Whole cell lysates were loaded at different dilutions (indicated as X, X/2, and X/3). subtilis == CCT129202 eLife digest == Bacteria use several different mechanisms to recognize and respond to changes in their environment. Protein sensors, for example, relay signals from the cell surface to target molecules within the cell. Additionally, RNA sensors can respond to internal levels of chemicals by regulating the expression of genes. Now, Subramaniam et al. have discovered a sensing mechanism in bacteria that does not rely on either protein sensors or RNA sensors. Bacteria normally live as free swimming cells in water. But sometimes, in response to certain environmental conditions, they form a multicellular community called a biofilm. In this biofilm, bacteria encase themselves with layers of carbohydrates and proteins, which then protect the bacteria from adverse chemicals such as antibiotics. A protein known as SinR plays a key role during biofilm formation in the model bacteriumBacillus subtilis. SinR normally prevents the formation of the carbohydrates and proteins that make up the biofilm. Upon the decision to form a biofilm,B. subtiliscounters the effect of SinR by producing an anti-SinR protein called SinI. Now Subramaniam et al. have found that as well as producing the SinI protein,B. subtilisuse an additional mechanism to promote biofilm formation. This mechanism relies on codons, the elements within genes that correspond to specific amino acids. Six different codons correspond to the amino acid serine, and the gene for the SinR protein contains above average numbers of four of them. These four codons are highly sensitive to serine levels, and they decrease the levels of the SinR protein when there is less serine in the environment, as happens to be the case in biofilms. And since SinR CCT129202 prevents the production of the carbohydrates and proteins that make up the Rabbit Polyclonal to EDG4 biofilms, a decrease in the levels of SinR leads to an increase in the production of biofilms. Since the serine codons at the heart of the sensing mechanism discovered by Subramaniam et al. are present in all forms of life, from viruses to humans, it is possible that similar sensing mechanisms might be found CCT129202 in contexts other than bacterial biofilms, such as in viral infection and cancer. DOI:http://dx.doi.org/10.7554/eLife.01501.002 == Introduction == Bacteria constantly monitor their environment and internal physiological state so that they can adapt to changing conditions. A wide variety of sensing mechanisms are deployed for this purpose, including CCT129202 dedicated protein sensors, such as histidine kinases, which mediate changes in gene expression by controlling the phosphorylation of cognate response regulators in response to environmental cues (West and Stock, 2001). Bacteria also sense changes in their environment and physiology by means of dedicated RNAs, such as the highly structured, leader RNA for the tryptophan operon, which controls the transcription of downstream genes in the operon by a mechanism involving ribosome stalling at tryptophan codons (Henkin and Yanofsky, 2002). Here we report the discovery of an unusually simple mechanism of environmental sensing involved in the process of biofilm formation by the bacteriumB. subtilisthat does not require a dedicated RNA or protein. Biofilm formation involves a switch from planktonic growth as individual cells to the formation of complex, multicellular communities in response to environmental cues (Kolter and Greenberg, 2006). InB. subtilis, these communities are embedded in a self-produced matrix consisting of polysaccharide and an amyloid-like protein, which are specified by theepsA-Oand thetapA-sipW-tasAoperons, respectively (Branda et al., 2001;Kearns et al., 2005). The transition to multicellularity is governed in part by four histidine kinases (KinA, KinB, KinC and KinD) that control the phosphorylation of the response regulator, Spo0A, a master regulator of post-exponential phase gene expression (Figure 1A) (Jiang et al., 2000;Vlamakis et al., 2013). Recent studies suggest that KinA and KinB respond to impaired respiration (Kolodkin-Gal et al., 2013), whereas KinC responds to membrane perturbations and KinD to unknown chemical signals (Lpez et al., 2009;Shemesh et al., 2010;Chen et al., 2012;Beauregard et al., 2013). Once phosphorylated, Spo0A turns onsinI, a gene encoding a small protein antagonist of the biofilm-specific regulatory protein SinR (Molle et al., 2003;Kearns et al., 2005). SinR, which is produced constitutively, is a repressor of the matrix operons,epsA-Oand thetapA-sipW-tasA, as well as other biofilm-related genes (Kearns et al., 2005;Chu et al., 2006;Chai et al., 2009). SinR is also a repressor of the.