No abstract

Most of Earth's biomass is composed of polysaccharides. During biomass decomposition, polysaccharides are degraded by heterotrophic bacteria as a nutrient and energy source and are thereby partly remineralized into CO2. As polysaccharides are heterogeneously distributed in nature, following the colonization and degradation of a polysaccharide hotspot the cells need to reach new polysaccharide hotspots. Even though these degradation-dispersal cycles are an integral part in the global carbon cycle, we know little about how cells alternate between degradation and motility, and which signal triggers this behavioral switch. Here, we studied the growth of the marine bacterium Vibrio cyclitrophicus ZF270 on the abundant marine polysaccharide alginate. We used microfluidics-coupled time-lapse microscopy to analyze motility and growth of individual cells, and RNA sequencing to study associated changes in gene expression. Single cells grow at reduced rate on alginate until they form large groups that cooperatively break down the polymer. Exposing cell groups to digested alginate accelerates cell growth and changes the expression of genes involved in alginate degradation and catabolism, central metabolism, ribosomal biosynthesis, and transport. However, exposure to digested alginate also triggers cells to become motile and disperse from cell groups, proportionally increasing with the group size before the nutrient switch, accompanied by high expression of genes involved in flagellar assembly, chemotaxis, and quorum sensing. The motile cells chemotax toward alginate hotspots, likely enabling cells to find new polysaccharide hotspots. Overall, our findings reveal the cellular mechanisms underlying bacterial degradation-dispersal cycles that drive remineralization in natural environments.

, commonly used in chemotaxis studies, is attracted mostly by amino acids, sugars, and peptides. We envisioned modifying the chemotaxis specificity of by expressing heterologous chemoreceptors from enabling attraction either to toluene or benzoate. The gene encoding the type 40-helical bundle (40H) methyl-accepting chemoreceptor for toluene from MT53 and the gene for the type 40H receptor for benzoate and related molecules from F1 were expressed from the promoter on a plasmid in motile wild-type MG1655. cells expressing McpT accumulated in chemoattraction assays to sources with 60 to 200 μM toluene, although less strongly than the response to 100 μM serine, but statistically significantly stronger than that to sources without any added attractant. An McpT-mCherry fusion protein was detectably expressed in and yielded weak but distinguishable membranes and polar foci in 1% of cells. cells expressing PcaY showed weak attraction to 0.1 to 1 mM benzoate, but 50 to 70% of cells localized the PcaY-mCherry fusion to their membrane. We conclude that implementing heterologous receptors in the chemotaxis network is possible and, upon improvement of the compatibility of the type 40H chemoreceptors, may bear interest for biosensing. Bacterial chemotaxis might be harnessed for the development of rapid biosensors, in which chemical availability is deduced from cell accumulation to chemoattractants over time. Chemotaxis of has been well studied, but the bacterium is not attracted to chemicals of environmental concern, such as aromatic solvents. We show here that heterologous chemoreceptors for aromatic compounds from at least partly functionally complement the chemotaxis network, yielding cells attracted to toluene or benzoate. Complementation was still inferior to native chemoattractants, like serine, but our study demonstrates the potential for obtaining selective sensing for aromatic compounds in.

25 26 27 28 Running title: Escherichia coli chemotactic to aromatic compounds 29 2 ABSTRACT (250 w.) 30 Escherichia coli, commonly used in chemotaxis studies, is attracted mostly by amino acids, 31 sugars and peptides. We envisioned modifying chemotaxis specificity of E. coli by expressing 32 heterologous chemoreceptors from Pseudomonas putida enabling attraction either to toluene 33 or benzoate. The mcpT gene encoding the type 40H methyl-accepting chemoreceptor for 34 toluene from Pseudomonas putida MT53 and the pcaY gene for the type 40H receptor for 35 benzoate and related molecules from P. putida F1 were expressed from the trg promoter on a 36 plasmid in motile wild-type E. coli MG1655. E. coli cells expressing McpT accumulated in 37 chemoattraction assays to sources with 60-200 µM toluene; less strongly than the response to 38 100 µM serine, but statistically significantly stronger than to sources without any added 39 attractant. An McpT-mCherry fusion protein was detectably expressed in E. coli and yielding 40 weak but distinguishable membrane and polar foci in 1% of cells. E. coli expressing PcaY 41 showed weak attraction to 0.1-1 mM benzoate but 50-70% of cells localized the PcaY-42 mCherry fusion to their membrane. We conclude that implementing heterologous receptors in 43 the E. coli chemotaxis network is possible and, upon improvement of the compatibility of the 44 type 40H chemoreceptors, may bear interest for biosensing . 45 46 IMPORTANCE (150 w.) 47 65Chemotaxis of Escherichia coli is strong and highly reproducible with known and 66 potent chemoattractants, such as serine or aspartate, and has been widely studied (4, 5). 67Unfortunately, E. coli does not naturally display chemotaxis towards molecules of potential 68 interest for environmental monitoring, such as aromatic or chlorinated solvents. Given its 69 relatively narrow native chemo-attractant range, it is interesting to investigate whether the E. 70 coli chemotaxis system can be complemented by heterologous chemoreceptors. One 71 important characteristic of methyl-accepting chemotaxis proteins (MCPs) and chemotaxis 72 effector proteins (e.g., CheY) is their structural conservation among bacteria (6-8). E. coli 73 possesses five chemotaxis receptors, but other environmental bacteria frequently encode 74 many more chemoreceptors albeit with often unknown effectors. For example, Pseudomonas 75 species can encode more than 20 MCPs in their genomes (9, 10). A few studies have 76 demonstrated successful expression of heterologous chemoreceptors in E. coli. For example, 77 several MCPs from Shewanella oneidensis could be expressed in E. coli, enabling energy 78 taxis with nitrate (11). Also, Aer-2, a soluble receptor from Pseudomonas aeruginosa 79 involved in aerotaxis, and PctApp, a putative MCP for amino acids from Pseudomonas putida 80 were shown to partially trigger chemotaxis response when expressed in E. coli (12, 13).81 However, no MCPs involved in sensing of environmental pollutants have to date been 82 functionally expressed in E. coli. 83 ...