Solitary foundation or colony fission in ants: an intraspecific study shows that worker presence and number increase colony foundation success

Dispersal and establishment strategies are highly variable. Each strategy is associated with specific costs and benefits, and understanding which factors favour or disfavour a strategy is a key issue in ecology and evolution. Ants exhibit several strategies of establishment, i.e. of colony foundation. Some species rely on winged queens that found new colonies alone when others found with accompanying workers (colony fission). The benefits conferred by these workers have been little studied and quantified, because comparing the costs and benefits of solitary foundation vs. colony fission is difficult when comparing different species. We investigated this using the ant Myrmecina graminicola, one of the few species that use both strategies. Young mated queens were allowed to found new colonies in the laboratory, with either zero (solitarily), two or four workers (colony fission). The presence of workers increased both survival and growth of the foundations over the first year, with more workers yielding higher growth. Few workers (as little as two workers) were sufficient to provide benefits, suggesting that in M. graminicola the strategy of colony fission may not dramatically decrease the number of new colonies produced compared to solitary foundation. Because queens performing solitary foundation or colony fission differ in dispersal (by flight vs. on foot), our results support the hypothesis that these two strategies of foundation coexist along a competition-colonization trade-off, where solitary foundation offers a colonization advantage, while colony fission has a competitive advantage.

Methods for Studying Swimming and Surface Motilities in Rhizobia

Rhizobia are soil proteobacteria able to establish a nitrogen-fixing interaction with legumes. In this interaction, rhizobia must colonize legume roots, infect them, and become hosted inside new organs formed by the plants and called nodules. Rhizobial motility, not being essential for symbiosis, might affect the degree of success of the interaction with legumes. Because of this, the study of rhizobial motility (either swimming or surface motility) might be of interest for research teams working on rhizobial symbiotic performance. In this chapter, we describe the protocols we use in our laboratories for studying the different types of motilities exhibited by Sinorhizobium fredii and Sinorhizobium meliloti, as well as for analyzing the presence of flagella in these bacteria. All these protocols might be used (or adapted) for studying bacterial motility in rhizobia.

Implication of Mn-cofactored superoxide dismutase in the tolerance of swarmer Pseudomonas aeruginosa to polymixin, ciprofloxacin and meropenem antibiotics

The protective role of superoxide dismutase (Sod) against oxidative stress, resulting from the common antibiotic pathway of action, has been studied in the wild type and mutant strains of swarmer Pseudomonas aeruginosa, lacking Cytosolic Mn-Sod (sodM), Fe-Sod (sodB) or both Sods (sodMB).Our results showed that inactivation of sodB genes leads to significant motility defects and tolerance to meropenem. This resistance is correlated with a greater membrane unsaturation as well as an effective intervention of Mn-Sod isoform, in antibiotic tolerance.Moreover, loss of Mn-Sod in sodM mutant, leads to polymixin intolerance and is correlated with membrane unsaturation. Effectivelty, sodM mutant showed an enhanced swarming motility and a conserved rhamnolipid production. Whereas, in the double mutant sodMB, ciprofloxacin tolerance would be linked to an increase in the percentage of saturated fatty acids in the membrane, even in the absence of superoxide dismutase activity.The overall results showed that Mn-Sod has a protective role in the tolerance to antibiotics, in swarmer P.aeruginosa strain. It has been further shown that Sod intervention in antibiotic tolerance is through change in membrane fatty acid composition.

Field bands of marching locust juveniles show carbohydrate, not protein, limitation

Locusts are grasshoppers that migrate en masse and devastate food security, yet little is known about the nutritional needs of marching bands in nature. While it has been hypothesized that protein limitation promotes locust marching behavior, migration is fueled by dietary carbohydrates. We studied South American Locust (Schistocerca cancellata) bands at eight sites across Argentina, Bolivia, and Paraguay. Bands ate most frequently from dishes containing carbohydrate artificial diets and minimally from balanced, protein, or control (vitamins and salts) dishes-indicating carbohydrate hunger. This hunger for carbohydrates is likely explained by the observation that local vegetation was generally protein-biased relative to locusts' preferred protein to carbohydrate ratio. This study highlights the importance of studying the nutritional ecology of animals in their environment and suggests that carbohydrate limitation may be a common pattern for migrating insect herbivores.

Understanding how bacterial collectives organize on surfaces by tracking surfactant flow

Swarming is a collective bacterial behavior in which a dense population of bacterial cells moves over a porous surface, resulting in the expansion of the population. This collective behavior can guide bacteria away from potential stressors such as antibiotics and bacterial viruses. However, the mechanisms responsible for the organization of swarms are not understood. Here, we briefly review models that are based on bacterial sensing and fluid mechanics that are proposed to guide swarming in the pathogenic bacterium Pseudomonas aeruginosa. To provide further insight into the role of fluid mechanics in P. aeruginosa swarms, we track the movement of tendrils and the flow of surfactant using a novel technique that we have developed, Imaging of Reflected Illuminated Structures (IRIS). Our measurements show that tendrils and surfactants form distinct layers that grow in lockstep with each other. The results raise new questions about existing swarming models and the possibility that the flow of surfactants impacts tendril development. These findings emphasize that swarm organization involves an interplay between biological processes and fluid mechanics.

Iron Memory in E. coli

The importance of memory in bacterial decision-making is relatively unexplored. We show here that a prior experience of swarming is remembered when E. coli encounters a new surface, improving its future swarming efficiency. We conducted >10,000 single-cell swarm assays to discover that cells store memory in the form of cellular iron levels. This memory pre-exists in planktonic cells, but the act of swarming reinforces it. A cell with low iron initiates swarming early and is a better swarmer, while the opposite is true for a cell with high iron. The swarming potential of a mother cell, whether low or high, is passed down to its fourth-generation daughter cells. This memory is naturally lost by the seventh generation, but artificially manipulating iron levels allows it to persist much longer. A mathematical model with a time-delay component faithfully recreates the observed dynamic interconversions between different swarming potentials. We also demonstrate that iron memory can integrate multiple stimuli, impacting other bacterial behaviors such as biofilm formation and antibiotic tolerance.

Motion behaviour recognition dataset collected from human perception of collective motion behaviour

Collective motion behaviour such as the movement of swarming bees, flocking birds or schooling fish has inspired computer-based swarming systems. They are widely used in agent formation control, including aerial and ground vehicles, teams of rescue robots, and exploration of dangerous environments with groups of robots. Collective motion behaviour is easy to describe, but highly subjective to detect. Humans can easily recognise these behaviours; however, it is hard for a computer system to recognise them. Since humans can easily recognise these behaviours, ground truth data from human perception is one way to enable machine learning methods to mimic this human perception. Hence ground truth data has been collected from human perception of collective motion behaviour recognition by running an online survey. In this survey, participants provide their opinion about the behaviour of 'boid' point masses. Each question of the survey contains a short video (around 10 seconds), captured from simulated boid movements. Participants were asked to drag a slider to label each video as either 'flocking' or 'not flocking'; 'aligned' or 'not aligned' or 'grouped' or 'not grouped'. By averaging these responses, three binary labels were created for each video. This data has been analysed to confirm that it is possible for a machine to learn binary classification labels from the human perception of collective behaviour dataset with high accuracy.

