger with central role in biofilm formation. Spirochete bacteria from Leptospira genus present a wide diversity, with species of medical importance and environmental species, named as saprophytic. Leptospira form biofilms in the rat's reservoir kidneys and in the environment. Here, we performed genomic analyses to identify enzymatic and effector c-di-GMP proteins in the saprophytic biofilm-forming species Leptospira biflexa serovar Patoc. We identified 40 proteins through local alignments. Amongst them, 16 proteins are potentially functional diguanylate cyclases, phosphodiesterases, or hybrid proteins. We also identified nine effectors, including PilZ proteins. Enrichment analyses suggested that c-di-GMP interacts with cAMP signaling system, CsrA system, and flagella assembly regulation during biofilm development of L. biflexa. Finally, we identified eight proteins in the pathogen Leptospira interrogans serovar Copenhageni that share high similarity with L. biflexa c-di-GMP-related proteins. This work revealed proteins related to c-di-GMP turnover and cellular response in Leptospira and their potential roles during biofilm development.

Synergistic antibacterial and biofilm eradication activity of quaternary-ammonium compound with copper ion

Antibiotics overuse and misuse increase the emergence of multidrug-resistant bacterial strains, which often leads to the failure of conventional antibiotic therapies. Even worse, the tendency of bacteria to form biofilms further increases the therapeutic difficulty, because the extracellular matrix prevents the penetration of antibiotics and triggers bacterial tolerance. Therefore, developing novel antibacterial agents or therapeutic strategies with diverse antibacterial mechanisms and destruction of bacteria biofilm is a promising way to combat bacterial infections. In the present study, the combination of quaternary ammonium compound poly(diallyl dimethyl ammonium chloride) (PDDA) with Cu²⁺ was screened out to fight common pathogenic Staphylococcus aureus (S. aureus) through multi-mechanisms. This combination appeared strong synergistic antibacterial activity, and the fractional inhibitory concentration index was as low as 0.032. The synergistic antibacterial mechanism involved the destruction of the membrane function, generation of intracellular reactive oxygen, and promotion more Cu²⁺ into the cytoplasm. Further, the combination of PDDA and Cu²⁺ reduced the extracellular polysaccharide matrix, meanwhile killing the bacteria embedded in the biofilm. The biocompatibility study in vitro revealed this combination exhibited low cytotoxicity and hemolysis ratio even at 8 times of minimum bactericidal concentration. This work provides a novel antibacterial agents combination with higher efficiency to fight planktonic and biofilm conditions of S. aureus.

Effects of biofilm and co-culture with Bacillus velezensis on the synthesis of esters in the strong flavor Baijiu

Biofilm plays an important role in resisting the adverse environment, improving the taste and texture, and promoting the synthesis of flavor substances. However, to date, the findings on the effect of biofilm and dominating bacteria Bacillus on the ester synthesis in the Baijiu field have been largely lacked. Therefore, the objectives of the present study were to primarily isolate biofilm-producing microbes in the fermented grains, evaluate the stress tolerance capacity, and unveil the effect of biofilm and co-culture with Bacillus on the ester synthesis in the strong flavor Baijiu. Results indicated that after isolation and evaluation of stress-tolerance capacity, bacterial strain BG-5 and yeast strains YM-21 and YL-10 were demonstrated as mediate or strong biofilm-producing microbes and were identified as Bacillus velezensis, Saccharomycopsis fibuligera, and Zygosaccharomyces bailii, respectively. Solid phase microextraction/gas chromatography-mass spectrometer indicated that biofilm could enhance the diversity of esters while reduce the contents of ester. The scanning electron microscopy showed an inhibitory effect of B. velezensis on the growth of S. fibuligera, further restraining the production of esters. Taken together, both biofilm and B. velezensis influence the ester synthesis process. The present study is the first to reveal the biofilm-producing microorganisms in fermented grains and to preliminarily investigate the effect of biofilm on the ester synthesis in the Baijiu field.

An alternative approach towards nitrification and bioremediation of wastewater from aquaponics using biofilm-based bioreactors: A review

Aquaponics combines the advantages of aquaculture and hydroponics as it suits the urban environment where a lack of agricultural land and water resources is observed. It is an ecologically sound system that completely reuses its system waste as plant fertilizer. It offers sustainable water savings, making it a supreme technology for food production. The two major processes that hold the system together are nitrification and denitrification. The remains of fish in form of ammonia reach the bio filters where it is converted into nitrite and further into nitrate in presence of nitrifying and denitrifying bacteria. Nitrate eventually is taken up by the plants. However, even after the uptake from the flow stream, the effluent contains remaining ammonium and nitrates, which cannot be directly released into the environment. In this review it is suggested how integrating the biofilm-based bioreactors in addition to aquaculture and hydroponics eliminates the possibility of remains of total ammonia nitrogen [TAN] contents, leading to bioremediation of effluent water from the system. Effluent water after releasing from a bioreactor can be reused in an aquaculture system, conditions provided in these bioreactors promote the growth of required bacteria and encourages the mutual development of plants and fishes and eventually leading to bioremediation of wastewater from aquaponics.

Hierarchical encapsulation of bacteria in functional hydrogel beads for inter- and intra- species communication

