Ecological and evolutionary patterns in the enigmatic protist genus Percolomonas (Heterolobosea; Discoba) from diverse habitats.

Denis V. Tikhonenkov,Alastair G. B. Simpson,Andrey Plotnikov,Jong Soo Park,Yana Eglit,Soo Hwan Jhin,Kai Miller,Alberto Amato

doi:10.1371/journal.pone.0216188

Abstract

The heterotrophic flagellate Percolomonas cosmopolitus (Heterolobosea) is often observed in saline habitats worldwide, from coastal waters to saturated brines. However, only two cultures assigned to this morphospecies have been examined using molecular methods, and their 18S rRNA gene sequences are extremely different. Further the salinity tolerances of individual strains are unknown. Thus, our knowledge on the autecology and diversity in this morphospecies is deficient. Here, we report 18S rRNA gene data on seven strains similar to P. cosmopolitus from seven geographically remote locations (New Zealand, Kenya, Korea, Poland, Russia, Spain, and the USA) with sample salinities ranging from 4‰ to 280‰, and compare morphology and salinity tolerance of the nine available strains. Percolomonas cosmopolitus-like strains show few-to-no consistent morphological differences, and form six clades separated by often extremely large 18S rRNA gene divergences (up to 42.4%). Some strains grow best at salinities from 75 to 125‰ and represent halophiles. All but one of these belong to two geographically heterogeneous clusters that form a robust monophyletic group in phylogenetic trees; this likely represents an ecologically specialized subclade of halophiles. Our results suggest that P. cosmopolitus is a cluster of several cryptic species (at least), which are unlikely to be distinguished by geography. Interestingly, the 9 Percolomonas strains formed a clade in 18S rRNA gene phylogenies, unlike most previous analyses based on two sequences.

Highlights

We examined six new Percolomonas cosmopolitus-like organisms, two previously sequenced strains of Percolomonas cosmopolitus, and a strain recently described by Mylnikov as Percolomonas lacustris [38]
Seven monoprotistan strains were isolated from brackish to high salinity (4–280‰) water/sediment interface samples collected from New Zealand, Kenya, Korea, Poland, Russia, Spain, Table 1
No amoeboid form was observed during the cultivation of the organisms, and a cyst form was observed occasionally in all cultures except for strain ATCC 50343

Summary

Methods

Isolation and cultivationSeven monoprotistan strains were isolated from brackish to high salinity (4–280‰) water/sediment interface samples collected from New Zealand, Kenya, Korea, Poland, Russia, Spain, Strain nameSampling locationLRS SD2A XLG1-P S4 P5-P HLM-6 (P. lacustris) ATCC 50343 WS LOSolar saltern at Ebre River Delta, Spain (40o35’13’’N, 0o41’10’’E) Chula Vista solar saltern, USA (32o35’36’’N, 117o6’50’’W) Lake Grassmere, New Zealand (41o44’00’’S, 174o09’00’’E) Seosin solar saltern, Korea (37o09’36’’N, 126o40’44’’E) Wielizka Salt Mine, Poland (49o58’59’’N, 20o3’21’’E)Novoe Lake, Orenburg oblast, Russia (51 ̊8’55"N, 54 ̊59’41"E)Marine Aquarium, Rockville, MD, USA (NA)Sredny Island, White Sea, Russia (NA)Lake Turkana, Kenya (2o50’00’’N, 36o41’50’’E)Source salinity (‰). Seven monoprotistan strains were isolated from brackish to high salinity (4–280‰) water/sediment interface samples collected from New Zealand, Kenya, Korea, Poland, Russia, Spain, Strain name. LRS SD2A XLG1-P S4 P5-P HLM-6 (P. lacustris) ATCC 50343 WS LO. Solar saltern at Ebre River Delta, Spain (40o35’13’’N, 0o41’10’’E) Chula Vista solar saltern, USA (32o35’36’’N, 117o6’50’’W) Lake Grassmere, New Zealand (41o44’00’’S, 174o09’00’’E) Seosin solar saltern, Korea (37o09’36’’N, 126o40’44’’E) Wielizka Salt Mine, Poland (49o58’59’’N, 20o3’21’’E). Novoe Lake, Orenburg oblast, Russia (51 ̊8’55"N, 54 ̊59’41"E).

Results

Discussion

Conclusion