Our understanding of the social lives of microbes has been revolutionized over the past 20 years. It used to be assumed that bacteria and other microorganisms lived relatively independent unicellular lives, without the cooperative behaviors that have provoked so much interest in mammals, birds, and insects. However, a rapidly expanding body of research has completely overturned this idea, showing that microbes indulge in a variety of social behaviors involving complex systems of cooperation, communication, and synchronization. Work in this area has already provided some elegant experimental tests of social evolutionary theory, demonstrating the importance of factors such as relatedness, kin discrimination, competition between relatives, and enforcement of cooperation. Our aim here is to review these social behaviors, emphasizing the unique opportunities they offer for testing existing evolutionary theory as well as highlighting the novel theoretical problems that they pose.

https://synergy.st-andrews.ac.uk/gardner/files/2015/05/West_et_al_2007.pdf

The Social Lives of Microbes

The basics of bio-flocs technology: The added value for aquaculture

Although unicellular, bacteria are highly interactive and employ a range of cell-to-cell communication or ‘quorum sensing (QS)’ systems for promoting collective behaviour within a population. QS is generally considered to facilitate gene expression only when the population has reached a sufficient cell density and depends on the synthesis of small molecules that diffuse in and out of bacterial cells. As the bacterial population density increases, so does the synthesis of QS signal molecules and consequently, their concentration in the external environment increases. Once a critical threshold concentration is reached, a target sensor kinase or response regulator is activated, so facilitating the expression of QS-dependent target genes. Several chemically distinct families of QS signal molecules have been described, of which the N-acylhomoserine lactone (AHL) family in Gram-negative bacteria have been the most intensively investigated. QS contributes to environmental adaptation by facilitating the elaboration of virulence determinants in pathogenic species and plant biocontrol characteristics in beneficial species as well as directing biofilm formation and colony escape. QS also crosses the prokaryotic–eukaryotic boundary in that QS signal molecules influence the behaviour of eukaryotic organisms in both the plant and mammalian worlds such that QS signal molecules may directly facilitate bacterial survival by promoting an advantageous lifestyle within a given environmental niche.

Quorum sensing, communication and cross-kingdom signalling in the bacterial world

For many years, bacterial cells were considered primarily as selfish individuals, but, in recent years, it has become evident that, far from operating in isolation, they coordinate collective behaviour in response to environmental challenges using sophisticated intercellular communication networks. Cell-to-cell communication between bacteria is mediated by small diffusible signal molecules that trigger changes in gene expression in response to fluctuations in population density. This process, generally referred to as quorum sensing (QS), controls diverse phenotypes in numerous Gram-positive and Gram-negative bacteria. Recent advances have revealed that bacteria are not limited to communication within their own species but are capable of ‘listening in’ and ‘broadcasting to’ unrelated species to intercept messages and coerce cohabitants into behavioural modifications, either for the good of the population or for the benefit of one species over another. It is also evident that QS is not limited to the bacterial kingdom. The study of two-way intercellular signalling networks between bacteria and both uni- and multicellular eukaryotes as well as between eukaryotes is just beginning to unveil a rich diversity of communication pathways.

/pdf/quorum-sensing-and-social-networking-in-the-microbial-world-5e5sw1skw2.pdf

Quorum sensing and social networking in the microbial world

We demonstrate the utility of the Raman confocal microscope to generate a spectral profile from a single microbial cell and the use of this approach to differentiate bacterial species. In general, profiles from different bacterial taxa shared similar peaks, but the relative abundances of these components varied between different species. The use of multivariate methods subsequently allowed taxa discrimination. Further investigations revealed that the single-cell spectra could be used to differentiate between growth phases of a single species, but these differences did not obscure the overall interspecies discrimination. Finally, we tested the efficacy of the method as a means to identify cells responsible for the uptake of a specific substrate. A single strain was grown in media containing incrementally varying ratios of 13C6 to 12C6 glucose, and it was found that 13C incorporation shifted characteristic peaks to lower wavenumbers. These findings suggest that Raman microscopy has significant potential for...

Raman microscopic analysis of single microbial cells

Summary

The role of intercellular signalling in the regulation of genes and phenotypes in a broad range of bacterial species is now firmly established. In contrast, the impact of intercellular signalling on microbial community parameters, such as species diversity and function, is less well understood. In this study the role of N-acyl-l-homoserine lactones (AHLs) in microbial community dynamics in an industrial wastewater treatment system is addressed. Seven proteobacterial strains producing compounds with AHL-like activity were isolated from the treatment plant. Three of these belong to genera with no previously identified AHL producing species. Addition of AHLs at 2 µM to sludge samples generated changes in both community function (phenol degradation) and composition as determined by length heterogeneity PCR and denaturing gradient gel electrophoresis. Phenol degradation was more stable as a result of the AHL augmentation. A dominant functional member of the Thauera genus was transiently supplanted by a member of the Comomonas genus in response to AHL addition. This suggests that AHLs can play a role in mediating microbial community parameters and has implications for ecosystem function and industrial wastewater treatment.