To sequester prokaryotic cells in a biofilm-like niche, the creation of a pertinent and reliable microenvironment that reflects the heterogeneous nature of biological systems is vital for sustenance. Design of a microenvironment that is conducive for growth and survival of organisms, should account for factors such as mass transport, porosity, stability, elasticity, size, functionality, and biochemical characteristics of the organisms in the confined architecture. In this work we present an artificial long-term confinement model fabricated by natural alginate hydrogels that are structurally stable and can host organisms for over 10 days in physiologically relevant conditions. A unique feature of the confinement platform is the development of stratified habitats wherein bacterial cells can be entrapped in the core as well as in the shell layers, wherein the thickness and the number of shell layers are tunable at fabrication. We show that the hydrogel microenvironment in the beads can host complex subpopulations of organisms similar to that in a biofilm. Dynamic interaction of bacterial colonies encapsulated in different beads or within the core and stratified layers of single beads was demonstrated to show intra- species communication. Inter- species communication between probiotic bacteria and human colorectal carcinoma cells was also demonstrated to highlight a possible bidirectional communication between the organisms in the beads and the environment. STATEMENT OF SIGNIFICANCE: Bacteria confinement in a natural soft hydrogel structure has always been a challenge due to the collapse of hydrogel architectures. Alternative methods have been attempted to encapsulate microorganisms by employing various processes to avoid/minimize rupturing of hydrogel structures. However, most of the past approaches have been unfavorable in balancing cell proliferation and functionality upon confinement. Our study addresses the fundamental gap in knowledge necessary to create favorable and complex 3D biofilm mimics utilizing natural hydrogel for microbial colonization for long-term studies. Our approach represents a cornerstone in the development of 3D functional architectures not only to advance studies in microbial communication, host-microbe interaction but also to address basic and fundamental questions in biology.

New Technological Approaches for Dental Caries Treatment: From Liquid Crystalline Systems to Nanocarriers

Dental caries is the most common oral disease, with high prevalence rates in adolescents and low-income and lower-middle-income countries. This disease originates from acid production by bacteria, leading to demineralization of the dental enamel and the formation of cavities. The treatment of caries remains a global challenge and the development of effective drug delivery systems is a potential strategy. In this context, different drug delivery systems have been investigated to remove oral biofilms and remineralize dental enamel. For a successful application of these systems, it is necessary that they remain adhered to the surfaces of the teeth to allow enough time for the removal of biofilms and enamel remineralization, thus, the use of mucoadhesive systems is highly encouraged. Among the systems used for this purpose, liquid crystalline systems, polymer-based nanoparticles, lipid-based nanoparticles, and inorganic nanoparticles have demonstrated great potential for preventing and treating dental caries through their own antimicrobial and remineralization properties or through delivering drugs. Therefore, the present review addresses the main drug delivery systems investigated in the treatment and prevention of dental caries.

Bioactive compounds: a goldmine for defining new strategies against pathogenic bacterial biofilms?

Most human infectious diseases are caused by microorganisms growing as biofilms. These three-dimensional self-organized communities are embedded in a dense matrix allowing microorganisms to persistently inhabit abiotic and biotic surfaces due to increased resistance to both antibiotics and effectors of the immune system. Consequently, there is an urgent need for novel strategies to control biofilm-associated infections. Natural products offer a vast array of chemical structures and possess a wide variety of biological properties; therefore, they have been and continue to be exploited in the search for potential biofilm inhibitors with a specific or multi-locus mechanism of action. This review provides an updated discussion of the major bioactive compounds isolated from several natural sources - such as plants, lichens, algae, microorganisms, animals, and humans - with the potential to inhibit biofilm formation and/or to disperse established biofilms by bacterial pathogens. Despite the very large number of bioactive products, their exact mechanism of action often remains to be clarified and, in some cases, the identity of the active molecule is still unknown. This knowledge gap should be filled thus allowing development of these products not only as novel drugs to combat bacterial biofilms, but also as antibiotic adjuvants to restore the therapeutic efficacy of current antibiotics.

Lactoferrin modulates the biofilm formation and bap gene expression of methicillin-resistant Staphylococcus epidermidis

Lactoferrin is an innate glycoprotein with broad antibacterial and antibiofilm properties. The autonomous antibiofilm activity of lactoferrin against Gram-positive bacteria is postulated to involve the cell wall and biofilm components. Thus, the prevention of biomass formation and eradication of preformed biofilms by lactoferrin was investigated using a methicillin-resistant Staphylococcus epidermidis (MRSE) strain. Additionally, the ability of lactoferrin to modulate the expression of the biofilm-associated protein gene (bap) was studied. The bap gene regulates the production of biofilm-associated proteins responsible for bacterial adhesion and aggregation. In the in vitro biofilm assays, lactoferrin prevented biofilm formation and eradicated established biofilms for up to 24 and 72 h, respectively. Extensive eradication of MRSE biofilm biomass was accompanied by the significant upregulation of bap gene expression. These data suggest the interaction of lactoferrin with the biofilm components and cell wall of MRSE, including the biofilm-associated protein.

The biofilm matrix: multitasking in a shared space

The biofilm matrix can be considered to be a shared space for the encased microbial cells, comprising a wide variety of extracellular polymeric substances (EPS), such as polysaccharides, proteins, amyloids, lipids and extracellular DNA (eDNA), as well as membrane vesicles and humic-like microbially derived refractory substances. EPS are dynamic in space and time and their components interact in complex ways, fulfilling various functions: to stabilize the matrix, acquire nutrients, retain and protect eDNA or exoenzymes, or offer sorption sites for ions and hydrophobic substances. The retention of exoenzymes effectively renders the biofilm matrix an external digestion system influencing the global turnover of biopolymers, considering the ubiquitous relevance of biofilms. Physico-chemical and biological interactions and environmental conditions enable biofilm systems to morph into films, microcolonies and macrocolonies, films, ridges, ripples, columns, pellicles, bubbles, mushrooms and suspended aggregates - in response to the very diverse conditions confronting a particular biofilm community. Assembly and dynamics of the matrix are mostly coordinated by secondary messengers, signalling molecules or small RNAs, in both medically relevant and environmental biofilms. Fully deciphering how bacteria provide structure to the matrix, and thus facilitate and benefit from extracellular reactions, remains the challenge for future biofilm research.

