the first to report about microbial butanol production was pasteur in 1862 ( pasteur 1862 ) .
pasteur named the culture vibrion butyrique  most probably though it was a mixed bacterial culture comprising at least one clostridium strain ( drre 2007 ) .
while scientific interest was documented by some further reports , commercial interest was only triggered in the beginning of the 20th century by the need for synthetic rubber production ( jones and woods 1986 ) . at this time
he isolated a new bacterial culture , readily fermenting starchy material into acetone and butanol .
starting from there , an industrial solvent production process was developed , based on available plants for ethanol fermentation .
interestingly , weizmann was a chemist by training and he set about training himself to become a microbiologist as necessary .
this underlines the close connection of industrial microbiology with chemistry , which tends to get a bit lost with the advent of genetic engineering and changing study courses .
nevertheless , renewed close collaboration of these two sciences is highly relevant  now more than in the past , as exemplary outlined by the thoughts of dusselier , mascal and sels ( 2014 ) , who provided a chemist 's view of the biorefinery . in 1915
, a patent was issued claiming acetone  butanol fermentation with c. acetobutylicum , and industrial production on large scale commenced in 1916 .
the outbreak of wwi led to a high demand of acetone for smokeless powder production , shifting the interest from butanol as a product to acetone . during the war , the requirement for acetone resulted in the accumulation of butanol as an unwanted by - product of the fermentation which was stored .
after the war , butanol again became a commercially important chemical  this time for the production of quick - drying lacquers , for the rapidly growing automobile industry .
starch was originally the carbon source on which the fermentation was based . however , molasses became cheaply available in large quantities and became the main carbon substrate for solvent production .
this became possible only because new bacterial strains , readily fermenting sugars , had been isolated by then . during wwii ,
the importance of microbial processes for acetone and butanol production declined rapidly after the war .
one reason was that petrochemistry was gaining scale and importance , and the production of solvents from petroleum became very cheap .
another reason was that molasses became increasingly sought after for the feed of cattle , leading to a significant price increase of the substrate . today , 50 years later , the weizmann process and modern derivatives of it are gaining interest and importance once more .
this time , the driver is the need for sustainability  the desire to shift back from petroleum to readily renewable resources , decreasing the carbon footprint and avoiding toxic chemicals as far as possible .
figure 1 depicts very generally the concept of microbial chemical production in biorefineries . a renewable resource , which can be biomass- , or waste - derived is converted into a substrate stream amenable to microbial conversion .
importantly , the product must be purified before reaching the market . while clearly the bioprocess is central , and very often of most interest to researchers , the price of the chemical or fuel produced , which decides over failure or success of the approach , is dictated mainly by substrate and purification costs ( porro et al .
this thematic issue will work along those lines , highlighting efforts not only on the microbiology itself , but on all steps of the process chain .
a renewable resource is converted into a substrate stream , which can be microbially converted into a base chemical .
the chemical has to be purified before it can be upgraded to more advanced products . a general overview about past achievements and pending challenges of ( acetone- ) butanol fermentation is given by moon et al .
they set the process into its historic and economic contexts in relation to the newest developments .
the current frontiers of the process , with a particular focus on cell and metabolic engineering , are given by chen and liao ( 2016 ) .
as outlined before , substrate and purification costs are decisive for the commercial success of any chemical ( and concomitantly microbial ) process . while starch was historically the substrate of choice ( and is still a major substrate for bioethanol production outside the countries which can grow sugar cane ) , a shift to molasses as a cheap waste product kept the profitability of the process high . with the opening of additional markets for molasses ,
its price increased , significantly contributing to the death of microbiological acetone and butanol fermentation .
nowadays , lignocellulose is seen as a promising carbon source for chemicals ( hasunuma et al .
it is abundant and not in direct competition with food production and a lot of effort is therefore being invested into the development of its use .
a relevant example for biobutanol production is the proposition of simultaneous saccharification and fermentation of pretreated corn stover ( dong et al .
an innovative co - culture system of recombinant escherichia coli for the bioconversion of cellulose hydrolysate has been suggested by saini et al ( 2016 ) .
2016 ) , give a general overview about the use of corn stover as carbon source with a focus on economical aspects .
finally , the use of gaseous substrates for the fermentation of solvents is a very different approach ( drre 2016 ) , which can be based on various sources for carbon - rich gas , opening ways to valorize industrial off gases or gasified carbon - rich waste streams .
a major focus of this thematic issue will therefore be to present different views and approaches for the microbial process itself , from its history to the high end of microbial cell design .
the history and importance of this process have led to a range of studies and reports , which can be used as a model for developing other microbial production processes .
this thematic issue aims therefore to show the reader how modern technologies and new discoveries in all fields of microbiology can be employed for industrial needs .
they are spore forming bacteria  what has medical relevance for some of the species  and which has technical relevance in context of solvent fermentation .
