Acinetobacter baylyi ADP1 is a gram-negative soil bacterium that exhibits competence and twitching motility. DNA uptake is achieved via the Type IV Pilus competence machine and twitching is performed by Type IV pili. Homologues of Type IV pili proteins are involved in transformation in a variety of bacteria. The similarities between proteins involved in DNA uptake, Type IV pilus systems and type II protein secretion systems suggests that they belong to evolutionary related systems containing cell envelope spanning structures with conserved architecture and core components. As many competence proteins of ADP1 are related to structural subunits and biogensis proteins of Type IV pili, a key question is whether Type IV pili of ADP1 are directly involved in DNA uptake and binding. Or, do the pilin-like components of the transformation system make up a completely different structure? Many bacteria can perform natural transformation; however, our knowledge regarding the structures and mechanisms needed for DNA uptake is scarce. Thus, our research involved determining which genes are needed for competence, which are used for twitching motility and which are possibly involved in both functions in ADP1. In order to test each protein’s role, tdk-kan knock out mutants were created and the mutants were compared to the wild type. An existing library of proteins predicted to encode various parts of the Type IV pilus with knock out genes was used. Our results showed that the majority of tested genes are needed for both competence and twitching, suggesting a physiological relationship. Specifically, mutants with a greater twitching ability were also more competent.
Acinetobacter baylyi is a gram-negative soil dwelling bacterium. The strain ADP1 is highly competent which allows for easy manipulation of its genes. The genes of interest here are a set of the genes encoding a type VI secretion system (T6SS), namely tssG, tssF, tssE, tssB, and tssC. This T6SS is homologous to the bacteriophage tail. The tail of the bacteriophage is used to inject DNA into a bacterial cell. Therefore, we hypothesized that the T6SS could be used to release DNA into the environment. Over the course of this research, we investigated ADP1 bacterial cells that contained knockouts of the various parts of the T6SS. The knockouts were used to determine which, if any, of the parts of the T6SS play a role in DNA release. We also tested the mutants for differences in growth rate and survival in long-term stationary phase (LTSP). LTSP is a phase in which 99% of the cells die off and the remaining 1% begin to eat waste and dead cells to survive. We examined survival in LTSP because another T6SS gene, vgrG (ACIAD0167), is known to be expressed during LTSP (Lostroh and Voyles, 2010). The gene is also necessary for survival during LTSP (Stanley and Lostroh, 2010) and twitching motility (Nguyen and Lostroh, 2013). We discovered that the core T6SS genes are not needed for a normal growth rate during exponential phase or for DNA release. However, we were unable to definitively determine if tssG, tssF, tssE, tssB, and tssC are necessary for survival during LTSP due to poor survival rates of the wild-type and mutants, likely caused by evaporation of water over the course of the experiments. Further research will be performed to determine which secretion system if any is responsible for DNA release and if tssG, tssF, tssE, tssB, and tssC are necessary for survival during LTSP.