Bacteriophages as Biotechnological Tools

Bacteriophages are ubiquitous organisms that can be specific to one or multiple strains of hosts, in addition to being the most abundant entities on the planet. It is estimated that they exceed ten times the total number of bacteria. They are classified as temperate, which means that phages can integrate their genome into the host genome, originating a prophage that replicates with the host cell and may confer immunity against infection by the same type of phage; and lytics, those with greater biotechnological interest and are viruses that lyse the host cell at the end of its reproductive cycle. When lysogenic, they are capable of disseminating bacterial antibiotic resistance genes through horizontal gene transfer. When professionally lytic-that is, obligately lytic and not recently descended from a temperate ancestor-they become allies in bacterial control in ecological imbalance scenarios; these viruses have a biofilm-reducing capacity. Phage therapy has also been advocated by the scientific community, given the uniqueness of issues related to the control of microorganisms and biofilm production when compared to other commonly used techniques. The advantages of using bacteriophages appear as a viable and promising alternative. This review will provide updates on the landscape of phage applications for the biocontrol of pathogens in industrial settings and healthcare.

eDNA-stimulated cell dispersion from Caulobacter crescentus biofilms upon oxygen limitation is dependent on a toxin-antitoxin system

In their natural environment, most bacteria preferentially live as complex surface-attached multicellular colonies called biofilms. Biofilms begin with a few cells adhering to a surface, where they multiply to form a mature colony. When conditions deteriorate, cells can leave the biofilm. This dispersion is thought to be an important process that modifies the overall biofilm architecture and that promotes colonization of new environments. In Caulobacter crescentus biofilms, extracellular DNA (eDNA) is released upon cell death and prevents newborn cells from joining the established biofilm. Thus, eDNA promotes the dispersal of newborn cells and the subsequent colonization of new environments. These observations suggest that eDNA is a cue for sensing detrimental environmental conditions in the biofilm. Here, we show that the toxin-antitoxin system (TAS) ParDE4 stimulates cell death in areas of a biofilm with decreased O2 availability. In conditions where O2 availability is low, eDNA concentration is correlated with cell death. Cell dispersal away from biofilms is decreased when parDE4 is deleted, probably due to the lower local eDNA concentration. Expression of parDE4 is positively regulated by O2 and the expression of this operon is decreased in biofilms where O2 availability is low. Thus, a programmed cell death mechanism using an O2-regulated TAS stimulates dispersal away from areas of a biofilm with decreased O2 availability and favors colonization of a new, more hospitable environment.

Antimicrobial Treatment of Staphylococcus aureus Biofilms

Staphylococcus aureus is a microorganism frequently associated with implant-related infections, owing to its ability to produce biofilms. These infections are difficult to treat because antimicrobials must cross the biofilm to effectively inhibit bacterial growth. Although some antibiotics can penetrate the biofilm and reduce the bacterial load, it is important to understand that the results of routine sensitivity tests are not always valid for interpreting the activity of different drugs. In this review, a broad discussion on the genes involved in biofilm formation, quorum sensing, and antimicrobial activity in monotherapy and combination therapy is presented that should benefit researchers engaged in optimizing the treatment of infections associated with S. aureus biofilms.

Distinct Long- and Short-Term Adaptive Mechanisms in Pseudomonas aeruginosa

Heterogeneous environments such as the chronically infected cystic fibrosis lung drive the diversification of Pseudomonas aeruginosa populations into, e.g., mucoid, alginate-overproducing isolates or small-colony variants (SCVs). In this study, we performed extensive genome and transcriptome profiling on a clinical SCV isolate that exhibited high cyclic diguanylate (c-di-GMP) levels and a mucoid phenotype. We observed a delayed, stepwise decrease of the high levels of c-di-GMP as well as alginate gene expression upon passaging the SCV under noninducing, rich medium growth conditions over 7 days. Upon prolonged passaging, this lagging reduction of the high c-di-GMP levels under noninducing planktonic conditions (reminiscent of a hysteretic response) was followed by a phenotypic switch to a large-colony morphology, which could be linked to mutations in the Gac/Rsm signaling pathway. Complementation of the Gac/Rsm signaling-negative large-colony variants with a functional GacSA system restored the SCV colony morphotype but was not able to restore the high c-di-GMP levels of the SCV. Our data thus suggest that expression of the SCV colony morphotype and modulation of c-di-GMP levels are genetically separable and follow different evolutionary paths. The delayed switching of c-di-GMP levels in response to fluctuating environmental conditions might provide a unique opportunity to include a time dimension to close the gap between short-term phenotypic and long-term genetic adaptation to biofilm-associated growth conditions. IMPORTANCE Extreme environments, such as those encountered during an infection process in the human host, make effective bacterial adaptation inevitable. While bacteria adapt individually by activating stress responses, long-term adaptation of bacterial communities to challenging conditions can be achieved via genetic fixation of favorable traits. In this study, we describe a two-pronged bacterial stress resistance strategy in the opportunistic pathogen Pseudomonas aeruginosa. We show that the production of adjusted elevated c-di-GMP levels, which drive protected biofilm-associated phenotypes in vivo, resembles a stable hysteretic response which prevents unwanted frequent switching. Cellular hysteresis might provide a link between individual adaptability and evolutionary adaptation to ensure the evolutionary persistence of host-adapted stress response strategies.

The Alginate and Motility Regulator AmrZ is Essential for the Regulation of the Dispersion Response by Pseudomonas aeruginosa Biofilms

