CrdR function in a curdlan-producing Agrobacterium sp. ATCC31749 strain.

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Agrobacterium sp. ATCC31749 efficiently produces curdlan under specific conditions (low pH, nitrogen starvation).
• The transcriptional regulator CrdR is crucial for curdlan production, but its direct role in activating the curdlan biosynthesis operon (crdASC) was unclear.

Purpose of the Study:

• To elucidate the molecular mechanism of CrdR in regulating curdlan biosynthesis.
• To determine if CrdR directly controls the expression of the curdlan biosynthesis operon.

Main Methods:

• Construction of a crdR knockout mutant and strains with CrdR expression vectors.
• Utilized a green fluorescent protein (GFP) reporter system driven by the curdlan operon promoter (crdP).
• Employed quantitative real-time PCR (q-RT-PCR), fluorescent microscopy, spectrometric assays, and protein-DNA binding assays.

Main Results:

• The crdR knockout mutant showed significantly reduced curdlan production and lacked capsule formation.
• Reintroduction of CrdR restored curdlan production in the mutant strain.
• CrdR overexpression increased the expression of curdlan biosynthesis genes (crdA, crdS, crdC) and GFP reporter activity.
• Purified CrdR protein specifically bound to the promoter region of the curdlan operon.

Conclusions:

• CrdR acts as a positive transcriptional regulator for the curdlan operon in Agrobacterium sp. ATCC31749.
• CrdR directly promotes curdlan biosynthesis by binding to the promoter region upstream of the crdA gene.