Novel energy utilization mechanisms of microorganisms in the hydrosphere

Abstract

This review focuses on new approaches adopted by microorganisms to acquire energy in oligotrophic and low-energy hydrosphere habitats, which involves increasing income, reducing expenditure and cooperation among different microorganisms. The various energy sources, electron transfer pathways and carbon, nitrogen, and sulfur cycles are involved in these processes. Specifically, this review delves into the potential molecular mechanisms on microbes utilizing photoelectrons from semiconducting minerals in natural photocatalytic systems. Also, it aims to reveal the regulation mechanisms of photoelectrons on interspecific electron transfer pathways and the energy synthesis processes in Geobacter, Pseudomonas, Halomonas and sulfate reducing bacteria, as well as the molecular mechanisms of perception and adaptation to different potentials of extracellular receptors and changes of oxygen gradients. Moreover, it demonstrates the network structure, formation and mechanisms of long-distance electron transfer driven by cable bacteria, particularly in the context of reducing CH₄ and N₂O coupled with the increase of dimethyl sulfide. This paper attempts to put forward new ideas for the energy utilization by microorganisms and their impact on element cycle in the hydrosphere, which contributes to a better understanding of the energy metabolism in interspecific, interspecies, and ecosystem contexts during the cycle-coupled processes of elements.

Keywords: Aquatic microorganisms; Ecological effect; Elemental cycle; Extracellular electron transfer; Photoelectric energy.

Fig. 1

Current research and progress of energy metabolism pathways of microorganisms in the hydrosphere. (a) The conversion of solar energy by semiconducting minerals provides a new energy source for microbial energy metabolism and carbon sequestration in the euphotic zone. (b) Long-distance electron transfer (LDET) networks extend the distance of microbial electron transport from micrometers to centimeters, overcoming spatial isolation of redox processes and niche constraints. (c) Trophic interaction and symbiotic relationship established through direct interspecies electron transfer overcome the energy barrier and maximize energy utilization.

Fig. 2

Production and transfer of mineral photoelectrons and energy metabolism of microorganisms.

Fig. 3

A new mechanism of visible light stimulated synergy between iron oxide semiconducting minerals and electroactive microorganisms for driving Cr(VI) reduction.

Fig. 4

The Arc system and simplified model of phosphate transfer in E. coli (A) and S. oneidensis (B), respectively.

Fig. 5

The Arc system of Geobacter.

Fig. 6

A schematic diagram of soil hypoxic methane oxidation in the Yellow River Delta wetlands.

Fig. 7

Conceptual summary of the influence of eDO on sediment biogeochemical processes and interspecific interactions involving cable bacteria and related functional microorganisms.

Fig. 8

Three representative microbial LDET models.

Fig. 9

Key scientific issues of energy conversion and metabolism of aquatic microorganisms in oligotrophic environments.