Multivariate landscapes constructed by Bayesian estimation over five hundred microbial electrochemical time profiles

Decoding in-cell respiratory enzyme dynamics by label-free in situ electrochemistry

Deciphering metabolic enzyme catalysis in living cells remains a formidable challenge due to the limitations of in vivo assays, which focus on enzymes isolated from respiration. This study introduces an innovative whole-cell electrochemical assay to reveal the Michaelis-Menten landscape of respiratory enzymes amid complex molecular interactions. We controlled the microbial current generation's rate-limiting step, extracting in vivo kinetic parameters (Km, Ki, and kcat) for the periplasmic nitrite (NrfA) and fumarate (FccA) reductases. Notably, while NrfA kinetics mirrored those of its purified form, FccA exhibited unique kinetic behavior. Further exploration using a mutant strain lacking CymA, a periplasmic hub protein, revealed its crucial role in modulating FccA's kinetics, challenging the prevailing view that molecular crowding is the main cause of discrepancies between in vivo and in vitro enzyme kinetics. This platform offers a groundbreaking approach to studying cellular respiratory enzymatic kinetics, paving the way for future research in bioenergetics and medicine.

Mechanistic study of a low-power bacterial maintenance state using high-throughput electrochemistry

Mechanistic studies of life's lower metabolic limits have been limited due to a paucity of tractable experimental systems. Here, we show that redox-cycling of phenazine-1-carboxamide (PCN) by Pseudomonas aeruginosa supports cellular maintenance in the absence of growth with a low mass-specific metabolic rate of 8.7 × 10-4 W (g C)-1 at 25°C. Leveraging a high-throughput electrochemical culturing device, we find that non-growing cells cycling PCN tolerate conventional antibiotics but are susceptible to those that target membrane components. Under these conditions, cells conserve energy via a noncanonical, facilitated fermentation that is dependent on acetate kinase and NADH dehydrogenases. Across PCN concentrations that limit cell survival, the cell-specific metabolic rate is constant, indicating the cells are operating near their bioenergetic limit. This quantitative platform opens the door to further mechanistic investigations of maintenance, a physiological state that underpins microbial survival in nature and disease.

Enriching electroactive microorganisms from ferruginous lake waters - Mind the sulfate reducers!

Electroactive microorganisms are pivotal players in mineral transformation within redox interfaces characterized by pronounced oxygen and dissolved metal gradients. Yet, their systematic cultivation from such environments remains elusive. Here, we conducted an anodic enrichment using anoxic ferruginous waters from a post-mining lake as inoculum. Weak electrogenicity (j = ∼5 µA cm-2) depended on electroactive planktonic cells rather than anodic biofilms, with a preference for formate as electron donor. Addition of yeast extract decreased the lag phase but did not increase current densities. The enriched bacterial community varied depending on the substrate composition but mainly comprised of sulfate- and nitrate-reducing bacteria (e.g., Desulfatomaculum spp. and Stenotrophomonas spp.). A secondary enrichment strategy resulted in different bacterial communities composed of iron-reducing (e.g., Klebsiella spp.) and fermentative bacteria (e.g., Paeniclostridium spp.). Secondary electron microscopy and energy-dispersive X-ray spectroscopy results indicate the precipitation of sulfur- and iron-rich organomineral aggregates at the anode surface, presumably impeding current production. Our findings indicate that (i) anoxic waters containing geogenically derived metals can be used to enrich weak electricigens, and (ii) it is necessary to specifically inhibit sulfate reducers. Otherwise, sulfate reducers tend to dominate over EAM during cultivation, which can lead to anode passivation due to biomineralization.