Bioprospecting for Cyanophages with Biocontrol Potential against Toxin Producing Cyanobacteria in Lake Magadi, Kenya

Abstract

Cyanobacteria are a phylum of blue-green algae in the domain bacteria that get their energy from sun light through photosynthesis. In anaerobic environments, photoautotrophic blue green algae derive electrons by reduction of sulphur. In the Kenyan soda lakes, cyanobacteria serve as the sole source of food for Lesser Flamingos. Also, detection of these blue green algae blooms, is evident in these environments. Due to this reason, it has been hypothesized that the blooms may lead to production of secondary metabolites referred to as cyanotoxins that could be the cause for mass mortalities of Lesser Flamingos in these lakes including Lake Magadi. Viruses are key in controlling microbial populations in any ecosystem and thus they could act as a biocontrol measure for toxin producing cyanobacteria. Therefore, this study aimed to isolate cyanobacteria, amplify for toxin production genes and screen for cyanophages that can control these toxin producing cyanobacteria. The study site was Lake Magadi in the Rift Valley which has highly alkaline pH (8-12). Water samples were collected from different points around Lake Magadi. Physiochemical variables such as pH, salinity and temperature were measured for each of the sample on site. Two techniques for the isolation of cyanobacteria were used: isolation by spread plating on agar and dilution to extinction technique. Five types of media were used: Blue green medium (BG11), Synechococcus medium (A+), artificial lake water medium (ALW), artificial sea water medium (ASW) and enriched lake water medium (M). For solid cultures, spread plating was done followed by subsequent sub-culturing to acquire axenic cultures. Dilution to extinction technique involved subsequent dilution of the enriched sample until an axenic culture was obtained. These isolates grew at conditions that are unique to haloalkaliphiles. The cyanobacteria were subjected to morphological and molecular identification. Molecular identification involved partial sequencing of 16Sr RNA gene. Potential of the isolates to produce cyanotoxins was assessed by amplification of their respective genes using toxin specific primers. Sequence analysis indicated that all 11 isolates were affiliated to Cyanobacterium Spp. Genera represented include Spirulina, Synechococcus, Oscillatoria and Anabaenopsis. PCR amplification showed that all the isolates had different genes for toxin production. Phage lysis was observed in 10 of the isolates indicating that they were hosts for the phages. This study provides an insight into the uncultured cyanobacterial species from extreme environments and their cyanophages. The recovered isolates are a useful resource in understanding the taxonomy, phylogeny and diversity of cyanobacteria as well as their cyanophages. The cyanophages can be useful in biotechnology application for biocontrol of toxin producing cyanophages.