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Reduction in photosynthetic capacity in a mutualistic algal-bacterial co-culture revealed by quantitative proteomics

ABSTRACT: Algae and bacteria are frequently observed to form mutualisms for the exchange of a range of nutrients. We have developed a stable co-culture in which the cobalamin (vitamin B12)-requiring unicellular green alga Lobomonas rostrata can grow stably in the absence of this organic micronutrient with the -proteobacterium Mesorhizobium loti, which supplies B12 in exchange for fixed carbon. In this study, we report the results of a comparative quantitative proteomics experiment to evaluate the protein expression profile of L. rostrata grown in co-culture vs. axenic treatments. For this, we have successfully developed and applied an isobaric tagging proteomics platform (iTRAQ) comparing the proteome of L. rostrata (an organism without a sequenced genome) grown axenically with B12 supplementation or in co-culture with M. loti. A total of 588 proteins could be identified using the related Chlamydomonas reinhardtii as a reference genome, and there was little interference from bacterial proteins. Comparisons of relative protein abundance in the two growth conditions highlighted proteins that were higher in co-cultures, including a number of heat-shock proteins, suggesting that the alga was experiencing stress in the presence of the bacterium. Several enzymes of amino acid biosynthesis were elevated, but total cellular protein and free amino acids were substantially lower in cells in co-culture relative those grown axenically. The most striking observation was that many proteins of photosynthesis, both the light-dependent reactions and the Calvin cycle, and those of chloroplast protein synthesis, were significantly lower in L. rostrata cells in co-culture. These observations were confirmed by measurement of electron transfer rates in cells grown under the two conditions, and strongly suggest that the alga is experiencing nutrient limitation when B12 is supplied directly from a bacterial source.

INSTRUMENT(S): QSTAR

ORGANISM(S): Mesorhizobium Loti Lobomonas Rostrata

SUBMITTER: Joseph Longworth

LAB HEAD: Jagroop Pandhal

PROVIDER: PXD005046 | Pride | 2017-10-17

REPOSITORIES: Pride

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Quantitative proteomics of a B12 -dependent alga grown in coculture with bacteria reveals metabolic tradeoffs required for mutualism.

Helliwell Katherine E KE Pandhal Jagroop J Cooper Matthew B MB Longworth Joseph J Kudahl Ulrich Johan UJ Russo David A DA Tomsett Eleanor V EV Bunbury Freddy F Salmon Deborah L DL Smirnoff Nicholas N Wright Phillip C PC Smith Alison G AG

The New phytologist 20171016 2

The unicellular green alga Lobomonas rostrata requires an external supply of vitamin B12 (cobalamin) for growth, which it can obtain in stable laboratory cultures from the soil bacterium Mesorhizobium loti in exchange for photosynthate. We investigated changes in protein expression in the alga that allow it to engage in this mutualism. We used quantitative isobaric tagging (iTRAQ) proteomics to determine the L. rostrata proteome grown axenically with B12 supplementation or ...[more]

PMID: 29034959

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Project description:The fertility of dairy cows is challenged during early lactation and better nutritional strategies need to be developed to address this issue. Combined supplementation of folic acid and vitamin B12 improves energy metabolism in the dairy cow during early lactation. Therefore, the present study was undertaken to explore the effects of this supplement on gene expression in granulosa cells from the dominant follicle during the postpartum period. Multiparous Holstein cows received weekly intramuscular injection of 320 mg folic acid and 10 mg vitamin B12 (treated group) beginning 24 (SD 4) d before calving until 56 d after calving, whereas the control group received saline. The urea plasma concentration was significantly decreased during the pre-calving period, and the concentration of both folate and vitamin B12 were increased in treated animals. Milk production and dry matter intake were not significantly different between the two groups. Plasma concentrations of folates and vitamin B12 were increased in vitamin-treated animals. Daily dry matter intake was not significantly different between the 2 groups before (13.5 kg SE 0.5) and after (23.6 kg SE 0.9) calving. Average energy-corrected milk tended to be greater in vitamin-treated cows, 39.7 (SE 1.4) and 38.1 (SE 1.3) kg/d for treated and control cows, respectively. After calving, average plasma concentration of BHBA tended to be lower in cows injected with the vitamin supplement, 0.47 (SE 0.04) vs. 0.55 (SE 0.03) for treated and control cows, respectively. The ovarian follicle ? 12 mm in diameter was collected by ovarian pick-up after estrus synchronization. Recovered follicular fluid volumes were greater in the vitamin-treated group. A microarray platform was used to investigate the impact of treatment on gene expression of granulosa cells. Lower expression of genes involved in the cell cycle and higher expression of genes associated with granulosa cell differentiation prior to ovulation were observed. Selected candidate genes were analyzed by reverse transcription quantitative polymerase chain reaction. Although the effects of intramuscular injections of folic acid and vitamin B12 on lactational performance and metabolic status of animals were limited, Ingenuity Pathway Analysis of gene expression in granulosa cells suggests a stimulation of cell differentiation in vitamin-treated cows, which may be the result of an increase in LH secretion. Two conditions experiment (Control and Treated). Granulosa cells from the 66h post second PGF2alpha injection. Biological replicates: 3 from each time point. Two technical replicates for each comparison (dye-swap).

			Action	DRS
	JL_AS2_c18_16a.wiff	Wiff
	JL_AS2_c18_17a.wiff	Wiff
	JL_AS2_c18_18a.wiff	Wiff
	JL_AS2_c18_18b.wiff	Wiff
	JL_AS2_c18_19a.wiff	Wiff

Dataset Information

Reduction in photosynthetic capacity in a mutualistic algal-bacterial co-culture revealed by quantitative proteomics

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Publications

Quantitative proteomics of a B<sub>12</sub> -dependent alga grown in coculture with bacteria reveals metabolic tradeoffs required for mutualism.

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