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 .