Succinate, iron chelation, and monovalent cations affect the transformation efficiency of Acinetobacter baylyi ATCC 33305 during growth in complex media.

Natural transformation is the acquisition of new genetic material via the uptake of exogenous DNA by competent bacteria. Acinetobacter baylyi is model for natural transformation. Here we focus on the natural transformation of A. baylyi ATCC 33305 grown in complex media and seek environmental conditions that appreciably affect transformation efficiency. We find that the transformation efficiency for A. baylyi is a resilient characteristic that remains high under most conditions tested. We do find several distinct conditions that alter natural transformation efficiency including addition of succinate, Fe2+ (ferrous) iron chelation, and substitution of sodium ions with potassium ones. These distinct conditions could be useful to fine tune transformation efficiency for researchers using A. baylyi as a model organism to study natural transformation.

Acinetobacter baylyi long-term stationary-phase protein StiP is a protease required for normal cell morphology and resistance to tellurite.

We investigated the Acinetobacter baylyi gene ACIAD1960, known from previous work to be expressed during long-term stationary phase. The protein encoded by this gene had been annotated as a Conserved Hypothetical Protein, surrounded by putative tellurite resistance ("Ter") proteins. Sequence analysis suggested that the protein belongs to the DUF1796 putative papain-like protease family. Here, we show that the purified protein, subsequently named StiP, has cysteine protease activity. Deletion of stiP causes hypersensitivity to tellurite, altered population dynamics during long-term batch culture, and most strikingly, dramatic alteration of normal cell morphology. StiP and associated Ter proteins (the StiP-Ter cluster) are therefore important for regulating cell morphology, likely in response to oxidative damage or depletion of intracellular thiol pools, triggered artificially by tellurite exposure. Our finding has broad significance because while tellurite is an extremely rare compound in nature, oxidative damage, the need to maintain a particular balance of intracellular thiols, and the need to regulate cell morphology are ubiquitous.

The role of core and accessory type IV pilus genes in natural transformation and twitching motility in the bacterium Acinetobacter baylyi.

Here we present an examination of type IV pilus genes associated with competence and twitching in the bacterium Acinetobacter baylyi (strain ADP1, BD413). We used bioinformatics to identify potential competence and twitching genes and their operons. We measured the competence and twitching phenotypes of the bioinformatically-identified genes. These results demonstrate that competence and twitching in A. baylyi both rely upon a core of the same type IV pilus proteins. The core includes the inner membrane assembly platform (PilC), a periplasmic assemblage connecting the inner membrane assembly platform to the secretin (ComM), a secretin (ComQ) and its associated pilotin (PilF) that assists with secretin assembly and localization, both cytoplasmic pilus retraction ATPases (PilU, PilT), and pilins (ComP, ComB, PilX). Proteins not needed for both competence and twitching are instead found to specialize in either of the two traits. The pilins are varied in their specialization with some required for either competence (FimT) and others for twitching (ComE). The protein that transports DNA across the inner membrane (ComA) specializes in competence, while signal transduction proteins (PilG, PilS, and PilR) specialize in twitching. Taken together our results suggest that the function of accessory proteins should not be based on homology alone. In addition the results suggest that in A. baylyi the mechanisms of natural transformation and twitching are mediated by the same set of core Type IV pilus proteins with distinct specialized proteins required for each phenotype. Finally, since competence requires multiple pilins as well as both pilus retraction motors PilU and PilT, this suggests that A. baylyi employs a pilus in natural transformation.