O -Mannosylation in Candida albicans Enables Development of Interkingdom Biofilm Communities

Abstract

Candida albicans is a fungus that colonizes oral cavity surfaces, the gut, and the genital tract. Streptococcus gordonii is a ubiquitous oral bacterium that has been shown to form biofilm communities with C. albicans. Formation of dual-species S. gordonii-C. albicans biofilm communities involves interaction of the S. gordonii SspB protein with the Als3 protein on the hyphal filament surface of C. albicans. Mannoproteins comprise a major component of the C. albicans cell wall, and in this study we sought to determine if mannosylation in cell wall biogenesis of C. albicans was necessary for hyphal adhesin functions associated with interkingdom biofilm development. A C. albicans mnt1Δ mnt2Δ mutant, with deleted α-1,2-mannosyltransferase genes and thus defective in O-mannosylation, was abrogated in biofilm formation under various growth conditions and produced hyphal filaments that were not recognized by S. gordonii. Cell wall proteomes of hypha-forming mnt1Δ mnt2Δ mutant cells showed growth medium-dependent alterations, compared to findings for the wild type, in a range of protein components, including Als1, Als3, Rbt1, Scw1, and Sap9. Hyphal filaments formed by mnt1Δ mnt2Δ mutant cells, unlike wild-type hyphae, did not interact with C. albicans Als3 or Hwp1 partner cell wall proteins or with S. gordonii SspB partner adhesin, suggesting defective functionality of adhesins on the mnt1Δ mnt2Δ mutant. These observations imply that early stage O-mannosylation is critical for activation of hyphal adhesin functions required for biofilm formation, recognition by bacteria such as S. gordonii, and microbial community development.

Streptococcus gordonii comCDE (competence) operon modulates biofilm formation with Candida albicans

“…Such communities may also contain C. albicans, which is carried by~40 % of the healthy adult population (Clayton & Noble, 1966), and it is suggested that synergistic interactions between C. albicans and streptococci can promote carriage as well as disease (Dutton et al, 2014;Falsetta et al, 2014;Xu et al, 2014b). The establishment and development of such communities involves small molecule signalling between microbial components, which maximizes metabolic efficiency and controls competition of species.…”

“…The ComCDE systems in S. gordonii, S. pneumoniae and S. mutans function as QS autoregulatory control systems, modulating gene expression patterns in different ways for the three streptococcal species (Vickerman et al, 2007;Mashburn-Warren et al, 2010;Son et al, 2012;Merritt & Qi, 2012). Since S. gordonii and C. albicans form fully integrated dual species biofilm communities (Dutton et al, 2014) we investigated the possible role of the ComCDE system in their regulation.…”

“…C. albicans strains were maintained on Sabouraud glucose agar (LabM) and suspension cultures were grown in YPD medium [10 g yeast extract l 21 , 20 g neopeptone l 21 , 2 % (w/v) glucose] at 37 uC with vigorous aeration. A defined medium (YPTGlc) supported the growth of S. gordonii and C. albicans and comprised 20 mM NaH 2 PO 4 (pH 7.0), 16 yeast nitrogen base, 1 g Bactotryptone l 21 and 0.4 % (w/v) glucose (Dutton et al, 2014). Antibiotics were used at the following concentrations: 100 mg ampicillin ml 21 ; 100 mg spectinomycin (Sp) ml 21 ; 5 mg erythromycin ml 21 .…”

“…Biofilms on coverslips were fixed with 0.5 ml paraformaldehyde (4 %) in PBS for 1 h at room temperature. Coverslips were rinsed with PBS and stained with FITC for 30 min in the dark (Dutton et al, 2014). In some experiments, C. albicans SBC156, derivative of SC5314 expressing red fluorescent protein (RFP) (Milne et al, 2011) was utilized.…”

“…These species of streptococci interact with a range of other oral microorganisms, thus establishing a foundation for the building of biofilm communities (Wright et al, 2013). S. gordonii forms biofilms with Porphyromonas gingivalis (Lamont et al, 2002), Actinomyces oris (Palmer et al, 2003), Fusobacterium nucleatum (Foster & Kolenbrander, 2004) and Aggregatibacter actinomycetemcomitans in dual or mixed species systems, and also produces dual species biofilms with the fungus Candida albicans (Bamford et al, 2009;Dutton et al, 2014).…”