| Bacteria are capable of forming multicellular communities, known as biofilms. Bacillus subtilis is a Gram-positive, rod shaped, soil-dwelling bacterium often used as a model organism to study biofilm formation. Both extracellular and intracellular signals can trigger biofilm formation through a signaling cascade, which turns on genes involved in production of the biofilm matrix. In B. subtilis, the matrix consists of an exopolysaccharide (EPS) component and two protein components, which are regulated on a genetic level by two master regulators, SinR and AbrB. Biosynthesis of the EPS is also regulated at the post-translational level, by a bacterial tyrosine kinase (BY-kinase), EpsB, which is encoded within the same operon as the enzymes involved in the biosynthesis of EPS. EpsB is activated by EpsA, which senses EPS in a quorum-sensing-like manner. We show genetic evidence for EpsB activation by TkmA, a modulator of a different BY-kinase can activate EpsB. This cross-talk allows B. subtilis to increase the signals to which it can respond.;Intracellularly, serine starvation triggers biofilm formation. We elucidate the mechanism by which this occurs and investigate the regulation of serine biosynthesis. Expression of serA, which encodes SerA, the enzyme responsible for the first and rate-limiting step of serine biosynthesis decreases upon entry into stationary phase and is regulated by catabolite control. This regulation allows cells to trigger biofilm formation based on available nutrients as well as external stimuli. Accompanying this decrease in serine is a decrease in seryl-tRNA isoacceptors, responsible for adding serine to growing peptide chains in the ribosome. It was previously observed that ribosomes pause on specific serine codons under serine starvation and this decrease in tRNAs may be causing this. |
