Expression of the Bacterial Catalase Genes During Sinorhizobium meliloti-Medicago sativa Symbiosis and Their Crucial Role During the Infection Process

Abstract

Sinorhizobium meliloti possesses three distinct catalases to cope with oxidative stress: two monofunctional catalases (KatA and KatC) and one bifunctional catalase-peroxydase (KatB). The katB gene is constitutively expressed during growth in batch culture and is not induced under oxidative stress conditions. In contrast, the expression of katA and katC genes is mainly regulated at the transcription level in these conditions. A differential expression of kat genes was observed during the development of the nodule. A high expression of katA gene was detected in bacteroids, suggesting that the nitrogen-fixation process induces a strong oxidative stress. In contrast, bacteria express katB and katC genes and not the H2O2-inducible katA gene in infection threads despite the detection of H2O2 around the bacteria. A katB katC double mutant nodulated poorly and displayed abnormal infection. After nonefficient release into plant cells, bacteria failed to differentiate into bacteroids and rapidly underwent senescence. Our results indicate that these two catalases are essential for the establishment of the symbiosis. They also suggest that the bacteria are in a nonexponential growth phase in infection threads and corroborate previous studies on the growth rate of bacteria inside the plant.

Disruption of sitA Compromises Sinorhizobium meliloti for Manganese Uptake Required for Protection against Oxidative Stress

“…S. meliloti contains three catalases, KatA, KatB, and KatC, none of which are manganese dependent (21,28,44). We speculated that since the sitA::mTn5 mutant exhibits increased sensitivity to H 2 O 2 , catalase activity may be altered in this strain.…”

“…It has become evident that S. meliloti must be able to manage oxidative stress while in the host plant, as the loss of certain oxidative stress defense mechanisms causes symbiotic defects. For example, S. meliloti strains deficient in both catalase B and catalase C (katB katC) or both catalase A and catalase C (katA katC), enzymes that detoxify H 2 O 2 , are symbiotically deficient (28,44). However, exactly which rhizobial defenses are required to combat oxidative stress is a complex question.…”

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

“…Single mutants in any of the three S. meliloti catalases, one of the two superoxide dismutases (sodB) or in the global regulator of H 2 O 2 protection, oxyR, are sensitive to ROS, but are not defective in symbiosis [53][54][55][56] . However, double mutants in the genes encoding catalase B and catalase C (katB/katC) or catalase A and catalase C (katA/katC) are compromised in their ability to invade the host plant 53,54 . Mutants in a second superoxide dismutase, sodC, a predicted sodM (Smc00911) or a secreted chloroperoxidase (Smc01944) have not yet been analysed 57 .…”

Defence of Rhizobium etli bacteroids against oxidative stress involves a complexly regulated atypical 2‐Cys peroxiredoxin

“…© 2005Blackwell Publishing Ltd, Molecular Microbiology , 55 , 1207-1221 The Sinorhizobium meliloti superoxide dismutase sodA mutant displays a severely reduced nodulation capacity as well as an impaired bacteroid development and nitrogen fixation capacity (Santos et al ., 2000). Furthermore, S. meliloti possesses two monofunctional catalase-encoding genes, katA and katC , and one catalase-peroxidaseencoding gene, katB (Herouart et al ., 1996;Sigaud et al ., 1999;Jamet et al ., 2003). None of the catalase single mutants shows an altered nodulation or nitrogen fixation capacity, in contrast to the katA katC and katB katC double mutants (Sigaud et al ., 1999;Jamet et al ., 2003).…”

“…Furthermore, S. meliloti possesses two monofunctional catalase-encoding genes, katA and katC , and one catalase-peroxidaseencoding gene, katB (Herouart et al ., 1996;Sigaud et al ., 1999;Jamet et al ., 2003). None of the catalase single mutants shows an altered nodulation or nitrogen fixation capacity, in contrast to the katA katC and katB katC double mutants (Sigaud et al ., 1999;Jamet et al ., 2003). In bacteroids, an increase of catalase activity correlating with KatA induction was observed (Sigaud et al ., 1999).…”