BackgroundMicrobial cell-cell interactions in the oral flora are believed to play an integral role in the development of dental plaque and ultimately, its pathogenicity. The effects of other species of oral bacteria on biofilm formation and virulence gene expression by Streptococcus mutans, the primary etiologic agent of dental caries, were evaluated using a dual-species biofilm model and RealTime-PCR analysis.ResultsAs compared to mono-species biofilms, biofilm formation by S. mutans was significantly decreased when grown with Streptococcus sanguinis, but was modestly increased when co-cultivated with Lactobacillus casei. Co-cultivation with S. mutans significantly enhanced biofilm formation by Streptococcus oralis and L. casei, as compared to the respective mono-species biofilms. RealTime-PCR analysis showed that expression of spaP (for multi-functional adhesin SpaP, a surface-associated protein that S. mutans uses to bind to the tooth surface in the absence of sucrose), gtfB (for glucosyltransferase B that synthesizes α1,6-linked glucan polymers from sucrose and starch carbohydrates) and gbpB (for surface-associated protein GbpB, which binds to the glucan polymers) was decreased significantly when S. mutans were co-cultivated with L. casei. Similar results were also found with expression of spaP and gbpB, but not gtfB, when S. mutans was grown in biofilms with S. oralis. Compared to mono-species biofilms, the expression of luxS in S. mutans co-cultivated with S. oralis or L. casei was also significantly decreased. No significant differences were observed in expression of the selected genes when S. mutans was co-cultivated with S. sanguinis.ConclusionsThese results suggest that the presence of specific oral bacteria differentially affects biofilm formation and virulence gene expression by S. mutans.

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A water balance study of a small subtropical rainforest catchment (10 ha, 1000 m altitude) was conducted at Gambubal State Forest, near the headwaters of the Condamine River, 200 km south-west of Brisbane, south-eastern Queensland. Mean annual rainfall of the site is approximately 1125 mm, but is variable and often less than 900 mm. Tree transpiration rates are low and depletion of the large soil moisture reserves enables extraction for lengthy periods of time, permitting survival during extended dry seasons (May–November). Fog deposition to the forest provides the equivalent of an additional 40% of rainfall to the site as measured using a conventional rain gauge. A frequently wet canopy results in reduced transpiration rates and direct foliar absorption of moisture alleviates water deficits of the upper crown leaves and branches during the dry season. These features of this vegetation type may enable long-term survival at what could be considered to be a marginal rainforest site.

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