Enzymatic manganese (Mn) oxidation, forming extracellular Mn oxide precipitates, is a ubiquitous natural process carried out by bacteria and fungi with broad biogeochemical implications. Specifically, Mn oxidation plays an important role in the environmental cycling of carbon, nitrogen, trace metal nutrients, and contaminants. However, the conditions and factors promoting enzymatic Mn(II) oxidation and Mn oxide precipitation remain unknown. Characterizing these conditions and factors will also help to better understand the ecological role of Mn oxidizers in nature, as well as their interactions with their surrounding environments through the precipitation of redox-active biominerals. Previous studies on Mn biomineralization have often relied on the presence or absence of Mn oxide precipitates as a proxy for biological activity. However, the complex chemistry of Mn oxides—including multiple oxidation states, high redox reactivity, and a tendency to undergo reductive dissolution—makes them an unreliable indicator of underlying cellular processes. To address this, our work focused on developing molecular tools to study Mn oxidation across the various stages of biomineralization, from regulation of gene expression and enzyme activity to mineral precipitation in the model Mn oxidizer Pseudomonas putida GB-1. The overall goal of this research is to elucidate the regulatory mechanisms and environmental signals that trigger microbial Mn oxidase activity, and to understand the potentially different roles of the various Mn oxidases for P. putida. Such advances are critical to understanding the physiological role for Mn oxidation, the interactions with other geochemical cycles, and to inform applied bioremediation strategies. First, we developed fluorescent gene reporters to track the activation of Mn oxidase encoding genes and follow their activation patterns over time and relative to microenvironments. Notably, we produced single-copy random insertions of transcriptional fusions of fluorescent protein genes to the mnxG and mcoA promoters, which drive the expression of two Mn oxidases in P. putida GB-1. As observed in both liquid-suspended cells and microcolonies, the two genes are silent in dividing cells but expressed upon entry into stationary phase and only in the presence of Mn(II). The first gene to be activated is mnxG and its activation correlates to detectable Mn oxide precipitation. Not all cells express the mxnG reporter, however. mcoA activation occurs later but also in a sub-population of cells, which do not necessarily overlap with those expressing mnxG. The spatial divergent expression pattern seem consistent with chemical gradients generated by the growth environment in e.g., colonies and aggregates. The phenotypic heterogeneity and dual activation of mnxG and mcoA, suggests that the two Mn oxidases expand the range of conditions in which GB-1 can perform Mn oxidation. Given that other bacterial strains also have multiple copies of Mn oxidases, this range expansion may have a more common biological value. Second, to explore how chemical gradients affect Mn biomineralization, we characterized the relationship between mnxG and mcoA in response to Mn(II) concentrations. Our results show that activation of both Mn oxidases in GB-1 is bimodal, with increasing concentrations of Mn(II) resulting in a higher fraction of cells expressing the respective fluorescence reporter, but not a higher expression of the reporter per cell. Interestingly, we observed an increase of cell fraction expressing mnxG in the range of 0.04 µM to 10 µM Mn(II), but expression of mcoA only at concentrations higher than 10 µM Mn(II). Kinetic modeling of enzymatic Mn oxidation using the wild-type (with both Mn oxidases) and the single gene deletion mutants (containing either mnxG or mcoA) showed that the dual activation of MnxG and McoA led to faster Mn oxidation rates and alleviated the enzyme saturation at high Mn(II) concentrations. The population-level control of gene activation and, ultimately, Mn oxidation in response to the initial Mn(II) concentration shows that P. putida can fine-tune the regulation of its Mn oxidases in response to specific chemical environments. Third, to investigate other chemical gradients encountered by bacteria that can further influence Mn oxidation in P. putida GB-1, we followed the mnxG and mcoA gene activation for a range of oxygen and pH gradients. In particular, we were interested to see whether the precipitation of Mn oxides provides some benefit to the bacteria. We found that both oxygen and pH influence the proportion of cells expressing mnxG and mcoA. Ideal conditions for biogenic Mn oxidation (pH = 7.0 and > 50% O2 saturation) led to the preferential activation of mnxG. However, sub-oxic, basic and acidic conditions led to an increase in mcoA co-activation. These results suggest that mcoA is an auxiliary gene that sustains the precipitation of Mn oxides under a wide range of chemically diverse environments that are less suitable for MnxG. However, neither Mn oxides nor Mn(II) concentration directly affected bacterial survival under these growth conditions. Interestingly, when cell suspensions were kept in anoxic conditions, P. putida GB-1 starts reducing the Mn oxides at a reductive dissolution rate of 8.2 µM day-1. Both the presence of Mn oxides and capacity to reduce Mn oxides led to a significant increase in the long-term survival of the population (13 days) in comparison to their absence. Our results thus show that GB-1 uses multiple Mn oxidases to produce Mn oxides under a broad range of chemical conditions and maximizes the storage of electron acceptors in anticipation of anoxic conditions. Mn oxidation may therefore be an investment (bet-hedging) strategy that allows for increased bacterial survival in anoxic conditions. Finally, we extended our study of Mn oxidizers to a passive Mn remediation wetland. Community analysis and isolation showed that Pseudomonas putida is naturally present and abundant in the Mn(II)-impacted site and therefore, a promising candidate for Mn bioremediation strategies. Using this native P. putida, isolate, we showed that biostimulation success depends heavily on the soil geochemistry and the competition among microorganisms for resources, with P. putida showing the highest tolerance at 3.7 mM Mn(II). However, such high Mn(II) concentrations inhibited enzymatic oxidation. We found that gradually introducing Mn(II) into the system led to the precipitation of Mn oxides and a removal efficiency of up to 2.4 mM. This provides a new approach for optimizing Mn(II) remediation by leveraging native Mn-oxidizing bacteria, improving bioaugmentation strategies, and tailoring biostimulation approaches to environmental contexts. The work presented here has provided some answers to longstanding questions in the area of biological Mn oxidation. By studying the external factors controlling biogenic Mn oxidation with help of fluorescent bioreporters we uncovered the conditions leading to Mn oxidase gene activation and understanding the complex environmental triggers for Mn oxide precipitation. Our findings demonstrate that Mn oxidation is a multifaceted process influenced by Mn(II) concentration, chemical gradients, and environmental conditions such as oxygen availability and pH. The dual activation of Mn oxidases, MnxG and McoA, revealed how Pseudomonas putida GB-1 can adapt Mn oxidation activity to optimize electron acceptor storage and enhance survival during anoxic periods. This work also underscores the potential of leveraging native Mn-oxidizing bacteria, like P. putida, for more effective bioremediation strategies, particularly in Mn-contaminated environments. The insights gained here provide a foundation for optimizing bioaugmentation and biostimulation approaches, tailoring them to specific geochemical contexts, and advancing the application of microbial-mediated Mn oxidation in environmental remediation.