Dispersion is an active process exhibited by Pseudomonas aeruginosa during the late stages of biofilm development or in response to various cues, including nitric oxide and glutamate. Upon cue sensing, biofilm cells employ enzymes that actively degrade the extracellular matrix, thereby allowing individual cells to become liberated. While the mechanism by which P. aeruginosa senses and relays dispersion cues has been characterized, little is known about how dispersion cue sensing mechanisms result in matrix degradation. Considering that the alginate and motility regulator AmrZ has been reported to regulate genes that play a role in dispersion, including those affecting virulence, c-di-GMP levels, Pel and Psl abundance, and motility, we asked whether AmrZ contributes to the regulation of dispersion. amrZ was found to be significantly increased in transcript abundance under dispersion-inducing conditions, with the inactivation of amrZ impairing dispersion by P. aeruginosa biofilms in response to glutamate and nitric oxide. While the overexpression of genes encoding matrix-degrading enzymes pelA, pslG, and/or endA resulted in the dispersion of wild-type biofilms, similar conditions failed to disperse biofilms formed by dtamrZ. Likewise, the inactivation of amrZ abrogated the hyperdispersive phenotype of PAO1/pJN-bdlA_G31A biofilms, with dtamrZ-impaired dispersion being independent of the expression, production, and activation of BdlA. Instead, dispersion was found to require the AmrZ-target genes napB and PA1891. Our findings indicate that AmrZ is essential for the regulation of dispersion by P. aeruginosa biofilms, functions downstream of BdlA postdispersion cue sensing, and regulates the expression of genes contributing to biofilm matrix degradation as well as napB and PA1891. IMPORTANCE In P. aeruginosa, biofilm dispersion has been well-characterized with respect to dispersion cue perception, matrix degradation, and the consequences of dispersion. While the intracellular signaling molecule c-di-GMP has been linked to many of the phenotypic changes ascribed to dispersion, including the modulation of motility and matrix production, little is known about the regulatory mechanisms leading to matrix degradation and cells actively leaving the biofilm. In this study, we report for the first time an essential role of the transcriptional regulator AmrZ and two AmrZ-dependent genes, napB, and PA1891, in the dispersion response, thereby linking dispersion cue sensing via BdlA to the regulation of matrix degradation and to the ultimate liberation of bacterial cells from the biofilm.

Biofilm Control in Flow-Through Systems Using Polyvalent Phages Delivered by Peptide-Modified M13 Coliphages with Enhanced Polysaccharide Affinity

Eradication of biofilms that may harbor pathogens in water distribution systems is an elusive goal due to limited penetration of residual disinfectants. Here, we explore the use of engineered filamentous coliphage M13 for enhanced biofilm affinity and precise delivery of lytic polyvalent phages (i.e., broad-host-range phages lysing multiple host strains after infection). To promote biofilm attachment, we modified the M13 major coat protein (pVIII) by inserting a peptide sequence with high affinity for Pseudomonas aeruginosa (P. aeruginosa) extracellular polysaccharides (commonly present on the surface of biofilms in natural and engineered systems). Additionally, we engineered the M13 tail fiber protein (pIII) to contain a peptide sequence capable of binding a specific polyvalent lytic phage. The modified M13 had 102- and 5-fold higher affinity for P. aeruginosa-dominated mixed-species biofilms than wildtype M13 and unconjugated polyvalent phage, respectively. When applied to a simulated water distribution system, the resulting phage conjugates achieved targeted phage delivery to the biofilm and were more effective than polyvalent phages alone in reducing live bacterial biomass (84 vs 34%) and biofilm surface coverage (81 vs 22%). Biofilm regrowth was also mitigated as high phage concentrations induced residual bacteria to downregulate genes associated with quorum sensing and extracellular polymeric substance secretion. Overall, we demonstrate that engineered M13 can enable more accurate delivery of polyvalent phages to biofilms in flow-through systems for enhanced biofilm control.

Pathogens transported by plastic debris: does this vector pose a risk to aquatic organisms?

Microplastics are small (<5 mm) plastic particles of varying shapes and polymer types that are now widespread global contaminants of marine and freshwater ecosystems. Various estimates suggest that several trillions of microplastic particles are present in our global oceanic system, and that these are readily ingested by a wide range of marine and freshwater species across feeding modes and ecological niches. Here, we present some of the key and pressing issues associated with these globally important contaminants from a microbiological perspective. We discuss the potential mechanisms of pathogen attachment to plastic surfaces. We then describe the ability of pathogens (both human and animal) to form biofilms on microplastics, as well as dispersal of these bacteria, which might lead to their uptake into aquatic species ingesting microplastic particles. Finally, we discuss the role of a changing oceanic system on the potential of microplastic-associated pathogens to cause various disease outcomes using numerous case studies. We set out some key and imperative research questions regarding this globally important issue and present a methodological framework to study how and why plastic-associated pathogens should be addressed.

Surface antimicrobial functionalization with polymers: fabrication, mechanisms and applications

Undesirable adhesion of microbes such as bacteria, fungi and viruses onto surfaces affects many industries such as marine, food, textile, and healthcare. In particular in healthcare and food packaging, the effects of unwanted microbial contamination can be life-threatening. With the current global COVID-19 pandemic, interest in the development of surfaces with superior anti-viral and anti-bacterial activities has multiplied. Polymers carrying anti-microbial properties are extensively used to functionalize material surfaces to inactivate infection-causing and biocide-resistant microbes including COVID-19. This review aims to introduce the fabrication of polymer-based antimicrobial surfaces through physical and chemical modifications, followed by the discussion of the inactivation mechanisms of conventional biocidal agents and new-generation antimicrobial macromolecules in polymer-modified antimicrobial surfaces. The advanced applications of polymer-based antimicrobial surfaces on personal protective equipment against COVID-19, food packaging materials, biomedical devices, marine vessels and textiles are also summarized to express the research trend in academia and industry.

Novel prokaryotic system employing previously unknown nucleic acids-based receptors

The present study describes a previously unknown universal system that orchestrates the interaction of bacteria with the environment, named the Teazeled receptor system (TR-system). The identical system was recently discovered within eukaryotes. The system includes DNA- and RNA-based molecules named "TezRs", that form receptor's network located outside the membrane, as well as reverse transcriptases and integrases. TR-system takes part in the control of all major aspects of bacterial behavior, such as intra cellular communication, growth, biofilm formation and dispersal, utilization of nutrients including xenobiotics, virulence, chemo- and magnetoreception, response to external factors (e.g., temperature, UV, light and gas content), mutation events, phage-host interaction, and DNA recombination activity. Additionally, it supervises the function of other receptor-mediated signaling pathways. Importantly, the TR-system is responsible for the formation and maintenance of cell memory to preceding cellular events, as well the ability to "forget" preceding events. Transcriptome and biochemical analysis revealed that the loss of different TezRs instigates significant alterations in gene expression and proteins synthesis.

