Aims This study evaluated whether by‐products from industrial processing of acerola (Malpighia glabra L.; AB) and guava (Psidium guajava L.; GB) fruit may stimulate the growth and metabolism of probiotic Lactobacillus and Bifidobacterium and induce changes in human colonic microbiota. Methods and Results The ability of non‐digested and digested AB or GB to stimulate the growth ad metabolism of Lactobacillus acidophilus LA‐05, Lactobacillus casei L‐26 and Bifidobacterium animalis subsp. lactis BB‐12 was evaluated. Changes in populations of distinct bacterial groups of human colonic microbiota induced by digested AB and GB were evaluated using an in vitro colonic fermentation system. Non‐digested and digested AB and GB favoured probiotic growth. No difference among counts of probiotics in media with glucose, fructooligosaccharides and non‐digested and digested AB and GB was found during a 48‐h cultivation. Cultivation of probiotics in media with non‐digested and digested AB and GB resulted in decreased pH, increased organic acid production and sugar consumption over time. Digested AB and GB caused overall beneficial changes in abundance of Bifidobacterium spp., Lactobacillus–Enterococcus, Eubacterium rectall–Clostridium coccoides and Bacteroides–Provotella populations, besides to decrease the pH and increase the short‐chain fatty acid production during a 24‐h in vitro colonic fermentation. Conclusion AB and GB could be novel prebiotic ingredients because they can stimulate the growth and metabolism of probiotics and induce overall beneficial changes in human colonic microbiota. Significance and Impact of the Study AB and GB stimulated the growth and metabolism of probiotics, in addition to induce beneficial alterations in human colonic microbiota composition and increase short‐chain fatty acid production. These results characterize AB and GB as potential prebiotic ingredients and fruit processing by‐products as sources of added‐value compounds.

The human oral microbiome heavily influences the status of oral and systemic diseases through different microbial compositions and complex signaling between microbes. Recent evidence suggests that investigation of interactions between oral microbes can be utilized to understand how stable communities are maintained and how they may preserve health. Herein, we investigate two highly abundant species in the human supragingival plaque, Streptococcus mitis and Corynebacterium matruchotii, to elucidate their real-time chemical communication in commensal harmony. Specifically, we apply nanoscale scanning electrochemical microscopy (SECM) using a submicropipet-supported interface between two immiscible electrolyte solutions as an SECM probe not only to image the permeability of S. mitis and C. matruchotii membranes to tetraethylammonium (TEA + ) probe ions but also to realtime visualize the metabolic interaction between two microbes via lactate production/consumption at a single-cell level. The metabolic relationship between two strains is quantitatively assessed by determining (1) the passive permeability of both bacterial membranes of 2.4 × 10 −4 cm/s to the free diffusion of TEA + , (2) 0.5 mM of the lactate concentration produced by a single S. mitis strain at a rate of 2.7 × 10 −4 cm/s, and (3) a lactate oxidation rate ≥5.0 × 10 6 s −1 by an individual C. matruchotii strain. Significantly, this study, for the first time, describes a mechanism of in situ metabolic interaction between oral commensals at the single-cell level through quantitative analysis, which supports the observed in vivo spatial arrangements of these microbes.

Complex polymicrobial biofilm communities are abundant in nature particularly in the human oral cavity where their composition and fitness can affect health. While the study of these communities during disease is essential and prevalent, little is known about interactions within the healthy plaque community. Here we describe interactions between two of the most abundant species in this healthy microbiome, Haemophilus parainfluenzae and Streptococcus mitis. We discovered that H. parainfluenzae typically exists adjacent to mitis group streptococci in vivo with which it is also positively correlated based on microbiome data. By comparing in vitro coculture data to ex vivo microscopy we revealed that this co-occurrence is density dependent and further influenced by H2O2 production. We discovered that H. parainfluenzae utilizes a more redundant, multifactorial response to H2O2 than related microorganisms and that this system’s integrity enhances streptococcal fitness. Our results indicate that mitis group streptococci are likely the in vivo source of NAD for H. parainfluenzae and also evoke patterns of carbon utilization in vitro for H. parainfluenzae similar to those observed in vivo. Our findings describe mechanistic interactions between two of the most abundant and prevalent members of healthy supragingival plaque that contribute to their in vivo survival.

Polymicrobial biofilms are present in many environments particularly in the human oral cavity where they can prevent or facilitate the onset of disease. While recent advances have provided a clear picture of both the constituents and their biogeographical arrangement, it is still unclear what mechanisms of interaction occur between individual species in close proximity within these communities. In this study we investigated two mechanisms of interaction between the highly abundant supragingival plaque (SUPP) commensal Corynebacterium matruchotii and Streptococcus mitis which are directly adjacent in vivo. We discovered that C. matruchotii enhanced the fitness of streptococci dependent on its ability to detoxify streptococcal-produced hydrogen peroxide and its ability to oxidize lactate also produced by streptococci. We demonstrate that the fitness of adjacent streptococci was linked to that of C. matruchotii and that these mechanisms support the previously described “corncob” arrangement between these species but that this is favorable only in aerobic conditions. Further we utilized scanning electrochemical microscopy (SECM) to quantify lactate production and consumption between individual bacterial cells for the 1st time, revealing that lactate oxidation provides a fitness benefit to S. mitis and not pH mitigation. This study describes mechanistic interactions between two highly abundant human commensals that can explain their observed in vivo spatial arrangements and suggest a way by which they may help preserve a healthy oral bacterial community.

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