Swarming Motility Assays in Salmonella

Salmonella enterica has six subspecies, of which the subspecies enterica is the most important for human health. The dispersal and infectivity of this species are dependent upon flagella-driven motility. Two kinds of flagella-mediated movements have been described-swimming individually in bulk liquid and swarming collectively over a surface substrate. During swarming, the bacteria acquire a distinct physiology, the most significant consequence of which is acquisition of adaptive resistance to antibiotics. Described here are protocols to cultivate, verify, and study swimming and swarming motility in S. enterica, and an additional "border-crossing" assay, where cells "primed" to swarm are presented with an environmental challenge such as antibiotics to assess their propensity to handle the challenge.

Comment on 'A physics perspective on collective animal behavior' 2022 Phys. Biol. 19 021004

In his insightful and timely review Ouellette [2022] noted three theoretical impediments to progress in understanding and modelling collective animal behavior. Here through novel analyses and by drawing on the latest research I show how these obstacles can be either overcome or negated. I suggest ways in which recent advances in the physics of collective behavior provide significant biological information.

Effect of samarium oxide nanoparticles on virulence factors and motility of multi-drug resistant Pseudomonas aeruginosa

Biofilm formation and quorum sensing (QS) dependent virulence factors are considered the major causes of the emergence of drug resistance, therapeutic failure and development of Pseudomonas aeruginosa infections. This study aimed to investigate the effects of samarium oxide nanoparticles (Sm₂O₃NPs) on biofilm, virulence factors, and motility of multidrug-resistant P. aeruginosa. Sm₂O₃NPs were synthesized using curcumin and characterized by Transmission Electron Microscopy, X-ray diffractometer, Field Emission Scanning Electron Microscopy, and Energy-dispersive X-ray spectroscopy. Minimum inhibitory concentration (MIC) was determined using broth microdilution method. The antibiofilm potential of Sm₂O₃NPs was also evaluated by crystal violet staining and light microscopy examination. Then, the effect of sub-MICs concentrations of Sm₂O₃NPs on the proteolytic and hemolytic activities of P. aeruginosa was investigated. Finally, the effect of Sm₂O₃NPs on various types of motility including swarming, swimming, and twitching was studied. Our results showed that Sm₂O₃NPs significantly inhibited biofilm formation of P. aeruginosa by 49-61%. Additionally, sub-MICs concentrations of Sm₂O₃NPs effectively decreased virulence factors including pyocyanin (33-55%), protease (24-45%), and hemolytic activity (22-41%). Moreover, swarming, swimming, and twitching motility remarkably was reduced after exposure to the NPs. The findings of this work showed that Sm₂O₃NPs have a high potential in inhibiting QS-dependent virulence of P. aeruginosa, which could be considered for antibacterial chemotherapy after further characterization.

Phytochemical composition and antimicrobial, and anti-quorum sensing activities of Punica granatum L. methanolic extract

Background and Objectives

In this work, our aims were to investigate the antimicrobial resistance, and anti-quorum sensing activities of Punica granatum L. methanolic extract.

Materials and Methods

Antibacterial and antifungal activities were performed against thirteen bacteria and five fungal pathogens. Ultra-high performance liquid chromatography was used to identify the polyphenolic extract. The inhibition of pyocyanin production, proteolytic and elastolytic activity and swarming motility in Pseudomonas aeruginosa PAO1 test strain were estimated.

Results

The methanolic extract from P. granatum L. was dominated by chlorogenic acid (34.028 mg/g), rutin (26.05 mg/g), epicatechin (12.207 mg/g), gallic acid (11.157 mg/g), and caffeic acid 9.768 mg/g). Results showed antibacterial activities against almost all tested microorganisms with mean diameter of growth inhibition zone ranging from 6 ± 0 to 30 ± 0 mm for Candida species and from 6 ± 0 to 22.66 ± 0.57 for bacterial strains. The lowest minimal inhibitory concentrations were recorded for Listeria monocytogenes ATCC 19115 and Salmonella enterica CECT 529 (0.14 mg/ml, respectively). The anti-quorum sensing activity of methanolic extract against P. aeruginosa showed a significant inhibition of swarming motility and an attenuation in virulence factors like pyocyanin production at low concentrations.

Conclusion

The obtained results indicates that P. granatum L. extracts is a rich source of phenolic compounds and highlighted the possibilities uses of pomegranate to attenuate the expression of quorum sensing controlled factors in P. aeruginosa PAO1 strain.

Strain-dependent motility defects and suppression by a flhO mutation for B. subtilis bactofilins

Objective

Bactofilins can assemble into polymeric structures and play important roles in cell shape maintenance, chromosome segregation and motility. Bacillus subtilis bactofilins BacE and BacF were shown to be important for swimming motility in strain PY79, and single gene deletions were reported to be lethal, in contrast to a double bacEF deletion.

Results

Extending this work, we show that motility defects vary between different B. subtilis strains, with strain 168 showing no defect in motility, and 3610 showing delayed induction of swimming. Generation of single gene deletions in PY79 was possible by transferring corresponding deletions from 168. In the natural isolate 3610, gene deletions also showed a negative effect on biofilm formation, revealing an additional function for BacE and BacF. A spontaneous arising suppressor mutation in PY79 was mapped to the flhO gene, a constituent of the flagellum, which obtained an 18 amino acid extension at its C-terminus. Our findings show that bactofilin gene deletions lead to different motility phenotypes dependent on the strain background, and affect biofilm formation in the natural isolate 3610. Our data reinforce the idea of a connection between bactofilins and motion via the flagellum, and suggest that they operate in a switch like manner.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-022-06048-6.

Behavior and interactions of the plant growth-promoting bacteria Azospirillum oryzae NBT506 and Bacillus velezensis UTB96 in a co-culture system

The objective of the present study was to evaluate possible interactions between two potential plant growth-promoting bacteria (PGPB): Azospirillum oryzae strain NBT506 and Bacillus velezensis strain UTB96. To do this, the growth kinetic, biofilm formation, motility, surfactin production, indole-3-acetic acid (IAA) production, phosphate solubilization and enzyme activities of the strains were measured in monoculture and co-culture. The maximum biomass production for the strains in monoculture and co-culture was about 10¹¹ CFU/ml, confirming that these two strains have the potential to grow in co-culture without reduction of biomass efficiency. The co-culture system showed more stable biofilm formation until the end of day 3. Azospirillum showed the maximum IAA production (41.5 mg/l) in a monoculture compared to other treatments. Surfactin promoted both swimming and swarming motility in all treatments. The Bacillus strain in the monoculture and co-culture showed high phosphate solubilizing capability, which increased continuously in the co-culture system after 6 days. The strains showed protease, amylase and cellulase activities in both monoculture and co-culture forms. Chitinase and lipase activities were observed in both the monoculture of the Bacillus strain and the co-culture. Overall, our findings highlight the promotion of biological and beneficial effects of these bacteria when growing together in co-culture.

Pathogenic potential of bacteria isolated from commercial biostimulants

Microbial-based products are a promising alternative to agrochemicals in sustainable agriculture. However, little is known about their impact on human health even if some of them, i.e., Bacillus and Paenibacillus species, have been increasingly implicated in different human diseases. In this study, 18 bacteria were isolated from 2 commercial biostimulants, and they were genotypically and phenotypically characterized to highlight specific virulence properties. Some isolated bacteria were identified as belonging to the genus Bacillus by BLAST and RDP analyses, a genus in-depth studied for plant growth-promoting ability. Moreover, 16S rRNA phylogenetic analysis showed that seven isolates grouped with Bacillus species while two and four clustered, respectively, with Neobacillus and Peribacillus. Unusually, bacterial strains belonging to Franconibacter and Stenotrophomonas were isolated from biostimulants. Although Bacillus species are generally considered nonpathogenic, most of the species have shown to swim, swarm, and produced biofilms, that can be related to bacterial virulence. The evaluation of toxins encoding genes revealed that five isolates had the potential ability to produce the enterotoxin T. In conclusion, the pathogenic potential of microorganisms included in commercial products should be deeply verified, in our opinion. The approach proposed in this study could help in this crucial step.

