VOLUME 16 NUMBER 2 (July to December 2023)

Bacteroides: From a Fecal Pollutant to a Useful Tool in Solving Water Pollution

Bacteroides spp. are Gram-negative bacilli, non-endospore-forming and obligate anaerobes, belonging to Phylum Bacteroidetes, Class Bacteroidia, Order Bacteroidales, Family Bacteroidaceae, with 40 taxonomically recognized species. They are anaerobes, and hence, commonly found in warm-blooded animals’ guts and fecal microbiome, where they are the most dominant bacteria, having either mutually or commensally co-evolved with their host. However, they are also disease-causing and carriers of antibiotic resistance genes. Hence, release of Bacteroides-dominated feces by hosts causes fecal pollution, especially in water bodies. Despite being anaerobes, Bacteroides have a short lifespan. They leave their genetic materials behind as environmental DNA, which remain viable for PCR. DNA isolation can determine the feces’ source—a technique known as microbial source tracking (MST). There are two types of MST: library-dependent (LDM) and -independent (LIM). Bacteroides use falls under LIM, wherein animal associated Bacteroides markers determine the fecal contamination’s source. Due to extensive co-evolution between Bacteroides and hosts, most LIM-MST biomarkers are Bacteroides-based [PigBac (pigs), CowBac (cows), ChickenBac (chicken)] and human-based (HF183, HumBac), etc. MST also effectively determines fecal pollution extent from anthropogenic and agricultural sources. Therefore, MST can directly determine a definitive fecal pollutant source. The main limitation of LIM-MST is the lack of markers for other animals. Most available MST markers are directed toward domesticated animals (chickens, cows, pigs). Moreover, even existing markers are affected by geography and animal diet. These limitations warrant continued efforts to fill the gaps by designing more specific and sensitive MST animal markers. This review aims to initiate interest in the use of Bacteroides for efficient water quality monitoring.