The fungus Candida albicans colonizes human oral cavity surfaces in conjunction with a complex microflora. C. albicans SC5314 formed biofilms on saliva-coated surfaces that in early stages of development consisted of ϳ30% hyphal forms. In mixed biofilms with the oral bacterium Streptococcus gordonii DL1, hyphal development by C. albicans was enhanced so that biofilms consisted of ϳ60% hyphal forms. Cell-cell contact between S. gordonii and C. albicans involved Streptococcus cell wall-anchored proteins SspA and SspB (antigen I/II family polypeptides). Repression of C. albicans hyphal filament and biofilm production by the quorum-sensing molecule farnesol was relieved by S. gordonii. The ability of a luxS mutant of S. gordonii deficient in production of autoinducer 2 to induce C. albicans hyphal formation was reduced, and this mutant suppressed farnesol inhibition of hyphal formation less effectively. Coincubation of the two microbial species led to activation of C. albicans mitogen-activated protein kinase Cek1p, inhibition of Mkc1p activation by H 2 O 2 , and enhanced activation of Hog1p by farnesol, which were direct effects of streptococci on morphogenetic signaling. These results suggest that interactions between C. albicans and S. gordonii involve physical (adherence) and chemical (diffusible) signals that influence the development of biofilm communities. Thus, bacteria may play a significant role in modulating Candida carriage and infection processes in the oral cavity.

SUMMARY Establishment of a community is considered to be essential for microbial growth and survival in the human oral cavity. Biofilm communities have increased resilience to physical forces, antimicrobial agents, and nutritional variations. Specific cell-to-cell adherence processes, mediated by adhesin-receptor pairings on respective microbial surfaces, are able to direct community development. These interactions co-localize species in mutually beneficial relationships, such as streptococci, veillonellae, Porphyromonas gingivalis and Candida albicans. In transition from the planktonic mode of growth to a biofilm community, microorganisms undergo major transcriptional and proteomic changes. These occur in response to sensing of diffusible signals, such as autoinducer molecules, and to contact with host tissues or other microbial cells. Underpinning many of these processes are intracellular phosphorylation events that regulate a large number of microbial interactions relevant to community formation and development.

Soil flooding reduced stomatal conductance (gs) and slowed transpiration, CO2 uptake and leaf elongation in Ricinus communis within 2–6 h. These flood‐induced responses developed further over the next 21 h. They were not associated with increased delivery of abscisic acid (ABA) in xylem sap. Instead, ABA delivery from flooded roots decreased 6‐fold within 3 h, and remained low thereafter. Root hydraulic conductance (Lp) was depressed 47% below control values within 2 h of soil flooding, and declined further during the next 21 h. The smaller Lp temporarily decreased leaf water potentials (ΨL) by up to −0.4 MPa, and caused visible wilting 3 h into the flooding treatment at 80% relative humidity. Consequently, ABA concentrations in the shoot were increased, as indicated by analyses of phloem sap. Wilting, fall in ΨL and a reduction in gs were delayed for 6 h when 0.6 MPa pneumatic pressure (technical maximum) was applied to the roots. In flooded plants, phloem sap ABA concentrations returned to normal after 24 h. The initial stomatal closure, caused by soil flooding in R. communis, is attributed to decreased leaf hydration arising from the reduced LP of oxygen‐deficient roots. Continued stomatal closure and slow leaf expansion beyond 24 h were presumably achieved by non‐hydraulic means.