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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.

Bacteria in nature often exist as sessile communities called biofilms. These communities develop structures that are morphologically and physiologically differentiated from free-living bacteria. A cell-to-cell signal is involved in the development of Pseudomonas aeruginosa biofilms. A specific signaling mutant, a /as/ mutant, forms flat, undifferentiated biofilms that unlike wild-type biofilms are sensitive to the biocide sodium dodecyl sulfate. Mutant biofilms appeared normal when grown in the presence of a synthetic signal molecule. The involvement of an intercellular signal molecule in the development of P. aeruginosa biofilms suggests possible targets to control biofilm growth on catheters, in cystic fibrosis, and in other environments where P. aeruginosa biofilms are a persistent problem., Certain bacteria, such as the fruiting bacteria, communicate with each other to form structured macroscopic groups(1,2). Recently, it has become apparent that in appropriate environments, common bacteria exhibit similar social [...]

Proteus mirabilis colonies have remarkable geometric regularity. Basic microbiological techniques and imaging methods were employed to measure periodic macroscopic events in swarm colony morphogenesis. There were three initial phases (lag phase, first swarming phase and first consolidation phase) followed by repeating cycles of subsequent swarming plus consolidation phases. Each Proteus swarm colony terrace corresponds to one swarming-plus-consolidation cycle.

The mechanism of signal processing in Escherichia coli is studied using photoactivated caged compounds and computer video analysis, revealing that the transfer of motor responses from opposing signals to same receptors are merged, whereas opposing signals transferred by different chemoreceptors are not unified, and therefore generate biphasic motor responses. A study of Tar and Tsre, two amino acid and pH sensing receptors, reveals that at alkaline pH, the Tar response in the wild strain of E. coli is higher compared than that of the Tsr signal. The experimental set up of the study is discussed.

The best indicator of spatial and seasonal variations in benthic bacterial production in various sediment types in the North Sea is temperature. Phytopigment content in sediment organic matter increased during summer, ensuring increased bacterial production in these sediment organic matter rich locations. During winter, temperature increase did not result in enhanced benthic bacterial production.

Communities form by interactions amongst individuals. In the beginning, a few wandering souls find an appropriate location in which to settle, As the population numbers increase at this spot, individuals [...]