Morphological changes in Streptomyces sp. MC1 during Cr(VI) removal in liquid medium

Abstract

Streptomyces sp. MC1 isolated from sugar cane, showed significant capacity to remove highly toxic Cr(VI) from a liquid minimal medium (MM) supplemented with sulphate or phosphate ions, which could have important implications in bioremediation process. This strain, like other filamentous microorganisms, displays peculiarities due to mycelia growth pattern. In this connection, diverse studies reported on morphological changes in microorganisms associated to oxidative stress caused by heavy metals. The aim of the present work was characterize the morphological changes of Streptomyces sp. MC1 during the Cr(VI) removal from MM. Cells were grown in the MM supplemented with 5mM of Na2SO4 or K2HPO4 either in the presence or absence of 20 mg/L of Cr(VI) as K2Cr2O7. Cultures were incubated for 96 h at 30 ºC in orbital shaker at 170 rpm. Biomass was determined by dry weight. Macroscopic and microscopic morphology was characterized utilizing a lupa and microscope Nikon Eclipse net software package. Cellular morphology was quantified by determining the hyphal growth unit length L/N, where L being the total hyphal length and N the number of hyphal tips. Supplement of sulphate or phosphate ions to MM significantly increased the biomass concentration but did not induced evident morphological changes. However, the presence of Cr(VI) affect both growth and morphology. Biomass concentration was decreased and L/N was increase compared to control cell. Moreover, the presence of Cr(VI) encouraged the pellets formation. These observations suggest us that, both growth and cell branching ability could be decreased as an adaptive response against stress conditions induced by Cr(VI).