Facultative aerobic bacteria / Facultative anaerobic organism

Key feature: Facultative anaerobes can grow with or without oxygen because they can metabolize energy aerobically or anaerobically. They gather mostly at the top because aerobic respiration generates more ATP than fermentation

Facultative anaerobic bacteria are different from Obligate anaerobes. They may consume dietary carbohydrates. This can divert nutrients from the host. It might also produce harmful compounds.
Caffrey et al. 2024 Cell Metab 36: 684-701

Their important enzymes are: Superoxide Dismutases (SODs), catalase, peroxidase
Willey et al. 2023 McGraw Hill, USA, ISBN 978-1-265-12303-1

Facultative aerobes are nondominant intestinal microbiota, such as Enterococcus and Enterobacter
Wu et al. 2021g Journal of Immunology Research 2021: Article ID 5061570

Facultative Anaerobic Bacteria / Facultative Anaerobic Organism initially colonize the gastrointestinal tract at birth and during the first three years of life
Browne et al. 2017

Firmicutes phylum is composed of both obligate and Facultative anaerobic bacteria / Facultative anaerobic organism
Kim et al. 2017 Immunol Rev. 279(1): 90-105

see also:
Composition & Gut microbiota