Isolation and molecular identification of Endophytic bacteria from Noni fruits (Morinda citrifolia l.) and their antibacterial activity

Diversity and community structure of endophytic Bacillus with antagonistic and antioxidant activity in the fruits of Xisha Wild Noni (Morinda citrifolia L.)

Noni (Morinda citrifolia L.) is a tropical crop with strong antibacterial, antioxidant and other abilities, and its fruit has a strong potential for adjuvant treatment of diseases. This study aimed to explore the dynamic change of endophytic bacteria in Noni fruit at different stages and the correlation between the antagonistic and antioxidant activity of the Bacillus which was screened and the change of the host's growth stage. In this study, though the high-throughput sequencing technology (HTS), 106 endophytic bacteria species were found in A, B, C, D, E and F stages of Noni fruit, among which the dominant group were Pantoea (0.3%-20.9%), and Candidatus_Uzinura (2.3%-35.2%) etc. The endophytic bacteria were isolated by culture-dependent method. Through their antagonistic experiments on Staphylococcus aureus and Escherichia coli, the results of 16S polyphasic taxonomic identification showed that the 34 antagonistic strains belonged to Bacillus. Five species of these Bacillus were identified by gyrA polyphase taxonomy, including Bacillus subtilis (76% of all Bacillus), Bacillus licheniformis (9%), Bacillus amyloliquefaciens (6%), Bacillus velezensis (6%) and Bacillus mojavensi (3%), and the RAPD showed these Bacillus are no signs of stable passage. In C, D, E and F stages, the average total antioxidant activity of Bacillus endophytic antagonists against Noni was 7.812 U/mL, 8.144 U/mL, 7.817 U/mL and 7.144 U/mL, which was much higher than that of Noni fruit, and antioxidant activity of Noni juice and Bacillus bacterial liquid vary with host's growth period showed the same trend, both rose slowly at first, and reached the highest in period E, then declined slightly in period F, it showed that the antagonistic Bacillus of Noni had synergistic function with Noni fruit. This study clarified the relationship of function between Noni fruit and endophytic bacteria, and laid a foundation for future study on the dynamic change of endophytic flora succession and efficacy.

Antibacterial Activity and Mechanism of Action of Methanol Extract from Kasturi Mango Fruit (Mangifera casturi) on Caries-Causing Bacterium Streptococcus mutans

One of the problems frequently found in the oral cavity is dental caries caused by Streptococcus mutans. Thus far, dental caries is treated using antibiotics. However, the bacterium is known to be resistant to many antibiotics; hence, another alternative is needed. An alternative option is found in the Kasturi mango (Mangifera casturi). This study aims to identify the bioactive compounds of  Kasturi mango and find out the mechanism of its action in inhibiting the growth of Streptococcus mutans. Kasturi mangoes were macerated using 96% methanol, then the phytochemical compounds were identified qualitatively. Antibacterial activity testing was carried out using the agar diffusion method, and bioactive compounds were identified using GCMS. The results showed that the methanol extract of Kasturi mango contains alkaloids, flavonoids, phenolics, terpenoids, and saponins. In 1 gr/mL of the methanol extract of Kasturi mango fruit has an inhibitory activity against the growth of Streptococcus mutans with a zone of inhibition of ± 10 mm and MIC (minimum inhibitory concentration) value of 25% extract. The inhibitory action is suspected to be through a mechanism where holes in the bacterial cell membrane are made. This can be seen from the results of SEM (scanning electron microscope) images showing that cell leakage or lysis has occurred. This research also, for the first time, revealed the types of bioactive compounds from the methanol extracts of Kasturi mango (Mangifera casturi) consisting of 18 compounds with the most abundance is 5-Hydroxymethylfurfural compounds, Octadecenoic acid, n-Hexadecanoic acid, Phenyl 4-methyl-1-piperidine carboxylate, and Methyl linolenate.