Construction of Molecular Robots from Microtubules for Programmable Swarming

Swarm robotics has been attracting much attention in recent years in the field of robotics. This chapter describes a methodology for the construction of molecular swarm robots through precise control of active self-assembly of microtubules (MTs). Detailed protocols are presented for the construction of molecular robots through conjugation of DNA to MTs and demonstration of swarming of the MTs. The swarming is mediated by DNA-based interaction and photoirradiation which act as processors and sensors respectively for the robots. Furthermore, the required protocols to utilize the swarming of MTs for molecular computation is also described.

The Social Life of Honey Bees

Honey bees have evolved to use pollen, nectar, and water as their principal food sources. Their success is linked to the establishment of large colonies with one female reproductive member, three distinct social castes, a division of labor among workers, and genetically diverse subfamilies. Colonies also have the ability to recruit and communicate through complex mechanisms including dance language and pheromones. Pheromones produced by the queen maintain social order in the colony and ensure that she remains as the only female to lay eggs. Finally, honey bee colonies reproduce and disperse through a mechanism called swarming.

Inhibition of swarming motility using in vitro hyperthermia

Hyperthermia is a therapeutic technique in which body tissue is exposed to temperatures in the region of 40-45 °C to induce a physiological or biological effect. Swarming motility is an important virulence factor for Proteus mirabilis and Pseudomonas aeruginosa and swarming phenomenon is a coordinated multicellular movement of differentiated bacterial population over semi-solid surfaces. In this study, we aimed to investigate the inhibitory effect of hyperthermia on bacterial swarming motility using a modified thermobiogram method and show the potential of this thermal method to treat bacterial infections. Ten P. mirabilis and 10 P. aeruginosa clinical isolates were included in the study. Sheep blood agar (SBA) plates were prepared and inoculated with bacterial suspensions of clinical isolates. Inoculated SBA plates were incubated inside 2 different incubators; at 37 °C and 45 °C for 20 h. The diameter of bacterial growing zones (swarming diameters) were measured every 2 h and noted. Finally, Gram stains of the isolates were prepared for microscopic examination. Wilcoxon signed-rank test was used to compare the swarming inhibition rates of the isolates incubated at 37 °C and 45 °C. Regarding P. mirabilis species, a significant difference was found between two different temperatures (P = 0.0078). So, a temperature at the level of hyperthermia significantly inhibited the swarming motility of P. mirabilis isolates. In addition, transformation to coccus form was observed at 45 °C. We speculate that these findings might be useful for employing thermal therapies including hyperthermia method to treat infectious diseases caused by swarming bacterial pathogens in the future.

Analyzing the Effect of Strigolactones on the Motility Behavior of Rhizobia

In the Rhizobium-legume symbiosis, strigolactones (SLs) promote root nodule formation; however, the exact mechanism underlying this positive effect remains unknown. The recent finding that an SL receptor legume mutant shows a wild-type nodulation phenotype suggests that SLs influence the symbiosis by acting on the bacterial partner. In agreement with this, the application of the synthetic SL analog GR24 on the alfalfa symbiont Sinorhizobium (Ensifer) meliloti has been shown to stimulate swarming, a specialized bacterial surface motility, which could influence infection of legumes by Rhizobia. Surface motility assays for many bacteria, and particularly for Rhizobia, are challenging. The establishment of protocols to study bacterial surface motility is key to decipher the role of SLs as rhizosphere cues for rhizobacteria. In this chapter, we describe a set of protocols implemented to study the different types of motility exhibited by S. meliloti.

Leadership Through Influence: What Mechanisms Allow Leaders to Steer a Swarm?

Collective migration of cells and animals often relies on a specialised set of “leaders”, whose role is to steer a population of naive followers towards some target. We formulate a continuous model to understand the dynamics and structure of such groups, splitting a population into separate follower and leader types with distinct orientation responses. We incorporate leader influence via three principal mechanisms: a bias in the orientation of leaders towards the destination (orientation-bias), a faster movement of leaders when moving towards the target (speed-bias), and leaders making themselves more clear to followers when moving towards the target (conspicuousness-bias). Analysis and numerical computation are used to assess the extent to which the swarm is successfully shepherded towards the target. We find that successful leadership can occur for each of these three mechanisms across a broad region of parameter space, with conspicuousness-bias emerging as the most robust. However, outside this parameter space we also find various forms of unsuccessful leadership. Forms of excessive influence can result in either swarm-splitting, where the leaders break free and followers are left rudderless, or a loss of swarm cohesion that leads to its eventual dispersal. Forms of low influence, on the other hand, can even generate swarms that move away from the target direction. Leadership must therefore be carefully managed to steer the swarm correctly.

Quorum quenching activity of Andrographis paniculata (Burm f.) Nees andrographolide compounds on metallo-β-lactamase-producing clinical isolates of Pseudomonas aeruginosa PA22 and PA247 and their effect on lasR gene expression

Andrographis paniculata (Burm f.) Nees is a tropical plant native to Southeast Asia that has been used as an effective remedy for a wide variety of illnesses in traditional Chinese and Ayurvedic medicine. The antimicrobial activity of its crude extract had been shown to be due to its quorum quenching activity. The study determined the effect of purified extracted compounds from the leaf of A. paniculata, namely: andrographolide, 14-deoxyandrographolide, 14-deoxy-12-hydroxyandrographolide and neoandrographolide on quorum sensing-mediated virulence mechanisms in clinical isolates of metallo-β-lactamase (MβL)-producing Pseudomonas aeruginosa. Their effect on the expression of the lasR gene, which codes for LasR, a transcription activator protein of the quorum sensing system in P. aeruginosa was also determined using RT-qPCR. All the pure compounds significantly decreased the biofilm formation, protease production and swarming motility of the P. aeruginosa isolates compared to the untreated controls (p < 0.05). Results of the RT-qPCR assay showed that all compounds significantly downregulated the expression of lasR compared to the untreated control (p < 0.05), supporting the position that the lower virulence activities of the treated group were due to quorum quenching activity of the pure compounds. Multiple comparisons using Tukey's HSD analysis revealed that the means of the relative expression of lasR of the isolates treated with the different compounds were not significantly different from each other (p > 0.05), suggesting equal potencies. Results show the potential of the isolated pure compounds from A. paniculata for use as antimicrobial agents as a result of their quorum quenching activities.

