Introduction
The rapidly growing industrialization of the world has an impact on the
quality of water, food, feed, and weather as results of high amounts of
toxic substances released by various industries to the environment (1,
2). Also, pesticides and chemical composts in agriculture as well as
vehicles for transportation cause to separate large quantities of
pollutants in atmosphere (3); The heavy metals as a main kind of these
pollutants considerably threaten the food safety because of their
accumulation in water and food (4-9), and consequently, affecting human
organs and tissues (1-3).
Heavy metals are classified into three categories including: toxic
metals, precious metals and radionuclides. One of the toxic metals, with
a significant role in water pollution is zinc (6, 10, 11). This
essential element is used in many growing economic sectors, and thereby,
large quantities of this heavy metal discharge into the industrial
effluents (12-15). Zinc as an essential element, has many important
biological impact such as: being as a major ion in structure of motifs,
act as a catalytic factor of enzymes (16), essential role in the
structure and function of nucleic acid and protein along with
accompanying in gene expression and immune system development(17, 18).
So, deficiency of zinc contributes to the impaired function of innate
immune response such as phagocytosis, cytokine secretion, neutrophils
and natural killer cells functions. Also, zinc deficiency impacts on
impaired antibody secretion, thymic atrophy and lymphopenia (19).
Microorganisms, like humans, are dependent on appropriate levels of zinc
for their vital reactions. For example; in yeast about 8% of the
proteome is thought to bind zinc (19, 20) and about 400 genes involved
in growth are zinc-dependent (20, 21). Several investigations have been
conducted mainly, in Saccharomyces cerevisiae, as a yeast, suggesting
the requirement of zinc homeostasis in growth and metabolism (20). There
are two main classes of eukaryotic zinc transporters in S.
cerevisiae . The Zrt1, Zrt2 and Zrt3 are classified in ZIP proteins
(ZRT-IRT-like protein) (19, 22, as well as, Zrc1, Cot1, Msc2 and Zrg17
that classified in cation diffusion facilitator (23, 24). In the case of
severe zinc limitation, extracellular uptake of zinc in S.
cerevisiae mediated by the high-affinity Zrt1 protein which contributes
to increasing of the ZRT1 expression up to 30-fold. Moreover, this
microorganism can partially adopt with conditions of low zinc by
expression of Fet4, a low-affinity metal transporter, to import zinc,
iron, and copper into the cell (19).
Biosorption strategies have been considered for many years to solve the
problem of heavy metal pollution and consequently environmental
remediation. Among all living organisms, applied to absorb toxic
elements, microorganisms have attracted increasing attention, because
they have safety in human aspects and are easier to work with (25-27).
Despite its mediocre capacity, the S. cerevisiae is a unique
biomaterial in heavy metals biosorption (28) and due to easy cultivation
in a large scale and manipulation at the molecular level as well as high
biomass production, makes the S. cerevisiae to be administered in
biomaterial approaches (11). Based on these considerations, our
investigation was conducted for study of yeasts with emphasis onS. cerevisiae as an industrially important strain, isolated from
industrial effluents, for biosorption of zinc and the applied the
produced biomass as zinc-enriched single cell protein (SCP) in feed and
food production.