This work aims to investigate the long-term behavior of interactions of electrochemically active bacteria in bioelectrochemical systems. The electrochemical performance and biofilm characteristics of pure cultures of Geobacter sulfurreducens and Shewanella oneidensis are being compared to a defined mixed culture of both organisms. While S. oneidensis pure cultures did not form cohesive and stable biofilms on graphite anodes and only yielded 0.034 ± 0.011 mA/cm 2 as maximum current density by feeding of each 5 mM lactate and acetate, G. sulfurreducens pure cultures formed 69 μm thick, area-wide biofilms with 10 mM acetate as initial substrate concentration and yielded a current of 0.39 ± 0.09 mA/cm 2 . Compared to the latter, a defined mixed culture of both species was able to yield 38% higher maximum current densities of 0.54 ± 0.07 mA/cm 2 with each 5 mM lactate and acetate. This increase in current density was associated with a likewise increased thickness of the anodic biofilm to approximately 93 μm. It was further investigated whether a sessile incorporation of S. oneidensis into the mixed culture biofilm, which has been reported previously for short-term experiments, is long-term stable. The results demonstrate that S. oneidensis was not stably incorporated into the biofilm; rather, the planktonic presence of S. oneidensis has a positive effect on the biofilm growth of G. sulfurreducens and thus on current production.

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Geobacter sulfurreducens was originally considered a strict anaerobe. However, this bacterium was later shown to not only tolerate exposure to oxygen but also to use it as terminal electron acceptor. Research performed has so far only revealed the general ability of G. sulfurreducens to reduce oxygen, but the oxygen uptake rate has not been quantified yet, nor has evidence been provided as to how the bacterium achieves oxygen reduction. Therefore, microaerobic growth of G. sulfurreducens was investigated here with better defined operating conditions as previously performed and a transcriptome analysis was performed to elucidate possible metabolic mechanisms important for oxygen reduction in G. sulfurreducens. The investigations revealed that cell growth with oxygen is possible to the same extent as with fumarate if the maximum specific oxygen uptake rate (sOUR) of 95 mg O2 g CDW -1 h -1 is not surpassed. Hereby, the entire amount of introduced oxygen is reduced. When oxygen concentrations are too high, cell growth is completely inhibited and there is no partial oxygen consumption. Transcriptome analysis suggests a menaquinol oxidase to be the enzyme responsible for oxygen reduction. Transcriptome analysis has further revealed three different survival strategies, depending on the oxygen concentration present. When prompted with small amounts of oxygen, G. sulfurreducens will try to escape the microaerobic area; if oxygen concentrations are higher, cells will focus on rapid and complete oxygen reduction coupled to cell growth; and ultimately cells will form protective layers if a complete reduction becomes impossible. The results presented here have important implications for understanding how G. sulfurreducens survives exposure to oxygen.

acid hydrolysis of starch has been used for over a century for the production of starch sirups and dextrose and as an analytical procedure for the determination of starch. This longcontinued use of the procedure would normally indicate wellestablished principles for the acid hydrolysis of starch. However, an examination of the literature on this subject indicates that the basic underlying conditions of hydrolysis are still not too well understood. The lack of clarity in published research may arise from two causes:The commercial hydrolysis of starch employs relatively high concentrations of starch and very low concentrations of acid in proportion to the starch.Published research on the reversion, polymerization, or condensation of dextrose by acid has employed high concentrations of acid in proportion to the dextrose so treated.The condensation polymerization of dextrose in more concentrated solutions under the influence of heat and small amounts of acid has received relatively little attention. This paper reports research on hydrolysis employing the usual variables of time, temperature, and acid concentration, more particularly the pH, but it is devoted chiefly to a study of the most neglected variable, carbohydrate concentration of the system, or the sugarwater ratio. This variable is shown to be more significant than any of the others on the final reducing sugar content. COMMERCIAL HYDROLYSIS OF STARCH

The concept of the microbial fuel cell (MFC) has existed for over 100 years, but only within the last decade, the practical implementation has become conceivable due to microbial and technical progress. This review article presents available strategies to increase the limiting extracellular electron transfer (EET) in the anode space of MFCs. Therefore, organism‐based improvements as well as the effects of (bio–)polymers and redox mediators on ETT will be demonstrated.