Identification and diversity assessment of cyanobacterial communities from some mine tailing sites in Benguet Province, Philippines using isolation-dependent and isolation-independent methods

Cyanobacteria are a group of diverse prokaryotes that are capable of oxygenic photosynthesis. They are ubiquitous in nature and have been reported to survive in extreme environments. This study aimed to identify and assess the diversity of the cyanobacteria present in some mine tailing sites in the towns of Itogon and Tuba, in Benguet Province, Philippines using isolation-dependent and isolation-independent methods. Analysis of the water and sediment samples from the mine tailing sites (designated as Acu, Ampu, TSF1 and TSF3) showed higher metal concentrations in the sediment samples (2930–11,500 mg/kg dry weight Ca, 10–34 mg/kg dry weight Cr, 83–6500 mg/kg dry weight Cu, 6–172 mg/kg dry weight Pb, 8310–32,600 mg/kg dry weight Mg, 640–3400 mg/kg dry weight K, 43–144 mg/kg dry weight Zn), which were then processed for cyanobacterial enrichment. Identification of cyanobacteria was performed using the conventional isolation-dependent method for the characterization of microorganisms, 16S rRNA gene sequencing, and isolation-independent 16S rRNA metabarcoding analysis. Both approaches revealed that Arthronema africanum (1.98–60.1%) and Leptolyngbya spp. (39.9–97.0%) of the Pseudoanabaenales dominated the cyanobacterial composition in all sites. The isolation-dependent method identified most of the dominant taxa such as Arthronema africanum, Leptolyngbya spp. and Calothrix spp. Nodosilinea spp. was also confirmed to be part of the cyanobacterial community through this method. Unicellular cyanobacteria such as Chroococcales and Synechococcales were also observed. However, they were not fully identified at lower taxonomic levels in both methods, especially Chroococcales. On the other hand, the isolation-independent method recovered other taxa in selected sites such as Calothrix (0.002–0.022%), Halomicronema (0.01%), Nostoc (0.006–0.03%), Phormidium (0.007–14.1%), Planktothrix (0.36%), Pseudoanabaena (0.02–0.6%), Acaryochloris (0.006%), and Thermosynechococcus (0.02–4.7%). Metabarcoding revealed that samples from small-scale mine tailing ponds of Acu and Ampu, and the inactive pond of the large scale mining site, TSF1, had higher species diversity and evenness as compared to its active pond, TSF3, based on Shannon and Simpson indices. However, TSF1 and TSF3 of the large-scale mine tailings had higher species richness than Acu and Ampu of small-scale mining based on Chao index. Altogether, this study provided an inventory of cyanobacteria that can survive even in extreme metal conditions giving insights to their future applications, particularly, in bioremediation.