Microbial profile during fermentation and aerobic stability of ensiled mixtures of maize stover and banana pseudostem in South Ethiopia.

AIMS: This study evaluated pH reduction and microbial growth during fermentation of maize stover (MS) mixed with banana pseudostem (BPS) under South Ethiopian conditions. MATERIALS AND RESULTS: The MS and BPS were chopped and mixed into six treatments (T): 80% BPS plus 20% DMS (T1), 70% BPS plus 30% DMS (T2), 40% BPS plus 60% FMS (fresh MS) (T3), 20% BPS plus 80% FMS (T4), 100% FMS (T5), and 95% BPS plus 5% molasses (T6). At 0, 7, 14, 30, 60, and 90 days, pH and dry matter were determined. Microbiological quality was assessed using plate counts and Illumina MiSeq sequencing. On day 60 and 90, aerobic stability was investigated. The results showed a significant reduction in pH in all mixtures, except in T1 and T2. Lactic acid bacteria counts reached a maximum in all treatments within 14 days. Sequencing showed marked changes in dominant bacteria, such as Buttiauxella and Acinetobacter to Lactobacillus and Bifidobacterium. CONCLUSIONS: The fresh MS and BPS mixtures and fresh maize showed significant pH reduction and dominance of desirable microbial groups. SIGNIFICANCE AND IMPACT OF THE STUDY: The study enables year-round livestock feed supplementation to boost milk and meat production in South Ethiopia.

The Pupal Parasitoid Trichopria drosophilae Is Attracted to the Same Yeast Volatiles as Its Adult Host.

There is increasing evidence that microorganisms, particularly fungi and bacteria, emit volatile compounds that mediate the foraging behaviour of insects and therefore have the potential to affect key ecological relationships. However, to what extent microbial volatiles affect the olfactory response of insects across different trophic levels remains unclear. Adult parasitoids use a variety of chemical stimuli to locate potential hosts, including those emitted by the host's habitat, the host itself, and microorganisms associated with the host. Given the great capacity of parasitoids to utilize and learn odours to increase foraging success, parasitoids of eggs, larvae, or pupae may respond to the same volatiles the adult stage of their hosts use when locating their resources, but compelling evidence is still scarce. In this study, using Saccharomyces cerevisiae we show that Trichopria drosophilae, a pupal parasitoid of Drosophila species, is attracted to the same yeast volatiles as their hosts in the adult stage, i.e. acetate esters. Parasitoids significantly preferred the odour of S. cerevisiae over the blank medium in a Y-tube olfactometer. Deletion of the yeast ATF1 gene, encoding a key acetate ester synthase, decreased attraction of T. drosophilae, while the addition of synthetic acetate esters to the fermentation medium restored parasitoid attraction. Bioassays with individual compounds revealed that the esters alone were not as attractive as the volatile blend of S. cerevisiae, suggesting that other volatile compounds also contribute to the attraction of T. drosophilae. Altogether, our results indicate that pupal parasitoids respond to the same volatiles as the adult stage of their hosts, which may aid them in locating oviposition sites.

Beer ethanol and iso-α-acid level affect microbial community establishment and beer chemistry throughout wood maturation of beer.

