Leite Deborah C A, Leão Pedro, Garrido Amana G, Lins Ulysses, Santos Henrique F, Pires Débora O, Castro Clovis B, van Elsas Jan D, Zilberberg Carla, Rosado Alexandre S, Peixoto Raquel S
Institute of Microbiology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
Institute of Biology, Federal University of Rio de Janeiro Rio de Janeiro, Brazil.
Front Microbiol. 2017 Feb 7;8:176. doi: 10.3389/fmicb.2017.00176. eCollection 2017.
The hologenome theory of evolution (HTE), which is under fierce debate, presupposes that parts of the microbiome are transmitted from one generation to the next [vertical transmission (VT)], which may also influence the evolution of the holobiont. Even though bacteria have previously been described in early life stages of corals, these early life stages (larvae) could have been inoculated in the water and not inside the parental colony (through gametes) carrying the parental microbiome. How is transmitted to offspring is also not clear, as only one study has described this mechanism in spawners. All other studies refer to incubators. To explore the VT hypothesis and the key components being transferred, colonies of the broadcast spawner species were kept in nurseries until spawning. Gamete bundles, larvae and adult corals were analyzed to identify their associated microbiota with respect to composition and location. and bacteria were detected by sequencing in gametes and coral planula larvae. However, no cells were detected using microscopy at the gamete stage, which could be related to the absence of those cells inside the oocytes/dispersed in the mucus or to a low resolution of our approach. A preliminary survey of diversity indicated that parental colonies harbored clades B, C and G, whereas only clade B was found in oocytes and planula larvae [5 days after fertilization (a.f.)]. The core bacterial populations found in the bundles, planula larvae and parental colonies were identified as members of the genera and , suggesting that these populations could be vertically transferred through the mucus. The collective data suggest that spawner corals, such as , can transmit cells and the bacterial core to their offspring by a coral gamete (and that this gamete, with its bacterial load, is released into the water), supporting the HTE. However, more data are required to indicate the stability of the transmitted populations to indicate whether the holobiont can be considered a unit of natural selection or a symbiotic assemblage of independently evolving organisms.
进化全息基因组理论（HTE）目前正处于激烈争论中，该理论假定微生物组的某些部分会从一代传递到下一代[垂直传播（VT）]，这也可能影响全生物的进化。尽管此前已在珊瑚的早期生命阶段发现了细菌，但这些早期生命阶段（幼虫）可能是在水中接种的，而非在携带亲代微生物组的亲代群体内部（通过配子）。微生物如何传递给后代也不清楚，因为只有一项研究描述了产卵珊瑚中的这种机制。所有其他研究都涉及孵化珊瑚。为了探究垂直传播假说以及正在传递的关键成分，将散播产卵物种的群体饲养在育苗场直至产卵。对配子束、幼虫和成年珊瑚进行分析，以确定其相关微生物群的组成和位置。通过测序在配子和珊瑚浮浪幼虫中检测到了细菌。然而，在配子阶段使用显微镜未检测到细胞，这可能与卵母细胞内不存在这些细胞/分散在黏液中有关，或者与我们方法的低分辨率有关。对微生物多样性的初步调查表明，亲代群体中含有B、C和G类群，而在卵母细胞和浮浪幼虫中[受精后5天（a.f.）]仅发现了B类群。在配子束、浮浪幼虫和亲代群体中发现的核心细菌种群被鉴定为属和属的成员，这表明这些种群可能通过黏液进行垂直传递。总体数据表明，像这样的产卵珊瑚可以通过珊瑚配子将细胞和细菌核心传递给后代（并且这个带有细菌负荷的配子被释放到水中），这支持了进化全息基因组理论。然而，需要更多数据来表明传递种群的稳定性，以确定全生物是否可被视为自然选择的一个单位或独立进化生物的共生组合。