( 2016 ) used flow cytometry to evaluate population heterogeneity with particular focus on spore numbers and quality during a solventogenic fermentation process .
spore formation constitutes a special challenge for the provision of the inoculum for large - scale microbial processes .
sandoval - espinola , chinn and bruno - barcena ( 2015 ) report about an optimized strategy for inoculum preparation .
the influence of calcium and zinc ions on fermentation performance has been characterized by wu et al .
however , the tolerance of the production organisms to high solvent concentrations remains a major challenge .
high concentrations are needed to decrease purification costs , but are detrimental to the survival and productivity of the cultures .
peabody and kao ( 2016 ) give an overview of the recent progress in increasing microbial solvent tolerance .
it is a complex property of living cells , which is only partially understood and rational engineering approaches have therefore been difficult .
an interesting approach by jones , venkataramanan and papoutsakis ( 2016 ) shows that an increase of butanol tolerance is achieved by overexpression of two stress - responsive small , non - coding rnas .
discovery of these new signalling molecules has brought a completely new level of cellular organisation to light , with implications for process understanding and bioengineering .
this indicates once more that the common separation between fundamental and applied research is in most cases not useful . fundamental research is not only a prerequisite for the development of applications , but engineering cell factories can lead to many fundamental discoveries .
essalem and mitchell ( 2016 ) describe the characterization of a clostridial glucose - mannose phosphotransferase system , shedding light on sugar uptake and guiding further metabolic engineering approaches which bring us to the next field of interest .
new methods for mutagenesis are being developed , such as an inducible transposon system for efficient random mutagenesis
furthermore , genetic engineering and thereby rational strain design are gaining importance also for abe fermentation .
the understanding of the metabolism of the cells is the basis for rational strain design .
metabolic modelling helps to identify genetic targets , which might very well be non - intuitive .
dash , ng and maranas ( 2016 ) give a concise overview about current developments and applications in the metabolic modelling of clostridia .
liao , seo and lu ( 2016 ) shed some light on approaches for systems - level modelling of the entire fermentation process .
while abe processes relied historically on clostridia as productions hosts , other microorganisms are now attracting attention  the exploitation of biodiversity becomes important .
branduardi and porro ( 2016 ) present a general outline of the requirements and provisions needed for a viable cell factory for butanol production .
they conclude that yeasts might very well be alternative production hosts , thereby agreeing with kuroda and ueda ( 2016 ) who summarize recent engineering approaches using baker 's yeast for advanced biobutanol production .
escherichia coli has also been suggested as an alternative production host ( saini et al .
another aspect in this context is that in nature many metabolic tasks are split over different species .
digestion of cellulose and hemicellulose and conversion of the carbon into volatile organic acids ( which are the actual nutritional basis of the ruminant ) are achieved by a complex community of microorganisms carrying out different biochemical reactions ( sauer , marx and mattanovich 2012 ) . such concepts are in their infancy in the field of industrial microbiology , but are now being considered for microbial butanol production , as shown by saini et al .
friedl ( 2016 ) summarizes various aspects of possible downstream processing strategies . in situ recovery of the solvents
intelligent bioreactor design can increase productivity from the downstream side of the process by influencing the microbe ( li et al .
clostridial fermentations proceed via two very distinct stages  an acidogenic phase , where organic acids such as butyric acid are the main products , followed by the solventogenic phase , when the acids are converted to the corresponding alcohols .
historically , the acids have been of minor industrial importance , while the alcohols were sought after .
however , the acids can be converted in many ways to alcohols or other products of interest as outlined by sjblom et al .
the message here is to keep the eyes open to find creative solutions to pending problems based on nature 's capabilities .
about 100 years after the first industrial exploitation of the clostridial acetone  butanol fermentation this process is still of high interest , commercially as well as scientifically .
it still poses many questions , holds a lot of secrets , and many aspects have yet to be understood .
future generations of scientists will have enough to do to understand and optimize the underlying metabolic processes . at the same time
, it is one of the oldest and best studied microbial chemical production processes , so we can learn a lot from its development .
the centennial year is a good point to stop for a moment , look at this development and think about what it has to teach us for many other endeavours .
this is of special relevance now , as our societies strive to free ourselves from our dependence on petroleum .
i hope that this thematic issue of fems microbiology letters contributes to this thinking , and the development of new ideas based on past experience .
the author 's research on microbial chemical production is being financed by the christian doppler research society , by the austrian research promotion agency ffg and by the federal ministry of science , research and economy ( bmwfw ) , the federal ministry of traffic , innovation and technology ( bmvit ) , the styrian business promotion agency sfg , the standortagentur tirol , the government of lower austria and zit  technology agency of the city of vienna through the comet - funding program managed by the austrian research promotion agency ffg .
 microbial production of acetone and butanol was one of the first large - scale industrial fermentation processes of global importance . during the first part of the 20th century 
 , it was indeed the second largest fermentation process , superseded in importance only by the ethanol fermentation . 
 after a rapid decline after the 1950s , acetone - butanol - ethanol ( abe ) fermentation has recently gained renewed interest in the context of biorefinery approaches for the production of fuels and chemicals from renewable resources . 
 the availability of new methods and knowledge opens many new doors for industrial microbiology , and a comprehensive view on this process is worthwhile due to the new interest . 
 this thematic issue of fems microbiology letters , dedicated to the 100th anniversary of the first industrial exploitation of chaim weizmann 's abe fermentation process , covers the main aspects of old and new developments , thereby outlining a model development in biotechnology . 
 all major aspects of industrial microbiology are exemplified by this single process . 
 this includes new technologies , such as the latest developments in metabolic engineering , the exploitation of biodiversity and discoveries of new regulatory systems such as for microbial stress tolerance , as well as technological aspects , such as bio- and down - stream processing . 
SOME HISTORY
THE PROCESSFROM SUBSTRATE VIA MICROBE TO PURIFICATION
CONCLUDING REMARKS
FUNDING