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Rhodopseudomonas palustris is unique among characterized nonsulfur purple bacteria because of its capacity for anaerobic photoheterotrophic growth using aromatic acids. Like growth with other reduced electron donors, this growth typically requires the presence of bicarbonate/C[O.sub.2] or some other added electron acceptor in the growth medium. Proteomic studies indicated that there was specific accumulation of form I ribulose 1, 5-bisphosphate carboxylase/oxygenase (RubisCO) subunit proteins (CbbL and CbbS), as well as the CbbX protein, in cells grown on benzoate without added bicarbonate; such cells used the small amounts of dissolved C[O.sub.2] in the medium to support growth. These proteins were not observed in extracts from cells grown in the presence of high levels (10 mM) of added bicarbonate. To confirm the results of the proteomics studies, it was shown that the total RubisCO activity levels were significantly higher (five- to sevenfold higher) in wild-type (CGA010) cells grown on benzoate with a low level (0.5 mM) of added bicarbonate. Immunoblots indicated that the increase in RubisCO activity levels was due to a specific increase in the amount of form I RubisCO (CbbLS) and not in the amount of form II RubisCO (CbbM), which was constitutively expressed. Deletion of the main transcriptional regulator gene, cbbR, resulted in impaired growth on benzoate-containing low-bicarbonate media, and it was established that form I RubisCO synthesis was absolutely and specifically dependent on CbbR. To understand the regulatory role of the CbbRRS two-component system, strains with nonpolar deletions of the cbbRRS genes were grown on benzoate. Distinct from the results obtained with photoautotrophic growth conditions, the results of studies with various CbbRRS mutant strains indicated that this two-component system did not affect the observed enhanced synthesis of form I RubisCO under benzoate growth conditions. These studies indicate that diverse growth conditions differentially affect the ability of the CbbRRS two-component system to influence cbb transcription.

The toxicity of selenite at high concentrations in biological organisms is caused by the generation of free radicals during its metabolism. In Rhodobacter sphaeroides, selenite is transported into cells by a polyol transporter.

Sucrose was found, when supplied exogenously, to be able to counter the growth inhibition of Sinorhizobium meliloti cells in media with inhibitory osmolarity. Sucrose was not accumulated by the bacteria in osmotically efficient quantities but it strongly induces the accumulation of the main endogenous osmolytes glutamate and N-acetylglutaminylglutamine amide. There was close relationship between the improvement of the osmotically active solute pool and the increase in cell volume.

A mutant having aberrant carboxysomes and a regular inorganic carbon uptake potential, but an alternated capacity to photosynthetically use the internal inorganic carbon pool, resulted from inactivation of ccmO in Synechococcus sp. strain PCC 7942. It requires high level of CO2 for development, and shows low ostensible photosynthetic affinity for extracellular inorganic carbon.