Sour beers produced by barrel-aging of conventionally fermented beers are becoming increasingly popular. However, as the intricate interactions between the wood, the microbes and the beer are still unclear, wood maturation often leads to inconsistent end products with undesired sensory properties. Previous research on industrial barrel-aging of beer suggests that beer parameters like the ethanol content and bitterness play an important role in the microbial community composition and beer chemistry, but their exact impact still remains to be investigated. In this study, an experimentally tractable lab-scale system based on an in-vitro community of four key bacteria (Acetobacter malorum, Gluconobacter oxydans, Lactobacillus brevis and Pediococcus damnosus) and four key yeasts (Brettanomyces bruxellensis, Candida friedrichii, Pichia membranifaciens and Saccharomyces cerevisiae) that are consistently associated with barrel-aging of beer, was used to test the hypotheses that beer ethanol and bitterness impact microbial community composition and beer chemistry. Experiments were performed using different levels of ethanol (5.2 v/v%, 8 v/v% and 11 v/v%) and bitterness (13 ppm, 35 ppm and 170 ppm iso-α-acids), and beers were matured for 60 days. Samples were taken after 0, 10, 20, 30 and 60 days to monitor population densities and beer chemistry. Results revealed that all treatments and the maturation time significantly affected the microbial community composition and beer chemistry. More specifically, the ethanol treatments obstructed growth of L. brevis and G. oxydans and delayed fungal growth. The iso-α-acid treatments hindered growth of L. brevis and stimulated growth of P. membranifaciens, while the other strains remained unaffected. Beer chemistry was found to be affected by higher ethanol levels, which led to an increased extraction of wood-derived compounds. Furthermore, the distinct microbial communities also induced changes in the chemical composition of the beer samples, leading to concentration differences in beer- and wood-derived compounds like 4-ethyl guaiacol, 4-ethyl phenol, cis-oak lactone, vanillin, furfural and 5-hydroxymethyl furfural. Altogether, our results indicate that wood-aging of beer is affected by biotic and abiotic parameters, influencing the quality of the final product. Additionally, this work provides a new, cost-effective approach to study the production of barrel-aged beers based on a simplified microbial community model.

Inoculation of pear flowers with Metschnikowia reukaufii and Acinetobacter nectaris enhances attraction of honeybees and hoverflies, but does not increase fruit and seed set.

Currently, one of the most important challenges is to provide sufficient and affordable food and energy for a fast-growing world population, alongside preserving natural habitats and maintaining biodiversity. About 35% of the global food production depends on animals for pollination. In recent years, an alarming worldwide decline in pollinators has been reported, putting our food production under additional pressure. Therefore, there is an urgent need to find sustainable ways to ensure this crucial ecosystem service. Recent studies have shown that floral nectar is generally colonized by microorganisms, specifically yeasts and bacteria, which may alter nectar chemistry and enhance attraction of pollinators. In this study, we investigated changes in pollinator foraging behavior and pollination success in European pear (Pyrus communis L.) cultivars 'Regal Red' and 'Sweet Sensation' (red sports of 'Doyenné de Comice') after flower inoculation with the typical nectar-inhabiting microorganisms Metschnikowia reukaufii and Acinetobacter nectaris, and a combination of both. Pollination success was monitored by measuring the number of flower visits, fruit set and seed set in two consecutive years, 2019 and 2020. Results revealed that application of a mixture of M. reukaufii and A. nectaris resulted in significantly higher visitation rates of honeybees and hoverflies. By contrast, no effects on flower visits were found when yeasts and bacteria were applied separately. Fruit set and seed set were not significantly affected by any of the inoculation treatments. The only factors affecting fruit set were initial number of flower clusters on the trees and the year. The absence of treatment effects can most likely be attributed to the fact that pollination was not a limiting factor for fruit set in our experiments. Altogether, our results show that inoculation of flowers with nectar microbes can modify pollinator foraging patterns, but did not lead to increased pollination success under the conditions tested.

Parasitism by endoparasitoid wasps alters the internal but not the external microbiome in host caterpillars.

BACKGROUND: The microbiome of many insects consists of a diverse community of microorganisms that can play critical roles in the functioning and overall health of their hosts. Although the microbial communities of insects have been studied thoroughly over the past decade, little is still known about how biotic interactions affect the microbial community structure in and on the bodies of insects. In insects that are attacked by parasites or parasitoids, it can be expected that the microbiome of the host insect is affected by the presence of these parasitic organisms that develop in close association with their host. In this study, we used high-throughput amplicon sequencing targeting both bacteria and fungi to test the hypothesis that parasitism by the endoparasitoid Cotesia glomerata affected the microbiome of its host Pieris brassicae. Healthy and parasitized caterpillars were collected from both natural populations and a laboratory culture. RESULTS: Significant differences in bacterial community structure were found between field-collected caterpillars and laboratory-reared caterpillars, and between the external and the internal microbiome of the caterpillars. Parasitism significantly altered the internal microbiome of caterpillars, but not the external microbiome. The internal microbiome of all parasitized caterpillars and of the parasitoid larvae in the caterpillar hosts was dominated by a Wolbachia strain, which was completely absent in healthy caterpillars, suggesting that the strain was transferred to the caterpillars during oviposition by the parasitoids. CONCLUSION: We conclude that biotic interactions such as parasitism have pronounced effects on the microbiome of an insect host and possibly affect interactions with higher-order insects.

