Silva Luis, Calleja Maria L, Huete-Stauffer Tamara Megan, Ivetic Snjezana, Ansari Mohd I, Viegas Miguel, Morán Xosé Anxelu G
Division of Biological and Environmental Sciences and Engineering, Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
Front Microbiol. 2019 Jan 7;9:3244. doi: 10.3389/fmicb.2018.03244. eCollection 2018.
Characterized by some of the highest naturally occurring sea surface temperatures, the Red Sea remains unexplored regarding the dynamics of heterotrophic prokaryotes. Over 16 months, we used flow cytometry to characterize the abundance and growth of four physiological groups of heterotrophic bacteria: membrane-intact (), high and low nucleic acid content (HNA and LNA) and actively respiring (CTC+) cells in shallow coastal waters. Chlorophyll , dissolved organic matter (DOC and DON) concentrations, and their fluorescent properties were also measured as proxies of bottom-up control. We performed short-term incubations (6 days) with the whole microbial community (Community treatment), and with the bacterial community only after removing predators by filtration (Filtered treatment). Initial bacterial abundances ranged from 1.46 to 4.80 × 10 cells mL. Total specific growth rates in the Filtered treatment ranged from 0.76 to 2.02 d. and HNA cells displayed similar seasonal patterns, with higher values during late summer and fall (2.13 and 2.33 d, respectively) and lower in late spring (1.02 and 1.01 d, respectively). LNA cells were outgrown by the other physiological groups (0.33-1.08 d) while CTC+ cells (0.28-1.85 d) showed weaker seasonality. The Filtered treatment yielded higher bacterial abundances than the Community treatment in all but 2 of the incubations, and carrying capacities peaked in November 2016 (1.04 × 10 cells mL), with minimum values (3.61 × 10 cells mL) observed in May 2017. The high temperatures experienced from May through October 2016 (33.4 ± 0.4°C) did not constrain the growth of heterotrophic bacteria. Indeed, bacterial growth efficiencies were positively correlated with environmental temperature, reflecting the presence of more labile compounds (high DON concentrations resulting in lower C:N ratios) in summer. The overall high specific growth rates and the consistently higher carrying capacities in the Filtered treatment suggest that strong top-down control by protistan grazers was the likely cause for the low heterotrophic bacteria abundances.
红海以一些自然出现的最高海表温度为特征，但其关于异养原核生物的动态仍未被探索。在16个月的时间里，我们使用流式细胞仪来表征浅海沿岸水域中异养细菌四个生理组的丰度和生长情况：完整细胞膜（）、高核酸含量和低核酸含量（HNA和LNA）以及活跃呼吸（CTC+）细胞。叶绿素、溶解有机物（DOC和DON）浓度及其荧光特性也作为自下而上控制的指标进行了测量。我们对整个微生物群落进行了短期培养（6天）（群落处理），并在通过过滤去除捕食者后仅对细菌群落进行了培养（过滤处理）。初始细菌丰度范围为1.46至4.80×10个细胞/毫升。过滤处理中的总比生长速率范围为0.76至2.02天。 和HNA细胞呈现出相似的季节模式，在夏末和秋季较高（分别为2.13和2.33天），在春末较低（分别为1.02和1.01天）。LNA细胞被其他生理组超越（0.33 - 1.08天），而CTC+细胞（0.28 - 1.85天）的季节性较弱。除了2次培养外，过滤处理在所有培养中产生的细菌丰度都高于群落处理，承载能力在2016年11月达到峰值（1.04×10个细胞/毫升），在2017年5月观察到最小值（3.61×10个细胞/毫升）。2016年5月至10月经历的高温（33.4±0.4°C）并未限制异养细菌的生长。事实上，细菌生长效率与环境温度呈正相关，反映出夏季存在更多不稳定化合物（高DON浓度导致较低的C:N比）。过滤处理中总体较高的比生长速率和持续较高的承载能力表明，原生生物捕食者的强烈自上而下控制可能是异养细菌丰度较低的原因。
