Study of Spirulina platensis (Arthrospira) Development under the Heavy Metals Influence, as a Potential Promoter of Wastewater Remediation

Abstract

Aquatic ecosystems polluted by heavy metals can affect microalgae growth when their concentrations overcome certain limits, depending on each involved heavy metal species. Yet, for heavy metal concentrations in the low range, microalgae exhibit metal tolerance and can accumulate a diversity of metal species from aqueous media. In particular, Spirulina platensis proved biosorption ability for heavy metals like Zn, Cd, Pb, or Cr, which can make it useful for the bioremediation of aquatic media polluted with heavy metals. This prokaryotic cyanobacteria from the microalgae species, which has a high protein, carbohydrate, and fats content, can interact with heavy metals through biosorption/bioaccumulation, leading to changes in the biomass yield, growth rate, and implicitly, biomass composition. This paper aims to investigate the influence of some heavy metal ions on the development and metabolic processes occurring in the cyanobacteria S. platensis, in order to establish its limitations in heavy metal bioremediation. In this regard, submerged cultures of S. platensis, involving standardized culture medium (Zarrouk), in the presence of nickel, cadmium, and lead ions in different concentrations (0.5 mg/L, 1.0 mg/L, and 1.5 mg/L, were considered. The cultivation of the microalgae was carried out for 28 days, with the determination of cell mass growth, dry biomass, protein accumulation, cell viability, and pH of the culture media, at certain time intervals (0, 3, 7, 13, 18, 24, and 28 days). Spirulina cultures were affected by the metal ions in different degrees, depending both on the type of metal ion and its concentration. The most toxic for cell growth and biomass accumulation were nickel and cadmium ions, at concentrations of 1.0 mg/L, and 1.5 mg/L, respectively. Cadmium, regardless of concentration, caused a decrease in dry biomass weight throughout the microalgae cultivation period. Instead, lead exhibited the lowest effect on the viability and integrity of spirulina cells, regardless of the concentration in which it was used.