A metabarcoding comparison of windward and leeward airborne algal diversity across the Ko‘olau mountain range on the island of O'ahu, Hawai‘i¹

Abstract

Airborne algae from sites on the windward (n = 3) and leeward (n = 3) sides of the Ko'olau Mountain range of O'ahu, Hawai'i, were sampled for a 16 d period during January and February 2015 using passive collection devices and were characterized using Illumina MiSeq sequencing of the universal plastid amplicon marker. Amplicons were assigned to 3,023 operational taxonomic units (OTUs), which included 1,189 cyanobacteria, 1,009 heterotrophic bacteria, and 304 Eukaryota (of which 284 were algae and land plants). Analyses demonstrated substantially more OTUs at windward than leeward O'ahu sites during the sampling period. Removal of nonalgal OTUs revealed a greater number of algal reads recovered from windward (839,853) than leeward sites (355,387), with the majority of these being cyanobacteria. The 1,234 total algal OTUs included cyanobacteria, diatoms, cryptophytes, brown algae, chlorophyte green algae, and charophyte green algae. A total of 208 algal OTUs were identified from leeward side samplers (including OTUs in common among samplers) and 1,995 algal OTUs were identified from windward samplers. Barcoding analyses of the most abundant algal OTUs indicated that very few were shared between the windward and leeward sides of the Ko'olau Mountains, highlighting the localized scale at which these airborne algae communities differ. Back trajectories of air masses arriving on O'ahu during the sampling period were calculated using the NOAA HY-SPLIT model and suggested that the sampling period was composed of three large-scale meteorological events, indicating a diversity of potential sources of airborne algae outside of the Hawaiian Islands.

The effects of contemporary selection and dispersal limitation on the community assembly of acidophilic microalgae

“…Moreover, we found no evidence for dispersal limitation in other common acidophilic microalgae besides ESU34 (G. maxima OTU1) and ESU35 (G. maxima OTU2). Indeed, dispersal by air or birds is reportedly common in different groups of microalgae (Proctor 1959, Sherwood et al 2017. Consistent with this observation, we found two acidophilic green algae (ESU7 and ESU11) in some air dust samples that we collected as part of our fieldwork (Fig.…”

“…Indeed, dispersal by air or birds is reportedly common in different groups of microalgae (Proctor , Sherwood et al. ). Consistent with this observation, we found two acidophilic green algae (ESU7 and ESU11) in some air dust samples that we collected as part of our fieldwork (Fig.…”

µgreen-db: a reference database for the 23S rRNA gene of eukaryotic plastids and cyanobacteria

“…However, in the past twenty years, phylogenetic analyses have demonstrated that an approach based on morphological determination alone is somewhat artificial for most of the microalgal genera and should be revised 25,26 . Several studies recently estimated the diversity of indigenous photosynthetic microbial communities in various environments using metabarcoding coupled with high-throughput sequencing (HTS) 3,[27][28][29][30][31][32][33][34] . A range of molecular markers has been used to describe cyanobacterial and photosynthetic microeukaryote diversity with varying degrees of resolution (e.g., 16S/18S/23S rRNA, tufA, psbA, rbcL, ITS) 32,[35][36][37][38][39] .…”

“…Moreover, UPA has a length (~410 bp) suitable for HTS Technologies 43 , such as Illumina 45 . UPA can also be used in addition to other markers to obtain a comprehensive overview of microbial diversity 31,37,39,46 .…”

“…The most popular databases are (i) SILVA, that groups SSU and LSU rRNA genes from eukaryotic and prokaryotic organisms 51 , (ii) PR 2 , a protist small subunit ribosomal reference database 52 , (iii) PhytoREF, a reference database of the plastidial 16S rRNA gene of photosynthetic eukaryotes 53 , (iv) R-Syst::diatom, that gathers the 18S rRNA gene and rbcL diatom sequences 54 , and (v) DINOREF, a reference database of the 18S rRNA of dinoflagellates 55 . Sherwood et al 31 recently made available a database (http://scholarspace.manoa.hawaii.edu/handle/10125/42782) that groups 97,194 UPA and LSU amplicon sequences from their own project, including sequences not found in SILVA. However, these sequences are mainly assigned to the Bacteria domain (75% of the total sequences with only <1% assigned to Cyanobacteria), whilst within the 10% of eukaryotic sequences, 80% are associated to the Metazoa group.…”