Hydrogen sulfide gas mediates the density-dependent growth of <i>met17</i>Δ on sulfate.

(A, B) Preventing gas escape allows low-density met17Δ cultures to grow. Growth curves of met17Δ (WY2035) in SD minimal medium, cultured in glass tubes either covered only with plastic lids (A, “Unsealed”) or additionally sealed with parafilm around the plastic lids (B, “Sealed”). Darker shades of gray represent higher initial cell densities. Each trendline represents a 3-ml culture in a tube of 13-mm diameter. At any given initial cell density, 6 identical cultures were initiated, 3 each for the unsealed and sealed treatment. Note that even low-density cultures could eventually grow to saturation when gas exchange was limited by parafilming, indicating that the accumulation of a gaseous growth mediator was enabling population growth. (C) Gas from high-density met17Δ cultures allowed low-density met17Δ cultures in the same plate to grow on sulfate. Growth curves of met17Δ (WY2548) at different initial cell densities (indicated by shade of gray) growing in different wells of the same 96-well plate sealed with parafilm. All densities can grow deterministically when the headspace is shared in a multiwell plate. (D) At all densities, met14Δ only showed residual growth in sulfate. Growth curves of met14Δ (WY2539) at different initial cell densities (indicated by shade of blue) growing in different wells of the same 96-well plate. (E) Gas from met17Δ cultures allowed met14Δ cultures to grow on sulfate. Growth curves of met17Δ (left panel, gray, WY2548) and met14Δ (right panel, blue, WY2539) at different initial cell densities sharing headspace in different wells of the same 96-well plate. (F) Lag time of low-density met17Δ cultures increased when sulfide was absorbed by lead acetate paper inserted into the gaps between the wells. Growth curves of met17Δ (WY2549) at different initial cell densities growing in different wells of the same 96-well plate either with (lower panel) or without (upper panel) lead acetate paper in the gaps. (G) Growth of low-density met17Δ on sulfate can be promoted by sodium hydrosulfide (NaHS), although high sulfide concentrations are toxic. At each sulfide concentration, each trendline represents one of 3 identical 3-ml liquid cultures (WY2531) in tubes sealed with plastic lids and parafilm. At 1,500 μM, population growth was inhibited. All met mutants were in the RM11 background. The data underlying this figure can be found in S2 Data.