Biofilms: Formation, Research Models, Potential Targets, and Methods for Prevention and Treatment

Due to the continuous rise in biofilm-related infections, biofilms seriously threaten human health. The formation of biofilms makes conventional antibiotics ineffective and dampens immune clearance. Therefore, it is important to understand the mechanisms of biofilm formation and develop novel strategies to treat biofilms more effectively. This review article begins with an introduction to biofilm formation in various clinical scenarios and their corresponding therapy. Established biofilm models used in research are then summarized. The potential targets which may assist in the development of new strategies for combating biofilms are further discussed. The novel technologies developed recently for the prevention and treatment of biofilms including antimicrobial surface coatings, physical removal of biofilms, development of new antimicrobial molecules, and delivery of antimicrobial agents are subsequently presented. Finally, directions for future studies are pointed out.

Eco-Friendly Solution Based on Rosmarinus officinalis Hydro-Alcoholic Extract to Prevent Biodeterioration of Cultural Heritage Objects and Buildings

Biodeterioration of cultural heritage is caused by different organisms capable of inducing complex alteration processes. The present study aimed to evaluate the efficiency of Rosmarinus officinalis hydro-alcoholic extract to inhibit the growth of deteriogenic microbial strains. For this, the physico-chemical characterization of the vegetal extract by UHPLC–MS/MS, its antimicrobial and antibiofilm activity on a representative number of biodeteriogenic microbial strains, as well as the antioxidant activity determined by DPPH, CUPRAC, FRAP, TEAC methods, were performed. The extract had a total phenol content of 15.62 ± 0.97 mg GAE/mL of which approximately 8.53% were flavonoids. The polyphenolic profile included carnosic acid, carnosol, rosmarinic acid and hesperidin as major components. The extract exhibited good and wide spectrum antimicrobial activity, with low MIC (minimal inhibitory concentration) values against fungal strains such as Aspergillus clavatus (MIC = 1.2 mg/mL) and bacterial strains such as Arthrobacter globiformis (MIC = 0.78 mg/mL) or Bacillus cereus (MIC = 1.56 mg/mL). The rosemary extract inhibited the adherence capacity to the inert substrate of Penicillium chrysogenum strains isolated from wooden objects or textiles and B. thuringiensis strains. A potential mechanism of R. officinalis antimicrobial activity could be represented by the release of nitric oxide (NO), a universal signalling molecule for stress management. Moreover, the treatment of microbial cultures with subinhibitory concentrations has modulated the production of microbial enzymes and organic acids involved in biodeterioration, with the effect depending on the studied microbial strain, isolation source and the tested soluble factor. This paper reports for the first time the potential of R. officinalis hydro-alcoholic extract for the development of eco-friendly solutions dedicated to the conservation/safeguarding of tangible cultural heritage.

Impacts from Waste Oyster Shell on the Durability and Biological Attachment of Recycled Aggregate Porous Concrete for Artificial Reef

Poor biological attachment of artificial reef (AR) prepared by the recycled aggregate limit the application in the area of marine engineering. In this study, the waste oyster shell (WOS) was used as raw materials to prepare the recycled aggregate porous concrete (RAPC), the compressive strength, split tensile strength, chloride penetration resistance, freezing-thawing resistance, low temperature resistance, and the biological attachment were tested, aiming to improve the biological attachment and decrease carbon dioxide emission. The experiment results demonstrate that the use of WOS can decrease the compressive and split tensile strength, but the effect of designed porous structure on the mechanical strength is higher than that of WOS. To ensure the durability of RAPC, the contents of WOS should not exceed 20%. Additionally, the addition of WOS and designed porous structure are beneficial to biological attachment. However, the porous structure of RAPC only improves biological attachment in the short term, and the reverse phenomenon is true in the long term. As the partial replacement of cement with WOS is 40%, the total carbon dioxide emission decreases by about 52%. In conclusion, the use of WOS in the RAPC is an eco-friendly method in the artificial reef (AR) with improved ecological attachment and reduced carbon dioxide emission.

The journey of hull-fouling mobile invaders: basibionts and boldness mediate dislodgement risk during transit

Vessel hull-fouling is responsible for most bioinvasion events in the marine environment, yet it lacks regulation in most countries. Although experts advocate a preventative approach, research efforts on pre-arrival processes are limited. The performance of mobile epifauna during vessel transport was evaluated via laboratory simulations, using the well-known invasive Japanese skeleton shrimp (Caprella mutica), and its native congener C. laeviuscula as case study. The invader did not possess any advantage in terms of inherent resistance to drag. Instead, its performance was conditioned by the complexity of secondary substrate. Dislodgement risk was significantly reduced when sessile fouling basibionts were added, which provided refugia and boosted the probability of C. mutica remaining attached from 7 to 65% in flow exposure trials. Interestingly, the invader exhibited significantly higher exploratory tendency and motility than its native congener at zero-flow conditions. Implications in terms of en-route survivorship, invasion success and macrofouling management are discussed.

Treatment of Pseudomonas aeruginosa infectious biofilms: Challenges and strategies

Pseudomonas aeruginosa, a Gram-negative bacterium, is one of the major pathogens implicated in human opportunistic infection and a common cause of clinically persistent infections such as cystic fibrosis, urinary tract infections, and burn infections. The main reason for the persistence of P. aeruginosa infections is due to the ability of P. aeruginosa to secrete extracellular polymeric substances such as exopolysaccharides, matrix proteins, and extracellular DNA during invasion. These substances adhere to and wrap around bacterial cells to form a biofilm. Biofilm formation leads to multiple antibiotic resistance in P. aeruginosa, posing a significant challenge to conventional single antibiotic therapeutic approaches. It has therefore become particularly important to develop anti-biofilm drugs. In recent years, a number of new alternative drugs have been developed to treat P. aeruginosa infectious biofilms, including antimicrobial peptides, quorum-sensing inhibitors, bacteriophage therapy, and antimicrobial photodynamic therapy. This article briefly introduces the process and regulation of P. aeruginosa biofilm formation and reviews several developed anti-biofilm treatment technologies to provide new directions for the treatment of P. aeruginosa biofilm infection.

