An alternative strategy for adaptation in bacterial behavior

The cognitive cell: bacterial behavior reconsidered

Research on how bacteria adapt to changing environments underlies the contemporary biological understanding of signal transduction (ST), and ST provides the foundation of the information-processing approach that is the hallmark of the ‘cognitive revolution,’ which began in the mid-20th century. Yet cognitive scientists largely remain oblivious to research into microbial behavior that might provide insights into problems in their own domains, while microbiologists seem equally unaware of the potential importance of their work to understanding cognitive capacities in multicellular organisms, including vertebrates. Evidence in bacteria for capacities encompassed by the concept of cognition is reviewed. Parallels exist not only at the heuristic level of functional analogue, but also at the level of molecular mechanism, evolution and ecology, which is where fruitful cross-fertilization among disciplines might be found.

Environmental modification and niche construction: developing O2 gradients drive the evolution of the Wrinkly Spreader

The evolutionary success of the novel Wrinkly Spreader (WS) genotypes in diversifying Pseudomonas fluorescens SBW25 populations in static liquid microcosms has been attributed to the greater availability of O(2) at the air-liquid (A-L) interface where the WS produces a physically cohesive-class biofilm. However, the importance of O(2) gradients in SBW25 adaptation has never been examined. We have explicitly tested the role of O(2) in evolving populations using microsensor profiling and experiments conducted under high and low O(2) conditions. Initial colonists of static microcosms were found to establish O(2) gradients before significant population growth had occurred, converting a previously homogenous environment into one containing a resource continuum with high and low O(2) regions. These gradients were found to persist for long periods by which time significant numbers of WS had appeared colonising the high O(2) niches. Growth was O(2) limited in static microcosms, but high O(2) conditions like those found near the A-L interface supported greater growth and favoured the emergence of WS-like genotypes. A fitness advantage to biofilm formation was seen under high but not low O(2) conditions, suggesting that the cost of biofilm production could only be offset when O(2) levels above the A-L interface were high. Profiling of mature WS biofilms showed that they also contained high and low O(2) regions. Niches within these may support further diversification and succession of the developing biofilm population. O(2) availability has been found to be a major factor underlying the evolutionary success of the WS genotype in static microcosms and illustrates the importance of this resource continuum in microbial diversification and adaptation.

Endocytosis-dependent desensitization and protein synthesis-dependent resensitization in retinal growth cone adaptation

It has been proposed that growth cones navigating through gradients adapt to baseline concentrations of guidance cues. This adaptation process is poorly understood. Using the collapse assay, we show that adaptation in Xenopus laevis retinal growth cones to the guidance cues Sema3A or netrin-1 involves two processes: a fast, ligand-specific desensitization that occurs within 2 min of exposure and is dependent on endocytosis, and a slower, ligand-specific resensitization, which occurs within 5 min and is dependent upon protein synthesis. These two phases of adaptation allow retinal axons to adjust their range of sensitivity to specific guidance cues.