Effects of the deficiency of the rhodanese‐like protein RhdA in Azotobacter vinelandii

Abstract

In Azotobacter vinelandii the rhdA gene codes for a protein (RhdA) of the rhodanese-homology superfamily. By combining proteomics, enzymic profiles and ultrastructural observations, the phenotype of an A. vinelandii rhdA mutant was analyzed. We found that the A. vinelandii rhdA mutant, and not the wild-type strain, accumulated polyhydroxybutyrate. RhdA deficiency enhanced the expression of enzymes of the polyhydroxybutyrate biosynthetic operon, and affected the activity of specific tricarboxylic acid cycle enzymes. The effect was dramatic on aconitase, in spite of comparable expression of aconitase polypeptides in both strains. By using a model system, we found that RhdA triggered protection from oxidants.

The rhodanese RhdA helps Azotobacter vinelandii in maintaining cellular redox balance

“…The phenotypic characterization of the A. vinelandii rhdA mutant strain MV474 (Cereda et al, 2007(Cereda et al, , 2009 clearly showed that inactivation of enzymes containing labile Fe-S clusters (Imlay, 2006) was enhanced in the absence of RhdA. Our goal was, therefore, to explore whether these effects could correlate with an altered redox balance in A. vinelandii cells lacking RhdA.…”

“…The first indication that RhdA could protect A. vinelandii from oxidative events stemmed from the observation that in the presence of the superoxide generator PMS, A. vinelandii growth was significantly impaired only in the rhdA mutant strain (Cereda et al, 2007(Cereda et al, , 2009 highlight whether the presence of RhdA could buffer the effects of oxidative stress.…”

“…Furthermore, in conditions of provoked oxidative stress by addition of the superoxide generator phenazine methosulfate (PMS), a stressor-dependent induction of the rhdA gene provided a link between RhdA and the PMS-resistance of the wild-type strain previously observed (Cereda et al, 2007(Cereda et al, , 2009. The potentiality of RhdA in buffering the general levels of oxidants in A. vinelandii cells is discussed.…”

“…To better identify a potential link between activation of defensive activities against oxidative damage and RhdA lack in A. vinelandii, we performed transcriptomic investigations by using growth conditions (i.e., sucrose as the carbon source) in which, in spite of the proved oxidative imbalance owing to the lack of RhdA (see Figure 1 and Table 1), MV474 grew as well as the wild-type strain UW136 (Cereda et al, 2007). Analysis of the expression of ahpC gene (coding for AhpC) revealed that also during cellular respiration the expression of the ahpC transcript in the RhdA mutant was approximately seven-fold higher than in wild-type cells (Figure 4).…”

“…Preliminary phenotypic characterizations of an A. vinelandii mutant strain (MV474) in which the rhdA gene was disrupted by deletion demonstrated some metabolic imbalance that pointed to an involvement of RhdA in protecting from inactivation enzymes containing labile Fe-S (Cereda et al, 2007). Accordingly, the defects of the A. vinelandii RhdA null mutant was elicited by using growth conditions that enhance the catalytic deficiency of enzymes with vulnerable Fe-S clusters (Cereda et al, 2009).…”