A novel slow-growing, obligatory heterofermentative, nonstarter lactic acid bacterium (NSLAB), Lactobacillus wasatchensis WDC04, was studied for growth and gas production in Cheddar-style cheese made using Streptococcus thermophilus as the starter culture. Cheesemaking trials were conducted using S. thermophilus alone or in combination with Lb. wasatchensis deliberately added to cheese milk at a level of similar to 10(4) cfu/mL. Resulting cheeses were ripened at 6 or 12 degrees C. At d 1, starter streptococcal numbers were similar in both cheeses (similar to 10(9) cfu/g) and fast-growing NSLAB lactobacilli counts were below detectable levels (<10(2) cfu/g). As expected, Lactobacillus wasatchensis counts were 3 x 10(5) cfu/g in cheeses inoculated with this bacterium and below enumeration limits in the control cheese. Starter streptococci decreased over time at both storage temperatures but declined more rapidly at 12 degrees C, especially in cheese also containing Lb. wasatchensis. Populations of fast-growing NSLAB and the slow-growing Lb. wasatchensis reached 5 x 107 and 2 x 10(8) cfu/g, respectively, after 16 wk of storage at 12 degrees C. Growth of NSLAB coincided with a reduction in galactose concentration in the cheese from 0.6 to 0.1%. Levels of galactose at 6 degrees C had similar decrease. Gas formation and textural defects were only observed in cheese with added Lb. wasatchensis ripened at 12 degrees C. Use of S. thermophilus as starter culture resulted in galactose accumulation that Lb. wasatchensis can use to produce CO2, which contributes to late gas blowing in Cheddar-style cheeses, especially when the cheese is ripened at elevated temperature.