A novel microbial interaction: obligate commensalism between a new gram-negative thermophile and a thermophilic Bacillus strain

Obligately commensal interaction between a new gram-negative thermophile an d a thermophilic Bacillus strain was investigated. From compost samples, a mixed culture showing tyrosine phenol-lyase activity was enriched at 60 deg rees C. The mixed culture consisted of a thermophilic gram-negative strain, SC-1, and a gram-positive spore-forming strain, SK-1. In mixed cultures, s train SC-1 started to grow only when strain SK-1 entered the stationary pha se. Although strain SC-1 showed tyrosine phenol lyase activity, we could no t isolate a colony with any nutrient medium. For the isolation and cultivat ion of strain SC-1, we added culture supernatant and cell extract of the mi xed culture to the basal medium, The supernatant and cell extract of the mi xed culture contained heat-stable and heat-labile factors, respectively, th at are essential to the growth of strain SC-1. During pure cultures of stra in SK-1, the heat-stable growth factors were released during the growth pha se and the heat-labile growth factors were produced intracellularly at the early stationary phase. Strain SC-1 was gram-negative and microaerophilic, and grows optimally at 60 degrees C. Based on these results, we propose a n ovel commensal interaction between a new gram-negative thermophile, strain SC-1, and Bacillus sp. strain SK-1.