Bacterial growth in multicellular aggregates leads to the emergence of complex life cycles

Facultative multicellular behaviors expand the metabolic capacity and physiological resilience of bacteria. Despite their ubiquity in nature, we lack an understanding of how these behaviors emerge from cellular-scale phenomena. Here, we show how the coupling between growth and resource gradient formation leads to the emergence of multicellular lifecycles in a marine bacterium. Under otherwise carbon-limited growth conditions, Vibrio splendidus 12B01 forms clonal multicellular groups to collectively harvest carbon from soluble polymers of the brown-algal polysaccharide alginate. As they grow, groups phenotypically differentiate into two spatially distinct sub-populations: a static "shell" surrounding a motile, carbon-storing "core." Differentiation of these two sub-populations coincides with the formation of a gradient in nitrogen-source availability within clusters. Additionally, we find that populations of cells containing a high proportion of carbon-storing individuals propagate and form new clusters more readily on alginate than do populations with few carbon-storing cells. Together, these results suggest that local metabolic activity and differential partitioning of resources leads to the emergence of reproductive cycles in a facultatively multicellular bacterium.

The Association between Biofilm Formation and Antimicrobial Resistance with Possible Ingenious Bio-Remedial Approaches

Biofilm has garnered a lot of interest due to concerns in various sectors such as public health, medicine, and the pharmaceutical industry. Biofilm-producing bacteria show a remarkable drug resistance capability, leading to an increase in morbidity and mortality. This results in enormous economic pressure on the healthcare sector. The development of biofilms is a complex phenomenon governed by multiple factors. Several attempts have been made to unravel the events of biofilm formation; and, such efforts have provided insights into the mechanisms to target for the therapy. Owing to the fact that the biofilm-state makes the bacterial pathogens significantly resistant to antibiotics, targeting pathogens within biofilm is indeed a lucrative prospect. The available drugs can be repurposed to eradicate the pathogen, and as a result, ease the antimicrobial treatment burden. Biofilm formers and their infections have also been found in plants, livestock, and humans. The advent of novel strategies such as bioinformatics tools in treating, as well as preventing, biofilm formation has gained a great deal of attention. Development of newfangled anti-biofilm agents, such as silver nanoparticles, may be accomplished through omics approaches such as transcriptomics, metabolomics, and proteomics. Nanoparticles’ anti-biofilm properties could help to reduce antimicrobial resistance (AMR). This approach may also be integrated for a better understanding of biofilm biology, guided by mechanistic understanding, virtual screening, and machine learning in silico techniques for discovering small molecules in order to inhibit key biofilm regulators. This stimulated research is a rapidly growing field for applicable control measures to prevent biofilm formation. Therefore, the current article discusses the current understanding of biofilm formation, antibiotic resistance mechanisms in bacterial biofilm, and the novel therapeutic strategies to combat biofilm-mediated infections.

Estuarine plastisphere as an overlooked source of N2O production

“Plastisphere”, microbial communities colonizing plastic debris, has sparked global concern for marine ecosystems. Microbiome inhabiting this novel human-made niche has been increasingly characterized; however, whether the plastisphere holds crucial roles in biogeochemical cycling remains largely unknown. Here we evaluate the potential of plastisphere in biotic and abiotic denitrification and nitrous oxide (N₂O) production in estuaries. Biofilm formation provides anoxic conditions favoring denitrifiers. Comparing with surrounding bulk water, plastisphere exhibits a higher denitrifying activity and N₂O production, suggesting an overlooked N₂O source. Regardless of plastisphere and bulk water, bacterial and fungal denitrifications are the main regulators for N₂O production instead of chemodenitrification. However, the contributions of bacteria and fungi in the plastisphere are different from those in bulk water, indicating a distinct N₂O production pattern in the plastisphere. These findings pinpoint plastisphere as a N₂O source, and provide insights into roles of the new biotope in biogeochemical cycling in the Anthropocene.

The roles of marine plastisphere in global nitrogen cycling are largely unknown. Here, the authors indicate that the plastisphere could act as a potential source of N2O production, which is mainly regulated by the biotic denitrification

Current treatments for biofilm-associated periprosthetic joint infection and new potential strategies

Periprosthetic joint infection (PJI) remains a devastating complication after total joint arthroplasty. Bacteria involved in these infections are notorious for adhering to foreign implanted surfaces and generating a biofilm matrix. These biofilms protect the bacteria from antibiotic treatment and the immune system making eradication difficult. Current treatment strategies including debridement, antibiotics, and implant retention, and one- and two-stage revisions still present a relatively high overall failure rate. One of the main shortcomings that has been associated with this high failure rate is the lack of a robust approach to treating bacterial biofilm. Therefore, in this review, we will highlight new strategies that have the potential to combat PJI by targeting biofilm integrity, therefore giving antibiotics and the immune system access to the internal network of the biofilm structure. This combination antibiofilm/antibiotic therapy may be a new strategy for PJI treatment while promoting implant retention.

Quorum sensing inhibitory potential of vaccenic acid against Chromobacterium violaceum and methicillin-resistant Staphylococcus aureus

Quorum sensing (QS) is a potential target for inhibiting bacterial antibiotic resistance and associated pathogenicity. The present study aimed to investigate vaccenic acid anti-QS and antibiofilm potential against Chromobacterium violaceum and methicillin-resistant Staphylococcus aureus (MRSA). In the broth microdilution method, we determined the minimum inhibitory concentration (MIC) of vaccenic acid against C. violaceum and MRSA. Then, we determined the vaccenic acid anti-QS potential against C. violaceum via a violacein inhibition assay. Vaccenic acid at a sub-MIC concentration significantly inhibited violacein pigment production. Vaccenic acid also inhibits C. violaceum and MRSA biofilm formation at sub-MIC concentrations. The effect of vaccenic acid antivirulence potential was evaluated by phenotypic virulence assays. The results showed that vaccenic acid at a sub-MIC concentration significantly inhibited the virulence production of C. violaceum (chitinase and motility) and MRSA (hemolysin and staphyloxanthin production). Quantitative PCR analysis revealed the downregulation of QS associated genes upon vaccenic acid treatment. This resulted in the downregulation of genes involved in QS mechanisms such as cviI, cviR, and SarA and pigment production such as vioB and crtM. The results of the present study suggest that vaccenic acid is a promising agent to combat C. violaceum and MRSA.

