Seasonal prokaryotic community and geochemical dynamics of an extreme environment: the Naftlije Mud Volcano, Iran

Abstract

Mud volcanoes (MVs) are unique terrestrial ecosystems that serve as analogs for hydrocarbon-rich extraterrestrial environments, yet their seasonal microbial dynamics remain poorly understood. This study investigates the seasonal shifts in the prokaryotic community of the Naftlije Mud Volcano (NMV) in northeastern Iran, utilizing 16 S rDNA amplicon sequencing (849 OTUs from 2.9 million reads) alongside comprehensive geochemical analysis over three sampling seasons from 2022 to 2023. We focused on Salsa Lake, a shallow sedimentary environment associated with the NMV, revealing salinity levels between 6% and 8.2%, sulfate concentrations ranging from 170 to 940 ppm, and total petroleum hydrocarbons (TPH) fluctuating between 430 and 989 ppm. Our findings demonstrate substantial community composition changes in response to environmental factors: sulfur-oxidizing Thiomicrospira dominated during the dry season (70% of reads), Arcobacter was prevalent in the wet season (55%), and anoxygenic phototrophic Halorhodospira constituted 76% of reads during the pink summer bloom. Marinobacter remained a consistent presence year-round (2–10%). Notably, unclassified OTUs accounted for 10–20% of sequences, indicating a reservoir of novel diversity. Richness (Chao1) declined from approximately 580 to 180 OTUs as TPH increased and sulfate decreased, while Shannon diversity peaked at 3.2 under diluted spring conditions. These results illustrate that even modest seasonal changes in environmental factors are reflected in the lake’s green-to-pink transitions, actively restructuring the microbial community responsible for sulfur and hydrocarbon cycling, and generating color-linked biosignatures with potential astrobiological implications.