Autoinducer 2 Is Required for Biofilm Growth ofAggregatibacter(Actinobacillus)actinomycetemcomitans

Abstract

Autoinducer 2 (AI-2) is required for the growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans in culture under conditions of iron limitation. However, in vivo this organism thrives in a complex multispecies biofilm that forms in the human oral cavity. In this report, we show that adherent growth of A. actinomycetemcomitans on a saliva-coated surface, but not planktonic growth under iron-replete conditions, is defective in a LuxS-deficient background. Biofilm growth of the luxS mutant exhibited lower total biomass and lower biofilm depth than those for the wild-type strain. Normal biofilm growth of the luxS mutant was restored genetically by introduction of a functional copy of luxS and biochemically by addition of partially purified AI-2. Furthermore, introduction of S-adenosylhomocysteine hydrolase, which restores the metabolism of S-adenosylmethionine in the absence of LuxS, into A. actinomycetemcomitans did not complement the luxS mutation unless AI-2 was added in trans. This suggests that AI-2 itself is required for biofilm growth by A. actinomycetemcomitans. A biofilm growth deficiency similar to that of the LuxS-deficient strain was also observed when a gene encoding the AI-2-interacting protein RbsB or LsrB was inactivated. Biofilm formation by A. actinomycetemcomitans was virtually eliminated upon inactivation of both rbsB and lsrB. In addition, biofilm growth by wild-type A. actinomycetemcomitans was reduced in the presence of ribose, which competes with AI-2 for binding to RbsB. These results suggest that RbsB and LsrB function as AI-2 receptors in A. actinomycetemcomitans and that the development of A. actinomycetemcomitans biofilms requires AI-2.

Escherichia coli transcription factor YncC (McbR) regulates colanic acid and biofilm formation by repressing expression of periplasmic protein YbiM (McbA)

“…In E. coli, AI-2 stimulates biofilm formation and changes its architecture by stimulating flagellar motility via the quorumsensing regulator MqsR that acts through the two-component motility regulatory system QseBC (González Barrios et al, 2006), which transcriptionally regulates FlhDC, the master regulator of flagella and motility genes fliLMNOPQR, fliAZ, flhBA and flgABCDMN (Liu and Matsumura, 1994;Claret and Hughes, 2002;Clarke and Sperandio, 2005). This result is consistent with the recent finding that in the oral bacterium Aggregatibacter actinomycetemcomitans, AI-2 regulates its biofilm formation most likely through its QseBC system (Shao et al, 2007). Also, in the human gastric pathogen Helicobacter pylori, AI-2 controls motility by controlling genes upstream of the motility and flagellar regulator FlhA (Rader et al, 2007).…”

Autoinducer-2 influences interactions amongst pioneer colonizing streptococci in oral biofilms

“…We hypothesize that the reduction in AI-2 activity is due to an active uptake system such as that which exists in Salmonella typhimurium and Aggregatibacter actinomycetemcomitans. These species can remove AI-2 from solution through the expression of ABC-type transporters (James et al, 2006;Shao et al, 2007;Taga et al, 2001Taga et al, , 2003. Assuming that the reduction of AI-2 activity by S. gordonii DL1 and S. oralis 34 is also due to the removal by transporters, the difference in rates of removal along with different rates of production of AI-2 will contribute to the amount of AI-2 that is bioavailable for cell-cell communication.…”

Heterologous Expression of sahH Reveals That Biofilm Formation Is Autoinducer-2-independent in Streptococcus sanguinis but Is Associated with an Intact Activated Methionine Cycle

“…The functionality of a SahH complemented interrupted AMC has been demonstrated only in Gram-negative bacteria (15,16). Consequently, in our study we examined for the suitability of such heterologous complementation in a Gram-positive bacterium.…”