LAUSR

The purpose of this study was to explore the microbial potential of a semi-arid sandy soil from south-central Algeria in order to isolate new chitinolytic actinobacteria. This soil is subjected to high temperatures (up to 43 °C) and has low nutrient content. Strains were isolated by plating soil suspensions on Bennett and Colloidal Chitin (CCM) medium. An initial clustering of isolates was made through BOX-PCR genetic profiling. Next, a 16S rRNA gene sequencing of representative isolates was realized. We also identified optimum physicochemical conditions for chitinolytic activity. A rapid in vitro assay based on glucose catabolic repression was developed to select isolates having a chitinase-dependent antifungal activity against two phytopathogenic fungi. Gene identification of glycosyl hydrolase family 18 (GH18) permitted us to assess the divergence of chitinase genes. Forty isolates were obtained from the semi-arid sandy soil. The molecular identification permitted us to assign them to Streptomyces or Micromonospora genera with seven possibly new bacterial species. For chitinolytic activity, 100% of isolates were able to grow and degrade colloidal chitin at pH 7 and at a temperature ranging from 30 to 40 °C. We also observed that Micromonospora strains had atypical activity patterns, with a strong chitinase activity maintained at high temperature. Finally, three strains presented an interesting chitinolytic potential to reduce fungal growth with new GH18 sequences. This study presents a new rapid method to detect antifungal chitinase-dependent activity that allowed to identify potentially new species of actinobacteria and new GH18 gene sequences.