Pleiotropic effects of potassium deficiency in a heterocystous, nitrogen-fixing cyanobacterium, Anabaena torulosa

Alahari, Anuradha; Apte, Shree Kumar

doi:10.1099/00221287-144-6-1557

Cited by 32 publications

(20 citation statements)

References 36 publications

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“…Changes in these soil variables, however, are unlikely to be driving changes in N fixation, as increases in K, P and Mg were correlated with decreases in N fixation. Limitation of P and K can inhibit N-fixation rates (Alahari and Apte, 1998;Moisander et al, 2003) indirectly by limiting growth, but there is no mechanism known by which the modest increases in K, P and Mg could inhibit N fixation. Thus, changes in soil characteristics caused by biomass retention cannot mechanistically explain the reductions in N-fixation rate that we observed.…”

Section: Discussionmentioning

confidence: 99%

Evidence for the functional significance of diazotroph community structure in soil

2008

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Microbial ecologists continue to seek a greater understanding of the factors that govern the ecological significance of microbial community structure. Changes in community structure have been shown to have functional significance for processes that are mediated by a narrow spectrum of organisms, such as nitrification and denitrification, but in some cases, functional redundancy in the community seems to buffer microbial ecosystem processes. The functional significance of microbial community structure is frequently obscured by environmental variation and is hard to detect in short-term experiments. We examine the functional significance of free-living diazotrophs in a replicated long-term tillage experiment in which extraneous variation is minimized and N-fixation rates can be related to soil characteristics and diazotroph community structure. Soil characteristics were found to be primarily impacted by tillage management, whereas N-fixation rates and diazotroph community structure were impacted by both biomass management practices and interactions between tillage and biomass management. The data suggest that the variation in diazotroph community structure has a greater impact on N-fixation rates than do soil characteristics at the site. N-fixation rates displayed a saturating response to increases in diazotroph community diversity. These results show that the changes in the community structure of free-living diazotrophs in soils can have ecological significance and suggest that this response is related to a change in community diversity.

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Section: Discussionmentioning

confidence: 99%

Evidence for the functional significance of diazotroph community structure in soil

2008

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“…In nitrogen-fixing cyanobacteria such as Anabaena spp., K ϩ also regulates gene expression and vital metabolic processes such as photosynthesis and nitrogen fixation (1,2). Despite very low levels of K ϩ available in most environments (0.1 to 10 mM), the bacteria maintain a very high concentration of K ϩ (0.2 to 0.6 M) within their cells and have evolved several distinct K ϩ uptake and efflux systems to regulate their internal K ϩ concentration (15).…”

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Differential Expression of the Two kdp Operons in the Nitrogen-Fixing Cyanobacterium Anabaena sp. Strain L-31

Ballal

Apte

2005

Appl Environ Microbiol

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In several types of bacteria, the Kdp ATPase (comprising of the KdpABC complex) is an inducible, high-affinity potassium transporter that scavenges K ؉ from the environment. The cyanobacterium Anabaena sp. strain L-31 showed the presence of not one but two distinct kdp operons in its genome. The kdp1 consisted of kdpA1B1G1C1D genes, whereas the kdp2 contained the kdpA2B2G2C2 genes. Among the regulatory genes, the kdpD open reading frame of Anabaena sp. strain L-31 was truncated compared to the kdpD of other bacteria, whereas a kdpE-like gene was absent in the vicinity of the two kdp operons. In response to K ؉ limitation (<0.05 mM external K ؉ ), only kdp2 (and not kdp1) expression could be detected as a 5.3-kb transcript on Northern blots, indicating that kdpA2B2G2C2 genes constitute a polycystronic operon. Unlike E. coli, addition of osmolytes like NaCl, or a change in pH of the medium did not enhance the kdp expression in Anabaena sp. strain L-31. Interestingly, the Anabaena sp. strain L-31 kdp2 operon was strongly induced in response to desiccation stress. The addition of K ؉ to K ؉ -starved cultures resulted in repression and degradation of kdp2 transcripts. Our results clearly show that kdp2 is the major kdp operon expressed in Anabaena sp. strain L-31 and may play an important role in adaptation to K ؉ limitation and desiccation stress.Potassium, the major intracellular cation in bacteria, is involved in various physiological processes such as turgor adaptation (15), activation of cellular enzymes (29), and pH homeostasis (12). In nitrogen-fixing cyanobacteria such as Anabaena spp., K ϩ also regulates gene expression and vital metabolic processes such as photosynthesis and nitrogen fixation (1, 2). Despite very low levels of K ϩ available in most environments (0.1 to 10 mM), the bacteria maintain a very high concentration of K ϩ (0.2 to 0.6 M) within their cells and have evolved several distinct K ϩ uptake and efflux systems to regulate their internal K ϩ concentration (15). In Escherichia coli the constitutively expressed TrkG, TrkH, and Kup uptake systems have a low affinity for K ϩ but are competent to maintain the required levels K ϩ under normal physiological conditions (20). Under conditions of severe K ϩ limitation or osmotic upshift or when the low-affinity transporters are unable to meet the cell's demand for K ϩ , the high-affinity KdpATPase (K ϩ -dependent ATPase) is expressed (4). The K m of E. coli KdpATPase for K ϩ is 2 M and the cells expressing Kdp can reduce the K ϩ concentration in the medium to as low as 50 nM (28).Earlier studies had shown the kdp homologs to be widely distributed among the gram-negative bacteria (32). Genome sequencing has now shown kdp homologs to be present also in cyanobacteria, gram-positive bacteria, and the Archaea. We have previously demonstrated the presence of KdpB-like polypeptide in three different strains of the nitrogen-fixing cyanobacteria Anabaena spp. (6). The KdpB was induced under conditions of K ϩ limitation, and the KdpB protein was shown to be loc...

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“…The medium was modified to obtain either BG-11/K0 (wherein K 2 HPO 4 was replaced by equimolar Na 2 HPO 4 ) or BG-11/K5 (BG-11/K0 containing 5 mM KCl) medium (2). When required, media were supplemented with nitrogen by the addition of 5 mM NH 4 Cl and 5 mM MOPS.…”

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“…Protein content was determined by the Folin phenol method (24). Cellular extracts containing proteins (150 g) were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electroblotted onto Boehringer Mannheim positively charged nylon mem-branes, as described earlier (2,5). The two antisera (anti-KdpB and anti-KdpABC) raised in rabbits against the corresponding purified proteins from E. coli were kindly provided by K. Altendorf (University of Osnabrück, Osnabrück, Germany) and were used at dilutions of 1:5,000 and 1:2,000, respectively.…”

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Regulation of Potassium-Dependent Kdp-ATPase Expression in the Nitrogen-Fixing Cyanobacterium Anabaena torulosa

2001

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Pleiotropic effects of potassium deficiency in a heterocystous, nitrogen-fixing cyanobacterium, Anabaena torulosa

Cited by 32 publications

References 36 publications

Evidence for the functional significance of diazotroph community structure in soil

Evidence for the functional significance of diazotroph community structure in soil

Differential Expression of the Two kdp Operons in the Nitrogen-Fixing Cyanobacterium Anabaena sp. Strain L-31

Regulation of Potassium-Dependent Kdp-ATPase Expression in the Nitrogen-Fixing Cyanobacterium Anabaena torulosa

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