Eugenol, citral, and hexanal, alone or in combination with heat, affect viability, biofilm formation, and swarming on Shiga-toxin-producing Escherichia coli

Shiga-toxin-producing Escherichia coli strains are pathogenic for humans and cause mild to severe illnesses. In this study, the antimicrobial effect of citral, eugenol, and hexanal in combination with heat shock (HS) was evaluated in terms of the growth, biofilm formation, swarming, and expression of virulence genes of STEC serotypes (O157:H7, O103, O111, and O26). Eugenol was the most effective compound against the growth of E. coli strains (MBC = 0.58 to 0.73 mg/mL), followed by citral (MBC = 0.86 to 1.26 mg/mL) and hexanal (MBC = 2.24 to 2.52 mg/mL). Biofilm formation and swarming motility have great variability between STEC strains. Natural compounds-alone or combined with HS-inhibited biofilm formation; however, swarming motility was induced by most treatments. The expression of the studied genes during biofilm formation and swarming under natural antimicrobials was affected but not in a uniform pattern. These treatments could be used to control contamination of STEC and inhibit biofilm formation.

Characterization of the relationship between polar and lateral flagellar genes in clinical Aeromonas dhakensis: phenotypic, genetic and biochemical analyses

Flagellar-mediated motility is a crucial virulence factor in many bacterial species. A dual flagellar system has been described in aeromonads; however, there is no flagella-related study in the emergent human pathogen Aeromonas dhakensis. Using 46 clinical A. dhakensis, phenotypic motility, genotypic characteristics (flagellar genes and sequence types), biochemical properties and their relationship were investigated in this study. All 46 strains showed swimming motility at 30 °C in 0.3% Bacto agar and carried the most prevalent 6 polar flagellar genes cheA, flgE, flgG, flgH, flgL, and flgN. On the contrary, only 18 strains (39%) demonstrated swarming motility on 0.5% Eiken agar at 30 °C and they harbored 11 lateral flagellar genes lafB, lafK, lafS, lafT, lafU, flgCL, flgGL, flgNL, fliEL, fliFL, and fliGL. No association was found between biochemical properties and motility phenotypes. Interestingly, a significant association between swarming and strains isolated from pus was observed (p = 0.0171). Three strains 187, 277, and 289 isolated from pus belonged to novel sequence types (ST522 and ST524) exhibited fast swimming and swarming profiles, and they harbored > 90% of the flagellar genes tested. Our findings provide a fundamental understanding of flagellar-mediated motility in A. dhakensis.

Binary Medical Nanofluids by Combination of Polymeric Eudragit Nanoparticles for Vehiculization of Tobramycin and Resveratrol: Antimicrobial, Hemotoxicity and Protein Corona Studies

The development of smart nanoparticles (NPs) became a trend to enhance the delivery of drugs. In the present work, Tobramycin (TB), an aminoglycoside antibiotic that displays several undesirable side effects, has been encapsulated into cationic Eudragit®E100 (E100) NPs for the treatment of infections caused by Pseudomonas aeruginosa. Combination with neutral Eudragit®NE30D (NE30D) NPs containing resveratrol (RSV), a strong natural antioxidant, increased the antimicrobial activity of TB (75% higher than free TB). NPs were stabilized with 1.0% (w/v) poloxamer 188 (P188) or poloxamer 407 (P407) as surfactants. E100 NPs showed 83.3 ± 8.5%, and 70.1 ± 2.7 encapsulation efficiency (EE) of TB with P188 and P407 coatings, respectively. The presence of NPs was confirmed by DLS and TEM studies. TB was controlled released from NPs for 6 h. Hemotoxicity tests of NPs in the range of MIC values on human blood gave negative results. Analysis of Surface Plasmon Resonance verified that NE30D/P407/RSV does not interact with plasma proteins BSA, IgG or fibrinogen, besides E100/P188/TB interact with BSA, findings that are compatible with a negligible in vivo clearance of the nanovehicles. The obtained results show a potential binary fluid composed of two NPs to highly improve the effectiveness of conventional antibiotics.

Evaluation of behavior, growth, and swarming formation of Escherichia coli and Staphylococcus aureus in culture medium modified with silver nanoparticles

Silver nanoparticles (AgNPs), as well as silver ions, are described as toxic to a broad spectrum of microorganisms, especially bacteria. In contrast to this, a current trend is to develop and carry out the in vitro cultivation of microorganisms, facilitating the study of interactions between populations of cells and species. Thus, the goal of this study was to evaluate the behavior, growth, and swarming formation of bacteria under conditions of co-culture in solid medium modified with AgNPs. The aqueous extract from the leaves of Handroanthus serratifolius was used to chemically reduce silver nitrate (AgNO₃) solution, forming AgNPs. This synthesis route was performed in an aqueous medium at 50 °C for 3 h. The hydrodynamic diameter (HD) and polydispersity index (PdI) were obtained by dynamic light scattering (DLS), and Zeta potential (ZP) of the AgNPs were measured by electrophoretic mobility. Atomic force microscopy (AFM) was used to evaluate the shape of the AgNPs. Luria Bertani (LB) medium was used for the liquid culture steps and for the solid medium, bacterial agar was added. Solutions containing AgNPs or AgNO₃ were added at final concentrations of 256, 128, or 64 μM. Subsequently, microorganism Escherichia coli ATCC® 8739 and Staphylococcus aureus ATCC® 25923 were plated with AgNPs, AgNO₃, and control media. Analyses of the AgNPs showed an average HD of 76.02 ± 3.08 nm, PdI of 0.461 ± 0.012, and ZP of -21.5 ± 2.2 mV; in addition, AgNPs were nearly spherical. The solid culture medium elaborated and modified with AgNPs at the concentrations of 256 and 128 μM inhibited the growth of the tested microorganisms and decreased the swarming formation. However, those media modified at a concentration of 64 μM did not induce any alteration in the growth and proliferation of the microorganisms. Furthermore, it was observed that plates containing modified culture media with 128 μM, increased proximity between both co-cultured bacteria occurred. Thus, the application of AgNPs in solid culture media becomes a promising and potentially reproducible strategy for evaluating the behavior, swarming formation, and toxicity of AgNPs, making the understanding of possible bactericidal or bacteriostatic effects, and also colonizing strategies.

Magnetic nanoparticles coated with carbohydrates for 3D culture of bacteria

Magnetic nanoparticles (MNPs) are a specific type of nanomaterial whose applications are widespread into several fields including biomedicine as a smart drug targeter and environmental engineering due to their interactions with contaminants. Lately, the use of MNPs has also been demonstrated in structuring three-dimensional (3D) cultures of mammalian cells. However, MNPs application to other cell types is still limited. In this sense, some planktonic microorganisms when adhered to surfaces perform the swarming phenomenon to guarantee the expansion of the colony and to guarantee more niches. Therefore, the aim of this study was to produce MNPs coated with four carbohydrates (galactose - gal, glucose - glu, sucrose - suc, and maltose - mal) aiming microorganism culture applications and also for possible 3D arrays. The results showed that carbohydrate-coated MNPs showed hydrodynamic diameters ranging from 100 to 200 nm and that their coatings influenced the chemical behavior in different ways. Indeed, when subjected to biological tests to determine their potential level of cytotoxicity, it was found that in concentrations of 1 mM, 800, 600, and 400 μM (iron equivalent), there was not any alteration on growth of model microorganisms when visually evaluated. Besides, magnetization of bacteria was promoted in different ways as well as the modulation of swarming formation in Escherichia coli when exposed to MNP-Glu. In sum, MNPs coated with carbohydrates and even uncoated were atoxic to bacteria and one of them was able to modulate E. coli swarming formation showing the potential for applications in 3D cultures of bacteria.

