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Interaction of Candida albicans cell wall Als3 protein with Streptococcus gordonii SspB adhesin promotes development of mixed-species communities

School of Oral and Dental Sciences, University of Bristol, Bristol, United Kingdom.
Infection and immunity (Impact Factor: 4.16). 11/2010; 78(11):4644-52. DOI: 10.1128/IAI.00685-10
Source: PubMed

ABSTRACT Candida albicans colonizes human mucosa and prosthetic surfaces associated with artificial joints, catheters, and dentures. In the oral cavity, C. albicans coexists with numerous bacterial species, and evidence suggests that bacteria may modulate fungal growth and biofilm formation. Streptococcus gordonii is found on most oral cavity surfaces and interacts with C. albicans to promote hyphal and biofilm formation. In this study, we investigated the role of the hyphal-wall protein Als3p in interactions of C. albicans with S. gordonii. Utilizing an ALS3 deletion mutant strain, it was shown that cells were not affected in initial adherence to the salivary pellicle or in hyphal formation in the planktonic phase. However, the Als3(-) mutant was unable to form biofilms on the salivary pellicle or deposited S. gordonii DL1 wild-type cells, and after initial adherence, als3Δ/als3Δ (ΔALS3) cells became detached concomitant with hyphal formation. In coaggregation assays, S. gordonii cells attached to, and accumulated around, hyphae formed by C. albicans wild-type cells. However, streptococci failed to attach to hyphae produced by the ΔALS3 mutant. Saccharomyces cerevisiae S150-2B cells expressing Als3p, but not control cells, supported binding of S. gordonii DL1. However, S. gordonii Δ(sspA sspB) cells deficient in production of the surface protein adhesins SspA and SspB showed >50% reduced levels of binding to S. cerevisiae expressing Als3p. Lactococcus lactis cells expressing SspB bound avidly to S. cerevisiae expressing Als3p, but not to S150-2B wild-type cells. These results show that recognition of C. albicans by S. gordonii involves Als3 protein-SspB protein interaction, defining a novel mechanism in fungal-bacterial communication.

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    • "To identify the CWPs on C. albicans involved, Nobbs et al. screened a panel of C. albicans CWPs for adhesion to biotic and abiotic surfaces and bacteria including S. gordonii and found that Als3, Eap1, and Hwp1 were able to enhance binding to S. gordonii (Nobbs et al., 2010) with the most important role for Als3. Further evidence suggested that SspB is the main bacterial ligand for this receptor and that both Als3 and SspB have amyloid properties, providing a model of adherence between both proteins (Silverman et al., 2010). Another important bacterial pathogen is S. aureus, which is associated with severe disease and high mortality (Harriott & Noverr, 2009). "
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    • "Especially the Als3 protein seems to play a vital role in adhesion, since its deletion strongly reduces adhesion to epithelial cells (Hoyer et al., 2008; Wächtler et al., 2012). In addition, this protein is also important for iron acquisition from ferritin (Almeida et al., 2008), formation of mixed-species biofilms (Silverman et al., 2010) and induction of endocytosis by host cells (Phan et al., 2007; Wächtler et al., 2012 and see also next section). As Als3 is hypha-associated (Argimon et al., 2007), it is expressed as the fungus forms filaments, for example upon physical contact with host cells, at body temperature and at ambient neutral pH. "
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    • "albicans is generally diploid) (Zhao et al., 2004). Als3p is hypha-specific (Murciano et al., 2012) and is in all probability involved in early establishment of biofilms in addition to interacting with oral streptococci (Silverman et al., 2010). "
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