Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, MD, United States of America.
PeerJ. 2023 Feb 28;11:e14924. doi: 10.7717/peerj.14924. eCollection 2023.
Cyanophages, viruses that infect cyanobacteria, are globally abundant in the ocean's euphotic zone and are a potentially important cause of mortality for marine picocyanobacteria. Viral host genes are thought to increase viral fitness by either increasing numbers of genes for synthesizing nucleotides for virus replication, or by mitigating direct stresses imposed by the environment. The encoding of host genes in viral genomes through horizontal gene transfer is a form of evolution that links viruses, hosts, and the environment. We previously examined depth profiles of the proportion of cyanophage containing various host genes in the Eastern Tropical North Pacific Oxygen Deficient Zone (ODZ) and at the subtropical North Atlantic (BATS). However, cyanophage host genes have not been previously examined in environmental depth profiles across the oceans.
We examined geographical and depth distributions of picocyanobacterial ecotypes, cyanophage, and their viral-host genes across ocean basins including the North Atlantic, Mediterranean Sea, North Pacific, South Pacific, and Eastern Tropical North and South Pacific ODZs using phylogenetic metagenomic read placement. We determined the proportion of myo and podo-cyanophage containing a range of host genes by comparing to cyanophage single copy core gene terminase (). With this large dataset (22 stations), network analysis identified statistical links between 12 of the 14 cyanophage host genes examined here with their picocyanobacteria host ecotypes.
Picyanobacterial ecotypes, and the composition and proportion of cyanophage host genes, shifted dramatically and predictably with depth. For most of the cyanophage host genes examined here, we found that the composition of host ecotypes predicted the proportion of viral host genes harbored by the cyanophage community. Terminase is too conserved to illuminate the myo-cyanophage community structure. Cyanophage was present in almost all myo-cyanophage and did not vary in proportion with depth. We used the composition of phylotypes to track changes in myo-cyanophage composition.
Picocyanobacteria ecotypes shift with changes in light, temperature, and oxygen and many common cyanophage host genes shift concomitantly. However, cyanophage phosphate transporter gene appeared to instead vary with ocean basin and was most abundant in low phosphate regions. Abundances of cyanophage host genes related to nutrient acquisition may diverge from host ecotype constraints as the same host can live in varying nutrient concentrations. Myo-cyanophage community in the anoxic ODZ had reduced diversity. By comparison to the oxic ocean, we can see which cyanophage host genes are especially abundant ( and ) or not abundant (myo ) in ODZs, highlighting both the stability of conditions in the ODZ and the importance of nitrite as an N source to ODZ endemic LLV .
感染蓝藻的噬藻体是海洋真光层中丰富的全球病毒，是海洋微囊藻藻种死亡率的潜在重要原因。病毒宿主基因被认为通过增加病毒复制所需核苷酸的基因数量，或者通过减轻环境直接施加的压力，从而提高病毒的适应性。通过水平基因转移将宿主基因编码到病毒基因组中是一种将病毒、宿主和环境联系起来的进化形式。我们之前研究了东热带北太平洋缺氧区（ODZ）和亚热带北大西洋（BATS）中含各种宿主基因的噬藻体的深度分布。然而，噬藻体宿主基因在海洋的环境深度分布中尚未被研究过。
我们使用系统发育宏基因组读序列放置法，检查了包括北大西洋、地中海、北太平洋、南太平洋以及东热带北太平洋和南太平洋 ODZ 在内的海洋盆地中微囊藻藻种、噬藻体及其病毒宿主基因的地理和深度分布。我们通过与噬藻体单拷贝核心基因终止酶（）比较，确定了含有一系列宿主基因的肌尾和 Podo-噬藻体的比例。通过对这里检查的 14 种噬藻体宿主基因中的 12 种进行网络分析，确定了它们与其微囊藻宿主生态型之间的统计联系。
微囊藻藻种以及噬藻体宿主基因的组成和比例随着深度的变化而显著且可预测地变化。对于这里检查的大多数噬藻体宿主基因，我们发现宿主生态型的组成预测了噬藻体群落中病毒宿主基因的比例。终止酶的保守性太高，无法阐明肌尾噬藻体的群落结构。几乎所有的肌尾噬藻体中都存在噬藻体，并且其比例与深度无关。我们使用 型的组成来跟踪肌尾噬藻体组成的变化。
微囊藻藻种随着光照、温度和氧气的变化而变化，许多常见的噬藻体宿主基因也随之变化。然而，噬藻体磷酸盐转运基因 似乎与海洋盆地有关，在低磷酸盐区域含量最丰富。与养分获取有关的噬藻体宿主基因的丰度可能会偏离宿主生态型的限制，因为同一宿主可以在不同的养分浓度下生存。缺氧区的肌尾噬藻体群落多样性降低。与含氧海洋相比，我们可以看到哪些噬藻体宿主基因在缺氧区特别丰富（ 和 ）或不丰富（肌尾 ），这突出了缺氧区条件的稳定性以及亚硝酸盐作为 ODZ 特有 LLV 的 N 源的重要性。
