Decreased temperature increases the expression of a disordered bacterial late embryogenesis abundant (LEA) protein that enhances natural transformation

Abstract

Late embryogenesis abundant (LEA) proteins are important players in the management of responses to stressful conditions, such as drought, high salinity, and changes in temperature. Many LEA proteins do not have defined three-dimensional structures, so they are intrinsically disordered proteins (IDPs) and are often highly hydrophilic. Although LEA-like sequences have been identified in bacterial genomes, the functions of bacterial LEA proteins have been studied only recently. Sequence analysis of outer membrane interleukin receptor I (BilRI) from the oral pathogen Aggregatibacter actinomycetemcomitans indicated that it shared sequence similarity with group 3/3b/4 LEA proteins. Comprehensive nuclearcgq magnetic resonance (NMR) studies confirmed its IDP nature, and expression studies in A. actinomycetemcomitans harboring a red fluorescence reporter protein-encoding gene revealed that bilRI promoter expression was increased at decreased temperatures. The amino acid backbone of BilRI did not stimulate either the production of reactive oxygen species from human leukocytes or the production of interleukin-6 from human macrophages. Moreover, BilRI-specific IgG antibodies could not be detected in the sera of A. actinomycetemcomitans culture-positive periodontitis patients. Since the bilRI gene is located near genes involved in natural competence (i.e., genes associated with the uptake of extracellular (eDNA) and its incorporation into the genome), we also investigated the role of BilRI in these events. Compared to wild-type cells, the Δ bilRI mutants showed a lower transformation efficiency, which indicates either a direct or indirect role in natural competence. In conclusion, A. actinomycetemcomitans might express BilRI, especially outside the host, to survive under stressful conditions and improve its transmission potential.

Deletion of competence genes represses expression of genes associated with anaerobic respiration/metabolism inAggregatibacter actinomycetemcomitans

“…The biofilm formation of ΔpilA::spe r has not been studied in detail, but the deletion mutant exhibits a colony morphology similar to that of the wild-type strain [21]. Although bilRI has been shown to decrease the transformation efficiency [23], deletion of the gene does not result in a completely nontransformable strain, as observed with deletion of hofQ in this study and with of pilA previously [21].…”

“…actinomycetemcomitans strain D7S was studied by the natural transformation assay described in [20] with modifications described in [23] using the wild-type D7S strain and the deletion mutant D7S…”

“…ΔhofQ. The construction of the linear DNA used in this assay (kanamycin resistance cassette flanked by sequences complementary to the genome of A. actinomycetemcomitans D7S) has been described in [23].…”

“…Furthermore, as both bilRI and hofQ are associated with natural competence [23], we sought to study how the deletion of an additional competence gene, pilA [21], affects gene expression in the naturally competent A. actinomycetemcomitans D7S strain.…”

“…Recently, we showed that the outer membrane lipoprotein BilRI also plays a role in efficient natural transformation [23]. The outer membrane secretin HofQ of A. actinomycetemcomitans is homologous to the competence protein ComE and exhibits structural and sequence properties similar to those of DNA-binding proteins [24].…”