Differences in metabolic potential indicate a selective pressure exerted in the subsurface for microbes with particular metabolic capabilities. For instance, within the Level 1 carbohydrate metabolism category, sequences related to Level 2 functional categories such as mono-, di-, oligo- and polysaccharides, and aminosugar metabolism were present in higher relative abundance in the produced water samples. This finding correlates well with the expected higher content of carbohydrates in produced water samples. Carbohydrates and polysaccharide compounds added during hydraulic fracturing can serve as carbon and energy sources for microbial activity. Within the Level 1 protein metabolism category, sequences affiliated with the Level 2 selenoprotein category were detected only in the produced water samples. One possible explanation is the role of selenoproteins in combating oxidative stress, which may arise from elevated concentrations of organic or inorganic dissolved constituents in produced water. Results showed that Rhodobacterales were the dominant population involved in oxidative stress response in source water and produced water day 1 samples. However, Alteromonadales and Vibrionales were the dominant orders involved in oxidative stress response in produced water day 9 sample. Within the Level 1 clustering subsystem, genes affiliated with the Level 2 carbohydrate metabolism show a relative increase in the produced water samples as compared to fracturing source water. An increase in the relative abundance of genes related to carbohydrate metabolism in produced water compared to fracturing source water suggests the potential for utilization of hydrocarbons added either as fracturing fluid amendments or those derived from the shale formation and an overall shift to a more heterotrophic microbial community. The phytochemistry of C. tagal has been reported, however, the work mainly focused on the isolation and identification of terpenoid compounds in root, with little attention on leaf tannins. The high level of tannins in the leaves of Rhizophoraceae is known to deter feeding by herbivores, but leaf tannins also show a diversity of other biological activities. The unexplored tannins could be novel potential resources of bioactive compounds in mangrove plants. So far, the chemical properties of C. tagal tannins have not yet been determined and the structure-activity relationships of tannins are still not clear. Tannins comprised as much as 20–40% dry weight in the leaf and bark of mangrove plants. Compared with hydrolysable tannins, condensed tannins are more SCH772984 structure abundant. They are commonly found in mangrove plants and are also the main component of the polyphenols in our diet. Because of their antioxidant activities and other potentially health-promoting qualities, proanthocyanidins have attracted more and more research interests in recent years. Proanthocyanidins are oligomers and polymers of flavan-3-ol that are bound together with B-type and Atype linkages. The chemistry and biological features of proanthocyanidins largely depend on their structure.