Boswellic Acids as Effective Antibacterial Antibiofilm Agents

Boswellic acids are biologically active pentacyclic terpenoid compounds derived from Boswellia sp. plants. Extracts containing these acids have a number of positive effects on human health, especially in the treatment of inflammation, arthritis, or asthma. With increasing resistance to common antibiotics, boswellic acid-containing extracts could serve as an alternative or work in synergy with commonly available preparations. This study aims to determine the effect of boswellic acids on suspension cells and biofilms of Staphylococcus epidermidis, Enterococcus faecalis, and Escherichia coli. The antimicrobial and antibiofilm effect found was compared with commonly available antibiotics to control these undesirable microorganisms. The synergistic effect of boswellic acids and common antibiotics on the growth of these microorganisms was also determined. All tested microorganisms showed a positive additive effect of antibiotics and boswellic acid extract. The most significant effect was found in Enterococcus faecalis ATCC 29212 in a combination of 0.2 × MIC80 erythromycin (0.2 mg/L) and 0.8 × MIC80 boswellic acid extract (16 mg/L).

Mechanisms Underlying Vibrio cholerae Biofilm Formation and Dispersion

Biofilms are a widely observed growth mode in which microbial communities are spatially structured and embedded in a polymeric extracellular matrix. Here, we focus on the model bacterium Vibrio cholerae and summarize the current understanding of biofilm formation, including initial attachment, matrix components, community dynamics, social interactions, molecular regulation, and dispersal. The regulatory network that orchestrates the decision to form and disperse from biofilms coordinates various environmental inputs. These cues are integrated by several transcription factors, regulatory RNAs, and second-messenger molecules, including bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP). Through complex mechanisms, V. cholerae weighs the energetic cost of forming biofilms against the benefits of protection and social interaction that biofilms provide. Expected final online publication date for the Annual Review of Microbiology, Volume 76 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Relationship Between Antibiotic Resistance, Biofilm Formation, and Biofilm-Specific Resistance in Escherichia coli Isolates from Ningbo, China

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Varied solutions to multicellularity: The biophysical and evolutionary consequences of diverse intercellular bonds

The diversity of multicellular organisms is, in large part, due to the fact that multicellularity has independently evolved many times. Nonetheless, multicellular organisms all share a universal biophysical trait: cells are attached to each other. All mechanisms of cellular attachment belong to one of two broad classes; intercellular bonds are either reformable or they are not. Both classes of multicellular assembly are common in nature, having independently evolved dozens of times. In this review, we detail these varied mechanisms as they exist in multicellular organisms. We also discuss the evolutionary implications of different intercellular attachment mechanisms on nascent multicellular organisms. The type of intercellular bond present during early steps in the transition to multicellularity constrains future evolutionary and biophysical dynamics for the lineage, affecting the origin of multicellular life cycles, cell-cell communication, cellular differentiation, and multicellular morphogenesis. The types of intercellular bonds used by multicellular organisms may thus result in some of the most impactful historical constraints on the evolution of multicellularity.

Characteristics of Initial Attachment and Biofilm Formation of Pseudomonas aeruginosa on Microplastic Surfaces

The toxic effect of microplastics on living organisms is emerging as a serious environmental issue nowadays. The biofilm formed on their surface by microorganisms can further increase the toxicity, but the mechanism of biofilm formation on microplastics is not yet fully understood because of the complexities of other factors. This study aimed to identify the factors with an important influence on biofilm formation on microplastic surfaces. The microtiter plate assay was used to evaluate the biofilms formed by Pseudomonas aeruginosa PAO1, a model microorganism, on four types of microplastics, including polyethylene, polystyrene, polypropylene, and polytetrafluoroethylene. The density of microplastics was found to be a key factor in determining the amount of biofilm formation because the density relative to water has a decisive effect on the behavior of microplastics. Biofilm formation on plastics with densities similar to that of water showed remarkable differences based on surface characteristics, whereas biofilm formation on plastics with a higher density was significantly influenced by particle movement in the experimental environment. Furthermore, biofilm formation was inhibited by adding a quorum quenching enzyme, suggesting that QS is critical in biofilm formation on microplastics. This study provides useful information on biofilm formation on microplastic surfaces.

Derivatives of Esculentin-1 Peptides as Promising Candidates for Fighting Infections from Escherichia coli O157:H7

New strategies are needed to fight the emergence of multidrug-resistant bacteria caused by an overuse of antibiotics in medical and veterinary fields. Due to the importance of biofilms in clinical infections, antibiofilm peptides have a great potential to treat infections. In recent years, an increased interest has emerged in antimicrobial peptides (AMPs). One of the richest sources of AMPs is represented by amphibian skin. In the present work, we investigated the effects of two peptides derived from the frog skin AMP esculentin-1, namely, Esc(1-21) and Esc(1-18), on the growth, biofilm formation, and gene expression of the non-pathogenic Escherichia coli strain K12 and of enterohemorrhagic E. coli O157:H7. Both peptides showed minimal bactericidal concentrations ranging from 4 to 8 µM for Esc(1-21) and from 32 to 64 µM for Esc(1-18). They also, at sub-MIC doses, reduced the formation of biofilm, as supported by both microbiological assays and scanning electron microscopy, while they displayed no marked activity against the planktonic form of the bacteria. Transcriptional analysis in E. coli O157:H7 showed that both AMPs induced the expression of several genes involved in the regulation of formation and dispersal of biofilm, as well as in the stress response. In conclusion, we demonstrated that these AMPs affect E. coli O157:H7 growth and biofilm formation, thus suggesting a great potential to be developed as novel therapeutics against infections caused by bacterial biofilms.

