Various bacterial strains with nitrate-reducing capacity (NRC), such as Haemophilus, Actinomyces, and Neisseria, are known to promote NH₃ production, control pH in the oral cavity, and inhibit the growth of aciduric bacteria. However, experimental evidence on various estimated bacterial networks within the salivary microbiome is insufficient. This study aims to explore potential bacterial compositional competition observed within saliva samples from dental caries patients through a co-culture assay of mitis Streptococci, which is a primary colonizer in the salivary microbiome, and nitrate-reducing bacteria Haemophilus parainfluenzae. We investigated bacterial growth efficiency change by co-culture time using the qRT-PCR method. In addition, we applied LC/Q-TOF-based metabolites screening to confirm metabolic interactions between oral bacterial species and their association with dental caries from a metabolomics perspective. As a result, we first found that the nitrate reduction ability of H. parainfluenzae is maintained even in a co-culture environment with the mitis Streptococci group through a nitrate reduction test. However, nitrate reduction efficiency was hindered when compared with monoculture-based nitrate reduction test results. Next, we designed species-specific primers, and we confirmed by qRT-PCR that there is an obvious competitive relationship in growth efficiency between H. parainfluenzae and two mitis Streptococci (S. australis and S. sanguinis). Furthermore, although direct effects of nitrate reduction on competition have not been identified, we have potentially confirmed through LC/Q-TOF-based metabolite screening analysis that the interaction of various metabolic compounds synthesized from mitis Streptococci is driving inter-strain competition. In particular, we constructed a basic reference core-metabolites list to understand the metabolic network between each target bacterial species (H. parainfluenzae and mitis Streptococci) within the salivary microbiome, which still lacks accumulated research data. Ultimately, we suggest that our data have potential value to be referenced in further metagenomics and metabolomics-based studies related to oral health care.

This experiment was performed to investigate the effect of two different CP levels, with or without NCG supplementation, on finishing pigs’ performance and meat quality. A total of 200 pigs ([Yorkshire × Landrace] × Duroc) with an initial average body weight (BW) of 50.06 ± 1.34 kg were randomly assigned to one of four treatments for 70 days. There were four treatment groups with ten replicates and five pigs (three males and two females) per pen. The dietary treatment includes low-protein NCG−, 13% CP (LP NCG−); low-protein NCG +, 13% CP + NCG 0.1% (1 kgton) (LP NCG+); high-protein NCG−, 15% CP (HP NCG−); high-protein NCG+, 15% CP + NCG 0.1% (1 kg/ton) (HP NCG+). After 6 weeks of experimentation on CP effect, blood urea nitrogen, total protein, glucose, and albumin levels in pigs fed LP NCG− diets were significantly lower (p < 0.05), while in terms of the effect of NCG on creatinine level, the levels in the HP NCG+ diet were significantly lower than those in LP NCG+. Dry matter intake and nitrogen intake in HP NCG− diets were significantly higher than in LP NCG−. Loin muscle area (LMA) and cooking loss in LP NCG+ diets were significantly higher than in HP NCG+. Isoleucine, histidine, lysine, alanine, and tyrosine showed higher values in HP NCG−diets than in LP NCG−. LP NCG+ feeds improved species diversity and abundance of Firmicutes, LP NCG− of Lactobacillus, and HP NCG+ of Bacilli. Thus, low dietary protein can be beneficial for nitrogen retention, blood profile, and carcass amino acids, and NCG supplementation at 0.1% for gut health and meat quality.

Actinomycetes are a representative group of bacteria that inhabit soil; in particular, Streptomyces coelicolor M511 produces actinorhodin and undecylprodiginine. Among them, undecylprodiginine has antibiotic and immunosuppression activity and is a secondary metabolite with high potential applications in biotechnological and pharmaceutical fields. High temperature stress (37 °C) reduced the biosynthesis of undecylprodiginine and induced specific branched chain alkylprodiginine derivatives, compared with the optimal growth temperature (30 °C). Also, the stress stimulated the synthesis of straight-chain FA for enhancing membrane rigidity. The inhibition of undecylprodiginine biosynthesis under high temperature stress seems to be induced by the heat sensitivity of the RedP enzyme, and this inhibition is compensated by FAS FabH. Since FabH, a homologue of RedP, has a broader substrate specificity, it leads to the production of methylundecylprodiginine and methyldodecylprodiginine. The external addition of isoleucine (as well as that of leucine and valine to a far lesser extent) enhances the synthesis of these derivatives since isoleucine catabolism generates precursors used for the biosynthesis of these compounds. These findings reveal temperature-dependent changes in precursor utilization and prodiginine diversity, providing insights into metabolic plasticity and strategies establishing a foundation for secondary metabolite derivatives engineering strategies through precursor supplementation or temperature regulation.