Oxidative stress responses induced by Hexachlorocyclohexane (HCH) in saprotrophic soil microfungi

Even if the usage of Hexachlorocyclohexane (HCH) was banned or severely restricted ages ago, its widespread adoption between 1950’s and 2000 has determined a global and severe environmental contamination. According to estimations, around 1.7 and 4.8 million tons of HCH residues are still present all over the world (1). HCH may cause serious acute and chronic adverse effects to health and, as all persistent organic pollutants, tends to bioaccumulate along the food chain (2). Over the years, the multiple damage caused by exposures to this pesticide has been widely demonstrated. It has been reported to be carcinogenic, teratogenic, genotoxic and an endocrine disrupter; chronic exposure can induce hepatic and renal damages besides adverse effects on reproductive and nervous systems in mammals (3). It is also possible to observe a notable increase of reactive oxygen species (ROS) in exposed organisms caused by these xenobiotics. It is also important to study the toxic response of microorganisms to xenobiotic stress in order to acquire more useful information about their tolerance. As ROS generate damaging effects the investigation of the oxidative stress response, which protects organisms, is key to study these important defence mechanisms. Therefore, the aim of this study was to investigate the oxidative stress responses due to the presence of HCH in two species of saprotrophic soil microfungi: Trichoderma piluliferum J. Webster & Rifai and Penicillium daleae K.M. Zalessky (Fig.1). The goal was to evaluate the expression linked specifically to the eventual activation, under stress conditions, of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and glutathione transferase (GST). The fungal strains studied were isolated from matrices deriving from sites interested by HCH contamination. Sporal suspensions have been prepared and inoculated in liquid medium (Czapek-Dox) (Fig. 2). A first cultivation was performed for a predetermined time without the oxidative stress-agent, followed by a second cultivation that was performed with and without the oxidative stress-agent. The measurements focused on the production of reactive oxygen species, and subsequently on changes in the glutathione transferase (GST) levels, as well as any superoxide dismutase (SOD) and catalase (CAT) activities (Fig.3-4). The results suggested that high level of HCH promoted the ROS formation. The specific activity of GST and CAT was increased compared to the control cultures in both species, while the SOD activity is visible only in Penicillium daleae. Taken together, our results suggested that the growth of the fungal strains in presence of HCH shows signs of increased oxidative stress and antioxidant enzymes responses against the stress condition for scavenging ROS.