Chemosensory and photosensory perception in purple photosynthetic bacteria utilize common signal transduction components

Abstract

The chemotaxis gene cluster from the photosynthetic bacterium Rhodospirillum centenum contains five open reading frames (ORFs) that have significant sequence homology to chemotaxis genes from other bacteria. To elucidate the functions of each ORF, we have made various mutations in the gene cluster and analyzed their phenotypic defects. Deletion of the entire che operon (⌬che), as well as nonpolar disruptions of cheAY, cheW, and cheR, resulted in a smooth-swimming phenotype, whereas disruption of cheB resulted in a locked tumbly phenotype. Each of these mutants was defective in chemotactic response. Interestingly, disruption of cheY resulted in a slight increase in the frequency of tumbling/reversal with no obvious defects in chemotactic response. In contrast to observations with Escherichia coli and several other bacteria, we found that all of the che mutant cells were capable of differentiating into hyperflagellated swarmer cells when plated on a solid agar surface. When viewed microscopically, the smooth-swimming che mutants exhibited active surface motility but were unable to respond to a step-down in light intensity. Both positive and negative phototactic responses were abolished in all che mutants, including the cheY mutant. These results indicate that eubacterial photosensory perception is mediated by light-generated signals that are transmitted through the chemotaxis signal transduction cascade.

Analysis of a chemotaxis operon from Rhodospirillum centenum

“…Indeed, half of the amino acid substitutions involve alterations in hydrophobicity or charge. Taken together with the results of our mutational analyses (17), these results indicate that the CheY domain of CheAY and CheY must serve distinct roles in chemotactic signal transduction in R. centenum.…”

“…Mutational analysis has demonstrated that FrzE is involved in controlling the gliding reversal frequency (24). Similar analysis of R. centenum indicates that CheAY is involved in controlling the tumbling frequency, thereby indicating that CheAY and FrzE may have comparable functions (17).…”

“…Since the presence of more than one CheY homolog has been found in R. meliloti and R. sphaeroides, the existence of two proteins with CheY sequence similarities is not unprecedented. Mutational analysis of the CheY in R. centenum indicates that it has a much more pronounced effect on swarmer cell motility than on swimmer cell motility (17). One model emerging from our mutational studies is that CheAY may control rotation of the polar motor and CheY may control the lateral motor.…”

“…An ⍀ spectinomycin resistance (⍀-Sp) cassette, which is polar (28), was inserted into the CheA portion of the cheAY hybrid gene by first cloning a 1,413-bp NcoI fragment within cheAY into the vector pBSIIKS ϩ . The ⍀-Sp cassette was then cloned into a unique BglII site at CheAY amino acid residue 375 (for details, see the accompanying report [17]). For creating chromosomal disruptions, the cheAY::⍀ construct was cloned into the suicide vector pGmLacZ and recombined into the chromosome by a double-recombination event as described in detail in reference 17.…”

Hypercyst Mutants in Rhodospirillum centenum Identify Regulatory Loci Involved in Cyst Cell Differentiation

“…Escherichia coli strain S17-1 ( pir)/pZJD17 was used for conjugation and transposition of the mini-Tn5 interposon (11). pZJD17 is derived from the previously described plasmid pUTmini-Tn5-Sm/Sp (15) with the 5Ј-and 3Ј-terminator sites deleted to decrease polarity effects caused by premature termination of transcription of downstream genes (10). Plasmid pSK(ϩ) (Bluescript; Stratagene) and E. coli strain DH5␣ were used for cloning and maintaining R. centenum chromosomal DNA fragments.…”