各种环境因素,包括H2可用性,代谢权衡,最佳生长温度,随机性,和水文学,进行了检查,以确定它们是否影响三个自养嗜热菌之间的微生物竞争。硫代硫酸盐还原剂热营养杆菌(Topt72°C)与72°C的产甲烷菌甲烷菌(Topt82°C)和65°C的高和低H2浓度的热嗜甲烷热球菌(Topt65°C)分别进行单培养和共培养。两种产甲烷菌均显示出代谢权衡,从高H2浓度下的高生长速率-低细胞产量转变为低H2浓度下的低生长速率-高细胞产量,以及与硫代硫酸盐还原剂共培养时。在1:1的初始比率中,D.热营养菌在高H2和低H2下都胜过产甲烷菌,在低H2上未检测到H2S,并且仅在CO2作为电子受体的情况下生长,表明与低H2的代谢权衡相似。当初始产甲烷菌与硫代硫酸盐的还原剂比率从1:1变化到104:1时,高H2时,D.在72°C下,嗜热菌总是胜过M.jannaschii。然而,当比例为103:1时,嗜热营养杆菌在65°C时胜过嗜热营养杆菌。将纯热流体与冷海水混合的反应性传输模型表明,在混合流体高于72°C的停留时间足够高的系统中,超热产甲烷菌占主导地位。停留时间较短,嗜热硫代硫酸盐还原剂占主导地位。如果停留时间随着沿流动路径的流体温度降低而增加,那么嗜热产甲烷菌可能占主导地位。如果嗜热产甲烷菌与硫代硫酸盐还原剂的初始比率增加,则嗜热产甲烷菌的优势会扩展到以前的硫代硫酸盐还原剂主导的条件。
目的:深层地下是地球上最大的微生物生物量库,是早期地球和外星环境中生命的类似物。甲烷生成和硫减少是在热缺氧热液喷口环境中发现的更常见的化学自养代谢。H2氧化硫还原剂与产甲烷菌之间的竞争主要由氧化还原反应与前者竞争的产甲烷菌的热力学有利性驱动。这项研究表明,热液喷口化学自养生物之间的竞争,嗜热甲烷热球菌,和热营养脱硫杆菌也受到其他重叠因素的影响,例如交错的最佳生长温度,随机性,和水文学。通过对微生物竞争的各个方面进行建模,再加上现场数据,更好地了解产甲烷菌如何在热缺氧环境中胜过硫代硫酸盐还原剂,以及深层地下如何促进生物地球化学循环。
Various environmental factors, including H2 availability, metabolic tradeoffs, optimal growth temperature, stochasticity, and hydrology, were examined to determine if they affect microbial competition between three autotrophic thermophiles. The thiosulfate reducer Desulfurobacterium thermolithotrophum (Topt72°C) was grown in mono- and coculture separately with the methanogens Methanocaldococcus jannaschii (Topt82°C) at 72°C and Methanothermococcus thermolithotrophicus (Topt65°C) at 65°C at high and low H2 concentrations. Both methanogens showed a metabolic tradeoff shifting from high growth rate-low cell yield at high H2 concentrations to low growth rate-high cell yield at low H2 concentrations and when grown in coculture with the thiosulfate reducer. In 1:1 initial ratios, D. thermolithotrophum outcompeted both methanogens at high and low H2, no H2S was detected on low H2, and it grew with only CO2 as the electron acceptor indicating a similar metabolic tradeoff with low H2. When the initial methanogen-to-thiosulfate reducer ratio varied from 1:1 to 104:1 with high H2, D. thermolithotrophum always outcompeted M. jannaschii at 72°C. However, M. thermolithotrophicus outcompeted D. thermolithotrophum at 65°C when the ratio was 103:1. A reactive transport model that mixed pure hydrothermal fluid with cold seawater showed that hyperthermophilic methanogens dominated in systems where the residence time of the mixed fluid above 72°C was sufficiently high. With shorter residence times, thermophilic thiosulfate reducers dominated. If residence times increased with decreasing fluid temperature along the flow path, then thermophilic methanogens could dominate. Thermophilic methanogen dominance spread to previously thiosulfate-reducer-dominated conditions if the initial ratio of thermophilic methanogen-to-thiosulfate reducer increased.
OBJECTIVE: The deep subsurface is the largest reservoir of microbial biomass on Earth and serves as an analog for life on the early Earth and extraterrestrial environments. Methanogenesis and sulfur reduction are among the more common chemolithoautotrophic metabolisms found in hot anoxic hydrothermal vent environments. Competition between H2-oxidizing sulfur reducers and methanogens is primarily driven by the thermodynamic favorability of redox reactions with the former outcompeting methanogens. This study demonstrated that competition between the hydrothermal vent chemolithoautotrophs Methanocaldococcus jannaschii, Methanothermococcus thermolithotrophicus, and Desulfurobacterium thermolithotrophum is also influenced by other overlapping factors such as staggered optimal growth temperatures, stochasticity, and hydrology. By modeling all aspects of microbial competition coupled with field data, a better understanding is gained on how methanogens can outcompete thiosulfate reducers in hot anoxic environments and how the deep subsurface contributes to biogeochemical cycling.