Description of the temporal dynamics in microbial community composition and beer chemistry in sour beer production via barrel ageing of finished beers.

Currently, there is a strong interest in barrel ageing of finished, conventionally fermented beers, as a novel way to produce sour beers with a rich and complex flavour profile. The production process, however, remains largely a process of trial and error, often resulting in profit losses and inconsistency in quality. To improve product quality and consistency, a better understanding of the interactions between microorganisms, wood and maturing beer is needed. The aim of this study was to describe the temporal dynamics in microbial community composition, beer chemistry and sensory characteristics during barrel ageing of three conventionally fermented beers that differed in parameters like alcohol content and bitterness. Beers were matured for 38 weeks in new (two types of wood) and used (one type of wood) oak barrels. Beer samples were taken at the start of the maturation and after 2, 12 and 38 weeks. Microbial community composition, determined using amplicon sequencing of the V4 region of the bacterial 16S rRNA gene and the fungal ITS1 region, beer chemistry and sensory characteristics substantially changed throughout the maturation process. Likewise, total bacterial and fungal population densities generally increased during maturation. PerMANOVA revealed significant differences in the bacterial and fungal community composition of the three beers and across time points, but not between the different wood types. By contrast, significant differences in beer chemistry were found across the different beers, wood types and sampling points. Results also indicated that the outcome of the maturation process likely depends on the initial beer properties. Specifically, results suggested that beer bitterness may restrain the bacterial community composition, thereby having an impact on beer souring. While the bacterial community composition of moderately-hopped beers shifted to a dominance of lactic acid bacteria, the bacterial community of the high-bitterness beer remained fairly constant, with low population densities. Bacterial community composition of the moderate-bitterness beers also resembled those of traditional sours like lambic beers, hosting typical lambic brewing species like Pediococcus damnosus, Lactobacillus brevis and Acetobacter sp. Furthermore, results suggested that alcohol level may have affected the fungal community composition and extraction of wood compounds. More specifically, the concentration of wood compounds like cis-3-methyl-4-octanolide, trans-3-methyl-4-octanolide, eugenol and total polyphenols was higher in beers with a high alcohol content. Altogether, our results provide novel insights into the barrel ageing process of beer, and may pave the way for a new generation of sour beers.

Silage making of maize stover and banana pseudostem under South Ethiopian conditions: evolution of pH, dry matter and microbiological profile.

The study was conducted to evaluate the microbial dynamics during silage of maize stover and banana pseudostem in the environmental conditions of southern Ethiopia. To meet this objective, microsilos containing either maize stover or banana pseudostem, both with and without molasses, were prepared. Subsequently, samples were analysed on day 0, 7, 14, 30, 60 and 90 of the fermentation process. As a result, on day 7, all treatments except banana pseudostem without molasses showed a significant reduction in pH. It was also this silage type that supported the growth of Enterobacteriaceae longer than three other silage types, i.e. until 30 days. The yeasts and moulds and the Clostridum endospore counts also showed a reducing trend in early fermentation and afterwards remained constant until day 90. Illumina MiSeq sequencing revealed that Leuconostoc, Buttiauxella species and Enterobacteriaceae were the most abundant bacteria in the initial phases of the fermentation. Later on, Buttiauxella, Lactobacillus, Weissella and Bifidobacterium species were found to be dominant. In conclusion, silage of the two crop by-products is possible under South Ethiopian conditions. For banana pseudostem, the addition of molasses is crucial for a fast fermentation, in contrast to maize. Upscaling needs to be investigated for the two by-products.