A hyaluronic acid-based nanogel for the co-delivery of nitric oxide (NO) and a novel antimicrobial peptide (AMP) against bacterial biofilms

Biofilms are a global health concern because they are associated with chronic and recurrent infections as well as resistance to conventional antibiotics. The aim of this study was to prepare a nanogel for the co-delivery of NO and AMPs against bacteria and biofilms. The NO-releasing nanogel was prepared by crosslinking HA solution with divinyl sulfone and extensively characterized. The nanogel was found to be biocompatible, injectable and NO release from the gel was sustained over a period of 24 h. In vitro antibacterial studies showed that the NO-AMP-loaded nanogel exhibited a broad spectrum antibacterial/antibiofilm activity. The NO-releasing nanogel had a greater antibacterial effect when compared to NO alone with MIC values of 1.56, 0.78 and 0.39 μg/ml against Escherichia coli, Methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa bacteria respectively. The antibiofilm results showed there was a 12.5 and 24-folds reduction in biofilms of MRSA, and P. aeruginosa respectively for catheters exposed to nanogel loaded with AMP/NO when compared to only NO, while a 7 and 9.4-folds reduction in biofilms of MRSA, and P. aeruginosa respectively was displayed by the nanogel loaded with only NO compared to only NO. The AMP/NO-releasing nanogel showed the potential to combat both biofilms and bacterial infections.

A new mode of swimming in singly flagellated Pseudomonas aeruginosa

SignificanceThe monotrichous Pseudomonas aeruginosa was usually thought to swim in a pattern of "run and reverse" (possibly with pauses in between), where straight runs alternated with reverses with angular changes of swimming direction near 180°. Here, by simultaneously tracking the cell swimming and the morphology of its flagellum, we discovered a swimming mode in P. aeruginosa-the wrap mode, during which the flagellar filament wrapped around the cell body and induced large fluctuation of the body orientation. The wrap mode randomized swimming direction, resulting in a broad distribution of angular changes over 0 to 180° with a peak near 90°. This allowed the bacterium to explore the environment more efficiently, which we confirmed by stochastic simulations of P. aeruginosa chemotaxis.

Spatial regulation of cell motility and its fitness effect in a surface-attached bacterial community

On a surface, microorganisms grow into a multi-cellular community. When a community becomes densely populated, cells migrate away to expand the community's territory. How microorganisms regulate surface motility to optimize expansion remains poorly understood. Here, we characterized surface motility of Proteus mirabilis. P. mirabilis is well known for its ability to expand its colony rapidly on a surface. Cursory visual inspection of an expanding colony suggests partial migration, i.e., one fraction of a population migrates while the other is sessile. Quantitative microscopic imaging shows that this migration pattern is determined by spatially inhomogeneous regulation of cell motility. Further analyses reveal that this spatial regulation is mediated by the Rcs system, which represses the expression of the motility regulator (FlhDC) in a nutrient-dependent manner. Alleviating this repression increases the colony expansion speed but results in a rapid drop in the number of viable cells, lowering population fitness. These findings collectively demonstrate how Rcs regulates cell motility dynamically to increase the fitness of an expanding bacterial population, illustrating a fundamental trade-off underlying bacterial colonization of a surface.

The possible modes of microbial reproduction are fundamentally restricted by distribution of mass between parent and offspring

Cells and simple cell colonies reproduce by fragmenting their bodies into pieces. Produced newborns need to grow before they can reproduce again. How big a cell or a cell colony should grow? How many offspring should be produced? Should they be of equal size or diverse? We show that the simple fact that the immediate mass of offspring cannot exceed the mass of parents restricts possible answers to these questions. For example, our theory states that, when mass is conserved in the course of fragmentation, the evolutionarily optimal reproduction mode is fragmentation into exactly two, typically equal, parts. Our theory also shows conditions which promote evolution of asymmetric division or fragmentation into multiple pieces.

Multiple modes of asexual reproduction are observed among microbial organisms in natural populations. These modes are not only subject to evolution, but may drive evolutionary competition directly through their impact on population growth rates. The most prominent transition between two such modes is the one from unicellularity to multicellularity. We present a model of the evolution of reproduction modes, where a parent organism fragments into smaller parts. While the size of an organism at fragmentation, the number of offspring, and their sizes may vary a lot, the combined mass of fragments is limited by the mass of the parent organism. We found that mass conservation can fundamentally limit the number of possible reproduction modes. This has important direct implications for microbial life: For unicellular species, the interplay between cell shape and kinetics of the cell growth implies that the largest and the smallest possible cells should be rod shaped rather than spherical. For primitive multicellular species, these considerations can explain why rosette cell colonies evolved a mechanistically complex binary split reproduction. Finally, we show that the loss of organism mass during sporulation can explain the macroscopic sizes of the formally unicellular microorganism Myxomycetes plasmodium. Our findings demonstrate that a number of seemingly unconnected phenomena observed in unrelated species may be different manifestations of the same underlying process.

Impact of different enzymes on biofilm formation and mussel settlement

Enzymes have been known to impact the biofilm forming capacity. However, how the enzymes mediate the biofilm formation and macrofouling remains little known. Here, we investigated the effects of the three kinds of proteases, four kinds of glycosidases and one kind of lipase on the detachment of biofilms of Shewanella marisflavi ECSMB14101, identified biofilm total proteins response to enzyme treatments, and then tested the effects of biofilms treated with enzymes on the settlement of the mussel Mytilus coruscus plantigrades. The results showed that the cell density of bacteria in biofilms formed at different initial bacterial density were noticeably reduced after treating with all tested enzymes, and Neutrase and α-Amylase exhibited best removing efficiency of > 90%. Bacterial total proteins in S. marisflavi biofilm noticeably reduced or disappeared after treated by Alcalase. For the settlements of the mussel M. coruscus plantigrades, inducing capacities of S. marisflavi biofilm were noticeably suppressed and downregulation was > 75% at the initial density of 5 × 10⁶ cells/cm². Thus, the tested enzymes could effectively remove the adhered bacterial cell, inhibit the biofilm formation and finally suppress the mussel settlement. Our findings extend novel knowledge to developing eco-friendly approach to control micro- and macro-fouling.