A novel bacterium isolated from Cheonggukjang was identified as a glutamate-dependent Bacillus subtilis HA with 98.3% similarity to Bacillus subtilis Z99104. Optimization of poly-$gamma$-glutamic acid ($gamma$-PGA) production by modulating fermentation factors including carbon sources, nitrogen sources, inorganic salts and fermentation time was investigated. Optimum culture broth for $gamma$-PGA production consisted of 3% glutamate, 3% glucose and various salts, resulting in the PGA production of 22.5 g/L by shaking culture for 72 hr at $37^{circ}C$. Average molecular weight of $gamma$-PGA was determined to be 1,220 kDa through MALLS analysis. The $gamma$-PGA solution showed a typical pseudoplastic flow behavior, and a great decrease in consistency below pH 6.0 regardless of the same molecular weight of $gamma$-PGA. The molecular weights of isolated $gamma$-PGA were drastically decreased by heat treatment in various acidic conditions, resulting in different hydrolysis of $gamma$-PGA. The consistency of $gamma$-PGA solution was greatly decreased with increase heating time in acidic conditions.