Comparison between the proteome of Escherichia coli single colony and during liquid culture

Most bacterial proteomic studies done to date utilise bacterial cells harvested from liquid culture media. However, it is widely accepted that many important determinants associated with virulence and host cell adhesion are exclusively expressed during growth on solid media, as a crude mimic of true biofilms. Here, we compare the observed proteome of Escherichia coli K12 from isolated single colonies on solid media with those observed at different growth phases in liquid culture; i.e. early-log, mid-log, early-, mid- and late-stationary growth phases. A total of 2044 protein groups covering approximately 47% of the total proteome were identified across all studied conditions, including 1650 proteins identified from single colonies and 1679 proteins from liquid cultured cells. Label-free quantitative analysis revealed that the E. coli proteome of single colonies on a solid agar differs from that observed in liquid culture. Notably, the presence of proteins in the Suf-operon that are involved in iron mobilisation and swarming motility was associated exclusively with single colony profiles, whereas proteins involved in motility such as motA, motB, fliH, flip, fliD and fliJ were associated exclusively with cells grown in liquid culture. The data presented here provide a valuable resource for understanding the role of key proteins within microenvironments surrounding E. coli single colonies. SIGNIFICANCE: To date, most proteomics studies have used E. coli cells harvested from liquid culture media even though many important determinants associated with virulence and host cell adhesion are exclusively expressed during growth on solid media. In this study, we compare the observed proteome of E. coli K12 from isolated single colonies on solid media with those observed at different growth phases in liquid culture; i.e. early-log, mid-log, early-, mid- and late-stationary growth phases. By using label-free quantitative analysis we demonstrate that the E. coli proteome of single colonies on a solid agar differs from that observed in liquid culture with an overlap of 68% of proteins between the two culture conditions. Our analysis further reveal the presence of proteins in the Suf-operon that are involved in iron mobilisation and swarming motility was associated exclusively with single colony profiles. While those proteins involved in motility such as motA, motB, fliH, flip, fliD and fliJ were associated exclusively with cells grown in liquid culture. By comparison to E. coli proteomic data available on liquid culture and solid media, this research represents a first effort to describe the differential expression of key E. coli proteins within microenvironments surrounding single colonies.

Attenuation of Proteus mirabilis colonization and swarming motility on indwelling urinary catheter by antibiofilm impregnation: An in vitro study

Proteus mirabilis is one of the important etiologic agents of urinary tract infections (UTI), which complicates the long-term urinary catheterization process in clinical settings. Owing to its crystalline biofilm forming ability and flagellar motility, elimination of P. mirabilis from urinary system becomes very difficult. Thus, the present study is focused to prepare antibiofilm-impregnated Silicone Foley Catheter (SFC) to prevent P. mirabilis instigated UTIs. Through solvent swelling method, the antibiofilm compounds such as linalool (LIN) and 2-hydroxy-4-methoxy benzaldehyde (HMB) were successfully infused into SFCs. Surface topography was studied using AFM analysis, which unveiled the unmodified surface roughness of normal and antibiofilm-impregnated SFCs. In addition, UV-spectrometric and FT-IR analyses revealed good impregnation efficacy and prolonged stability of antibiofilm compounds. Further, in vitro biofilm biomass quantification assay exhibited a maximum of 87 % and 84 % crystalline biofilm inhibition in LIN (350 μg/cm³) and HMB (120 μg/cm³) impregnated SFCs, respectively against P. mirabilis in artificial urine medium. Also, the LIN & HMB-impregnated SFCs demonstrated long-term crystalline biofilm inhibitory activity for more than 30 days, which is ascribed to the sustained release of the compounds. Furthermore, the results of swarming motility analysis revealed the efficacy of antibiofilm-impregnated catheters to mitigate the migration of pathogens over them. Thus, antibiofilm-impregnated catheter is proposed to act as a suitable strategy for reducing P. mirabilis infections and associated complications in long-term urinary catheter users.

Analysis of two Mexican Pectobacterium brasiliense strains reveals an inverted relationship between c-di-GMP levels with exopolysaccharide production and swarming motility

Pectobacterium is a diverse genus of phytopathogenic species from soil and water that cause infection either to restricted or multiple plant hosts. Phylogenetic analysis and metabolic fingerprinting of large numbers of genomes have expanded classification of Pectobacterium members. Pectobacterium brasiliense sp. nov has been elevated to the species level having detached from P. carotovorum. Here we present two P. brasiliense strains BF20 and BF45 isolated in Mexico from Opuntia and tobacco, respectively, which cluster into two different groups in whole genome comparisons with other Pectobacterium. We found that BF20 and BF45 strains are phenotypically different as BF45 showed more severe and rapid symptoms in comparison to BF20 in the host models celery and broccoli. Both strains produced similar levels of the main autoinducers, but BF45 shows an additional low abundant autoinducer compared to strain BF20. The two strains had different levels of c-di-GMP, which regulates the transition from motile to sessile lifestyle. In contrast to BF45, BF20 had the highest levels of c-di-GMP, was more motile (swarming), non-flocculant and less proficient in biofilm formation and exopolysaccharide production. Genomic comparisons revealed that differences in c-di-GMP accumulation and perhaps the associated phenotypes might be due to unique c-di-GMP metabolic genes in these two strains. Our results improve our understanding of the associations between phenotype and genotype and how this has shaped the physiology of Pectobacterium strains.

Cognitive swarming in complex environments with attractor dynamics and oscillatory computing

Neurobiological theories of spatial cognition developed with respect to recording data from relatively small and/or simplistic environments compared to animals' natural habitats. It has been unclear how to extend theoretical models to large or complex spaces. Complementarily, in autonomous systems technology, applications have been growing for distributed control methods that scale to large numbers of low-footprint mobile platforms. Animals and many-robot groups must solve common problems of navigating complex and uncertain environments. Here, we introduce the NeuroSwarms control framework to investigate whether adaptive, autonomous swarm control of minimal artificial agents can be achieved by direct analogy to neural circuits of rodent spatial cognition. NeuroSwarms analogizes agents to neurons and swarming groups to recurrent networks. We implemented neuron-like agent interactions in which mutually visible agents operate as if they were reciprocally connected place cells in an attractor network. We attributed a phase state to agents to enable patterns of oscillatory synchronization similar to hippocampal models of theta-rhythmic (5-12 Hz) sequence generation. We demonstrate that multi-agent swarming and reward-approach dynamics can be expressed as a mobile form of Hebbian learning and that NeuroSwarms supports a single-entity paradigm that directly informs theoretical models of animal cognition. We present emergent behaviors including phase-organized rings and trajectory sequences that interact with environmental cues and geometry in large, fragmented mazes. Thus, NeuroSwarms is a model artificial spatial system that integrates autonomous control and theoretical neuroscience to potentially uncover common principles to advance both domains.

Culture Methods for Proteus mirabilis

Proteus mirabilis is generally easy to culture, but its tendency to swarm on a wide variety of media can interfere with isolation of single colonies or identification of other species in a sample. Therefore, specialized media may be needed to control swarming or to study the bacteria under chemically defined conditions. Here, methods are described for routine culture of P. mirabilis, isolation of P. mirabilis from mixed cultures, and culture of P. mirabilis on physiologically relevant media.

