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 strain ADP1 is a gram-negative bacterium normally studied because of its high competence for genetic transformation and its ability to catabolize plant-derived aromatic compounds. A previous study has identified that the gene cluster ACIAD1969-ACIAD1952 contains genes that may be responsible for potassium tellurite resistance, as well as other proteins that are “hypothetical.” Our goal was to use bioinformatics to investigate this gene cluster and to determine whether it played a role in potassium tellurite resistance as well as twitching motility. Our results indicate that the gene cluster is actually composed of four different operons that play a role in tellurite resistance. We also found that the gene cluster was most likely inherited from horizontal gene transfer, as it is not found in any other Acinetobacter strains. Furthermore, all genes except ACIAD1956, ACIAD1962 and ACIAD1964 are responsible for potassium tellurite resistance in ADP1 and all mutants exhibit twitching motility defects. Our results indicate that the genes in the gene cluster ACIAD1969-ACIAD1952 encode proteins and should no longer be considered “hypothetical.”
Acinetobacter baylyi ADP1 has been studied in laboratories because of their competence for natural transformation and ability to adapt to different environmental conditions. A previous study has found 30 different genes in A. baylyi ADP1 that are induced by starvation during the long term stationary phase. ACIAD0167 is one of them, encoding a Vgr-like protein. The goal of this study was to test whether ACIAD0167 and other genes in its operon (ACIAD0166, ACIAD0168 and ACIAD0169) are required for twitching motility, or for surviving stressful conditions including heat shock, desiccation and DNA damage. Our study found that ACIAD0167 and the other three genes in the operon play a role in twitching motility in A. baylyi but apparently not in other phenotypes. The likely first gene in the operon, ACIAD0166, was cloned into wild-type ADP1 and over-expression of the gene caused a smaller twitching zone than one produced by wild type cells, further implicating the role of ACIAD0167-containing operon in twitching motility. These results indicate that ACIAD0166, ACIAD0167, ACIAD0168, and ACIAD0169 genes encode proteins, and should no longer be considered “hypothetical” genes. We also found a novel link among ACIAD0167, twitching motility and the type VI secretion system (T6SS). ACIAD0167 is found in the STRING network to be associated with genes involved the T6SS, whose structure resembles an inverted bacteriophage tail.