Table 2. Hydrogen peroxide degradation rates of Prochlorococcus in co-culture with ‘helper’ bacterium Alteromonas and axenic Alteromonas.

Culture	Ambient CO2 (modern)	Elevated CO2 (year 2100)	P-value
Co-cultures	2.57±1.86	0.42±0.23	0.03
Axenic Alteromonas	1.09±1.00	0.77±0.30	NS

Normalized degradation rates of hydrogen peroxide (10⁻⁹ min⁻¹ Alteromonas cell⁻¹) mean±s.d. (n=4 for co-culture and n=6 for axenic Alteromonas) with P-value for differences between ambient and elevated CO₂ (t-test, one-tailed), NS indicates not significant.