*2.3. Electrolytes*

Two types of electrolytes were used in this study. One electrolyte was low-nutrient loaded artificial seawater (SW) that was used for exposure of samples without MIC contribution. The SW was freshly prepared using chemicals presented in Table 3 [24].

**Table 3.** Chemical concentration (g/L) in the artificial seawater.


The other electrolyte was SW+bacteria (MIC), which was for investigating the susceptibility to MIC. In this electrolyte, microorganisms collected at Makassar Strait and cultured in the laboratory were added to the artificial seawater.

To support the bacteria to grow, an additional nutrient supply of 0.004 g FeSO4 ·7H2O, 0.30g Na3C6H5O7 ·2H2O and 0.10 g C6H8O6 dissolved in 10 mL deionised water was added through a 0.2 μm pore size filter.

Moreover, once a week 250 mL of the electrolyte was exchanged with fresh solution to supply enough nutrients for a continuous microbial growth.

#### *2.4. Inoculation of Microorganisms*

Different groups of corrosion relevant microorganisms have been detected from mooring chain environment in Makassar Strait and were enriched under laboratory conditions. Bacteria included sulfate-reducing bacteria (SRB), iron-reducing bacteria, sulfur-oxidizing bacteria, acid-producing bacteria, slime-formers and manganese-oxidizing bacteria. The bacteria were grown in specific media to keep them active until the start of the experiment. A total amount of 6 × 10<sup>6</sup> cells/mL were added to the vessel (counted using a Thoma counting chamber).

#### *2.5. Electrochemical Measurements*

#### 2.5.1. Potentiodynamic Polarization (PDP) Curve Measurements

The PDP curve measurements were performed to obtain the Tafel slopes of polarization curves to calculate the corrosion current density and corrosion rate. These slopes were used to calculate the corrosion rate from the corrosion resistance measured by the LPR and EIS measurements. The PDP measurements were carried out after holding the cells at open circuit for 1 h and the open circuit potential (OCP) was measured in SW, open to air. The polarization curves were measured by scanning the potential, started at −0.25 V vs. OCP and ended at 0.35 V vs. OCP. The scan rate was 0.167 mV/s.

2.5.2. Linear Polarization Resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) Measurements

The LPR measurements were performed in closed vessels (see Figure 1) after holding open the circuit for 0.5 h, and OCP was measured. A linear polarization line was scanned from −0.01 V vs OCP to +0.01 V vs OCP. The EIS were measured using ac, amplitude 0.01 V, in frequency range 0.01–100,000 Hz. The LPR and EIS measurements were carried out after 7, 14, 21 and/or 28 days of exposure.
