BIODIVERSITAS ISSN: 1412-033X Volume 23, Number 9, September 2022 E-ISSN: 2085-4722 Pages: 4852-4860 DOI: 10.13057/biodiv/d230954 Propolis extract as a green bacterial corrosion inhibitor on three types of metals NI LUH WATINIASIH 1, , I NYOMAN BUDIARSA 2 , I NYOMAN GDE ANTARA 2 , PUTU ANGGA WIRADANA 3 1 Program of Biology, Faculty of Mathematics and Natural Sciences, Universitas Udayana. Jl. Raya Kampus Unud, Jimbaran, Badung 80361, Bali, Indonesia. Tel./Fax.: +62-813-37891231,  email: luhwatiniasih@unud.ac.id 2 Program of Mechanical Engineering, Faculty of Engineering, Universitas Udayana. Jl. Raya Kampus Unud, Jimbaran, Badung 80361, Bali, Indonesia 3 Program of Biology, Faculty of Health, Science and Technology, Universitas Dhyana Pura. Jl. Raya Padang Luwih, Dalung, Badung 80351, Bali, Indonesia Manuscript received: 24 July 2022. Revision accepted: 16 September 2022. Abstract. Watiniasih NL, Budiarsa IN, Antara ING, Wiradana PA. 2022. Propolis extract as a green bacterial corrosion inhibitor on three types of metals. Biodiversitas 23: 4852-4860. Corrosion causes severe damage to various types of metals, which is a serious problem in the infrastructure sector. Several studies have been conducted to find more efficient natural inhibitors. This study was aimed to determine the effectiveness of antioxidants from propolis extract in inhibiting the growth of bacteria that cause corrosion on various metals. The ethanol extract was carried out to obtain the bioactive contained in the propolis extract, then analyzed its antioxidant activity with DPPH and characterized using GC-MS. Various concentration of propolis extract were tested on NA+1% Fe medium to determine its resistance to corrosion-causing bacteria. Propolis extract was tested on several types of metals in inhibiting the corrosion rate. The results showed that the tested propolis extract had strong antioxidant activity with an IC50 value of 82.496 ppm. The characterization of the metabolite profile showed that the propolis extract was dominated by chemical components that act as antioxidants and antibacterial agents. In the future, the results of this study can be used as a practical guide for the application of bioactive compounds through a biocontrol approach to the growth of corrosion-causing bacteria. Keywords: Antioxidant, antimicrobial, corrosion, green-corrosion inhibitor, propolis extracts INTRODUCTION Metals have an important role in supporting the progress of a nation's development and in the global economy (Zakeri et al. 2022). However, problems often occur especially when metallic materials come into contact with hydrogen atoms or molecules during the manufacturing, processing and service processes (Li et al. 2021). Hydrogen is able to be adsorbed onto the metal surface, therefore causes damage to mechanical properties and causes premature failure of the resulting steel structure (Liu et al. 2016). Corrosion is a natural process in which metals and their alloys attempt to return to a more stable thermodynamic state, as a result of a series of chemical processes or reactivity with the surrounding environment (Li et al. 2021; Prestat and Thierry 2021; Shang and Zhu 2021; Tanwer and Shukla 2022). Globally, corrosion is a huge problem and it is estimated that around USD 2.5 trillion is spent annually to address the problems associated with rust. Interestingly, this amount is around 3-4 percent of the Gross World Product (GWP) each year (Koch 2017). High humidity environment has potential to produce corrosive activity, because of dissolving gases, like O2, CO2 and other minerals (Barker et al. 2018). For example, in the oil and natural gas industry, oilfield formation always contains high concentrations of chlorides, carbonates, sulfates, and dissolved gases, such as H2S and CO2, which react with pipelines, causing corrosion, so oil leaking to the environment (Yin et al. 2020). Corrosion causes the pipe lifespan decreases, causing economic losses and environmental pollution (Wasim et al. 2018). Corrosion has always been a major problem in declining productivity of an industry, and researchers have focused on overcoming this problem (Angst 2018). Efforts in reducing and preventing the impact of corrosion are believed to save some economic losses (Yang et al. 2016; Zhang et al. 2012). In addition to environmental or abiotic factors, corrosion can also be caused by biotic factors, known as “Microbial Influences Corrosion (MIC)”, the main cause of leakage in pipes (Li et al. 2018). The process starts with cell adhesion to a wet iron surface and results in a biofilm composed of a polymeric matrix and various cell populations in microcolonies (Muhammad et al. 2020). Adsorption of macromolecules (proteins, polysaccharides, and humic acids) and micromolecules (fatty acids and lipids) on the metal surface initiates the creation of biofilms, which affects the physical and chemical properties of the metal (Rodríguez et al. 2021). The types and abilities of microbial metabolites that cause corrosion have not been comprehensively understood (Nikolova and Gutierrez 2020; Salgar-Chaparro et al. 2020). However, the most dominant corrosion-causing species encountered were sulfate-reducing bacteria, residing in complex microbial communities (Hussain et al. 2016; Souza et al. 2017). A review on green corrosion inhibitors shows that biological agents must meet important requirements to be used as corrosion inhibitors, should containing