Also the addition of 1% Tween80 (v/v) had no effect on growth of ΔhemA. However, hemin supplementation in the presence of low ALA concentrations, by itself insufficient to sustain

full development of ΔhemA [20 μM in MM or 100 μM in CM (limited ALA)], resulted in wild-type growth (Fig. 2), indicating that hemin can be used as an external haem source. Sirohaem synthesis is dependent on ALA availability (Franken et al., 2011). Therefore, sulphur and nitrogen metabolism could be impaired in ΔhemA because of inactive sulphite Roscovitine cell line and nitrite reductases. To examine whether growth of ΔhemA could be improved by avoiding the need for nitrite reductase activity and/or sulphite reductase activity, supplementation assays were performed using ammonium instead of nitrate as N-source and addition of l-methionine in hemin-based

media. Supplementation of l-methionine did not improve growth of ΔhemA under any of the conditions tested (results not shown). The use of ammonium, however, significantly improved the hemin supplemented growth of ΔhemA under limited ALA conditions and supported minimal growth when ALA supplementation was omitted, whereas no significant growth was observed on nitrate-containing media (Fig. 2). These results indicate that the inability to synthesize sirohaem impaired nitrate assimilation because of the lack FG 4592 of nitrite reductase activity in ΔhemA, but not sulphite reductase activity. As even in the presence of ammonium, no wild-type growth is achieved without ALA supplementation, our results may indicate that some metabolic processes are still impaired, possibly due to insufficient intracellular haem levels. Amino acids, present in CM, can serve as alternative N-source but could also compete for uptake of components such as ALA or hemin. In the ΔhemA, they could also supplement unexpected

deficiencies. Therefore, several amino acids (See ‘Materials and methods’) were analysed for their potential involvement in growth of the ΔhemA mutant. No specific altered growth was observed in combination with ALA supplementation. In combination with hemin supplementation, improved growth was observed only with cysteine addition resulting in similar growth as observed for the WT strain (results not shown). Analyses many in CM media (Fig. 3) support the finding that amino acids do not interfere with hemin uptake or N-source utilization as omitting all casamino acids or ammonium does not result in an improved growth. Also competition of amino acids with ALA uptake is unlikely. Growth of ΔhemA was found to be improved when nitrate was omitted from ALA-supplemented media, possibly due to inhibitory effects of impaired nitrate utilization (e.g. by forming of nitrite intermediate and nitrosative stress). However, no wild-type growth was achieved as was observed in the presence of ammonium.