N‐acyl‐l‐homoserine lactones (AHLs) affect microbial community composition and function in activated sludge

Two sulfonylurea herbicides, chlorsulfuron and metsulfuron-methyl, were studied under laboratory conditions, in order to elucidate the biodegradation pathway operated by Aspergillus niger, a common soil fungus, which is often involved in the degradation of xenobiotics. HPLC-UV was used to study the kinetic of degradation, whereas LC-MS was used to identify the metabolites structure. In order to avoid the chemical degradation induced by a decrease in pH, due to the production of citric acid by the fungus, the experiments were performed in a buffered neutral medium. No significant degradation for both compounds was observed in mineral medium with 0.2% sodium acetate. On the contrary, in a rich medium, after 28 days the degradations, chemical degradation excluded, were about 30% for chlorsulfuron and 33% for metsulfuron-methyl. The main microbial metabolites were obtained via cleavage of the sulfonylurea bridge. In addition the fungus seems to be able to hydroxylate the aromatic ring of chlorsulfuron. In the case of metsulfuron-methyl the only detected metabolite was the triazine derivative, while the aromatic portion was completely degraded. Finally, the demethylation of the methoxy group on the triazine ring, previously observed with a Pseudomonas fluorescens strain, was not observed with A. niger.

Biodegradation of chlorsulfuron and metsulfuron-methyl by Aspergillus niger in laboratory conditions.

Aims: This research focused on the effects of low electric current (LEC) on the cell viability and metabolic activity of Escherichia coli and Bacillus cereus. Methods and Results: Different LEC intensities at fixed amperage were applied, employing either graphite or copper electrode pairs, and the effects were determined by conventional cultural methods and bioindicators. On E. coli, the LEC with graphite electrodes at 5 and 10 mA led to no significant variation, but at 20 and 40 mA there was increasing inhibition of both the enzymatic activities and growth, and a reduction in ATP content. On B. cereus, similar experiments at the lower amperages did not have any inhibitor effects, however, the 40 mA current stimulated growth, ATP content and some enzymatic activities. The LEC treatment using copper electrodes caused, already at 5 mA, inhibition of bacterial growth and metabolic and enzymatic activities in both E. coli and B. cereus. Conclusions: On the basis of the obtained results using different amperages and electrodes, we can conclude that E. coli seem to be more sensitive compared with B. cereus. Significance and Impact of the Study: The study increases the knowledge on LEC treatment effects on the pure bacterial cultures.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2672.2007.03374.x

Effects of low electric current (LEC) treatment on pure bacterial cultures.

Aims: Azimsulfuron is a recently introduced sulfonylurea herbicide useful in controlling weeds in paddy fields. To date very little information is available on the biodegradation of this pesticide and on its effect on the soil microbial community. The aim of this work was to study its biodegradation both in slurry soil microcosms and in batch tests with mixed and pure cultures.



Methods and Results:  Azimsulfuron was applied to forest bulk soil in order to study its effect on the structure of the bacterial soil community, as detectable by denaturant gradient gel electrophoresis (DGGE) analyses. Biodegradation and abiotic processes were investigated by HPLC analyses. In addition, a microbial consortium was selected, that was able to use azimsulfuron as the sole energy and carbon source. One of the metabolites produced by the consortium was isolated and identified through LC-MS analyses. Cultivable bacteria of the consortium were isolated and identified by 16S rDNA sequencing (1400 bp).



Conclusions:  Azimsulfuron treatment seems to have the ability to cause changes in the bacterial community structure that are detectable by DGGE analyses. It is easily biodegraded both in microcosms and in batch tests, with the formation of an intermediate that was identified as 2-methyl-4-(2-methyl-2H-tetrazol-5-yl)-2H-pyrazole-3-sulfonamide.



Significance and Impact of the Study:  The study increases the knowledge on the biodegradation of azimsulfuron and its effects on the soil microbiota.

The microbial degradation of azimsulfuron and its effect on the soil bacterial community

Animal, civil and industrial waste matter is a source of potential chemical, microbiological and air pollutants. In populated areas the presence of faecal bacteria and the production of malodorous compounds during waste storage and in the tanks of wastewater treatment plants, can cause concern. The general aim of the work was to study electrolytic waste treatment (recently applied on animal slurry) using low electric current across graphite and copper electrodes, determining its effect on the microflora of sludge, collected from the equalisation basin of an industrial aerobic wastewater treatment plant, and on odour emission abatement. Biochemical and enzymatic indicators like ATP content and a pool of 19 enzymatic activities were tested, comparing them with viable cell counts by traditional microbiological methods, to verify the validity of such indicators in monitoring the electrolytic treatment and to assess their correlation with odour reduction. The preliminary results of our laboratory-scale trials showed that in the presence of inert electrodes, such as graphite, metabolic activity is stimulated, whereas with copper electrodes the ATP content and some enzymatic activities are inhibited quite considerably after only four days, this being accompanied by a marked reduction in odour. Consideration was also given to the total copper released from the electrodes and its recovery using iron electrodes.

A. Valle

Papers

N‐acyl‐l‐homoserine lactones (AHLs) affect microbial community composition and function in activated sludge

Biodegradation of chlorsulfuron and metsulfuron-methyl by Aspergillus niger in laboratory conditions.

Effects of low electric current (LEC) treatment on pure bacterial cultures.

The microbial degradation of azimsulfuron and its effect on the soil bacterial community

Laboratory-scale trials of electrolytic treatment on industrial wastewaters: microbiological aspects