Optimized plant compound with potent anti-biofilm activity across gram-negative species

Many human diseases, including cystic fibrosis lung infections, are caused or exacerbated by bacterial biofilms. Specialized modes of motility, including swarming and twitching, allow gram-negative bacteria to spread across surfaces and form biofilms. Compounds that inhibit these motilities could slow the spread of biofilms, thereby allowing antibiotics to work better. We previously demonstrated that a set of plant-derived triterpenes, including oleanolic acid and ursolic acid, inhibit formation of Escherichia coli and Pseudomonas aeruginosa biofilms, and alter expression of genes involved in chemotaxis and motility. In the present study, we have prepared a series of analogs of oleanolic acid. The analogs were evaluated against clinical isolates of E. coli and P. aeruginosa in biofilm formation assays and swarming assays. From these analogs, compound 9 was selected as a lead compound for further development. Compound 9 inhibits E. coli biofilm formation at 4 µg/mL; it also inhibits swarming at ≤1 µg/mL across multiple clinical isolates of P. aeruginosa, E. coli, Burkholderia cepacia, and Salmonella enterica, and at <0.5 µg/mL against multiple agricultural strains. Compound 9 also potentiates the activity of the antibiotics tobramycin and colistin against swarming P. aeruginosa; this is notable, as tobramycin and colistin are inhaled antibiotics commonly used to treat P. aeruginosa lung infections in people with cystic fibrosis. qPCR experiments suggested that 9 alters expression of genes involved in regulating Type IV pili; western blots confirmed that expression of Type IV pili components PilA and PilY1 decreases in P. aeruginosa in the presence of 9.

Ex Vivo Human Neutrophil Swarming Against Live Microbial Targets

Neutrophils often communicate with each other and coordinate their actions to seal off large sites of injury and infection that individual neutrophils could not cover. The concerted actions of neutrophils are essential for the expeditious protection of healthy tissues from wounds and microbes. These processes, collectively known as swarming, are typically studied in vivo in mice. However, these studies are low throughput and their relevance to human disease is limited. Recently, new tools have been developed for the study of human neutrophil swarming ex vivo. The emergent microscale swarming assays are providing significant insights into the molecular mediators of swarming. By enabling the direct study of human cells, these assays also shed new light on human diseases and host responses against infections. Here, we describe a robust technique for manufacturing microscale swarming arrays with live microbial targets (e.g., clusters of Candida albicans). These arrays allow for the direct, precise, and efficient interrogation of the antimicrobial functions of human swarming against a variety of targets.

Assessing Different Ways of Bacillus subtilis Spreading over Abiotic Surfaces

Surface-associate motility on biotic and abiotic environments is a key mechanism used by the model bacterium Bacillus subtilis and its closest relatives (i.e., B. amyloliquefaciens, B. thuringiensis, B. cereus, B. pumilus) for surface colonization and spreading across surfaces. The study of this mechanism in a research, industrial or clinic laboratory is essential; however, precautions should be taken for the reproducibility of the results, for example, the procedure to inoculate the bacteria on the testing plate, the humidity of the plate and the agar concentration. In this protocol, we describe, using Bacillus subtilis, how to perform these assays and, in addition, we show how by varying the agar concentration in the plate, you can make a first approximation of what type of motility has other bacterial species.

Precopulatory acoustic interactions of the New World malaria vector Anopheles albimanus (Diptera: Culicidae)

Background

Anopheles albimanus is a malaria vector in Central America, northern South America and the Caribbean. Although a public health threat, An. albimanus precopulatory mating behaviors are unknown. Acoustics play important roles in mosquito communication, where flight tones allow males to detect and attract potential mates. The importance of sound in precopulatory interactions has been demonstrated in Toxorhynchites brevipalpis, Aedes aegypti, Culex quinquefasciatus and Anopheles gambiae; convergence in a shared harmonic of the wing beat frequency (WBF) during courtship is thought to increase the chance of copulation. To our knowledge, An. albimanus precopulatory acoustic behaviors have not been described to date. Here, we characterized An. albimanus (i) male and female flight tones; (ii) male–female precopulatory acoustic interactions under tethered and free flight conditions; and (iii) male-male acoustic interactions during free flight.

Results

We found significant increases in the WBFs of both sexes in free flight compared to when tethered. We observed harmonic convergence between 79% of tethered couples. In free flight, we identified a female-specific behavior that predicts mate rejection during male mating attempts: females increase their WBFs significantly faster during mate rejection compared to a successful copulation. This behavior consistently occurred during mate rejection regardless of prior mating attempts (from the same or differing male). During group flight, males of An. albimanus displayed two distinct flying behaviors: random flight and a swarm-like, patterned flight, each associated with distinct acoustic characteristics. In the transition from random to patterned flight, males converged their WBFs and significantly decreased flight area, male-male proximity and the periodicity of their trajectories.

Conclusions

We show that tethering of An. albimanus results in major acoustic differences compared to free flight. We identify a female-specific behavior that predicts mate rejection during male mating attempts in this species and show that male groups in free flight display distinct flying patterns with unique audio and visual characteristics. This study shows that An. albimanus display acoustic features identified in other mosquito species, further suggesting that acoustic interactions provide worthwhile targets for mosquito intervention strategies. Our results provide compelling evidence for swarming in this species and suggests that acoustic signaling is important for this behavior.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3648-8) contains supplementary material, which is available to authorized users.

Testing the Ability of Compounds to Induce Swarming

One of the most distinctive features of Proteus mirabilis is its ability to undergo differentiation from short, rod-shaped vegetative cells with peritrichous flagella to massively elongated swarm cells that express hundreds to thousands of flagella. The unique bull's-eye pattern that forms from cycles of active swarming and consolidation back to the vegetative state has long been a distinguishing characteristic of this species. Many factors involved in regulation of flagellar synthesis and swarm cell differentiation have been characterized, but the exact conditions sensed by P. mirabilis that send a signal to initiate differentiation and motility have yet to be fully elucidated. Here we describe a method for using several types of media to investigate compounds that induce swarming motility under conditions that would not normally be permissive.

Proteus mirabilis Overview

Proteus mirabilis, a Gram-negative bacterium, commonly causes catheter-associated urinary tract infections, wound infections, gastroenteritis and, in some cases, bacteremia. The phenotypic hallmarks of this bacterium include swarming motility, urease and hemolysin production, and synthesis of numerous adherence fimbriae. While routine bacteriological methodology may often be used to study this pathogen, frequently one requires specialized techniques to investigate the pathogenesis of this species. Here, a brief overview of the discoveries associated with this fascinating bacterium illuminates the need for the development of specialized techniques to further probe the biology of P. mirabilis.

Methods for Transposon Mutagenesis in Proteus mirabilis

Several methods for transposon mutagenesis have been employed for use in P. mirabilis. The first method involves the use of mini-Tn5 derivatives, which are delivered by conjugation of a suicide plasmid containing this transposon, followed by transposition into the chromosome. A second method is the use of preformed transposon/transposase complexes (transposomes), which are introduced into P. mirabilis cells by electroporation. Each of these methods will be discussed along with the advantages and disadvantages of each.

Quercetin inhibits swarming motility and activates biofilm production of Proteus mirabilis possibly by interacting with central regulators, metabolic status or active pump proteins

BACKGROUND

Via its virulence factors such as swarm differentiation, biofilm and hemolysin production, urease enzyme, Proteus mirabilis causes urinary tract infections (UTIs), especially in complicated cases. Anti-pathogenic compounds attenuate the virulence of bacteria without showing 'cidal' activity and carry the potential to be used in the prevention and treatment of infectious diseases.

PURPOSE

Search for anti-pathogenic effects of quercetin, which is a widely known and biologically active phytochemical, on Proteus mirabilis was the purpose of this study. In this context, the potential inhibitory activity of quercetin on swarming motility and biofilm production of a wild-type strain, P. mirabilis HI4320, was investigated in both phenotypically and genotypically.

