Effects Of Photoelectron On The Metabolites Of Alcaligenes Faecalis And Rhodop Seudanonas Palustris

Since the concept of "photoelectric microbes" has been proposed,there have been many microorganisms that can use photoelectron to promote their growth were screened out.A lot of research have shown that the reducing substances in nature can capture the photohole produced by photocatalytic reaction and release the free photoelectron.Some microorganisms secrete flavin and quinones,which can act as electronic shuttles to allow photoelectrons to enter cells and participate in material circulation(i.e.,tricarboxylic acid cycle)and energy metabolism.The ubiquitous interaction between the microbe and the semiconductor minerals influenced the growth and metabolism of microorganisms in the past,present and future.There is no doubt that photoelectrons play an important role in the evolution of life in the thousands of years via interaction between the microbe and the semiconductor minerals.Thereofore,it can provide some evidence for life evoluation to investigate the effect of photoelectron on different microbial metabolism and to explore the corresponding influence mechanisms.In this study,we used nano-TiN as a semiconductor material,non-photo synthetic bacteria Alcaligenes faecalis and photosynthetic bacteria Rhodop seudomonas palustris as the investigation object,to study their interaction via simulating oligotrophic condition of early earth.The three-dimensional fluorescence technology and HPLC were used to analyze the change of metabolites from Alcaligenes faecalis and Rhodop seudonmonas palustris under the action of photoelectrons,thus discussing the influence of photoelectron on different types of microbs.The results are as follows:(1)The Alcaligenes faecalis had a higher growth rate under the photoelectron condition,exhibiting a shorter adaptive phase and a better adaptive capacity to oligotrophic conditions.In stationary phase,more NADHs were produced.Additionally,humus was produced in the later stages of culture,accompanied by the higher amount of NADH and protein in the photoelectron system.The result proved that photoelectrons can promote the production of humus substances by Alcaligenes faecalis and concurrently provide the energy and materials for microbial growth.Rhodopseudomonas palustris had a shorter adaptation period under photoelectron conditions as well.However,no significant increase of protein amount was observed in the stationary and later stage of culture.Only the production of NADH increased slightly.This proved that photoelectron can improve the adaptability of Rhodopseudomonas palustris to oligotrophic nutrition,while has no obvious effect on its growth.(2)The photoelectron had no obvious effect on the synthesis of oxalic acid and fumaric acid by Alcaligenes faecalis's,but reduced the consumption of malic acid and promoted the synthesis of citric acid,concurrently weakened the synthesis of succinic acid.The photoelectron had no significant effect on the synthesis of oxalic acid,malic acid,succinic acid and citric acid by Rhodopseudomonas palustris,but promoted the synthesis of fumaric acid.This difference suggested that the way that photoelectron participate the tricarboxylic acid cycle of Alcaligenes faecalis and Rhodopseudomonas palustris is different.For Alcaligenes faecalis,photoelectron was mainly involved in the the stage of oxaloacetic acid and NADH under the action of malic acid dehydrogenase in malic acid.The decrease of malic acid consumption indicated that photoelectron promoted the synthesis of oxaloacetic acid.The accumulation of oxaloacetic acid increased citric acid content,and inhibited the synthesis of succinic acid and fumaric acid.For Rhodopseudomonas palustris,photoelectron mianly worked in the pathway of fumaric acid under the action of succinic acid dehydrogenase.During the mixed culture,the Alcaligenes faecalis was dominant in the early stage due to the stronger adaptability and shorter growth period,while the Rhodopseudomonas palustris was predominant in the later stage.In the simultaneous inoculation experiment,the growth trend of the blank group was better than that of TiN group,which was different from that of single inoculation of two microorganism.The trend of the blank group and TiN group had no obvious difference in the experiment without simultaneous inoculation,which was similar to the trend of single cultivation of Rhodopseudomonas palustris.This indicated the mutually beneficial relationships of the two bacteria.Certain substance were generated by Rhodop seudomonas palustris duringit s growth period,which can promote the growth of Alcaligenes faecalis.Moreo verwhich the effect of this substance is much higher than that of photoelectron.In turn,some metabolites produced by Alcaligenes faecalis can promote the growth of Rhodopseudomonas palustris as well.