SUPPLEMENTARY GROWTH PROMOTING EFFECT OF 2-METHYL-1,4-NAPHTHOQUINONE ON LACTOBACILLUS BIFIDUS VAR. PENNSYLVANICUS

Identifying the essential nutritional requirements of the probiotic bacteria Bifidobacterium animalis and Bifidobacterium longum through genome-scale modeling

Although bifidobacteria are widely used as probiotics, their metabolism and physiology remain to be explored in depth. In this work, strain-specific genome-scale metabolic models were developed for two industrially and clinically relevant bifidobacteria, Bifidobacterium animalis subsp. lactis BB-12® and B. longum subsp. longum BB-46, and subjected to iterative cycles of manual curation and experimental validation. A constraint-based modeling framework was used to probe the metabolic landscape of the strains and identify their essential nutritional requirements. Both strains showed an absolute requirement for pantethine as a precursor for coenzyme A biosynthesis. Menaquinone-4 was found to be essential only for BB-46 growth, whereas nicotinic acid was only required by BB-12®. The model-generated insights were used to formulate a chemically defined medium that supports the growth of both strains to the same extent as a complex culture medium. Carbohydrate utilization profiles predicted by the models were experimentally validated. Furthermore, model predictions were quantitatively validated in the newly formulated medium in lab-scale batch fermentations. The models and the formulated medium represent valuable tools to further explore the metabolism and physiology of the two species, investigate the mechanisms underlying their health-promoting effects and guide the optimization of their industrial production processes.

Sex Steroid Hormones as a Balancing Factor in Oral Host Microbiome Interactions

Sex steroid hormones (SSH) are cholesterol-derived molecules. They are secreted into saliva and enter the oral cavity, triggering physiological responses from oral tissues, with possible clinical implications, such as gingival inflammation and bleeding. SSH and hormonal changes affect not only oral host cells but also oral microorganisms.

Historically, most research has focused on the effect of hormonal changes on specific bacteria and yeasts. Recently a broader effect of SSH on oral microorganisms was suggested. In order to assess the role of SSH in host-microbe interactions in the oral cavity, this review focuses on how and up to what extent SSH can influence the composition and behavior of the oral microbiome. The available literature was reviewed and a comprehensive hypothesis about the role of SSH in host-microbiome interactions is presented. The limited research available indicates that SSH may influence the balance between the host and its microbes in the oral cavity.

Bacterial interactions in dental biofilm development

Recent analyses with ribosomal RNA-based technologies have revealed the diversity of bacterial populations within dental biofilms, and have highlighted their important contributions to oral health and disease. Dental biofilms are exceedingly complex and multispecies ecosystems, where oral bacteria interact cooperatively or competitively with other members. Bacterial interactions that influence dental biofilm communities include various different mechanisms. During the early stage of biofilm formation, it is known that planktonic bacterial cells directly attach to surfaces of the oral cavity or indirectly bind to other bacterial cells that have already colonized. Adherence through co-aggregation may be critical for the temporary retention of bacteria on dental surfaces, and may facilitate eventual bacterial colonization. It is likely that metabolic communication, genetic exchange, production of inhibitory factors (e.g., bacteriocins, hydrogen peroxide, etc.), and quorum-sensing are pivotal regulatory factors that determine the bacterial composition and/or metabolism. Since each bacterium can easily access a neighboring bacterial cell and its metabolites, genetic exchanges and metabolic communication may occur frequently in dental biofilms. Quorum-sensing is defined as gene regulation in response to cell density, which influences various functions, e.g., virulence and bacteriocin production. In this review, we discuss these important interactions among oral bacteria within the dental biofilm communities.

Reduction of vitamin K concentration by salivary Bifidobacterium strains and their possible nutritional competition with Porphyromonas gingivalis

AIMS

To assess the possibility that bifidobacteria compete with Porphyromonas gingivalis for their mutual growth factor vitamin K. This study also examined whether salivary Bifidobacterium species decrease vitamin K concentration in the growth medium.

METHODS AND RESULTS

Sixty-five strains of Bifidobacterium were obtained from 20 of 24 periodontally healthy subjects. Bifidobacterium dentium was most frequently detected in the saliva of subjects, followed by Bifidobacterium adolescentis, Bifidobacterium longum, and Bifidobacterium urinalis. The growth of most Bifidobacterium isolates, except that of B. urinalis, was stimulated by vitamin K. Moreover, the isolates were capable of decreasing vitamin K after incubation, which suggests that bifidobacteria compete with P. gingivalis for vitamin K. In a co-culture, a representative strain -B. adolescentis S2-1 - inhibited the growth of P. gingivalis if it was inoculated in the medium before P. gingivalis.

CONCLUSIONS

B. adolescentis S2-1 decreased vitamin K concentration and inhibited the growth of P. gingivalis by possibly competing for the growth factor.

SIGNIFICANCE AND IMPACT OF THE STUDY

Salivary bifidobacteria may possess the potential to suppress the growth of P. gingivalis by reducing the growth factor(s) in the environment.

PHTHIOCOL AND MENADIONE AS ACETATE-REPLACING FACTORS FOR LACTOBACILLUS DELBRUECKII

MaciasR, Frank M. (Northrop Corporation, Hawthorne, Calif.). Phthiocol and menadione as acetate-replacing factors for Lactobacillus delbrueckii . J. Bacteriol. 82: 657–661. 1961.— Lactobacillus delbrueckii (ATCC 9649), when cultured under nitrogen, or in ferrous iron-containing media exposed to air, requires, for the initiation of growth, compounds that are known to behave as electron acceptors. The ferrous iron probably induces what amounts to anaerobic conditions; that is, it blocks access of the organism to oxygen. Several electron carriers, such as methylene blue and naphthoquinones, stimulate growth of the organism in acetate-free media exposed to air. The most active acetate-replacing agent found is phthiocol. Methylene blue does not stimulate growth under nitrogen. It is suggested that the naphthoquinones bring about the initial oxidations required for growth by transferring the electrons to some other constituent of the medium. Growth of the organism in acetate-free media under CO 2 indicates that CO 2 or its fixation product can behave also as an initial oxidant.