METHODS

Quercetin's effect on swarming motility was examined on LB agar plates, containing quercetin at various concentrations, by measuring the swarming diameter. The effect on biofilm formation, on the other hand, was analyzed by staining the formed biofilm of the bacterium, exposed to quercetin at various concentrations, with crystal violet and reading spectrophotometrically. Differences in expression levels of selected genes involved in swarming regulation were determined by real-time reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) to evaluate the mechanism of inhibitory action on swarming. Further investigations were carried out repeating swarming assays with the clones that derived from the wild-type strain by a TA system kit for direct one-step cloning and overexpressing the relevant genes.

RESULTS

Our study revealed that quercetin inhibited swarming motility while activating biofilm production of P. mirabilis in direct proportion to the dose. Although all selected genes are inhibited in the same manner in liquid medium, and no significant differences could be detected in solid medium as demonstrated by RT-qPCR, experiments repeated with the clones overexpressing flhC (a component of flagellar transcriptional activator), speB (an agmatinase enzyme) and ompF (an outer membrane porin) genes showed that the respective clones could restore swarming, compensating for the inhibitory effect of quercetin.

CONCLUSION

Quercetin's inhibitory effect on P. mirabilis swarming was possibly due to interactions with components of swarming regulators, the genes expressing polyamine coding enzymes that trigger swarm differentiation, or active pump proteins.

Allelic Exchange Mutagenesis in Proteus mirabilis

This chapter outlines a method for making unmarked, in-frame deletion mutations in Proteus mirabilis by allelic replacement. This method utilizes an R6K-based suicide plasmid allowing for integration of the plasmid by homologous recombination via a cloned insert. The plasmid also contains the sacB gene to select for plasmid loss (excision) in the presence of sucrose to create a mutant allele. This method has been applied to the P. mirabilis strains PM7002 and BB2000 and should be generally applicable to other P. mirabilis strains. The same methods described in this chapter can be used to introduce marked or point mutations in a given gene.

Stress-induced adaptive morphogenesis in bacteria

Bacteria thrive in virtually all environments. Like all other living organisms, bacteria may encounter various types of stresses, to which cells need to adapt. In this chapter, we describe how cells cope with stressful conditions and how this may lead to dramatic morphological changes. These changes may not only allow harmless cells to withstand environmental insults but can also benefit pathogenic bacteria by enabling them to escape from the immune system and the activity of antibiotics. A better understanding of stress-induced morphogenesis will help us to develop new approaches to combat such harmful pathogens.

Methods for Studying Swarming and Swimming Motility

Proteus mirabilis is well known for using its flagella to swim through liquids or swarm across solid surfaces. Both phenomena are easy to observe. Described here are two agar-based assays for studying both swimming and swarming behavior, and considerations that affect the outcome.

Specific type IV pili groups in clinical isolates of Pseudomonas aeruginosa

The relationships between specific type IV pili (TFP) groups and antibiotic resistance, biofilm formation, and bacterial motility were determined in 190 Pseudomonas aeruginosa clinical isolates. While motility and biofilm formation were determined by phenotypic assays, the presence of TFP was determined by PCR assay and antibiotic susceptibility by disk diffusion. The results showed a high ability to form biofilm (97.4%), multidrug resistance (44.7%), and the presence of a high number of motile isolates. We also found an association between strong biofilm production and multidrug resistance. Furthermore, TFP group III was associated with strong biofilm production. In contrast, the isolates with TFP group II and those without any TFP were associated with non-strong biofilm production. Regarding motility, TFP group II was associated with higher percentages of swarming, swimming, and twitching, while TFP group I showed lower percentages of swarming and twitching, and TFP group III showed lower levels of swarming and swimming. In conclusion, these findings highlight the differences in P. aeruginosa phenotypes related to the presence of specific TFP groups and their potential implications in clinical settings.

The neglected bee trees: European beech forests as a home for feral honey bee colonies

It is a common belief that feral honey bee colonies (Apis mellifera L.) were eradicated in Europe through the loss of habitats, domestication by man and spread of pathogens and parasites. Interestingly, no scientific data are available, neither about the past nor the present status of naturally nesting honeybee colonies. We expected near-natural beech (Fagus sylvatica L.) forests to provide enough suitable nest sites to be a home for feral honey bee colonies in Europe. Here, we made a first assessment of their occurrence and density in two German woodland areas based on two methods, the tracing of nest sites based on forager flight routes (beelining technique), and the direct inspection of potential cavity trees. Further, we established experimental swarms at forest edges and decoded dances for nest sites performed by scout bees in order to study how far swarms from beekeeper-managed hives would potentially move into a forest. We found that feral honey bee colonies regularly inhabit tree cavities in near-natural beech forests at densities of at least 0.11-0.14 colonies/km2. Colonies were not confined to the forest edges; they were also living deep inside the forests. We estimated a median distance of 2,600 m from the bee trees to the next apiaries, while scout bees in experimental swarms communicated nest sites in close distances (median: 470 m). We extrapolate that there are several thousand feral honey bee colonies in German woodlands. These have to be taken in account when assessing the role of forest areas in providing pollination services to the surrounding land, and their occurrence has implications for the species' perception among researchers, beekeepers and conservationists. This study provides a starting point for investigating the life-histories and the ecological interactions of honey bees in temperate European forest environments.

Molecular and physiological analysis of Anopheles funestus swarms in Nchelenge, Zambia

Background

Anopheles funestus has been recognized as a major malaria vector in Africa for over 100 years, but knowledge on many aspects of the biology of this species is still lacking. Anopheles funestus, as with most other anophelines, mate through swarming. A key event that is crucial for the An. funestus male to mate is genitalia rotation. This involves the 135° to 180° rotation of claspers, which are tipped with claws. This physical change then enables the male to grasp the female during copulation. The aim of this investigation was to molecularly characterize wild An. funestus swarms from Zambia and examine the degree of genitalia rotation within the swarm.

Methods

Anopheles funestus swarms were collected from Nchelenge, northern Zambia, during dusk periods in May 2016. All the adults from the swarm were analysed morphologically and identified to species level using a multiplex PCR assay. Anopheles funestus s.s. specimens were molecularly characterized by restriction fragment length polymorphism type and Clade type assays. The different stages of genitalia rotation were examined in the adult males.

Results

A total of six swarms were observed during the study period and between 6 and 26 mosquitoes were caught from each swarm. Species analysis revealed that 90% of the males from the swarms were An. funestus s.s. MW-type, with 84% belonging to clade I compared to 14% clade II and 2% failed to amplify. Very few specimens (3.4%) were identified as Anopheles gambiae s.s. Eighty percent of the males from the swarm had complete genitalia rotation.

Conclusions

This is the first time that An. funestus swarms have been molecularly identified to species level. Anopheles funestus swarms appear to be species-specific with no evidence of clade-type differentiation within these swarms. The An. funestus swarms consist mainly of males with fully rotated genitalia, which strongly suggests that swarming behaviour is triggered primarily when males have matured.

