Dynamics and diversity of the bacterial community during the spontaneous decay of açai (Euterpe oleracea) fruits

b r a z i l i a n j o u r n a l o f m i c r o b i o l o g y 4 9 S (2 0 1 8) 25–33 http://www.bjmicrobiol.com.br/ Environmental Microbiology Dynamics and diversity of the bacterial community during the spontaneous decay of açai (Euterpe oleracea) fruits Fábio Gomes Moura a , Diego Assis das Graças b , Agenor Valadares Santos b , Artur Luiz da Costa da Silva b , Hervé Rogez a,∗ a Universidade Federal do Pará, Centro de Valorização de Compostos Bioativos da Amazônia (CVACBA), Belém, PA, Brazil b Universidade Federal do Pará, Instituto de Ciências Biológicas, Belém, PA, Brazil a r t i c l e i n f o a b s t r a c t Article history: The biodiversity and evolution of the microbial community in açai fruits (AF) between Received 12 September 2017 three geographical origins and two spontaneous decay conditions were examined by apply- Accepted 13 April 2018 ing culture-independent methods. Culture-independent methods based on 16S rRNA from Available online 30 April 2018 fifteen samples revealed that Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes and Aci- Associate Editor: Valeria Oliveira Keywords: Food Microbial contamination High-throughput partial 16S rRNA gene sequencing Diversity dobacteria were the most abundant phyla. At the genus level, Massilia (taxon with more than 50% of the sequences remaining constant during the 30 h of decay), Pantoea, Naxibacter, Enterobacter, Raoultella and Klebsiella were identified, forming the carposphere bacterial microbiota of AF. AF is fibre-rich and Massilia bacteria could find a large quantity of substrate for its growth through cellulase production. Beta diversity showed that the quality parameters of AF (pH, soluble solids, titratable acidity and lipids) and elemental analysis (C, N, H and C/N ratio) were unable to drive microbial patterns in AF. This research offers new insight into the indigenous bacterial community composition on AF as a function of spontaneous postharvest decay. © 2018 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). Introduction Euterpe oleracea Martius is a palm tree that occurs all across the Amazon basin and is particularly abundant in the eastern Amazon. This species grows in floodplains, on land and in swampland soils. Fruiting occurs throughout the year, with a period of higher production from July to December. Açai fruits (AF) have a round shape with a diameter of 1–2 cm and a weight of 0.8–2.3 g. These fruits are composed of kernel (endosperm), which represents approximately 85–95% of the fruit volume. The mesocarp has a thickness of only 1–2 mm, and the exocarp is a thin layer that is covered with a wax cuticle when ripe.1 Just prior to harvest, AF suffer a rupture at their apex, allowing access to microorganisms and oxygen. In addition, ∗ Corresponding author at: Universidade Federal do Pará, Centro de Valorização de Compostos Bioativos da Amazônia (CVACBA), Av. Perimetral s/n, 66.095-780 Belém, PA, Brazil. E-mail: (H. Rogez). https://doi.org/10.1016/j.bjm.2018.04.006 1517-8382/© 2018 Sociedade Brasileira de Microbiologia. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 26 b r a z i l i a n j o u r n a l o f m i c r o b i o l o g y 4 9 S (2 0 1 8) 25–33 as AF do not have a thick exocarp for effective protection, they can be easily damaged during handling and transportation. Shipping occurs via small vessels across the Amazon estuary under optimal temperature (30 ◦ C), moisture (99%) and nutrient availability conditions for microbial growth. The transport time to the main trading centres in the region is between 8 and 30 h, which is another important variable in this context.2 During transport, AF deterioration can occur in the holds of boats due to a lack of ventilation, causing nutritional and functional losses mainly through the activity of polyphenoloxidase, which can be easily followed by anthocyanin degradation.1 High levels of Total Mesophilic Bacteria (TMB) in the açai juice have been reported, reaching average values of 6 log CFU g−1 dry matter (DM) and gaining a 1st and 2nd logarithmic order 11.3 and 29 h after harvest.2 Initial values of TMB, acetic and lactic acid bacteria in AF of 6, 4, and 6.5 log CFU g−1 fruit, respectively, were observed before suffering spontaneous decay.3 The isolation and identification of lactic acid bacteria in enrichment cultures from AF have been reported.4 However, the diversity and dynamics of microflora of AF were never investigated using high-throughput sequencing and quantification of bacterial diversity, to the best of the author’s knowledge. Recently, açai market began to be affected due to the occurrence of outbreaks of human infection by Trypanosoma cruzi, the protozoan responsible for Chagas disease. The native bacterial community present in AF is responsible for production of volatile organic compounds, detectable by triatomine (vectors) antennas and attracting them to the fruit.3,5 Metagenomic techniques provide insight for documenting the unexplored biodiversity and ecological characteristics of either whole communities or individual microbial taxa.6 Among AF, little is known about the bacterial communities that are involved in this habitat (e.g., high lipid and phenolic compound content), and in these conditions, the possibility of finding technologically promising species is high. This study is the first to investigate the dynamics and diversity of the native bacterial community in AF during postharvest decay. The quantitative effects of quality parameters of juice on this microbial community were investigated using cultivation-independent approaches. Due to the microbiological contamination in the supply chain of AF, the scope will illustrate the potential function of these bacterial communities in the context of postharvest decay, field location and environmental conditions. cultivars and were located in floodplain areas. AF from Abaetetuba were chosen because this municipality is part of the largest producer microregion in Brazil with 66,177 tonnes (2014 data). Fruits from Belém were selected because of the proximity to the laboratory. AF were collected in October-November 2013. 50 kg of fruits were collected from each location and transported under refrigeration (10 ± 2 ◦ C) to the laboratory. The total time between harvest and the beginning of the experiment was 0.5 h (Combu island), 2 h (Benfica) and 5 h (Campompema island). To assess the potential variation in the bacterial community in AF arising from environmental heterogeneity and to reduce bias for replication, the total mass of AF was obtained from 11 to 23 bunches (two bunches per tree with height of 15 ± 5 m) with 2–4 kg of fruits per bunch. The maturity stages of the fruits ranged between 9 and 11 according to Rogez et (...truncated)