Functional genes required for microbial (dissimilatory) metal reduction display high sequence divergence, which limits their utility as molecular biomarkers for tracking the presence and activity of metal-reducing bacteria in natural and engineered systems. In the present study, homologs of the outer membrane beta-barrel protein MtrB of metal-reducing Gammaproteobacteria were found to contain a unique N-terminal CXXC motif that was missing from MtrB homologs of nonmetal-reducing Gammaproteobacteria and metal- and nonmetal-reducing bacteria outside the Gammaproteobacteria. To determine whether the N-terminal CXXC motif of MtrB was required for dissimilatory metal reduction, each cysteine in the CXXC motif of the representative metal-reducing gammaproteobacterium Shewanella oneidensis was replaced with alanine, and the resulting site-directed mutants were tested for metal reduction activity. Anaerobic growth experiments demonstrated that the first, but not the second, conserved cysteine was required for metal reduction by S. oneidensis. The ability to predict metal reduction by Gammaproteobacteria with unknown metal reduction capability was confirmed with Vibrio parahaemolyticus, a pathogen whose genome encodes an MtrB homolog with an N-terminal CXXC motif. MtrB homologs with an N-terminal CXXC motif may thus represent a molecular signature unique to metal-reducing members of the Gammaproteobacteria.

Electroactive bacteria can transfer electrons to electrodes to generate electricity in the microbial fuel cell (MFC). Electroactive bacteria can generate energy for growth via the oxidation of organic compounds and transfer electrons to the electrodes that serve as the terminal electron acceptor. In this study, electricity generation in a double chamber evaluated MFC by four newly isolated electroactive bacteria strains (ESPK 22, ESPK 26, KP20, and KP22). ESPK22 and ESPK26 were previously identified as gram-positive Bacillus genera, while KP20 and KP22 belong to gram-negative Klebsiella genera. Among all the strains tested, the gramnegative KP20 strain shows the highest electricity generation value is 222.08 mV and the lowest electricity generation was ESPK26 of 44.82 mV.

Corrosion of mild steel has been attributed to the respiratory activity of microbes under different growth conditions. Under nitrate-reducing condition, nitrate-reducing bacteria were postulated to inhibit corrosion, yet existing literatures reported contradicting findings. Newly isolated Cronobacter sp. KP 19 from Kuantan Port is capable of reducing ferric iron (Fe3+) and nitrate (NO3-) as electron acceptors. To investigate the effect of Cronobacter sp. KP 19 on mild steel corrosion under nitrate-reducing condition, the Cronobacter sp. KP 19 was cultured as nitrate-reducing facultative bacteria in a defined growth M1 media amended with 15 mM of sodium nitrate as the sole electron acceptor. Mild steel coupons were immersed in growth media for 46 days. The deteriorations of the mild steel coupons were then evaluated by corrosion rate analysis and the morphology was characterized via scanning electron microscopy (SEM) followed by X-ray diffraction (XRD) analyses. Our results indicated that under nitrate-reducing condition, Cronobacter sp. KP 19 remarkably accelerates the corrosion rates of mild steel by approximately ten folds. XRD analysis confirmed the formation of magnetite (Fe3O4) and vivianite [Fe3(PO4)2·8H2O] as the corrosion products. Results from current study provide insight on how facultative anaerobes affect the corrosion processes under different respiratory growth conditions.