A discrete particle model reproducing collective dynamics of a bee swarm

In this article, we present a microscopic discrete mathematical model describing collective dynamics of a bee swarm. More specifically, each bee is set to move according to individual strategies and social interactions, the former involving the desire to reach a target destination, the latter accounting for repulsive/attractive stimuli and for alignment processes. The insects tend in fact to remain sufficiently close to the rest of the population, while avoiding collisions, and they are able to track and synchronize their movement to the flight of a given set of neighbors within their visual field. The resulting collective behavior of the bee cloud therefore emerges from non-local short/long-range interactions. Differently from similar approaches present in the literature, we here test different alignment mechanisms (i.e., based either on an Euclidean or on a topological neighborhood metric), which have an impact also on the other social components characterizing insect behavior. A series of numerical realizations then shows the phenomenology of the swarm (in terms of pattern configuration, collective productive movement, and flight synchronization) in different regions of the space of free model parameters (i.e., strength of attractive/repulsive forces, extension of the interaction regions). In this respect, constraints in the possible variations of such coefficients are here given both by reasonable empirical observations and by analytical results on some stability characteristics of the defined pairwise interaction kernels, which have to assure a realistic crystalline configuration of the swarm. An analysis of the effect of unconscious random fluctuations of bee dynamics is also provided.

Antagonistic activities of some probiotic lactobacilli culture supernatant on Serratia marcescens swarming motility and antibiotic resistance

BACKGROUND AND OBJECTIVES

Serratia marcescens, a potentially pathogenic bacterium, benefits from its swarming motility and resistance to antibiotic as two important virulence factors. Inappropriate use of antibiotics often results in drug resistance phenomenon in bacterial population. Use of probiotic bacteria has been recommended as partial replacement. In this study, we investigated the effects of some lactobacilli culture supernatant on swarming, motility and antibiotic resistance of S. marcescens.

MATERIALS AND METHODS

Antimicrobial activity of lactobacilli supernatant and susceptibility testing carried out on S. marcescens isolates. Pretreatment effect of lactobacilli culture supernatant on antibiotic - resistance pattern in S. marcescens was determined by comparison of the MIC of bacteria before and after the treatment.

RESULTS

Our results showed that pretreatment with L. acidophilus ATCC 4356 supernatant can affect the resistance of Serratia strains against ceftriaxone, but it had no effect on the resistance to other antibiotics. Furthermore, culture supernatant of lactobacilli with concentrations greater than 2%, had an effect on the swarming ability of S. marcescens ATCC 13880 and inhibited it.

CONCLUSION

Probiotic bacteria and their metabolites have the ability to inhibit virulence factors such as antibiotic resistance and swarming motility and can be used as alternatives to antibiotics.

Differential signal sensitivities can contribute to the stability of multispecies bacterial communities

Background

Bacterial species present in multispecies microbial communities often react to the same chemical signal but at vastly different concentrations. The existence of different response thresholds with respect to the same signal molecule has been well documented in quorum sensing which is one of the best studied inter-cellular signalling mechanisms in bacteria. The biological significance of this phenomenon is still poorly understood, and cannot be easily studied in nature or in laboratory models. The aim of this study is to establish the role of differential signal response thresholds in stabilizing microbial communities.

Results

We tested binary competition scenarios using an agent-based model in which competing bacteria had different response levels with respect to signals, cooperation factors or both, respectively. While in previous scenarios fitter species outcompete slower growing competitors, we found that stable equilibria could form if the fitter species responded to a higher chemical concentration level than the slower growing competitor. We also found that species secreting antibiotic could form a stable community with other competing species if antibiotic production started at higher response thresholds.

Conclusions

Microbial communities in nature rely on the stable coexistence of species that necessarily differ in their fitness. We found that differential response thresholds provide a simple and elegant way for keeping slower growing species within the community. High response thresholds can be considered as self-restraint of the fitter species that allows metabolically useful but slower growing species to remain within a community, and thereby the metabolic repertoire of the community will be maintained.

Reviewers

This article was reviewed by Michael Gromiha, Sebastian Maurer-Stroh, István Simon and L. Aravind.

Electronic supplementary material

The online version of this article (doi:10.1186/s13062-017-0192-3) contains supplementary material, which is available to authorized users.

Honeybee workers with higher reproductive potential live longer lives

Social insects, especially honeybees, have received much attention in comparative gerontology because of their peculiar and flexible ageing patterns that differ across genetically similar individuals. The longevity of honeybee individuals varies and depends on patterns of gene expression during development; females developing into reproductive individuals (queens) live longer than facultatively sterile workers. Here, we show that rebel workers, which develop under queenless conditions after swarming and have high reproductive potential, live approximately 4days longer in hives and approximately 3days longer in cages than individuals that develop in queenright colonies and have lower reproductive potential; this difference in longevity occurs in both free-flying and caged workers. Moreover, we show that both rebel and normal workers live longer when their ovaries contain more ovarioles. Longer-living rebel workers can benefit the colony because they can fill the generation gap that emerges between workers after queen exchange during swarming. Our findings provide novel evidence that the fecundity of workers in a social insect colony impacts their intrinsic longevity.

Influence of twitching and swarming motilities on biofilm formation in Pseudomonas strains

The genus Pseudomonas mainly includes opportunistic pathogens that rely on type IV pili as an important virulence factor, which is associated with adherence and biofilm formation. Pseudomonas infections are well known to be persistent and resilient in nature largely because of the tendency of the species to form biofilms. This study aimed at analyzing environmental strains of Pseudomonas genus with respect to their ability to execute twitching and swarming motilities as well as with respect to their ability to form biofilms both in the presence as well as in the absence of furanone, a substance that has the potential to prevent the formation of biofilms. Strains of Pseudomonas aeruginosa and strains belonging to other species of the genus were analyzed. Twitching and swarming motility assays and biofilm-formation assays, both in the presence as well as in the absence of furanone, were performed. In twitching assay strains belonging to P. aeruginosa outperformed those belonging to other species. Interestingly, it was seen that the presence of furanone had a negative impact on formation of twitching and swarming motility zones. In the case of biofilm assays, it was observed that the presence of furanone resulted in an observable decrease in the degree of adhesion in 30% of the analyzed strains. Thus, from our results, it can be concluded that, as compared to other species, the strains belonging to P. aeruginosa exhibit a higher potential for twitching motility and similar performance in swarming motility and biofilm formation. It can also be concluded that furanone has the potential to interfere with both motilities as well as with biofilm formation.

The effect of changing topography on the coordinated marching of locust nymphs

Collective motion has traditionally been studied in the lab in homogeneous, obstacle-free environments, with little work having been conducted with changing landscapes or topography. Here, the impact of spatial heterogeneity on the collective motion exhibited by marching desert locust nymphs was studied under controlled lab conditions. Our experimental circular arenas, incorporating a funnel-like narrowing followed by re-widening, did not constitute a major barrier to the locusts but, rather, mimicked a changing topography in the natural environment. We examined its effects on macroscopic features of the locust collective behavior, as well as the any changes in their marching kinematics. A major finding was that of the limited extent to which the changing topography affected system-level features of the marching locust group, such as the order parameter and the fraction of walking individuals, despite increased crowding at the funnel. Overall, marching kinematics was also very little affected, suggesting that locust marching bands adjust to the environment, with little effect on the overall dynamics of the group. These findings are in contrast to recent theoretical results predicting that environmental heterogeneities qualitatively alter the dynamics of collectively moving particles; and highlight the crucial role of rapid individual plasticity and adaptability in the dynamics of flocks and swarms. Our study has revealed other important features of the marching behavior of the desert locust in addition to its robustness: the locusts demonstrated both, clear thigmotaxis and a tendency to spread-out and fill the available space.